Elsevier

Energy Conversion and Management
能量转换与管理

Volume 255, 1 March 2022, 115278
第 255 卷,2022 年 3 月 1 日,115278
Energy Conversion and Management

Review  评论
Pathways toward high-efficiency solar photovoltaic thermal management for electrical, thermal and combined generation applications: A critical review
为电力、热能和联合发电应用实现高效太阳能光伏热管理的途径:重要综述

https://doi.org/10.1016/j.enconman.2022.115278Get rights and content  获取权利和内容
Under a Creative Commons license
采用知识共享许可协议
open access  开放存取

Highlights  亮点

  •   -
    Diverse thermal management solutions for photovoltaic applications are reviewed.
    回顾了光伏应用的各种热管理解决方案。
  •   -
    Technical characteristics, design and operational aspects and challenges are presented.
    介绍了技术特点、设计和运行方面的问题和挑战。
  •   -
    Emphasis is placed on recent approaches based on novel radiative and nanofluid cooling.
    重点是基于新型辐射冷却和纳米流体冷却的最新方法。
  •   -
    Insights are provided on effective hybrid techniques in various solar applications.
    对各种太阳能应用中的有效混合技术进行了深入探讨。
  •   -
    Comparative analyses, challenges and future research directions are also provided.
    还提供了比较分析、挑战和未来研究方向。

Abstract  摘要

Photovoltaic (PV) panels convert a portion of the incident solar radiation into electrical energy and the remaining energy (>70 %) is mostly converted into thermal energy. This thermal energy is trapped within the panel which, in turn, increases the panel temperature and deteriorates the power output as well as electrical efficiency. To obtain high-efficiency solar photovoltaics, effective thermal management systems is of utmost. This article presents a comprehensive review that explores recent research related to thermal management solutions as applied to photovoltaic technology. The study aims at presenting a wide range of proposed solutions and alternatives in terms of design approaches and concepts, operational methods and other techniques for performance enhancement, with commentary on their associated challenges and opportunities. Both active and passive thermal management solutions are presented, which are classified and discussed in detail, along with results from a breadth of experimental efforts into photovoltaic panel performance improvements. Approaches relying on radiative, as well as convective heat transfer principles using air, water, heat pipes, phase change materials and/or nanoparticle suspensions (nanofluids) as heat-exchange media, are discussed while including summaries of their unique features, advantages, disadvantages and possible applications. In particular, hybrid photovoltaic-thermal (PV-T) collectors that use a coolant to capture waste heat from the photovoltaic panels in order to deliver an additional useful thermal output are also reviewed, and it is noted that this technology has a promising potential in terms of delivering high-efficiency solar energy conversion. The article can act as a guide to the research community, developers, manufacturers, industrialists and policymakers in the design, manufacture, application and possible promotion of high-performance photovoltaic-based technologies and systems.
光伏(PV)电池板将部分入射太阳辐射转化为电能,剩余的能量(>70%)大部分转化为热能。这些热能滞留在电池板内,反过来又会增加电池板的温度,降低输出功率和电气效率。要获得高效太阳能光伏发电,有效的热管理系统至关重要。本文全面综述了应用于光伏技术的热管理解决方案的最新研究成果。研究旨在从设计方法和概念、操作方法和其他提高性能的技术等方面介绍各种拟议的解决方案和替代方案,并对其相关的挑战和机遇进行评述。报告介绍了主动和被动热管理解决方案,并对其进行了详细分类和讨论,同时还介绍了为提高光伏电池板性能而开展的大量实验工作的结果。文章讨论了利用空气、水、热管、相变材料和/或纳米颗粒悬浮液(纳米流体)作为热交换介质的辐射和对流传热原理的方法,并总结了这些方法的独特之处、优点、缺点和可能的应用。特别是使用冷却剂捕获光伏板废热以提供额外有用热输出的光伏-热(PV-T)混合集热器,该技术在提供高效太阳能转换方面具有广阔的发展前景。 这篇文章可作为研究界、开发商、制造商、工业家和政策制定者在设计、制造、应用和推广高性能光伏技术和系统方面的指南。

Keywords  关键词

Active cooling
Cooling techniques
Efficiency enhancement
Nanofluids
Passive cooling
Phage change materials
Photovoltaic
PV-T cooling
Thermal management

主动冷却冷却技术能效提升纳米流体被动冷却光变材料光伏 PV-T 冷却热管理

Nomenclature  术语

    Symbols  符号

    A
    Solar cell area  太阳能电池面积
    Eg0
    Bandgap  带隙
    FF
    Fill factor  填充系数
    G
    Solar irradiance  太阳辐照度
    Gc
    Generation rate of carriers
    载体生成率
    I0  0
    Reverse saturation current
    反向饱和电流
    IL  L
    Photogenerated current  光生电流
    Imax  max
    Maximum value of the current
    电流的最大值
    IPV  PV
    Current of PV cells  光伏电池的电流
    Isc  sc
    Short circuit current  短路电流
    k
    Ln
    Diffusion lengths of electrons
    电子的扩散长度
    Lp
    Diffusion lengths of holes
    孔的扩散长度
    n
    Pmax
    Maximum power produced by solar panel
    太阳能电池板产生的最大功率
    q
    Element charge  元件电荷
    T
    Operating temperature  工作温度
    Tref
    Reference temperature  参考温度
    V
    Output voltage  输出电压
    Vmax
    Maximum value of the voltage
    电压最大值
    Voc
    Open-circuit voltage  开路电压

    Greek  希腊文

    β
    Temperature coefficient of PV cell
    光伏电池的温度系数
    γ
    Irradiance coefficient  辐照度系数
    ηel  el
    Electrical efficiency  电气效率
    ηref  ref
    Electrical efficiency at the reference temperature
    参考温度下的电效率
    λ
    Wavelength  波长

1. Introduction  1.导言

Energy is an indispensable resource, linked closely to human, economic and societal development, and the empowerment of mankind. It is often broadly classified into conventional and alternative (including renewable) forms [1]. At present, the majority of the world’s energy demand is fulfilled by non-renewable sources, such as fossil fuels and nuclear energy [2], [3], [4], [5], although the deployment of renewables continues to accelerate. Key characteristics of non-renewable resources are that they can be found in finite quantities and that their rate of replenishment is considerably slower than the rate at which they are being utilised or consumed. Their continuous usage at significant rates of consumption poses a serious risk of continued energy security and environmental impact. This has given rise to extensive worldwide efforts by a wide range of diverse stakeholders (e.g., researchers, scientists, companies, organisations, policymakers, governments) to increase renewable energy penetration for meeting the growing global demands for energy in its various forms [6], [7], [8], [9], [10]. Arguably, amongst all renewable energy resources, solar energy is the most abundant, widespread and promising in terms of its ability to cater to a global energy demand [11], [12], [13].
能源是一种不可或缺的资源,与人类、经济和社会发展以及人类赋权密切相关。能源通常可大致分为传统形式和替代形式(包括可再生形式)[1]。目前,世界能源需求的大部分是由化石燃料和核能等不可再生资源满足的[2]、[3]、[4]、[5],尽管可再生能源的应用仍在加速。不可再生资源的主要特点是数量有限,而且其补充速度大大低于其利用或消耗速度。以巨大的消耗速度持续使用这些资源,会给持续的能源安全和环境影响带来严重风险。因此,世界各地的各种利益相关者(如研究人员、科学家、公司、组织、决策者、政府)都在努力提高可再生能源的普及率,以满足全球日益增长的各种形式的能源需求 [6]、[7]、[8]、[9]、[10]。可以说,在所有可再生能源中,太阳能是最丰富、最广泛、最有希望满足全球能源需求的能源[11]、[12]、[13]。
The two main solar energy technologies are solar thermal collectors and photovoltaic (PV) panels. A solar thermal collector transforms solar radiation into useful thermal energy, typically by using a heat transfer fluid whose temperature (and, therefore, enthalpy) increases as it passes through the collector. On the other hand, a PV panel converts solar radiation falling on its surface directly into electrical energy via the photovoltaic effect. Typically, the efficiency of commercial solar PV panels ranges from about 10 % to 23 % [14], [15], [16]. The most widely used PV panels are based on silicon (Si) cells and are categorised into three types: mono-crystalline, poly-/multi-crystalline, and amorphous. More recently, silicon heterojunction cells, as well as thin-film technologies (e.g., CdTe, CIGS) have also entered the market [17], [18].
两种主要的太阳能技术是太阳能集热器和光伏(PV)电池板。太阳能集热器将太阳辐射转化为有用的热能,通常是通过使用一种导热流体,当流体通过集热器时,其温度(也就是焓)会升高。另一方面,光伏板通过光伏效应将落在其表面的太阳辐射直接转化为电能。通常,商用太阳能光伏板的效率约为 10 % 到 23 % [14]、[15]、[16]。最广泛使用的光伏电池板以硅(Si)电池为基础,可分为三种类型:单晶、多晶和非晶。最近,硅异质结电池以及薄膜技术(如碲化镉、铜铟镓硒)也进入了市场 [17],[18]。
In a PV panel, photons with energy greater than the band gap energy support the photovoltaic effect through which electricity is generated, however, the remaining photon energy is mostly converted into heat, causing the cell temperature to increase. This temperature rise, in turn, is deleterious to the open-circuit voltage (Voc), fill factor and output power, thus ultimately decreasing the electrical efficiency of the panel. Common factors that influence the operating temperature of a solar cell, beyond the local solar irradiance include climatic conditions such as wind speed, ambient temperature and relative humidity, as well as factors such as accumulated dust on the panel. In this context, any solution capable of cooling a PV panel by removing some of the unwanted or accumulated thermal energy is of interest as this can reduce cell temperatures, improve electrical efficiency, and prevent the irreversible damage to the panel caused by the cells temperature rise and periodic thermal cycling over the day- and night-time operation.
在光伏电池板中,能量大于带隙能的光子支持光伏效应,通过这种效应产生电力,但剩余的光子能量大部分转化为热量,导致电池温度升高。这种温度上升反过来又会对开路电压(V oc )、填充因子和输出功率产生不利影响,从而最终降低电池板的电气效率。除了当地的太阳辐照度之外,影响太阳能电池工作温度的常见因素还包括风速、环境温度和相对湿度等气候条件,以及电池板上的积尘等因素。在这种情况下,任何能够通过去除一些不需要的或积累的热能来冷却光伏电池板的解决方案都会引起人们的兴趣,因为这可以降低电池温度,提高电能效率,并防止电池温度上升和昼夜周期性热循环对电池板造成不可逆转的损坏。
Various thermal management methods have been proposed, developed and tested over the years specifically aimed at the cooling of PV panels, and some commercial products that implement such solutions are available on the market. These thermal management methods can be classified as active and passive. The former category relies on forced convective heat transfer, whereas approaches that fall into the latter category rely on free convective, conductive and/or radiative heat transfer control.
多年来,人们提出、开发并测试了各种专门针对光伏电池板冷却的热管理方法,市场上也出现了一些采用此类解决方案的商业产品。这些热管理方法可分为主动和被动两种。前者依靠强制对流传热,而属于后者的方法则依靠自由对流、传导和/或辐射传热控制。
When surveying studies relevant to this domain in the literature, a number of comprehensive and informative reviews can be identified. Siecker et al. [19], for example, presented an extensive overview of various hybrid cooling techniques, and covered techniques including: (i) floating tracked concentrated cooling systems, (ii) PV-thermoelectric systems cooled by a heat sink, (iii) PV panels with integrated phase change materials (PCMs), (iv) PV panels cooled via immersion cooling, (v) PV panels with transparent coatings, (vi) hybrid PV-thermal (PV-T) systems cooled by water spraying, and (vii) PV-T systems cooled by forced fluid circulation. This review extended to providing insight into these cooling techniques, however, it did not cover all the available techniques, e.g., the potential employment of nanofluids, heat pipe cooling, or radiative methods, along with a presentation of their thermal and electrical performance. Furthermore, Maleki et al. [20] and Hasanuzzaman et al. [21] presented an overview of active and passive cooling techniques available for regulating PV panel temperatures and suggested that passive techniques are more feasible for small-scale implementation with active techniques being more useful in commercial-scale systems given the added costs and additional power requirements.
在对文献中与该领域相关的研究进行调查时,可以发现一些全面而翔实的综述。例如,Siecker 等人[19] 综述了各种混合冷却技术,涵盖的技术包括:(i) 浮动跟踪集中冷却系统,(ii) 由散热器冷却的光伏热电系统,(iii) 集成了相变材料 (PCM) 的光伏面板,(iv) 通过浸入冷却冷却的光伏面板,(v) 具有透明涂层的光伏面板,(vi) 通过喷水冷却的混合光伏热电 (PV-T) 系统,以及 (vii) 通过强制流体循环冷却的 PV-T 系统。这篇综述对这些冷却技术进行了深入探讨,但并未涵盖所有可用技术,例如纳米流体、热管冷却或辐射方法的潜在应用,以及对其热性能和电性能的介绍。此外,Maleki 等人[20] 和 Hasanuzzaman 等人[21] 概述了可用于调节光伏面板温度的主动和被动冷却技术,并认为被动技术更适合小规模实施,而主动技术由于增加了成本和额外的电力要求,在商业规模系统中更有用。
Velmurugan et al. [22] presented a comprehensive review on PCM types and passive cooling using PCMs, and Muhammad Ali [23] elucidated the recent advancements in PV cooling, especially with PCM systems holistically, while Sargunanathan et al. [24] presented an extensive review on a range of cooling concepts such as heat pipe cooling, liquid immersion cooling, and active cooling by water flowing over the front surface of PV panels or by integrating air/water/fin cooling systems on the rear side of the panels. An analysis was presented of the role of these methods on decreasing PV panel operating temperatures. Kandeal et al. [25] presented a state-of-art review on PV performance enhancement techniques where the authors specifically focus on cooling techniques based on convection, conduction and radiation. Bahaidarah et al. [26] and Hamzat et al. [27] also presented an overview of different thermal management methods, relying on the employment of: (i) heat pipes, (ii) microchannels, (iii) liquid immersion, (iv) heat sinks, (v) impingement jets, and (vi) PCMs.
Velmurugan 等人[22]对 PCM 类型和使用 PCM 的被动冷却进行了全面综述,Muhammad Ali [23]阐明了光伏冷却的最新进展,特别是 PCM 系统的整体进展,而 Sargunanathan 等人[24]则对一系列冷却概念进行了广泛综述,如热管冷却、液体浸入冷却以及通过水流过光伏面板前表面或通过在面板后侧集成空气/水/翅冷却系统进行主动冷却。他们分析了这些方法对降低光伏板工作温度的作用。Kandeal 等人[25] 综述了光伏性能提升技术的最新进展,作者特别关注了基于对流、传导和辐射的冷却技术。Bahaidarah 等人[26]和 Hamzat 等人[27]也概述了不同的热管理方法,主要依赖于以下几种方法的应用:(i) 热管,(ii) 微通道,(iii) 液体浸入,(iv) 散热器,(v) 喷射流和 (vi) PCM。
Together the aforementioned reviews contain very interesting information on such solutions and their development, however, they do not cover more recent research topics, including the use of nano-liquid cooling, radiative thermal management methods and novel designs, or recent developments in the field of combined hybrid PV-T collectors, which also involve thermal energy removal from PV cells. This leaves a gap in the literature for a comprehensive review of PV thermal management methods.
上述综述包含了有关此类解决方案及其发展的非常有趣的信息,但是,它们并没有涵盖更多最新的研究课题,包括纳米液体冷却的使用、辐射热管理方法和新型设计,以及光伏-太阳能混合集热器领域的最新发展,其中也涉及从光伏电池中去除热能。这为全面回顾光伏热管理方法留下了文献空白。
In this context, the present article presents a thorough review of thermal management techniques aimed at increasing the efficiency of PV panels. The main aspects covered in this article include:
在此背景下,本文全面回顾了旨在提高光伏电池板效率的热管理技术。本文涉及的主要方面包括
  •   -
    Discussion of the effect of temperature on PV cell/panel performance.
    讨论温度对光伏电池/电池板性能的影响。
  •   -
    Summary of thermal management techniques.
    热管理技术摘要。
  •   -
    Overview, where relevant, of key implementation, operational and performance characteristics.
    在相关情况下,概述主要的实施、运行和绩效特点。
  •   -
    Consideration of the advantages and disadvantages of each approach or solution.
    考虑每种方法或解决方案的优缺点。
  •   -
    Discussion of the application of each technology based on its characteristics and limitations.
    根据每种技术的特点和局限性讨论其应用。
  •   -
    Outlook of important research gaps and future research directions.
    重要研究空白和未来研究方向展望。
To perform a comprehensive review, a significant volume of data is required. The information presented and summarised in this review was collected both from the academic literature, i.e., articles from reputed journals or books that have been peer-reviewed by experts, and from the grey literature, which comprises reports (technical or other), information on official websites (e.g., government websites, the private sector and other non-governmental organisations), white papers, and many reputed sources. Initially, a literature survey was performed by keyword search in renowned journal publishing platforms such as Elsevier, IEEE, MDPI, and similar. This yielded more than 3000 articles containing the desired keywords. In a second step, ‘title screening’ was performed, by considering specifically the titles of the pre-selected articles relevant to the core subject of this review, which accounted for about 1260 studies. By reviewing the abstract, the subject and focus of each study were estimated, and based on requirements such as novelty, clear objectives, methods, high impact, a further screening step was undertaken in the step termed ‘abstract screening’. As a result of this step, 388 articles were identified, the content of which was investigated for the methods employed, the key findings, and the quality of the conceptual discussion. This led to the filtering of the most appropriate 239 studies, of which 212 studies were original research articles while the remaining 27 studies were reviews.
要进行全面审查,需要大量数据。本综述中介绍和总结的信息既来自学术文献,即经专家同行评审的知名期刊或书籍中的文章,也来自灰色文献,其中包括报告(技术或其他)、官方网站(如政府网站、私营部门和其他非政府组织)上的信息、白皮书和许多知名资料来源。起初,我们通过在 Elsevier、IEEE、MDPI 等知名期刊出版平台上进行关键词搜索来开展文献调查。结果发现有 3000 多篇文章包含所需的关键词。第二步是 "标题筛选",特别考虑了与本综述核心主题相关的预选文章的标题,约有 1260 项研究。通过审查摘要,对每篇研究的主题和重点进行了估计,并根据新颖性、明确的目标、方法、高影响力等要求,在 "摘要筛选 "步骤中进行了进一步筛选。经过这一步骤,共确定了 388 篇文章,并对其内容所采用的方法、主要发现和概念讨论的质量进行了调查。最终筛选出最合适的 239 项研究,其中 212 项研究为原创研究文章,其余 27 项研究为综述。

2. Motivation for thermal management
2.热管理的动机

The useful electrical output of a solar PV panel mainly relies on the incident radiation and the electrical efficiency of the panel. The electrical efficiency of a PV panel is highly dependent on its temperature. Specifically, for every degree in temperature rise, the efficiency of a PV panel drops by between 0.2 % and 0.5 % for silicon cells, as confirmed by many researchers [28], [29], [30], [31]. Furthermore, the panel’s output power varies with other atmospheric conditions such as solar irradiance, wind speed, cloud coverage and relative humidity, as well as material composition [32]. In concentrated PV (CPV) collectors, the operating PV cell temperatures are much higher than in flat PV panel systems, which, in turn, significantly reduces the lifespan of CPV panels. In these systems, cooling is crucial for reducing the cell temperature and enhancing overall performance, irrespective of their type.
太阳能光伏电池板的有用电力输出主要取决于入射辐射和电池板的电气效率。光伏电池板的电气效率在很大程度上取决于其温度。具体来说,温度每升高一度,硅电池板的效率就会下降 0.2 % 到 0.5 %,这一点已被许多研究人员证实 [28]、[29]、[30]、[31]。此外,电池板的输出功率还会随其他大气条件(如太阳辐照度、风速、云层覆盖率和相对湿度以及材料成分)的变化而变化 [32]。在聚光光伏(CPV)集热器中,光伏电池的工作温度远高于平板光伏系统,这反过来又大大缩短了 CPV 面板的使用寿命。在这些系统中,无论电池类型如何,冷却对于降低电池温度和提高整体性能都至关重要。
During the conversion process of solar energy to electricity, the generation of (waste) heat elevates the temperature of a PV cell. This lowers the gap between the valance and conduction bands of the PV cell, which decreases the open-circuit voltage (Voc) by about 2 mV/°C [33], [34], [35] and fill factor, while also causing a slight increase in the short circuit current (Isc). Due to the noticeable decrease in Voc relative to the increase in Isc, the overall output power of the PV panel, which depends on the multiple of both, decreases. Other than decreased efficiency, higher operating temperatures also lead to the degradation of PV cells and, thereby, affecting their effective lifespan.
在太阳能转化为电能的过程中,(废)热的产生会使光伏电池的温度升高。这会降低光伏电池价带和导带之间的间隙,从而使开路电压(V oc )降低约 2 mV/°C [33]、[34]、[35] 和填充因子,同时也会使短路电流(I sc )略有增加。由于相对于 I sc 的增加,V oc 明显下降,光伏电池板的总体输出功率(取决于两者的倍数)也随之下降。除效率下降外,较高的工作温度还会导致光伏电池退化,从而影响其有效寿命。
The accumulation of thermal energy within the PV panels as a consequence of continuous exposure to sunlight is detrimental as it results in a deterioration in electrical performance. An equivalent electrical circuit of a PV cell is shown in Fig. 1, and this can be considered to characterise this deterioration [36].
由于持续暴露在阳光下,光伏电池板内的热能会不断积累,从而导致电气性能下降。光伏电池的等效电路如图 1 所示,可用于描述这种劣化[36]。
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Fig. 1. Equivalent electrical circuit of a PV cell.
图 1.光伏电池的等效电路。

With reference to Fig. 1, the current IPV in a single-junction solar cell is given by [37]:IPV=IL-I0expqVPVnkT-1where I0 is the reverse saturation current corresponding to the diode, q is the element charge, VPV is the output voltage of the solar cell, n is the ideality factor, k is the Boltzmann constant, and T is the operating temperature. The photogenerated current is given by IL = Aq∙Gc∙(Ln + Lp), where A is the solar cell area, Gc is the generation rate of carriers, and Ln and Lp are the diffusion lengths of electrons and holes, respectively.
参照图 1,单结太阳能电池中的电流 I PV 由 [37] 给出: IPV=IL-I0expqVPVnkT-1 其中 I 0 是二极管对应的反向饱和电流,q 是元件电荷,V PV 是太阳能电池的输出电压,n 是表意系数,k 是玻尔兹曼常数,T 是工作温度。光生电流的计算公式为 I L = A∙q∙G c ∙(L n + L p ),其中 A 是太阳能电池面积,G c 是载流子的产生率,L n 和 L p 分别是电子和空穴的扩散长度。
Moreover, the open-circuit voltage Voc of the cell is [38]:(2)Voc=Voc(T0)-Eg0q-Voc(T0)TT0-1-3kTqlnTT0where T0 is the reference temperature, and Eg0 is the bandgap where the temperature dependency of the open-circuit voltage is directly evident. The change of Voc with temperature is described by [39]:(3)dVocdT=-Eg0q-Voc(T0)T0-3kTqwhere T0 = 300 K, Eg0 = 1.1 eV, and Voc = 0.55 V, typically for silicon cells. The Voc decreases with the cell temperature with a coefficient of dVoc/dT of -2.45 mV/K at 25 °C [39].
此外,电池的开路电压 V oc 为 [38]: (2)Voc=Voc(T0)-Eg0q-Voc(T0)TT0-1-3kTqlnTT0 其中,T 0 为参考温度,E g0 为带隙,开路电压的温度依赖性在此直接显现。V oc 随温度的变化可以用 [39] 来描述: (3)dVocdT=-Eg0q-Voc(T0)T0-3kTq 其中 T 0 = 300 K,E g0 = 1.1 eV,V oc = 0.55 V,通常用于硅电池。V oc 随着电池温度的升高而降低,在 25 °C 时,dV oc /dT 的系数为 -2.45 mV/K[39]。
The fill factor FF of the solar cell is determined from the maximum values of the output voltage and current, Vmax and Imax, the open-circuit voltage Voc and short-circuit current Isc [14]:(4)FF=VmaxImaxVocIsc
太阳能电池的填充因子 FF 是根据输出电压和电流的最大值 V max 和 I max 以及开路电压 V oc 和短路电流 I sc 确定的 [14]: (4)FF=VmaxImaxVocIsc
such that the maximum power Pmax in the numerator is given by [14]:(5)Pmax=VmaxImax=(FF)VocIsc
这样,分子中的最大功率 P max 由 [14] 给出: (5)Pmax=VmaxImax=(FF)VocIsc
Since the fill factor FF and open-circuit voltage Voc depend on the cell temperature, it follows that the output power is also affected by the temperature. Therefore, the electrical efficiency of a PV cell can be calculated from the expression [40]:(6)ηel=ηref1+βT-Tref+γlnG/1000where β = -0.0045 K−1 is the typical temperature coefficient of silicon cells, Tref = 25 °C is the reference temperature at the standard test condition, ηref is the cell reference efficiency at a temperature of 25 °C and solar irradiance of 1000 W/m2, γ = 0.085 is the irradiance coefficient, and G is the solar irradiance. Typical temperature coefficient ranges for different solar cell technologies are shown in Fig. 2. For most solar panels, with the notable exception of amorphous silicon (a-Si) which has a non-monotonic behaviour, the observed decrease of electrical efficiency is linear with the cell’s temperature increase.
由于填充因子 FF 和开路电压 V oc 取决于电池温度,因此输出功率也受温度影响。因此,光伏电池的电效率可通过表达式 [40] 计算得出: (6)ηel=ηref1+βT-Tref+γlnG/1000 其中,β = -0.0045 K −1 是硅电池的典型温度系数,T ref = 25 °C 是标准测试条件下的参考温度,η ref 是温度为 25 °C 和太阳辐照度为 1000 W/m 2 时的电池参考效率,γ = 0.085 是辐照度系数,G 是太阳辐照度。不同太阳能电池技术的典型温度系数范围如图 2 所示。对于大多数太阳能电池板来说,除了非晶硅(a-Si)具有非单调行为外,观察到的电效率下降与电池的温度升高呈线性关系。
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Fig. 2. Variation of normalised efficiency of different PV technologies with temperature [41].
图 2.不同光伏技术的归一化效率随温度的变化 [41]。

Finally, the PV efficiency can also be related to maximum power output Pmax via:(7)ηel=Pmax/GA
最后,光伏效率还可以通过以下方式与最大功率输出 P max 联系起来: (7)ηel=Pmax/GA
Chander et al. [42] examined the performance of mono-crystalline PV panels by varying the cell temperature from 25 °C to 60 °C and the light intensity from 215 W/m2 to 515 W/m2. The results showed that the temperature coefficient has a negative effect on the open-circuit voltage, fill factor and maximum electrical output, whereas it has a positive impact on the short-circuit current. Jiang et al. [43] examined the effects of temperature and irradiation intensity variations on PV performance and found that higher temperatures inherently decrease the output power of PV panels. The I-V characteristics of the PV panel measured in this work at various ambient temperatures are shown in Fig. 3. Nevertheless, the PV panel temperature can be controlled by employing thermal management techniques.
Chander 等人[42] 通过将电池温度从 25 °C 变为 60 °C 以及将光照强度从 215 W/m 2 变为 515 W/m 2 ,研究了单晶硅光伏电池板的性能。结果表明,温度系数对开路电压、填充因子和最大电输出有负面影响,而对短路电流有正面影响。Jiang 等人[43] 研究了温度和辐照强度变化对光伏性能的影响,发现温度越高,光伏电池板的输出功率越小。图 3 显示了在不同环境温度下测量的光伏板的 I-V 特性。不过,可以通过采用热管理技术来控制光伏板的温度。
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Fig. 3. I-V characteristics of a PV panel over a range of ambient temperatures [43].
图 3.环境温度范围内光伏电池板的 I-V 特性 [43]。

3. Convective thermal management approaches
3.对流热管理方法

Convective thermal management techniques for PV panels can be split into two types: active and passive [44], [45]. Active methods consume energy due to the use of pumps and/or fans in order to circulate the heat transfer fluids or coolants which removes heat through (most often) forced convection, whereas passive methods rely primarily on processes such as natural convection, capillary flow, etc., that do not require additional energy in order to achieve the same goal, i.e., to remove heat from the PV panels. In all cases, the benefits of implementing any solution onto conventional PV panels and systems incur added complexity and cost, and it is necessary to ensure that these are significantly outweighed by the performance benefits that they enable. If this cannot be ensured, the practical implementation of a solution cannot be justified. Fig. 4 shows the classification of convective PV cooling methods. The sections below discuss different active convective cooling methods in terms of their effectiveness to improve standalone, solar PV panel efficiency. A summary of the surveys is also provided in the form of tables for ease of access.
光伏电池板的对流热管理技术可分为两类:主动式和被动式 [44], [45]。主动式方法由于使用泵和/或风扇来循环导热液体或冷却剂,通过(最常见的)强制对流带走热量而消耗能源,而被动式方法主要依靠自然对流、毛细管流动等过程,不需要额外的能源就能实现相同的目标,即带走光伏板上的热量。在任何情况下,在传统光伏电池板和系统上采用任何解决方案都会增加复杂性和成本,因此有必要确保这些复杂性和成本大大超过其带来的性能优势。如果不能确保这一点,就没有理由实际实施解决方案。图 4 显示了对流光伏冷却方法的分类。下文将讨论不同的主动对流冷却方法在提高独立太阳能光伏板效率方面的效果。为便于查阅,还以表格形式提供了调查摘要。
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Fig. 4. Classification of convective PV thermal management methods, focussing on cooling.
图 4.对流光伏热管理方法的分类,侧重于冷却。

3.1. Active thermal management
3.1.主动热管理

Active thermal management is almost invariably aimed at cooling using pumps/fans to circulate air or water to cool PV panels. Since it consumes power, the cost is high compared to passive cooling, nevertheless, it generally gives better performance than passive cooling techniques.
主动热管理的目的几乎都是利用泵/风扇循环空气或水冷却光伏板。由于主动热管理需要消耗电能,因此成本比被动冷却高,但通常比被动冷却技术性能更好。

3.1.1. Air cooling  3.1.1.空气冷却

Air cooling is one of the most straightforward and simple ways for PV panel cooling because of its availability, simplicity and low cost. Teo et al. [46] studied cooling techniques for PV panels in an experimental arrangement that consisted of a parallel array of air ducts connected to the underneath surface of PV panels to actively cool the panels. To enhance the rate of heat transfer, fins were connected to the air ducts and a blower was used to extract air from the surroundings and to control the air flow rate. A second PV panel without cooling was included in the study for comparison purposes. It was found that an air flow rate of 0.055 kg/s was effective in reducing the temperature of the panel. The results revealed a temperature reduction from 68 °C (reference panel without cooling) to 38 °C with air cooling when the solar irradiance was 1000 W/m2. It was also observed that the efficiencies of the panels improved significantly (by ∼ 50 %) from 8 to 9 % without cooling to 12–14 % with cooling. Farhana et al. [47] used a brushless DC fan in experiments with an inlet/outlet manifold design for a constant flow of air. This cooling system consisted of aluminium fitted under a PV panel and the DC brushless fan attached to the heat sink. Air flow from the fan removed heat from the PV panel and transferred this to the heat sink, which promoted heat transfer to the surroundings. With this approach, the authors were able to demonstrate a reduction in the panel temperature by 40 % compared to a panel without cooling.
空气冷却因其可用性、简便性和低成本而成为最直接、最简单的光伏板冷却方式之一。Teo 等人[46]在实验中研究了光伏板的冷却技术,该技术包括连接到光伏板下表面的平行空气管道阵列,以主动冷却光伏板。为了提高热传导率,空气管道上连接了散热片,并使用鼓风机从周围抽取空气和控制空气流速。研究中还包括第二块不带冷却装置的光伏电池板,以便进行比较。研究发现,0.055 千克/秒的空气流速可有效降低面板温度。结果显示,当太阳辐照度为 1000 W/m 2 时,温度从 68 °C (无冷却的参考面板)降至 38 °C。此外,还观察到电池板的效率显著提高(提高了 50%),从无冷却时的 8% 至 9% 提高到有冷却时的 12% 至 14%。Farhana 等人[47]在实验中使用了无刷直流风扇,采用进气/出气歧管设计,以获得恒定的气流。该冷却系统由安装在光伏板下的铝和连接到散热器上的直流无刷风扇组成。风扇的气流带走光伏板上的热量,并将热量传递到散热器上,从而促进热量向周围传递。通过这种方法,作者证明与没有冷却装置的面板相比,面板温度降低了 40%。
Syafiqah et al. [48] computationally studied PV panel cooling by using a DC brushless fan at the rear surface with six different speeds The results revealed that the PV power output, along with the parasitic input power to the fan, both increased with an increase in the fan speed. A fan speed of 3.1 m/s was chosen as the optimum speed for cooling since it had the highest net power output compared to other speeds. Boulfaf et al. [49] examined the thermal behaviour of a hybrid PV-T solar air collector using a finite element method. A diagrammatic representation of this collector is shown in Fig. 5. Their simulation results showed that the solar cell temperature decreased from 78 °C to 62 °C as the air flow rate increased from 0.05 kg/s to 1 kg/s with a solar irradiance of 1000 W/m2. These results showed that at high fluid flow rates, and therefore speeds, the PV temperature and fluid outlet temperature both decreased more effectively, as expected. Further insights on solar PV-T air collectors for cogenerated heat and power are provided in detail in Section 7. Dehghan et al. [50] assessed the techno-economic perspectives of PV air cooling in two scenarios in the northwest of Iran where the difference between the scenarios lies with the use of 3 and 6 low-energy fans. The energy balance analysis indicated the production of more electrical output in the scenario where 3 fans were utilised. Net specific energy improvements amounting to 4.4 % and 4.1 % for Scenarios 1 and 2 were reported, respectively. The techno-economic analysis highlighted that the proposed thermal management can be easily justifiable only at high feed-in-tariff rates.
Syafiqah 等人[48]通过计算研究了在后表面使用直流无刷风扇以六种不同速度冷却光伏板的方法。结果显示,光伏功率输出和风扇的寄生输入功率都随着风扇速度的增加而增加。由于 3.1 米/秒的风扇速度与其他速度相比具有最高的净功率输出,因此被选为最佳冷却速度。Boulfaf 等人[49]使用有限元方法研究了 PV-T 混合型太阳能空气集热器的热性能。该集热器的示意图如图 5 所示。他们的模拟结果表明,在太阳辐照度为 1000 W/m 2 时,当空气流速从 0.05 kg/s 增加到 1 kg/s 时,太阳能电池温度从 78 °C 下降到 62 °C 。这些结果表明,在流体流速较高的情况下,光伏温度和流体出口温度都会如预期般有效降低。第 7 节将详细介绍太阳能 PV-T 空气集热器在热电联产中的应用。Dehghan 等人[50] 在伊朗西北部的两个方案中评估了光伏空气冷却的技术经济前景,方案之间的差异在于使用 3 台和 6 台低能耗风机。能源平衡分析表明,在使用 3 台风机的方案中,发电量更大。据报告,方案 1 和方案 2 的具体能源净改善量分别为 4.4 % 和 4.1 %。技术经济分析突出表明,只有在上网电价较高的情况下,建议的热能管理方案才有合理性。
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Fig. 5. Diagrammatic representation of a hybrid PV-T air collector [49].
图 5.PV-T 混合空气集热器示意图 [49]。

Almuwailhi and Zeitoun [51] investigated the effects of cooling on the performance of poly-crystalline PV panels by using three different techniques namely: (i) natural convection, (ii) forced convection, and (iii) evaporative cooling with natural and forced convection in Riyadh, Saudi Arabia. From the experiments, it was deduced that natural convection cooling (with a 120 mm air gap) enhanced the daily energy generation and efficiency of the panels by 1.7 % and 1.2 %, respectively, whereas forced convection (with an airspeed of 3 m/s) enhanced the daily energy generation and efficiency by 4.4 % and 4.0 %. The greater enhancement with forced convection was attributed to a higher convective heat transfer coefficient underpinned by the velocity of air flow. On the other hand, forced convection evaporative cooling (using a speed of 2 m/s) enhanced both the daily energy generation and efficiency of PV panels by 3.8 %. The evaporative cooling was accomplished with a layout similar to the natural convection one, but with the addition of a wet fabric placed at the bottom of the channel and its wetness maintained by a water spraying system. Therefore, in the case of evaporative cooling, the latent heat of water plays a role in absorbing more heat compared to natural convection. In the same study, it is observed that the natural convection with a narrower air gap (30 mm and 60 mm) proves to be ineffective since it raises the panel temperature. This is due to the resistance offered by the friction to the natural convection currents in the cooling channel.
Almuwailhi 和 Zeitoun [51] 在沙特阿拉伯利雅得研究了冷却对多晶光伏电池板性能的影响,他们使用了三种不同的技术,即:(i) 自然对流、(ii) 强制对流和 (iii) 蒸发冷却与自然对流和强制对流。实验结果表明,自然对流冷却(气隙为 120 毫米)使电池板的日发电量和效率分别提高了 1.7% 和 1.2%,而强制对流(气流速度为 3 米/秒)使电池板的日发电量和效率分别提高了 4.4% 和 4.0%。强制对流之所以能提高效率,是因为气流速度提高了对流传热系数。另一方面,强制对流蒸发冷却(使用 2 米/秒的速度)使光伏电池板的日发电量和效率提高了 3.8%。蒸发冷却的布局与自然对流类似,但在通道底部增加了一块湿布,并通过喷水系统保持湿度。因此,在蒸发冷却的情况下,与自然对流相比,水的潜热起到了吸收更多热量的作用。在同一项研究中还发现,空气间隙较窄(30 毫米和 60 毫米)的自然对流效果不佳,因为它会使面板温度升高。这是由于摩擦对冷却通道中的自然对流产生了阻力。
In summary, previous studies had shown that active cooling via forced air flow can enhance the efficiency of PV panels. The effectiveness of cooling using forced (active) air flows depends on several factors such as the speed of the fans used (i.e., typically more cooling can be achieved at higher fan speeds), whether the fan is used either at the rear or the front of the PV panel (with front cooling generally more effective than rear cooling) and the environmental conditions (e.g., higher wind speeds, lower ambient temperatures and/or greater cloud coverage all increase PV cooling). Simultaneous cooling using front water cooling and rear air cooling has shown particular promise, compared to using such approaches independently. Either way, as stated earlier, any efficiency benefits need to be placed in the context of the added system complexity, cost, and power consumption. The implementation of these solutions will be feasible only if the performance benefits outweigh the added costs, which in many cases is a challenge.
总之,先前的研究表明,通过强制气流进行主动冷却可以提高光伏电池板的效率。利用强制(主动)气流进行冷却的效果取决于多个因素,如使用的风扇速度(即风扇速度越高,冷却效果越好)、风扇是在光伏板后部还是前部使用(前部冷却通常比后部冷却更有效)以及环境条件(如风速越大、环境温度越低和/或云层覆盖越多,光伏冷却效果越好)。与单独使用前置水冷却和后置空气冷却相比,同时使用前置水冷却和后置空气冷却显示出特别的前景。无论采用哪种方法,如前所述,任何效率优势都需要与增加的系统复杂性、成本和功耗相结合。只有当性能优势超过增加的成本时,实施这些解决方案才是可行的,而这在很多情况下都是一个挑战。

3.1.2. Liquid cooling  3.1.2.液体冷却

The cooling of PV panels can be achieved by using several liquids, but the most common liquid is water. Water has a higher density (997 kg/m3), specific heat capacity (4184 J/kg K) and thermal conductivity (0.6 W/m K) than air (density = 1.225 kg/m, specific heat capacity = 1012 J/kg K, thermal conductivity = 0.020 W/m K) and can deliver higher heat transfer coefficients relative to air (for a given geometry and similar flow velocities). This is because the convective heat transfer coefficient depends on the fluid density, thermal conductivity, and specific heat capacity. Relevant thermal management can be done by front or rear cooling based on the surface of the PV panel from which the heat is extracted.
光伏电池板的冷却可通过多种液体实现,但最常见的液体是水。与空气(密度 = 1.225 kg/m,比热容 = 1012 J/kg K,热导率 = 0.020 W/m K)相比,水的密度(997 kg/m 3 )、比热容(4184 J/kg K)和热导率(0.6 W/m K)都更高,因此相对于空气,水能提供更高的传热系数(对于给定的几何形状和类似的流速)。这是因为对流传热系数取决于流体密度、导热系数和比热容。相关的热管理可根据光伏板的散热表面,通过前置或后置冷却来实现。
Mah et al. [52] tested the performance of a retrofitted rooftop PV system with water-film cooling on the front of the PV panels. The electrical performance was improved by 15 % with an optimised water flow rate of 6 L/min at solar irradiance of 1150 W/m2. Similarly, Prudhvi and Sai [53] studied the performance of a PV panel by cooling the panel using a front water-cooling technique. Water was circulated over the front side (top) of the panel with the help of a pump, which in this work had a power consumption of 36 W. The hot water leaving the panel was then circulated through an underground pipe using “groundwater tunnelling”. An assessment of energy savings in this work showed an improvement of 7.8 % in the net efficiency of the panel. Kordzadeh [54] suggested that one of the best ways for improving PV system operation and performance involves cooling with thin water films. A schematic of their PV water-pumping system is shown in Fig. 6. Results generated with this apparatus revealed that there was a significant increase in the generated electricity as the system water pumping rate was increased.
Mah 等人[52] 测试了在光伏板前部采用水膜冷却的屋顶光伏改造系统的性能。在太阳辐照度为 1150 W/m 2 时,优化水流量为 6 L/min,电气性能提高了 15%。同样,Prudhvi 和 Sai [53] 通过使用正面水冷技术冷却光伏板,研究了光伏板的性能。水借助水泵在面板的正面(顶部)循环,在这项研究中,水泵的功耗为 36 W。这项工作的节能评估显示,热板的净效率提高了 7.8%。Kordzadeh [54] 认为,改善光伏系统运行和性能的最佳方法之一是使用薄膜水进行冷却。他们的光伏水泵系统示意图如图 6 所示。使用该设备得出的结果显示,随着系统水泵速率的增加,发电量也显著增加。
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Fig. 6. Schematic of a PV water pumping system used in the study [54].
图 6.研究中使用的光伏水泵系统示意图 [54]。

Shahverdian et al. [55] utilised a dynamic multi-objective optimisation method to optimise and control the flow rate of the water used for cooling PV panels, with the aim of minimising water consumption while maximising power output. Their simulations showed that the average and maximum temperatures of the water-cooled PV panel with the optimal flow rate can be reduced by 54 % and 61 %, compared to a PV panel without water cooling. Hadipour et al. [56] compared the performance of steady-spray and pulsed-spray water cooling systems for PV panels. The testing results showed that the maximum power output of the PV panel increased by 33% and 26 % by using the steady-spray and pulsed-spray water cooling, compared to a PV panel without water cooling. The water consumption of the pulsed-spray cooling system is only one-ninth of that of the steady-spray cooling system. Therefore, the levelised cost of energy (LCOE) of the PV panel with pulsed-spray cooling was reduced by 76 % relative to the PV panel with steady-state cooling owing to the significantly reduced water consumption.
Shahverdian 等人[55] 利用动态多目标优化方法来优化和控制用于冷却光伏板的水流量,目的是在最大限度地提高功率输出的同时最大限度地降低耗水量。他们的模拟结果表明,与没有水冷却的光伏面板相比,采用最佳流速的水冷却光伏面板的平均温度和最高温度分别降低了 54% 和 61%。Hadipour 等人[56] 比较了光伏板稳定喷淋和脉冲喷淋水冷却系统的性能。测试结果表明,与无水冷却的光伏板相比,使用稳定喷淋和脉冲喷淋水冷却系统的光伏板的最大功率输出分别提高了 33% 和 26%。脉冲喷淋冷却系统的耗水量仅为稳定喷淋冷却系统的九分之一。因此,与采用稳态冷却的光伏板相比,采用脉冲喷淋冷却的光伏板的平准化能源成本(LCOE)降低了 76%,原因是耗水量大幅减少。
Dorobantu et al. [57] also considered a front water-cooling technique. The water flowed from a tube over the top of the panel, cooling the panel and also eliminating debris, which can affect performance detrimentally but also lead to physical damage. The experiment was done using a PV panel with an area of 0.56 m2 using free-flowing water at a rate of 0.03 kg/s. It was noted that the output electric power increased by 4 W due to a corresponding decrease in the PV temperature. In related work, Moharram et al. [58] also conducted experiments in which water was used for PV panel cooling, although no air-cooling was considered. In these experiments, non-pressurised water was sprayed over PV panels when the panel attained a maximum attainable temperature (MAT), i.e., 45 °C. It was observed that the water cooling enhanced the efficiency of the panel, and that operating the cooling system for 5 min resulted in a decrease in the solar cells temperature by 10 °C, and thereby an increase in the solar cell efficiency by 13 %.
Dorobantu 等人[57]还考虑了前置水冷技术。水从一个管子流过面板顶部,冷却面板的同时也消除了碎屑,因为碎屑不仅会对性能产生不利影响,还会导致物理损坏。实验使用了一块面积为 0.56 米 2 的光伏板,以 0.03 千克/秒的速度自由流水。结果表明,由于光伏温度的相应降低,输出电功率增加了 4 W。在相关工作中,Moharram 等人[58] 也进行了用水冷却光伏板的实验,但没有考虑空气冷却。在这些实验中,当光伏板达到最高可达到温度 (MAT)(即 45 °C)时,在光伏板上喷洒非加压水。据观察,水冷却提高了电池板的效率,冷却系统工作 5 分钟可使太阳能电池温度降低 10 °C,从而使太阳能电池效率提高 13%。
From the aforementioned studies, it can be deduced that front surface cooling is effective in reducing pumping costs, especially in hot climate conditions. However, a key drawback is the evaporation of water over the solar cells, which requires continuous replenishment, but which also significantly hinders the solar radiation reaching the cells through absorption. With respect to the various front water-cooling approaches and designs, spray cooling can lead to more water wastage compared to film cooling, and pulsed spray cooling can minimise the wastage. At the same time, film cooling is the most suitable for water reuse, via recovery and recirculation. It remains uncertain whether pulsed spray cooling at regular intervals or spraying the water after the PV panel achieves a set maximum temperature is the most effective cooling solution, so further research should be conducted to compare these two front water-cooling scenarios.
从上述研究中可以推断出,前表面冷却可以有效降低泵送成本,尤其是在炎热的气候条件下。然而,一个关键的缺点是太阳能电池上的水会蒸发,这需要不断补充,同时也大大阻碍了通过吸收到达电池的太阳辐射。就各种前置水冷却方法和设计而言,喷雾冷却会比薄膜冷却造成更多的水浪费,而脉冲喷雾冷却则可以最大限度地减少浪费。同时,薄膜冷却最适合通过回收和再循环实现水的再利用。目前仍不确定定期脉冲喷淋冷却或在光伏板达到设定的最高温度后喷淋水是否是最有效的冷却解决方案,因此应开展进一步研究,对这两种前置水冷方案进行比较。
Concerning rear water cooling, Zondag et al. [59] developed an advanced numerical model for determining the thermal output of a hybrid PV-T collector based on a sheet-and-tube design. The temperature distribution and heat flow over the surface of and through the integrated panel are shown in Fig. 7. Their results revealed that the electrical and thermal efficiencies of the combined system were 6.7 % and 33 %, respectively, compared to 7.2 % for a conventional standalone PV panel and 54 % for a conventional standalone solar-thermal collector. Active rear water cooling is usually accomplished with the aid of pipes that are fitted at the rear side of a panel, with such arrangements also suitable in PV-T applications. A further discussion on hybrid PV-T water collectors is provided in Section 7.
关于后部水冷却,Zondag 等人[59] 开发了一种先进的数值模型,用于确定基于片管设计的光伏-T 混合集热器的热输出。图 7 显示了集成板表面和穿过集成板的温度分布和热流量。他们的研究结果表明,组合系统的电效率和热效率分别为 6.7% 和 33%,而传统独立光伏板的电效率和热效率分别为 7.2% 和 54%。主动式后部水冷却通常借助安装在面板后侧的管道来实现,这种安排也适用于 PV-T 应用。第 7 节将进一步讨论光伏-热混合集热器。
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Fig. 7. Temperature distribution over a PV panel with water circulation [59].
图 7.有水循环的光伏板上的温度分布[59]。

Beyond conventional rear water-cooling systems designed for PV-T applications, some further innovative designs have been proposed by researchers aimed at reducing the water utilisation necessary for PV cooling. Musthafa [60] considered a sponge attached to the backside of a PV panel for cooling purposes. The results from these experiments showed a 4 °C temperature reduction and a 2.6 % efficiency increase. Such a sponge system uses capillary action to drive a cooling water flow, and the utilisation of a reduced quantity of water might be attributed to the decreased volume of water contacting the rear surface of the panel due to the presence of the sponge. The cost of the sponge in this solution is low, however, a projected lifetime of about 6 months for the sponge requires a level of maintenance in this solution, which nevertheless is relatively simple to undertake.
除了为 PV-T 应用设计的传统后置水冷系统外,研究人员还提出了一些进一步的创新设计,旨在降低光伏冷却所需的水利用率。Musthafa [60]考虑将海绵附在光伏板背面进行冷却。实验结果表明,温度降低了 4 °C,效率提高了 2.6%。这种海绵系统利用毛细作用驱动冷却水流,由于海绵的存在,接触面板后表面的水量减少,从而减少了水的使用量。本方案中海绵的成本较低,但预计海绵的使用寿命约为 6 个月,因此需要对本方案进行一定程度的维护,但维护工作相对简单。
Abdelrahman et al. [61] studied the effects of front cooling (film water cooling), direct contact rear water cooling and combined cooling, accomplished via the use of two water pumps. The first pump was operated to provide a water film flow over the front side of the panel, while the second pump was used to recirculate water through a finned duct attached to the bottom of the panel. The experimental results showed that the PV panel temperature was reduced by 16 °C, 18 °C and 25 °C and the daily power output was enhanced by 22 %, 30% and 35% for front cooling, rear cooling and combined cooling, in all cases relative to a standalone PV panel without additional cooling, with tests done on typical sunny June and July days in Cairo. The rear cooling was more efficient than the front cooling. The combination of the front and rear cooling resulted in the best cooling performance.
Abdelrahman 等人[61]研究了前部冷却(薄膜水冷却)、直接接触后部水冷却以及通过使用两个水泵进行组合冷却的效果。第一台水泵用于在面板前侧提供水膜流,而第二台水泵则用于通过连接在面板底部的翅片管道进行水循环。实验结果表明,与没有额外冷却的独立光伏板相比,前部冷却、后部冷却和组合冷却的光伏板温度分别降低了 16°C、18°C 和 25°C,日输出功率分别提高了 22%、30% 和 35%。后冷却比前冷却效率更高。前置和后置冷却组合的冷却效果最佳。
Several studies have compared water and air cooling, which has aided our understanding of the potential and relative technical (performance, operational) and economic characteristics of each approach. Specifically, Bevilacqua et al. [62] performed a long-term evaluation (8 months) of different cooling methods based on spray cooling, spray cooling with metallic plate and forced ventilation, on the rear side of the panel. A maximum temperature reduction of about 26 °C was obtained on sunny days for spray cooling relative to the panel with no cooling. Spray cooling at the rear side produced a maximum cooling effect in the hot months, as a higher cooling demand is satisfied with water-based cooling. Meanwhile, forced ventilation provided a better cooling effect in winter months since the ambient air temperature was low enough to serve as an effective heat-carrying fluid. Irwan et al. [63] compared the performance of a PV panel with front water cooling with that of a PV panel with regular air cooling. Their outdoor experiment results showed that water cooling is more effective than air cooling. The PV panel with front water cooling generated 6.8 % more output power than the PV panel with air cooling on a typical March day in Malaysia. Furthermore, studies have also employed combined active water and air cooling. Leow et al. [64] demonstrated an enhanced cooling effect by using a brushless fan for rear cooling and a water pump for front cooling. This system was controlled by a microcontroller and temperature sensor. Sensors were used to control the on and off switching of the hybrid system automatically when the temperature changed beyond the set maximum temperature. The outdoor experiment results indicated an increase in the average output voltage, current and output power by 5 %, 40 % and 43 %, respectively. The panel temperature decreased by 6.8 °C on a typical March day in Malaysia with an average ambient temperature of 33.6 °C.
有几项研究对水冷和风冷进行了比较,这有助于我们了解每种方法的潜力和相对技术(性能、操作)及经济特性。具体而言,Bevilacqua 等人[62]对面板后侧的喷淋冷却、金属板喷淋冷却和强制通风等不同冷却方法进行了长期评估(8 个月)。在晴天,喷雾冷却相对于无冷却的面板温度最高降低了约 26 °C。在炎热的月份,后侧的喷淋降温能产生最大的降温效果,因为水基降温能满足更高的降温需求。同时,由于环境空气温度低到足以成为有效的载热流体,因此强制通风在冬季能提供更好的冷却效果。Irwan 等人[63]比较了采用前置水冷却的光伏电池板和采用普通空气冷却的光伏电池板的性能。他们的室外实验结果表明,水冷比风冷更有效。在马来西亚一个典型的三月天,采用前置水冷却的光伏电池板比采用空气冷却的光伏电池板多产生 6.8% 的输出功率。此外,也有研究采用了主动水冷和空气冷却相结合的方法。Leow 等人[64] 通过使用无刷风扇进行后部冷却和水泵进行前部冷却,展示了增强的冷却效果。该系统由微控制器和温度传感器控制。当温度变化超过设定的最高温度时,传感器自动控制混合系统的开关。 室外实验结果表明,平均输出电压、电流和输出功率分别增加了 5%、40% 和 43%。在马来西亚平均环境温度为 33.6 ° C 的典型三月天,电池板温度降低了 6.8 °C。
Other research has considered oils as a cooling medium. Sun et al. [65] investigated direct-liquid cooling of a CPV panel using dimethyl silicone oil as the liquid, which flowed through a narrow rectangular chamber in thermal contact with the PV cell, thereby maintaining an average cell temperature within the range of 20–30 °C at 910 W/m2 with the oil inlet temperature of 15 °C. It was reported that the cell temperature was relatively uniform and that the electrical performance of the cells immersed in the silicon oil was stable, with no obvious efficiency degradation observed even after being immersed for 270 days.
其他研究也将油类作为冷却介质。Sun 等人[65] 研究了使用二甲基硅油作为液体对 CPV 面板进行直接液体冷却的方法,液体流经一个与光伏电池热接触的狭窄矩形腔,从而在 910 W/m 2 、进油温度为 15 °C 的条件下将电池平均温度维持在 20-30 °C 的范围内。据报告,电池温度相对均匀,浸入硅油中的电池电气性能稳定,即使浸入 270 天也没有观察到明显的效率下降。
The studies summarised above demonstrated that active (i.e., pumped) water or oil flows can be used to cool PV panels effectively. Water can be circulated through a PV panel either over or under the PV cells, or both over and the cells at the same time. Using water as a coolant has shown better results than active air cooling, however, careful consideration is needed for the use of water in the water-stressed area. It is noted that passive cooling techniques based on air and water, which are discussed in the next section, are arguably considered by some investigators as more effective than active cooling techniques overall since additional parasitic power consumption is not required to promote cooling. A summary of further studies on PV panel efficiency enhancement by active water cooling is provided in Table 1.
上文总结的研究表明,主动(即泵送)水流或油流可用于有效冷却光伏板。水可以在光伏电池板上方或下方循环,也可以同时在电池板上方和下方循环。使用水作为冷却剂比主动空气冷却效果更好,但在缺水地区使用水时需要慎重考虑。值得注意的是,下一节将讨论基于空气和水的被动冷却技术,一些研究人员认为这种技术总体上比主动冷却技术更有效,因为促进冷却不需要额外的寄生功耗。表 1 提供了通过主动水冷却提高光伏电池板效率的进一步研究摘要。

Table 1. Summary of research aimed at efficiency enhancement of PV panels by active water cooling.
表 1.旨在通过主动水冷提高光伏电池板效率的研究综述。

Nature of work  工作性质Method  方法PV panel temperature reduction
降低光伏板温度
Efficiency enhancement  提高效率Observation/remark  意见/评论Ref.  参考文献
Experimental  实验性Thin-film water cooling on the film side and finned water duct at the rear side
薄膜侧采用薄膜水冷却,后侧采用翅片式水管
Average temperature reduction by 4 °C
平均气温降低 4 °C
Electrical efficiency enhancement by 12 %
电气效率提高 12
Integration of water absorption sponge on the rear of PV panels can reduce their temperature over prolonged periods by passing water drop by drop through a sponge to maintain wet conditions over the panel.
在光伏电池板的背面集成吸水海绵,通过将水一滴一滴地滴在海绵上,使电池板保持湿润状态,从而长时间降低电池板的温度。
[60]
Experimental and numerical
实验和数值
Water splashed on the front side of the panel in a non-pressurised way
水以非加压方式溅到面板正面
Cooling of PV panel for 5 min resulted in a 10 °C temperature drop
光伏板冷却 5 分钟后,温度下降 10 °C
Water cooling resulted in electrical efficiency enhancement of 13 %
水冷使电气效率提高了 13
It was observed that water cooling can clean and cool PV panels in hot and sandy regions, resulting in better performance.
据观察,水冷可以清洁和冷却炎热多沙地区的光伏电池板,从而提高其性能。
[58]
Experimental  实验性Water flowed through a tube over the array surface
水通过一根管子流过阵列表面
Temperature reduction of about 25 °C at solar noon
太阳正午时温度降低约 25 °C
  -Results show that this method can improve the optical properties of the array surface and increase the overall efficiency of the system.
结果表明,这种方法可以改善阵列表面的光学特性,提高系统的整体效率。
[54]
Experimental and numerical
实验和数值
Water flowed through multi-header microchannels
水流通过多头微通道
Temperature reduction of 19 % for multi-header channel
多头通道温度降低 19
Power output increased by 28 % for the multi-header micro-channel compared to a single-header channel
与单头微通道相比,多头微通道的功率输出增加了 28
The multi-header channel can allow a greater temperature reduction and electrical efficiency improvements to the wider system.
多集电极通道可以进一步降低温度,提高整个系统的电气效率。
[66]
Experimental and numerical
实验和数值
Surface cooling technique
表面冷却技术
Average temperature reduction by 16 °C
平均温度降低 16 °C
Power enhancement of about 15 % during peak radiation conditions
在辐射峰值条件下,功率提升约 15
Better PV cooling due to the straight connection between the PV panel surface and water. The surface can be dust-free thanks to continuous water flow. Overall PV efficiency is higher.
由于光伏板表面与水直通,因此光伏冷却效果更好。由于持续的水流,光伏板表面无灰尘。整体光伏效率更高。
[67]
Experimental  实验性Spraying of water over the PV panel front surface
在光伏板正面喷水
Decrease in operating temperature by 5 °C to 23 °C
工作温度降低 5 °C 至 23 °C
With water cooling, the output power of the PV panel increased by 9.7 % to 22 %
采用水冷却后,光伏电池板的输出功率增加了 9.7% 至 22
Results showed a reduction in operating temperature and an increase in output power of the PV panel with a water-cooling system.
结果表明,使用水冷系统后,光伏电池板的工作温度降低,输出功率增加。
[68]
Experimental  实验性Water spray cooling on the front and back sides of the panel
面板前后两侧喷水冷却
Average PV panel temperature dropped to 32 °C from 52 °C
光伏板平均温度从 52 °C降至 32 °C
Front and back side PV panel cooling by spraying water results in an increase in power output by 16 % and 5.9 % respectively
通过喷水冷却光伏面板的正面和背面,可使输出功率分别增加 16 % 和 5.9 %。
The proposed water spray cooling procedure enhanced the performance of the PV panel and also kept the panel clean from dust particles.
拟议的喷水冷却程序提高了光伏电池板的性能,还保持了电池板的清洁,使其免受灰尘颗粒的影响。
[69]
Experimental and numerical
实验和数值
Water cooling on the backside of the panel
面板背面的水冷却
The temperature of the PV panel dropped to 34 °C from 45 °C
光伏板的温度从 45 °C 降至 34 °C
The PV panel electrical efficiency increased by 9.1 %
光伏电池板的发电效率提高了 9.1
Energy generated by the hybrid water cooled PV system was nearly four times that of the PV without cooling.
混合水冷光伏系统产生的能量几乎是无冷却光伏系统的四倍。
[70]

3.2. Passive thermal management
3.2.被动热管理

Although active cooling by forced convection has been proven to be capable of improving the electrical efficiency of PV panels, major drawbacks arise from the parasitic power consumption associated with circulating the coolant and the additional costs of the pumping and hydraulic components (e.g., valves, fittings), as well as the necessary fluid circuits and conduits. These difficulties are not encountered or are circumvented by employing passive cooling methods, which have therefore also attracted attention.
虽然通过强制对流进行主动冷却已被证明能够提高光伏电池板的电能效率,但其主要缺点是冷却剂循环会产生寄生功耗,泵和液压元件(如阀门、配件)以及必要的流体回路和导管会增加成本。采用被动冷却方法就不会遇到或避免了这些困难,因此也引起了人们的关注。
Passive cooling relies on the cooling of PV panels without the use of pumps or fans, but often using natural convection of fluids such as air, water, etc., and/or by using radiative heat loss enhancement, surface structures, emissivity control, etc. Since no pump, fan or associated components are required by these methods, the pumping/blowing costs (and the related system complexity) are removed, making these solutions, generally, more cost-effective, with less required maintenance. Furthermore, since the energy required for coolant circulation is no longer required, and even though the use of forced convection is associated with higher heat transfer rates and can allow lower PV temperatures, it is still possible for passive cooling methods to reach higher overall efficiencies relative to active cooling alternatives. Passive cooling that relies on convective heat removal can be sub-divided into air cooling, water cooling, fin cooling, heat pipe cooling, and PCM integrated cooling, and these are addressed in the present section.
被动冷却是指在不使用泵或风扇的情况下冷却光伏电池板,但通常使用空气、水等流体的自然对流,和/或使用辐射热损增强、表面结构、发射率控制等方法。由于这些方法不需要泵、风扇或相关组件,因此消除了泵/吹风的成本(以及相关系统的复杂性),使这些解决方案通常更具成本效益,所需的维护也更少。此外,由于不再需要冷却剂循环所需的能量,尽管强制对流的热传导率更高,光伏温度也更低,但被动冷却方法仍有可能达到比主动冷却方法更高的总体效率。依靠对流散热的被动冷却可细分为空气冷却、水冷却、翅片冷却、热管冷却和 PCM 集成冷却,本节将讨论这些方法。

3.2.1. Passive air cooling
3.2.1.被动式空气冷却

Air cooling via passive approaches has attracted particular attention in recent decades. Advantages of this approach include: (i) minimal material requirements, (ii) low operating costs, (iii) no power consumption compared to active cooling, and (iv) easy handling. However, some disadvantages also arise, primarily from key thermal properties of air relative to those of water, e.g.: (i) poor thermal conductivity (i.e., heat transfer), and (ii) low heat capacity (i.e., storage density).
近几十年来,通过被动方式进行空气冷却尤其受到关注。这种方法的优点包括(i) 所需材料最少,(ii) 运行成本低,(iii) 与主动冷却相比不耗电,(iv) 易于处理。然而,这种方法也存在一些缺点,主要是由于空气相对于水的主要热特性造成的,例如:(i) 热传导性差(即热传递),(ii) 热容量低(即存储密度)。
Naghavi et al. [71] investigated the natural air movement beneath a PV panel through numerical assessments. Their results showed that temperature differences of 12 ± 5 °C and 18 ± 5 °C could be obtained when the air gap between the rooftop and panel rear surface was 200 mm and 250 mm, respectively, relative to a panel with no gap. A larger air gap allows a greater volume of air to flow and, thus, it can remove heat from the rear side of the panel through convection effectively. Hernandez et al. [72] studied PV panel cooling by placing a panel on the steel roof of an industrial building. The PV panel was cooled by placing air channels underneath it with natural or forced convection cooling. The experimental results showed that the PV panel temperature with the natural convection cooling is around 5 °C lower than that without natural cooling on the back. In this case, research can be extended to analyse the temperature on the roof and relate it to the panel temperature since higher roof temperatures can decrease the effectiveness of the cooling effect produced by natural convection of air because air gets heated by both panels as well as the roof. Although the PV panel with forced convection cooling was able to generate 3–5 % more electricity than the PV panel with natural convection cooling, the forced convection cooling required a fan to maintain the air flow at 4 m/s in the channels. Therefore, comparing the net power produced by both active and passive cooling approaches will be a more pragmatic approach, but in the reviewed study, proper inference could be made due to the paucity of power consumption data of the fan.
Naghavi 等人[71] 通过数值评估研究了光伏面板下方的自然空气流动。他们的研究结果表明,相对于无间隙的面板,当屋顶和面板后表面之间的空气间隙分别为 200 毫米和 250 毫米时,温差可分别达到 12 ± 5 °C和 18 ± 5 °C。空气间隙越大,空气流动量就越大,从而能有效地通过对流从面板后侧带走热量。Hernandez 等人[72]通过在工业建筑的钢结构屋顶上安装光伏板,研究了光伏板的冷却问题。通过在光伏板下方放置空气通道,利用自然或强制对流冷却光伏板。实验结果表明,采用自然对流冷却的光伏板温度比背面不采用自然冷却的温度低约 5 °C。在这种情况下,研究可以扩展到分析屋顶温度,并将其与面板温度联系起来,因为较高的屋顶温度会降低空气自然对流产生的冷却效果,因为空气会被面板和屋顶同时加热。虽然采用强制对流冷却的光伏电池板比采用自然对流冷却的光伏电池板多发电 3-5 %,但强制对流冷却需要风扇将通道中的气流保持在每秒 4 米的速度。因此,比较主动冷却和被动冷却两种方法产生的净电量将是一种更加务实的方法,但在所审查的研究中,由于风扇的耗电数据较少,因此无法做出适当的推断。
Tonui and Tripanagnostopoulos [73] developed a validated model to investigate the natural convection cooling performance of two different types of low-cost air channels designs, i.e., inserting a flat thin metal sheet (TMS) in the middle of the air channel in one type and attaching fins on the back wall of the channel on the other type. The fins configuration exhibited better thermal performance relative to TMS configuration, which can be explained due to the higher surface area achieved by the extended surface offered by fins, which provides a better overall heat removal rate.
Tonui 和 Tripanagnostopoulos [73]建立了一个验证模型,研究两种不同类型的低成本空气通道设计的自然对流冷却性能,一种是在空气通道中间插入平面金属薄板 (TMS),另一种是在通道后壁安装鳍片。相对于 TMS 配置,翅片配置具有更好的热性能,这可能是由于翅片提供的扩展表面实现了更高的表面积,从而提供了更好的整体散热率。
Shahsavar et al. [74] attached an air channel with TMS below a glazed PV panel as shown in Fig. 8. The air channel was used to cool the PV panel by natural convection cooling. The outlet air temperature reached 48 °C when the solar irradiance was 880 W/m2. The air channel was able to effectively remove the waste heat in the PV panel and generate additional thermal energy. The electrical and thermal efficiencies were around 8 % and 32 %, respectively. However, the authors did not mention the PV temperature change compared to a standalone PV panel, and this hinders solid inferences regarding the effectiveness of the implemented cooling system. This is because it is uncertain whether the air channel offers better performance since channelling can either reduce the replacement rate of air or can increase the velocity of the air flow compared to the case without channels. To verify this, experimental research is recommended to compare performance relative to a reference PV system.
如图 8 所示,Shahsavar 等人[74] 在有玻璃的光伏板下方安装了一个带有 TMS 的空气通道。该空气通道用于通过自然对流冷却光伏板。当太阳辐照度为 880 W/m 2 时,出口空气温度达到 48 °C。空气通道能够有效去除光伏板中的余热,并产生额外的热能。电效率和热效率分别约为 8% 和 32%。然而,作者并未提及与独立光伏板相比的光伏温度变化,这阻碍了对所实施的冷却系统有效性的可靠推断。这是因为空气通道是否能提供更好的性能尚不确定,因为与无通道的情况相比,通道可以降低空气的置换率,也可以提高气流的速度。为了验证这一点,建议进行实验研究,比较与参考光伏系统的性能。
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Fig. 8. Photograph of the practical implementation of the PV-T air system used in Ref. [74].
图 8.参考文献 [74] 中使用的 PV-T 空气系统的实际应用照片。[74].

Rahimi et al. [75] investigated the idea of integrating wind and solar energy to produce more electrical power efficiently. In this concept, which is shown in Fig. 9, the air flows through a converging section (conical tube) and strikes the turbine (wind vane rotor). The experiment was performed for various solar intensities and two different wind velocities of 0.88 and 2.67 m/s. The turbine was designed to direct the air flow radially outwards to the divergent section and the opening of which faced the PV panel’s rear surface for producing the required cooling effect. Therefore, the wind collected from the conical tube served two purposes: (i) acting as coolant fluid for the PV cells, whose operating temperature was observed to decrease on average by 21 °C at a constant solar irradiance of 910 W/m2, and (ii) for generating electrical energy using a turbine. The results showed an overall increase in power generation by 36 % relative to a standalone PV cell without cooling.
Rahimi 等人[75] 研究了将风能和太阳能结合起来以高效生产更多电力的想法。在图 9 所示的这一概念中,空气流经一个汇聚部分(锥形管)并撞击涡轮机(风向叶片转子)。实验针对不同的太阳强度和 0.88 和 2.67 米/秒两种不同的风速进行。涡轮机的设计是将气流径向引向发散部分,发散部分的开口朝向光伏板的后表面,以产生所需的冷却效果。因此,从锥形管收集的风有两个用途:(i) 作为光伏电池的冷却液,在太阳辐照度恒定为 910 W/m 2 的情况下,观察到光伏电池的工作温度平均降低了 21 °C;(ii) 利用涡轮机产生电能。结果表明,与没有冷却的独立光伏电池相比,发电量总体增加了 36%。
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Fig. 9. Schematic of the hybrid wind-PV jet-impingement system for PV panel cooling [75].
图 9.用于光伏板冷却的风光互补喷气增焓系统示意图 [75]。

Another study by Valeh-e-Sheyda et al. [76] experimented with a similar concept of integrating wind turbines and solar energy into a single system. In this system, the turbine used was of an axial type and the velocity of air flow (3 m/s and 5 m/s) was greater than that used in the previous study. The results indicated an enhancement of power output by 47 %. This larger improvement can be pinpointed to design characteristics and higher wind velocity. In general, the exit velocity of the fluid from axial turbines is higher than from radial turbines, which makes axial turbines less effective and suitable for multi-stage purposes [77]. But in the case of PV cooling, the exit velocity of air from the turbine is significant in providing effective cooling since convective heat transfer is enhanced with an increase in fluid velocity and the higher the heat transfer rate, the better will be the PV performance. On the other hand, the input velocity itself is higher in the later study, which favours the improvement of the performance of both the wind turbine as well as the PV cooling. Therefore, a greater enhancement in power was obtained in the later study compared to the former study. However, a major limitation with this hybrid solar and wind turbine power generation approach arises from its complex design and channeling of the air flow which makes it more suitable for active cooling. Such cooling systems may be appropriate for windy regions, while the velocity of air flow can be hampered (due to turbine) even if the system employs active cooling that, in turn, affect the thermal performance of the cooling system.
Valeh-e-Sheyda 等人的另一项研究[76] 尝试了将风力涡轮机和太阳能整合到一个系统中的类似概念。在该系统中,使用的涡轮机是轴流式的,气流速度(3 m/s 和 5 m/s)比前一项研究中使用的要大。结果表明,输出功率提高了 47%。这种较大的改进可归因于设计特点和较高的风速。一般来说,轴流式涡轮机的流体出口速度高于径流式涡轮机,因此轴流式涡轮机的效率较低,不适合用于多级用途 [77]。但就光伏冷却而言,涡轮机的空气出口速度对提供有效冷却非常重要,因为对流传热随着流体速度的增加而增强,传热率越高,光伏性能就越好。另一方面,在后面的研究中,输入速度本身较高,这有利于提高风力涡轮机和光伏冷却的性能。因此,与前一项研究相比,后一项研究获得了更大的功率提升。然而,这种太阳能和风力涡轮机混合发电方法的主要局限性在于其复杂的设计和气流通道,这使其更适用于主动冷却。这种冷却系统可能适用于多风地区,而即使系统采用主动冷却,气流速度也会受到阻碍(由于涡轮机),进而影响冷却系统的热性能。
A range of studies that have been undertaken in the context of achieving PV panels efficiency improvements by passive air cooling is tabulated in Table 2.
表 2 列出了在通过被动式空气冷却提高光伏电池板效率方面进行的一系列研究。

Table 2. Summary of research aimed at efficiency improvement of PV panels by passive air cooling.
表 2.旨在通过被动式空气冷却提高光伏电池板效率的研究综述。

Nature of work  工作性质Temperature reduction  降低温度Efficiency enhancement  提高效率Observation/remark  意见/评论Ref.  参考文献
Numerical  数字Minimum temperature reduction of 10 °C was achieved
温度最低降低 10 °C
Maximum power output of the PV panel increased from 7.0 % to 7.6 % relative to a conventional PV panel
与传统光伏电池板相比,光伏电池板的最大输出功率从 7.0% 提高到 7.6
Results showed that the heat transfer rate and air flow inside the ventilated channel were influenced by the angle of the ribs; specifically, PV panel cooling was directly proportional to the height and inversely proportional to the inclination angle of the ribs.
结果表明,通风通道内的传热率和空气流量受肋条角度的影响;具体而言,光伏板的冷却与高度成正比,与肋条的倾斜角度成反比。
[74]
Experimental and numerical
实验和数值
Average temperature decrease of 21 °C was accomplished
平均气温下降 21 °C
Overall power output of both PV panels and wind turbines increased by 36 %
光伏电池板和风力涡轮机的总输出功率增加了 36
The combined hybrid system was capable of cooling PV panels, thereby increasing their power output and producing power from a turbine.
联合混合动力系统能够冷却光伏电池板,从而提高其功率输出,并通过涡轮机发电。
[75]
Experimental  实验性Operating temperature reduced by 18.3 °C
工作温度降低 18.3 °C
Electrical efficiency increased by 7.9 %
电气效率提高了 7.9
The temperature of PV panels was maintained lower while operating under direct sunlight by radiative passive cooling. A thin material layer over the solar cells was used, which was transparent at solar wavelengths but had higher emissivity in the IR (thermal) wavelengths, thereby emitting significant thermal radiation that cooled the PV panel and enhanced performance.
通过辐射被动冷却,光伏电池板在阳光直射下工作时的温度保持在较低水平。在太阳能电池上使用了一层薄薄的材料,在太阳光波长下是透明的,但在红外(热)波长下具有较高的发射率,从而发出大量热辐射,冷却光伏板并提高性能。
[78]
Numerical  数字PV cell temperature reduced by about 7 to 16 °C when the flow rate reached 1.6 to 5 g min−1
当流速达到每分钟 1.6 至 5 克时,光伏电池温度降低了约 7 至 16 °C −1
Electrical efficiency is enhanced between 12 % and 23 %
电气效率提高了 12% 至 23
A mixture of air and naturally occurring water vapour used as the heat transfer fluid enhanced the electrical performance of a PV panel. The studied system performed best at low flow rates. To improve the performance of PV panels, it was suggested that the panels can be installed in locations where vaporisation occurs naturally.
使用空气和天然水蒸气的混合物作为传热流体,可提高光伏电池板的电气性能。所研究的系统在低流量时性能最佳。为了提高光伏电池板的性能,建议将电池板安装在自然产生水蒸气的地方。
[79]
Experimental  实验性PV panel integrated with clay reached a maximum temperature of 45 °C whereas PV panel without clay reached a temperature as high as 85 °C
集成粘土的光伏板的最高温度为 45 °C,而不集成粘土的光伏板的温度高达 85 °C
Maximum increase in both output voltage and power of 19 % was achieved
输出电压和功率最大提高了 19
Incorporated a clay layer on the back side of a PV panel and a thin film of water vaporised. This lowered the PV operating temperature and enhanced its efficiency. The method was reported as being efficient, cost-effective, stable and environmentally friendly.
在光伏电池板背面加入粘土层,形成一层水蒸气薄膜。这降低了光伏的工作温度,提高了其效率。据报道,这种方法高效、经济、稳定且环保。
[80]
Experimental  实验性An average PV temperature drop of 14 °C was achieved
光伏温度平均下降了 14 °C
Overall power output of the system improved up to 47 %
系统的总体功率输出提高了 47
A hybrid wind-driven ventilator and PV system maintained a suitable environment inside the building by air ventilation and maintained a lower PV cell temperature. The hybrid system resulted in higher electrical energy generation from the PV and dynamo.
风力通风器和光伏发电混合系统通过空气流通维持建筑物内的适宜环境,并保持较低的光伏电池温度。该混合系统提高了光伏发电和发电机的发电量。
[76]

3.2.2. Heat sink and fin cooling
3.2.2.散热器和散热片冷却

A heat sink in this context is a heat exchanger that transfers the heat generated, e.g., at the surface of a PV panel, to a fluid medium, often air or a liquid coolant, thereby dissipating the heat away from the panel and regulating the device’s temperature. When heat dissipation at the heat sink relies on natural convection, the rate of heat dissipation achieved will vary with the angle at which it is placed. Nair et al. [34], demonstrated that it is possible to reduce the temperature of a PV panel by using a passive cooling technique employing a heat sink. The experiment was performed on a clear summer day and it was shown that the PV panel temperature reached at a heat-sink angle of 45° was lower than that reached at 135°, which was recorded to be the maximum temperature. The maximum power production from the same study was also measured and found to increase by 7.0 % at a heat-sink angle of 90° and 7.6 % at 45°, relative to benchmark PV panels that did not adopt any cooling.
这里所说的散热器是一种热交换器,它能将光伏板表面等处产生的热量转移到流体介质(通常是空气或液体冷却剂)中,从而将热量从光伏板上散发出去,并调节设备的温度。当散热器依靠自然对流散热时,其散热率会随着放置角度的变化而变化。Nair 等人[34]证明,利用散热片的被动冷却技术可以降低光伏板的温度。实验是在一个晴朗的夏日进行的,结果表明,散热片角度为 45°时的光伏板温度低于 135°时的温度,而 135°时的温度是记录的最高温度。对同一研究的最大发电量也进行了测量,发现与未采用任何冷却措施的基准光伏板相比,散热角为 90°时的发电量增加了 7.0%,散热角为 45°时的发电量增加了 7.6%。
In related work, Chandrasekar and Senthilkumar [81] experimentally cooled a PV panel by using fins and natural convection. Cotton wicks were attached to aluminium fins and connected to the back of the PV panel, as shown in Fig. 10, to enhance the overall heat transfer rate. It was shown that the aluminium heat spreader along with wet cotton wicks showed better cooling performance compared to the heat spreader alone. It was noted that the maximum PV temperature decreased by around 6 °C and that there was a 14 % increase in the electrical power output from the PV panel. Similarly, Varkute et al. [82] also performed an experiment using fins to cool a 160× CPV panel. In this work, a multi-junction solar cell was placed on a copper block with fins. The rate at which the heat is dissipated from the block with fins was further enhanced by circulating water actively below the fins. The panel temperature was maintained at around 45 °C, which was significantly lower than that expected for the case in which no thermal management was employed (by about 58 °C). In another study, Zubeer et al. [83] examined the role of forced and natural air circulation on the performance of PV panels. An experiment was performed using an air channel modified to boost the transfer of heat in two different ways: (i) by inserting a thin flat metallic sheet in the centre of the channel, and (ii) by joining rectangular fins at the rear side of the panel. The results revealed that fins allowed greater thermal efficiency and better operating performance than the metal sheet system.
在相关研究中,Chandrasekar 和 Senthilkumar [81] 通过实验利用鳍片和自然对流冷却光伏板。如图 10 所示,棉芯被连接到铝鳍片上,并与光伏板背面相连,以提高整体热传导率。结果表明,与单独的散热器相比,铝散热器和湿棉芯的冷却效果更好。据指出,光伏板的最高温度降低了约 6 °C,光伏板的电力输出增加了 14%。同样,Varkute 等人[82] 也进行了一项使用散热片冷却 160× CPV 面板的实验。在这项工作中,一个多接面太阳能电池被放置在带鳍片的铜块上。通过在鳍片下方积极循环水,进一步提高了带鳍片铜块的散热速度。电池板的温度保持在 45 °C左右,大大低于未采用热管理的情况下的预期温度(约 58 °C)。在另一项研究中,Zubeer 等人[83] 研究了强制和自然空气循环对光伏电池板性能的影响。实验使用了一个经过改装的空气通道,以两种不同的方式促进热量的传递:(i) 在通道中心插入一个薄的平面金属片;(ii) 在面板后侧连接矩形鳍片。结果表明,与金属片系统相比,鳍片的热效率更高,运行性能更好。
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Fig. 10. Experimental photographs from [81]: (a) backside of PV panel, (b) thermocouple locations, (c) fins joined with wick structures, (d) stiffeners, and (e) final fabricated arrangement.
图 10.来自文献[81]的实验照片:(a)光伏板背面,(b)热电偶位置,(c)与灯芯结构连接的散热片,(d)加强筋,(e)最终制作的布置。

Idoko et al. [84] explored the operating performance of a PV panel involving two different passive techniques, namely passive air and passive water cooling. As shown in Fig. 11, aluminium fins were attached to the bottom of a PV panel for air cooling, while cold water was manually sprayed over the top surface of the same PV panel to further enhance the cooling effect. It was observed that the temperature of the PV panel with the integrated air and water cooling was reduced by 20 °C and the power output was raised by 21 W relative to a PV panel without cooling under a solar irradiance of 1080 W/m2.
Idoko 等人[84] 利用两种不同的被动技术,即被动风冷和被动水冷,探索了光伏板的运行性能。如图 11 所示,在光伏板的底部安装铝翅片进行空气冷却,同时在同一光伏板的上表面手动喷洒冷水,以进一步提高冷却效果。据观察,在太阳辐照度为 1080 W/m 2 的条件下,与未进行冷却的光伏板相比,集成了空气和水冷却的光伏板温度降低了 20 °C,功率输出提高了 21 W。
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Fig. 11. Experimental apparatus showing fins connected to the backside of a PV panel [84].
图 11.实验装置,显示连接到光伏板背面的鳍片 [84]。

Othman et al. [85] investigated a hybrid PV-T solar air heater system with fins connected to the absorber surface to enhance the heat convection. The schematic of the hybrid PV-T system explored in this study is shown in Fig. 12. Air flows through the upper channel and then through the bottom channel with fins. The thermal and electrical efficiencies were absolutely improved by around 20 % and 0.5 % as the air mass flow rate increased from 0.027 to 0.181 kg/s.
Othman 等人[85] 研究了一种 PV-T 混合型太阳能空气加热器系统,该系统在吸收器表面连接了翅片,以增强热对流。该研究中探讨的 PV-T 混合系统示意图如图 12 所示。空气流经上部通道,然后流经带有翅片的底部通道。当空气质量流量从 0.027 千克/秒增加到 0.181 千克/秒时,热效率和电效率分别提高了约 20% 和 0.5%。
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Fig. 12. Schematic of the PV-T solar air heater with fins investigated in the study [85].
图 12.研究[85]中使用的带鳍片的 PV-T 太阳能空气加热器示意图。

Recent scientific literature has also emphasised modifying the heatsink profile and fin orientation to enhance the heat transfer rate. For instance, Hernandez-Perez et al. [86] modified the heatsink geometric parameters to enhance the passive cooling ability of the fins attached to PV panels. The authors proposed a discontinued finned heatsink that helped in inducing air flow in multiple directions which in turn enhanced the heat transfer rate. Numerical simulation showed a temperature reduction of 7 °C which was close to the experimental results (a drop of 5 °C).
最近的科学文献也强调通过修改散热片外形和鳍片方向来提高热传导率。例如,Hernandez-Perez 等人[86] 修改了散热片的几何参数,以增强附着在光伏面板上的散热片的被动冷却能力。作者提出了一种不连续的鳍状散热片,有助于诱导多个方向的气流,进而提高热传导率。数值模拟显示温度降低了 7 °C,与实验结果(降低 5 °C)接近。
The typical fin shapes/geometries used for the passive cooling of PV panels (or, similarly, of PV cells in PV-T collectors) often tend to be longitudinal, rectangular and baffled fins. The performance of PV panels can also be enhanced by using heat pipes, which is the subject of the following section. Research results have shown that heat sinks and fins are effective in reducing the operating temperature and increasing the electrical conversion efficiency of PV panels. The cooling effect of fins strongly depends on the material and geometric parameters of the fins. The performance of fin cooling for PV panels is summarised and compared in Table 3. The cooling effect of fins usually increases with an increase in the fin length. Most research only focusses on the improvement of panel efficiencies induced by the additional fin structures, but only a few studies investigate the additional cost of the fins (and other related components), which should be considered in future research. Fin structures have also been widely investigated and applied in other fields such as electronic cooling systems and domestic space heaters. Therefore, lessons from the use of fins in other fields can also be applied to PV panels for cooling.
用于光伏板(或类似于 PV-T 集热器中的光伏电池)被动冷却的典型翅片形状/几何形状通常是纵向、矩形和障板翅片。使用热管也能提高光伏板的性能,这就是下一节的主题。研究结果表明,散热器和散热片可有效降低光伏板的工作温度,提高其电能转换效率。散热片的冷却效果在很大程度上取决于散热片的材料和几何参数。表 3 总结和比较了光伏电池板散热翅片的性能。翅片的冷却效果通常随着翅片长度的增加而提高。大多数研究只关注附加翅片结构对面板效率的改善,但只有少数研究调查了翅片(及其他相关组件)的额外成本,这一点应在未来的研究中加以考虑。翅片结构在其他领域也得到了广泛的研究和应用,如电子冷却系统和家用空间加热器。因此,在其他领域使用翅片的经验教训也可应用于光伏板冷却。

Table 3. Summary of research aimed at efficiency enhancement of PV panels by fin cooling.
表 3.旨在通过翅片冷却提高光伏电池板效率的研究综述。

Nature of work  工作性质Temperature reduction  降低温度Efficiency enhancement  提高效率Observation/remark  意见/评论Ref.  参考文献
Experimental  实验性  -Up to 5.5 % relative increase in peak power
峰值功率最高可相对提高 5.5
Passive cooling technique in aluminium fins was mounted on the rear side of a PV panel with conductive epoxy glue, which resulted in lower PV temperatures and enhanced efficiency and lifetime of PV panel.
利用导电环氧胶在光伏板背面安装铝翅片的被动冷却技术可降低光伏板的温度,提高光伏板的效率和使用寿命。
[87]
Experimental and numerical
实验和数值
Overall thermal resistance with a flared-fin heat sink was 10 % lower than that of a rectangular-fin heat sink
喇叭形鳍片散热器的整体热阻比矩形鳍片散热器低 10
  -The number and length of fins in a flared-fin heat sink had a significant influence on thermal performance. However, the inclination angle of the fins did not strongly affect thermal performance. It was observed that 15 to 18 fins resulted in optimum system performance.
扩口鳍片散热器中鳍片的数量和长度对散热性能有很大影响。不过,散热片的倾斜角度对散热性能的影响不大。据观察,15 至 18 片鳍片可实现最佳系统性能。
[88]
Experimental  实验性Maximum surface temperature obtained by a finned panel (with 10 mm thick and 5 mm high porous aluminium fins) was 48 °C
翅片面板(厚 10 毫米、高 5 毫米的多孔铝翅片)的最高表面温度为 48 °C
Highest output power of the panel without fins, with 6 mm fins and 10 mm fins, was 41.8 W, 44.7 W and 47.9 W, respectively, and panel with 10 mm fins showed maximum power enhancement of 14 % compared to panel without fins
与不带鳍片的面板相比,带 6 毫米鳍片和 10 毫米鳍片的面板的最高输出功率分别为 41.8 瓦、44.7 瓦和 47.9 瓦。
Integrating porous fins into a PV panel enhanced the overall performance.
将多孔鳍片集成到光伏板中可提高整体性能。
[89]
Experimental  实验性Average temperature of the front surface was reduced by 6.1 °C
前表面的平均温度降低了 6.1 °C
Electrical efficiency enhanced by 1.8 %
电气效率提高 1.8
PV panel temperature was always lower than the maximum allowable temperature due to constant heat absorption by the finned plate which acted efficiently as a heat sink.
由于散热片持续吸热,光伏板的温度始终低于最高允许温度。
[90]
Numerical  数字Reported a 3 °C drop in operating temperature
报告工作温度下降了 3 °C
Electrical efficiency enhanced by 2.6 %
电气效率提高 2.6
Integration of fins can reduce operating temperature and improve efficiency. Fins can be integrated with other solutions/approaches for much better results.
集成翅片可以降低工作温度,提高效率。翅片可与其他解决方案/方法相结合,以获得更好的效果。
[91]

3.2.3. Heat pipe cooling  3.2.3.热管冷却

Another method for passive cooling relies on the use of heat pipes, owing to their simplicity and low-cost relative to active cooling approaches. The characteristic feature of heat pipe cooling is that a very high rate of heat transfer can be achieved relative to other passive cooling means, due to internal phase change [92]. For this reason, one area where the employment of heat pipes has attracted attention, owing to their high heat transfer rates, is in the cooling of CPV systems. For CPV, a review study highlighted that acetone and ethanol yield better performance (when used as heat transfer fluids, HTFs) since they can produce 7- and 3-times higher cooling effects, respectively, compared to water [93]. Further, the inclusion of fins in the condenser section could improve the thermal performance but the spacing of fins is recommended to be higher than the thickness of the fluid boundary layer to prevent flow blockage due to the boundary layer.
另一种被动冷却方法是使用热管,因为与主动冷却方法相比,热管简单、成本低。热管冷却的特点是,与其他被动冷却方法相比,由于内部相变,可以实现非常高的热传导率[92]。因此,由于热管的高热传导率,其在 CPV 系统冷却中的应用备受关注。对于 CPV,一项综述研究强调,丙酮和乙醇(用作导热液体时)性能更佳,因为它们的冷却效果分别是水的 7 倍和 3 倍 [93]。此外,在冷凝器部分加入鳍片可以提高热性能,但建议鳍片的间距应大于流体边界层的厚度,以防止边界层造成的流动阻塞。
Heat pipes are readily used in combination with other solutions and approaches, such as air or water cooling, as applied to both PV panels and also hybrid PV-T collectors, aimed at further maximising the overall performance of PV panels [73], [82]. In most designs where heat pipes are employed, the heat absorbed by the working fluid is eventually rejected to the surroundings (most often, ambient air), possibly through a heat sink, by using natural convection (air cooling). In these cases, a challenge arises from the fact that the dominant thermal resistance lies in the latter process of heat rejection.
热导管很容易与其他解决方案和方法(如空气或水冷却)结合使用,既适用于光伏电池板,也适用于混合型光伏-T 集热器,旨在进一步最大限度地提高光伏电池板的整体性能 [73],[82]。在大多数采用热管的设计中,工作流体吸收的热量最终会通过自然对流(空气冷却)排出到周围环境(通常是环境空气),也可能通过散热片排出。在这种情况下,主要热阻在于后一个排热过程,这就给设计带来了挑战。
Al-Amri [94] experimented with PV panels using passive and active cooling techniques in the harsh climate of Saudi Arabia, with passive cooling accomplished in this work with the aid of heat sinks in one configuration, while another configuration integrated heat sinks with a PCM. On the other hand, the actively cooled PV modules consisted of heat pipes and a liquid immersion cooling technique. The results showed that a PVT collector with heat pipes and also immersed in water can result in uniform distribution of temperature across the panel and an overall maximum temperature drop of 53 % was obtained relative to the best passively cooled configuration (heat sinks). Since the climatic conditions of Saudi Arabia are extreme, the cooling demand is greater and thus, the heat pipe configuration was effective in transferring heat while the water medium absorbed the heat from the collector. The result also showed that the steady-state temperature of the PV panel was reduced by 21 %, 25 % and 48 %, for ethylene glycol, engine oil, and active cooling without immersion, respectively.
Al-Amri [94]在沙特阿拉伯恶劣的气候条件下使用被动和主动冷却技术对光伏板进行了实验,其中一种配置是借助散热器实现被动冷却,而另一种配置则将散热器与 PCM 集成在一起。另一方面,主动冷却的光伏组件由热管和液体浸入冷却技术组成。结果表明,带有热管且浸入水中的 PVT 集热器可使整个面板的温度分布均匀,与最佳被动冷却配置(散热片)相比,总体最大温降为 53%。由于沙特阿拉伯的气候条件极端恶劣,冷却需求较大,因此热管配置能有效传递热量,而水介质则能吸收来自集热器的热量。结果还显示,乙二醇、机油和无浸泡主动冷却的光伏板的稳态温度分别降低了 21%、25% 和 48%。
Hughes et al. [92] conducted an experiment in which a PV panel was cooled by using a heat pipe passive cooling technique. These experiments showed that fins on the heat pipe were significantly more effective than bare heat pipes alone, which suggests that (as mentioned above), the dominant thermal resistance in this system is outside of the heat pipe component itself. Similarly, Tang et al. [95] experimentally examined the cooling performance of heat pipe array for PV panel cooling. The evaporator section of the heat pipe array was attached to the back of the PV panel while the condenser section was passively cooled by water or air. The results showed that when using the passive air cooling on one end of the heat pipes, the electrical power output of the panel could be increased by 8.4 % and the temperature reduced by 4.7 °C relative to a PV panel without cooling, whereas when using the passive water cooling, the power output could be further increased by 14 % and the temperature reduced by 8 °C. The authors concluded that the use of heat pipes along with water cooling was better than natural (passive) air cooling.
Hughes 等人[92]进行了一项实验,使用热管被动冷却技术冷却光伏板。实验结果表明,热管上的散热片明显比单独裸露的热管更有效,这表明(如上所述)该系统中的主要热阻在热管部件本身之外。同样,Tang 等人[95] 通过实验研究了用于光伏板冷却的热管阵列的冷却性能。热管阵列的蒸发器部分与光伏板背面相连,而冷凝器部分则由水或空气被动冷却。结果表明,在热管一端使用被动空气冷却时,与没有冷却的光伏板相比,光伏板的电力输出可提高 8.4%,温度降低 4.7 °C;而使用被动水冷却时,电力输出可进一步提高 14%,温度降低 8 °C。作者的结论是,使用热管和水冷却比自然(被动)风冷更好。
Gang et al. [96] proved that the heat-pipe-based PV-T collector had an anti-freezing ability and had a good performance in cold regions. The distance between adjacent heat pipes had a significant influence on the performance of the PV-T collector. The overall energy efficiency (electrical + thermal) increased from 45 % to 55 % as the distance decreased from 0.15 m to 0.05 m. However, the cost of heat pipes also increased linearly as the decrease of distance. Gang et al. [97] went a step further and undertook an annual energy analysis of a heat pipe integrated PV-T system for three different climatic regions in China, i.e., Beijing, Lhasa and Hong Kong. A schematic view of the heat pipe integrated PV-T collector and overall testing arrangement are shown in Fig. 13 and Fig. 14, respectively. With auxiliary heating equipment, these systems delivered annual thermal energy outputs of 1870 MJ/m2, 3330 MJ/m2, and 2350 MJ/m2, and annual electrical energy outputs of 265 MJ/m2, 466 MJ/m2, and 328 MJ/m2, for Hong Kong, Lhasa, and Beijing, respectively.
Gang 等人[96]的研究证明,基于热管的 PV-T 集热器具有抗冻能力,在寒冷地区性能良好。相邻热管之间的距离对 PV-T 集热器的性能有显著影响。当间距从 0.15 米减小到 0.05 米时,整体能效(电能+热能)从 45% 提高到 55%。Gang 等人[97]更进一步,针对中国三个不同的气候区,即北京、拉萨和香港,对热管集成 PV-T 系统进行了年能量分析。图 13 和图 14 分别显示了热管集成 PV-T 集热器的示意图和整体测试布置图。在辅助加热设备的作用下,这些系统在香港、拉萨和北京的年热能输出分别为 1870 MJ/m 2 、3330 MJ/m 2 和 2350 MJ/m 2 ,年电能输出分别为 265 MJ/m 2 、466 MJ/m 2 和 328 MJ/m 2
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Fig. 13. Schematic cross-sectional view of the heat pipe PV-T collector in the study [97].
图 13.研究[97]中热管 PV-T 集热器的横截面示意图。

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Fig. 14. Schematic diagram of heat pipe integrated PV-T collectors and system used in the study by [97].
图 14.热管集成 PV-T 集热器和系统示意图,用于 [97] 的研究。

Ren et al. [98] focussed on reducing the cost of loop-heat pipe for solar PV-T systems. When the width of the heat pipe’s evaporator portion was reduced from 26 to 10 mm, the electrical and thermal efficiency was decreased by only 0.03 % and 2.5 %. As a whole, the system cost was estimated to be mitigated by 29 % with a minor trade-off in performance. Hongbing et al. [99] studied a PV-T system integrated with a heat pipe arrangement. Heat pipes were used to transfer the thermal energy from the PV-T collectors to a water tank for water heating purposes. The results showed that the thermal efficiency increased at higher solar irradiance, as expected, but also that the thermal efficiency of the collectors decreased during the afternoon when the water temperature was high compared to the condensation temperature of the heat pipe. Interestingly, these experiments showed that heat pipes can improve the total operating performance of the system with additional thermal output, thereby giving higher thermal efficiency and also a higher electrical efficiency than conventional air/water-based cooling methods. A summary of studies published in the area of PV cooling via the use of heat pipes is summarised in Table 4.
Ren 等人[98]的研究重点是降低太阳能光伏发电系统环形热管的成本。当热管蒸发器部分的宽度从 26 毫米减小到 10 毫米时,电效率和热效率仅分别降低了 0.03% 和 2.5%。总体而言,系统成本估计降低了 29%,而性能却略有折损。Hongbing 等人[99] 研究了一个集成热管布置的光伏发电系统。热管用于将 PV-T 集热器的热能传输到水箱中,以达到水加热的目的。结果表明,正如预期的那样,太阳辐照度越高,热效率越高,但在下午,当水温高于热管的冷凝温度时,集热器的热效率也会降低。有趣的是,这些实验表明,与传统的空气/水基冷却方法相比,热导管可以通过额外的热输出提高系统的总体运行性能,从而提供更高的热效率和更高的电效率。表 4 总结了通过使用热导管进行光伏冷却的研究成果。

Table 4. Summary of research aimed at efficiency enhancement of PV panels by heat pipe cooling.
表 4.旨在通过热管冷却提高光伏电池板效率的研究综述。

Nature of work  工作性质Temperature reduction  降低温度Efficiency enhancement  提高效率Observation/remark  意见/评论Ref.  参考文献
Experimental and numerical
实验和数值
PV cell maintained at an operating temperature of 30 °C
工作温度保持在 30 °C 的光伏电池
  -Finned heat pipe arrangement maintained the PV cell at lower temperature and both thermal and electrical energy were obtained simultaneously.
鳍状热管布置可使光伏电池保持较低温度,同时获得热能和电能。
[92]
Experimental  实验性Temperature reduction of 8 °C achieved
温度降低 8 °C
Electrical efficiency increased by 3.0 % with a maximum power output increase of 14 %
电气效率提高了 3.0%,最大输出功率提高了 14
Heat pipe array using air- and water-cooling techniques resulted in temperature reduction and energy enhancement of the PV panel.
采用空气和水冷技术的热管阵列降低了温度,提高了光伏板的能量。
[95]
Experimental  实验性  -  -Reduction in useful thermal energy between 23 % and 38 % and the electrical energy efficiency varied between 1.5 % and 4.3 % because, in the system without auxiliary heating equipment, the water was heated only by solar energy.
有用热能减少了 23 % 至 38 %,电能效率则在 1.5 % 至 4.3 % 之间,因为在没有辅助加热设备的系统中,水只能通过太阳能加热。
[97]
Experimental  实验性  -With an increase in water flow from 5 L/min to 9 L/min, the electrical efficiency decreased from 12 % to 11 % and the thermal efficiency decreased from 19 % to 16 %
当水流量从 5 升/分钟增加到 9 升/分钟时,电效率从 12 % 下降到 11 %,热效率从 19 % 下降到 16 %。
Thermal efficiency of heat pipe PV-T system increased at higher solar irradiance and decreased with increasing inlet water temperature and water flow rates, while the electrical efficiency decreased with increasing solar irradiance, inlet water temperature and flow rate.
热管光伏-热系统的热效率在太阳辐照度较高时提高,随着进水温度和水流量的增加而降低,而电效率则随着太阳辐照度、进水温度和水流量的增加而降低。
[99]

4. Radiative thermal management
4.辐射热管理

Radiative thermal management comprises a variety of passive design and operational methods that typically do not require external energy consumption [100], [101]. The earth’s atmosphere has a transparent window for infrared (IR) radiation from 8 to 13 µm, corresponding to peak thermal radiation wavelengths at 362 K and 223 K according to Wien’s law. Thus, terrestrial bodies with a typical ambient temperature can dissipate heat to outer space by thermal radiation. Radiative cooling technology for PV cells has generated significant interest in recent years.
辐射热管理包括各种被动设计和操作方法,通常不需要外部能源消耗 [100]、[101]。地球大气层对 8 至 13 µm 的红外辐射有一个透明窗口,根据维恩定律,对应的热辐射峰值波长为 362 K 和 223 K。因此,具有典型环境温度的陆地天体可以通过热辐射向外层空间散热。近年来,光伏电池的辐射冷却技术引起了人们的极大兴趣。
The first study of radiative cooling for silicon cells was conducted by Zhu et al. [78] at Stanford University in 2014. They investigated three radiative cooling emitters: the ideal emitter, a 5-mm-thick SiO2 flat emitter, and a SiO2 pyramid emitter, as shown in Fig. 15(a). SiO2 is transparent at solar wavelengths while also having a high emissivity at IR wavelengths as shown in Fig. 15(b). The emissivity of the SiO2 pyramids structure approximated the ideal emitter. Their simulation results showed that passive radiative cooling was able to lower the operating temperature of a silicon solar cell by 18.3 °C at a solar irradiance of 800 W/m2. Zhu et al. [102] tested the practical radiative cooling effect for silicon solar cells in an outdoor experiment. A 500-µm-thick SiO2 wafer was drilled with a 4-µm-diameter micro-holes array as shown in Fig. 15(c) and covered on a silicon cell as a radiative cooling emitter. The solar cell with passive radiative cooling is about 13 °C cooler than the bare silicon solar cell in a non-wind environment.
2014 年,斯坦福大学的 Zhu 等人[78] 首次对硅电池的辐射冷却进行了研究。他们研究了三种辐射冷却发射器:理想发射器、5 毫米厚的 SiO 2 平面发射器和 SiO 2 金字塔发射器,如图 15(a) 所示。如图 15(b)所示,SiO 2 在太阳光波长下是透明的,而在红外波长下则具有很高的发射率。SiO 2 金字塔结构的发射率接近理想发射器。他们的模拟结果表明,在太阳辐照度为 800 W/m 2 时,被动辐射冷却能够将硅太阳能电池的工作温度降低 18.3 °C。Zhu 等人 [102] 在户外实验中测试了硅太阳能电池的实际辐射冷却效果。如图 15(c)所示,在 500 微米厚的 SiO 2 硅片上钻有直径为 4 微米的微孔阵列,并将其覆盖在硅电池上作为辐射冷却发射器。在无风环境下,采用被动辐射冷却技术的太阳能电池比裸硅太阳能电池的温度低约 13 °C。
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Fig. 15. (a) Different radiative structures for silicon cells [78]. (b) Emissivity of different emitters in the IR wavelength range [78]. (c) SEM image of the radiative cooling emitter and the outdoor test rig [102].
图 15.(a) 硅电池的不同辐射结构[78]。(b) 不同辐射器在红外波长范围内的辐射率[78]。(c) 辐射冷却发射器和室外测试台的扫描电子显微镜图像[102]。

A detailed review of passive daytime radiative cooling can be found in Bijarniya et al. [103]. In this work, the authors elucidated the fundaments, material aspects, structures and configurations, influence of environmental factors as well as potential research opportunities and challenges. Safi and Munday [104], [105] proposed a different passive radiative cooling structure for solar cells as shown in Fig. 16. A radiative emitter with micro fins was placed on the back of a solar cell to absorb waste heat and then dissipated heat by thermal radiation to cold outer space through the atmosphere transparent window. Their simulation results showed that GaAs solar cell was cooled by 18 °C with the assist of radiative cooling in the standard terrestrial environment, which yielded a 0.9 % higher efficiency in absolute terms. The effect of passive radiative cooling for solar cells was more significant in an extra-terrestrial environment where convective cooling can be ignored. The electrical efficiency of GaAs solar cells was absolutely improved by 0.4–2.6 % in an extra-terrestrial environment of near-earth orbit.
Bijarniya 等人[103]对白天被动辐射冷却进行了详细综述。在这项工作中,作者阐明了基本原理、材料方面、结构和配置、环境因素的影响以及潜在的研究机会和挑战。Safi 和 Munday [104], [105] 提出了一种不同的太阳能电池被动辐射冷却结构,如图 16 所示。他们在太阳能电池背面放置了一个带有微型鳍片的辐射发射器来吸收废热,然后通过大气透明窗口向寒冷的外层空间进行热辐射散热。他们的模拟结果表明,在标准地球环境中,借助辐射冷却,砷化镓太阳能电池的温度降低了 18 °C,绝对效率提高了 0.9%。在可以忽略对流冷却的地外环境中,太阳能电池的被动辐射冷却效果更为显著。在近地轨道的地外环境中,砷化镓太阳能电池的电气效率绝对提高了 0.4-2.6%。
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Fig. 16. Passive radiative cooling with a radiative emitter attached to the back of a solar cell [104], [105].
图 16.太阳能电池背面附带辐射发射器的被动辐射冷却 [104], [105]。

However, the feasibility of the above passive radiative methods was questioned by Gentle and Smith [106]. Commercial PV panels usually have a low-iron glass coversheet above the cells. These authors found that commercial glass is a good radiative cooling emitter with an emissivity even slightly higher than SiO2 at IR wavelengths. Their simulation results showed that even the ideal black-body emitter could not add an extra cooling of 1.5 °C compared to normal glass-covered solar panels in a real terrestrial environment. Green and Bremner [107] also declared a similar doubt in their review article. They thought low-iron glass in standard PV panels approximated the ideal radiative cooling emitter. Zaite et al. [108] used a night-time radiative cooling technique on a PV-T water-based collector system to enhance electrical efficiency and the reliability of PV panels. The results showed that with the proposed technique, the daily temperature of the PV panel could be reduced by 3 °C to 5 °C and the electrical energy generated by the system enhanced by 5.5 % to 6.2 % compared to a conventional PV-T collector. The results also showed that the proposed method saved 18.5 kWh of annual electrical energy due to the night radiative cooling.
然而,Gentle 和 Smith [106] 对上述被动辐射方法的可行性提出了质疑。商用光伏电池板的电池上方通常有一层低铁玻璃盖板。这些作者发现,商用玻璃是一种良好的辐射冷却发射器,在红外波段的发射率甚至略高于 SiO 2 。他们的模拟结果表明,在真实的陆地环境中,即使是理想的黑体辐射器也无法比普通玻璃覆盖的太阳能电池板额外冷却 1.5 °C。Green 和 Bremner [107] 在他们的评论文章中也提出了类似的疑问。他们认为标准光伏板中的低铁玻璃近似于理想的辐射冷却发射器。Zaite 等人[108] 在 PV-T 水基集热器系统上使用了夜间辐射冷却技术,以提高光伏板的电气效率和可靠性。结果表明,与传统的 PV-T 集热器相比,采用该技术后,光伏板的日温度可降低 3 °C 至 5 °C,系统产生的电能可提高 5.5 % 至 6.2 %。结果还显示,由于夜间辐射冷却,拟议方法每年可节省 18.5 千瓦时的电能。
Zhao et al. [109] tried to improve the radiative cooling effect of a commercial glass-covered silicon PV panel. However, the PV panel temperature could only be further reduced by 1.8 °C even in an ideal situation, so they concluded that enhancing the radiative cooling of commercial PV panels might have limited value. Li et al. [110] compared the performance of PV panels with and without an additional radiative cooling coating. Their experimental results showed that additional radiative cooling could only reduce the PV panel temperature by less than 1 °C (the limitation is around 2 °C). More recently, Wang et al. [111] utilised a pyramid-textured PDMS film to provide radiative cooling for encapsulated commercial silicon cells. A 2 °C drop in the PV temperature was observed during outdoor testing.
Zhao 等人[109] 尝试改善商用玻璃覆盖硅光伏板的辐射冷却效果。然而,即使在理想情况下,光伏板的温度也只能进一步降低 1.8 °C,因此他们得出结论:增强商用光伏板的辐射冷却效果可能价值有限。Li 等人[110] 比较了有和没有附加辐射冷却涂层的光伏板的性能。他们的实验结果表明,额外的辐射冷却只能将光伏板的温度降低不到 1 °C(极限值约为 2 °C)。最近,Wang 等人[111] 利用金字塔纹理的 PDMS 薄膜为封装的商用硅电池提供辐射冷却。在室外测试中观察到光伏温度下降了 2 °C。
A review on photonic structures, configurations and spectral modification approaches suitable for PV is presented by Shanmugam et al. [112]. Li and Fan [113] designed a comprehensive photonic approach for solar cell cooling as illustrated in Fig. 17(a). A spectral-selective photonic cooler was covered on a silicon PV panel. Only the effective spectrum for silicon cells of 0.4–1.1 µm could pass through the layer of the photonic cooler. The rest of the solar spectrum of 1.1–4 µm, which could not be utilised by silicon cells, was reflected to the sky and thus reduced waste heat in solar cells. This thin-film photonic cooler also had a high emissivity at the infrared wavelength range and thus had a good radiative cooling effect. The thin-film photonic cooler is a stack of Al2O3/SiN/TiO2/SiO2 layers as shown in Fig. 17(b). This kind of thin-film spectral splitting material has also been widely investigated and applied in concentrated hybrid PV and thermal (CPVT) systems [114]. Sun et al. [115] investigated comprehensive spectral-splitting and radiative cooling for different solar cells. Their results presented that this comprehensive cooling method could lower the temperature of a commercial PV panel by 6 °C which yielded a 0.5 % absolute increase in electrical efficiency and may extend the lifetime by 80 % under one-sun conditions. More recently, Zahir et al. [116] also utilised a similar selectively-reflective and radiative cooling coating to reduce the operating temperature of Si PV panels. The operating temperature of a tested PV panel was reduced by 5.4 °C with the aid of the cooling coating. However, the final cost of such advanced photonic structures remains unclear at present, and the PV efficiency improvement is still limited, thus it is still difficult to justify the techno-economic benefits of such photonic structures. Future research on PV radiative cooling should also consider the balance between the additional cost and electrical (or other, if relevant) energy efficiency improvements.
Shanmugam 等人[112] 综述了适用于光伏的光子结构、配置和光谱修正方法。Li 和 Fan [113] 设计了一种用于太阳能电池冷却的综合光子方法,如图 17(a)所示。硅光伏板上覆盖了一个光谱选择性光子冷却器。只有 0.4-1.1 µm 的硅电池有效光谱能穿过光子冷却器层。硅电池无法利用的其余 1.1-4 微米太阳光谱被反射到天空,从而减少了太阳能电池的废热。这种薄膜光子冷却器在红外线波长范围内的发射率也很高,因此具有良好的辐射冷却效果。如图 17(b)所示,这种薄膜光子冷却器由 Al 2 O 3 /SiN/TiO 2 /SiO 2 层堆叠而成。这种薄膜分光材料也被广泛研究并应用于聚光混合光伏和热能(CPVT)系统[114]。Sun 等人[115] 研究了不同太阳能电池的综合分光和辐射冷却。他们的研究结果表明,这种综合冷却方法可将商用光伏电池板的温度降低 6 °C,从而使电气效率绝对值提高 0.5%,并可在单太阳条件下将使用寿命延长 80%。最近,Zahir 等人[116] 也利用类似的选择性反射和辐射冷却涂层来降低硅光伏板的工作温度。在冷却涂层的帮助下,测试光伏板的工作温度降低了 5.4 °C。 然而,目前这种先进光子结构的最终成本仍不明确,而且光伏效率的提高仍然有限,因此仍难以证明这种光子结构的技术经济效益。未来的光伏辐射冷却研究还应考虑额外成本与电气(或其他相关)能效改善之间的平衡。
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Fig. 17. (a) A comprehensive photonic approach for solar cell cooling with spectral splitting and radiative cooling, and (b) structure of the photonic cooler [113].
图 17(a) 利用光谱分裂和辐射冷却技术冷却太阳能电池的综合光子方法,以及 (b) 光子冷却器的结构 [113]。

5. Phase change material integration
5.相变材料集成

The use of phase changing materials (PCMs) for thermal management (and/or the provision and integration of thermal storage capabilities) can be considered a conduction-based passive thermal management method. Here, a PCM with suitable characteristics, such as a large heat of fusion and a sharp melting point, is employed to absorb and release heat as it changes phase from solid to liquid and vice versa at a near-constant temperature, thereby acting as a latent heat storage medium [117], [118], [119].
使用相变材料(PCM)进行热管理(和/或提供并整合热存储能力)可被视为一种基于传导的被动热管理方法。在这种方法中,具有适当特性(如熔融热大和熔点高)的 PCM 在近乎恒定的温度下从固态变为液态或从液态变为固态时吸收和释放热量,从而起到潜热存储介质的作用 [117]、[118]、[119]。
Predicting accurately the heat transfer and phase-change processes in any PCM store/space requires sophisticated computational tools. Models for predicting the solid–liquid interface location in PCM stores have been developed, along with models to predict and compare temperature and heat flux distributions and how these evolve within various stores/spaces, with various materials and in different applications (e.g., [22], [120], [121], [122]). A model of PCM melting in a finned PCM store was developed by Lamberg [123], who showed that the model was valid when the weight to height ratio was less than 6 and when the fin length was less than 0.06 m. An error of ± 10 % was obtained while preferring a one-dimensional analytical solution compared to a two-dimensional analytical solution. This derived model resulted in a better prediction of solid–liquid location in a finned PCM based system and is suitable for pre-designing PCM based systems, including in PV applications. Elsheniti et al. [124] proposed an enhanced one-dimensional PV-PCM model, which showed good agreement with data for various orientations ranging from 0 to 90° as well as for the aspect ratios of two, four and eight. The maximum values of errors/deviations for the lowest and highest aspect ratios were 0.7 % and 1.8 %.
要准确预测任何 PCM 储藏室/空间的传热和相变过程,都需要复杂的计算工具。目前已开发出用于预测 PCM 储藏室中固液界面位置的模型,以及用于预测和比较温度和热通量分布的模型,以及这些分布在不同储藏室/空间、不同材料和不同应用中的演变情况(例如 [22]、[120]、[121]、[122])。Lamberg [123]建立了翅片状 PCM 储藏室中 PCM 熔化的模型,他的研究表明,当重量高度比小于 6 和翅片长度小于 0.06 米时,该模型是有效的。这一推导出的模型能更好地预测基于鳍片 PCM 系统中的固液位置,适用于基于 PCM 系统的预先设计,包括光伏应用。Elsheniti 等人[124] 提出了一种增强型一维 PV-PCM 模型,该模型在 0 至 90° 的不同方向以及 2、4 和 8 的纵横比下与数据显示出良好的一致性。最低和最高纵横比的最大误差/偏差值分别为 0.7 % 和 1.8 %。
Similar research is encouraged as this is crucial in developing a range of suitable numerical design tools. Nizetic et al. [125] undertook a study where instead of using a single container filled with a PCM, several smaller containers filled with PCMs were integrated at the back of a PV panel. Their experimental results showed that using multiple containers enhanced the performance of the panel by 11 % and at the same time resulted in reductions in both PCM and aluminium costs by 47 % and 36 %. Mahdi et al. [126] also showed that longer and more effective thermal management of PV panels can be achieved by integrating multiple PCMs. Their results showed that by choosing multiple PCMs with appropriate thermophysical properties, the energy charge capacity and melting time can be improved up to 3.4 %, and 18 % relative to a single PCM. In other related work, Yousef et al. [127] experimented on a PV panel integrated with paraffin wax (PV-PCM), and a PV panel integrated with aluminium foam embedded in PCM (PV-PCM/AF), and compared results with conventional unmodified PV panels in both summer and winter weather conditions. In this work, it was shown that during the summer the electrical efficiencies of the PV-PCM and PV-PCM/AF systems were higher by 9 % and 14 % relative to a reference panel, whereas in the winter these modified panels enhanced the PV panel efficiency by 3.7 % and 4.8 %, respectively. Gao et al. [128] experimentally showed that combining a phase change cooling technique with porous media in a PV-T collector. The average electrical efficiency of the PV panel was enhanced by 9.7 %, 17 % and 15 % for flow rates of 0.004 kg/s, 0.007 kg/s and 0.009 kg/s.
类似的研究值得鼓励,因为这对于开发一系列合适的数值设计工具至关重要。Nizetic 等人[125] 开展了一项研究,在光伏电池板的背面集成了多个装有 PCM 的较小容器,而不是使用单个容器。他们的实验结果表明,使用多个容器可将电池板的性能提高 11%,同时可将 PCM 和铝的成本分别降低 47% 和 36%。Mahdi 等人[126]的研究也表明,通过集成多个 PCM,可以实现更长、更有效的光伏电池板热管理。他们的研究结果表明,通过选择具有适当热物理性质的多种 PCM,与单一 PCM 相比,充能容量和熔化时间可分别提高 3.4% 和 18%。在其他相关工作中,Yousef 等人[127] 对集成了石蜡的光伏板(PV-PCM)和集成了嵌入 PCM 的泡沫铝的光伏板(PV-PCM/AF)进行了实验,并在夏季和冬季天气条件下将实验结果与传统的未改性光伏板进行了比较。研究结果表明,在夏季,PV-PCM 和 PV-PCM/AF 系统的电气效率分别比参考面板高出 9% 和 14%,而在冬季,这些改良面板的光伏面板效率分别提高了 3.7% 和 4.8%。Gao 等人[128]的实验表明,将相变冷却技术与多孔介质结合应用于 PV-T 集热器中,可提高光伏电池板的平均电效率。当流量为 0.004 千克/秒、0.007 千克/秒和 0.009 千克/秒时,光伏板的平均电效率分别提高了 9.7%、17% 和 15%。
Lamberg [129] performed a numerical investigation regarding phase-change processes in PCMs. The results revealed that, during the melting process of PCM, natural convection in the liquid phase was critical for heat transfer enhancement. This agreed with many other studies, which found that melting (charging) is faster than freezing (discharging) owing to the solid PCM layer that is first formed over the heat exchanger surfaces in the latter, which has a higher thermal resistance than natural convection heat transfer [121], [130]. It was observed that on average, installing a layer of PCM at 2.6 kg per m2 over the rear surface of PV panels reduced the operating temperature by 1 °C during peak hours [131]. Thus, the PCM can reduce a panel’s operating temperature by up to 20 °C and the electrical conversion efficiency can be increased by 5 % [132], [133]. The experimental arrangement by Brano et al. [134] for performance analysis of PV on integration with PCM is shown in Fig. 18.
Lamberg [129] 对 PCM 中的相变过程进行了数值研究。结果表明,在 PCM 的熔化过程中,液相中的自然对流对热传递的增强至关重要。这与许多其他研究一致,这些研究发现,熔化(充电)比冷冻(放电)更快,原因是后者在热交换器表面首先形成了固体 PCM 层,其热阻高于自然对流传热[121]、[130]。据观察,在光伏电池板后表面安装一层每米 2.6 千克的 PCM 2 ,在高峰时段可将工作温度平均降低 1 °C[131]。因此,PCM 最多可将电池板的工作温度降低 20 °C,电能转换效率可提高 5 % [132]、[133]。图 18 显示了 Brano 等人[134]对集成 PCM 的光伏性能分析的实验安排。
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Fig. 18. (a) PCM encapsulated in plastic bags, and (b) PV-PCM integrated panel [134].
图 18.(a) 封装在塑料袋中的 PCM,以及 (b) PV-PCM 集成面板 [134]。

Wei et al. [135] conducted an experiment using tea-light candles as the PCM for solar panel cooling. In this experimental arrangement, PCM was used to fill the gaps between parallel aluminium tubes, which were fitted into a stainless-steel container, which was covered by a wooden plate for thermal insulation. The surface temperatures at all parts of the PV panel were recorded. It was noted in this study that the highest temperature was recorded in the centre of the PV panel. The PV electrical efficiency with cooling was 15 %, which was only slightly higher (by ∼ 3 %) than that without cooling, so it was concluded that a tea-light candle material may not be an effective PCM for the thermal management of PV panels. One of the important reasons behind this finding was that the melting point of the tea-light candle is too high (>50 °C), leading to a high operating temperature (∼ 53 °C) of the PV panel. The authors then concluded that a PCM with a melting point lower than 40 °C is more suitable for PV cooling.
Wei 等人[135] 利用茶点蜡烛作为 PCM 进行了太阳能电池板冷却实验。在该实验安排中,PCM 被用于填充平行铝管之间的间隙,铝管被安装在不锈钢容器中,容器上覆盖了一块木板作为隔热层。光伏板各部分的表面温度都被记录下来。研究发现,光伏板中央的温度最高。有冷却效果的光伏发电效率为 15%,仅比无冷却效果的光伏发电效率略高(高出 3%),因此得出结论:茶烛材料可能不是光伏面板热管理的有效 PCM。这一结论背后的一个重要原因是茶点蜡烛的熔点过高(>50 °C),导致光伏板的工作温度过高(∼ 53 °C)。作者随后得出结论,熔点低于 40 °C 的 PCM 更适合用于光伏冷却。
Paraffins, which are common organic materials whose phase-change properties lend them to PCM latent energy storage, are prominently used in the thermal management of electronics. Sharma et al. [136] found that building-integrated PV systems (BIPV) with paraffin (RT42) based PCM can improve electrical efficiency by 7.7 % while decreasing the temperature by 3.8 % at an irradiance of 1000 W/m2. Preet et al. [137] explored different PV-T collectors with water circulation and PCM integration and compared these to conventional PV panels. The developments in this work demonstrated that the operating temperatures of the water-based PV-T and PVT-PCM collectors were much lower than those of conventional PV panels. Specifically, temperature reductions of up to 20 °C were achieved in water-based PV-T and up to 30 °C in water-based PVT-PCM collectors were reported. Fig. 19 shows the heat transfer mechanisms in a PVT-PCM collector and how the PCM was integrated within the structure.
石蜡是一种常见的有机材料,其相变特性使其适用于 PCM 潜能存储,在电子设备的热管理中得到了广泛应用。Sharma 等人 [136] 发现,在辐照度为 1000 W/m 2 时,使用基于石蜡 (RT42) 的 PCM 的建筑一体化光伏系统 (BIPV) 可将电效率提高 7.7%,同时将温度降低 3.8%。Preet 等人[137] 探索了不同的 PV-T 集热器与水循环和 PCM 集成,并将其与传统的 PV 面板进行了比较。研究结果表明,基于水的 PV-T 和 PVT-PCM 集热器的工作温度远低于传统的 PV 面板。具体而言,水基 PV-T 和水基 PVT-PCM 集热器的温度分别降低了 20 ℃ 和 30 ℃。图 19 显示了 PVT-PCM 集热器的传热机制以及如何将 PCM 集成到结构中。
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Fig. 19. Heat transfer path to and from PV with PCM [137].
图 19.光伏与 PCM 之间的传热路径 [137]。

In the case of most PCMs, including organic PCMs, although these materials have a high energy density thanks to their high latent heat capacity, the thermal conductivity is low. The addition of high thermal conductivity material additives can be used to improve the thermal conductivity of suitable PCMs [130], [138], [139], [140]. Tan et al. [141] undertook a thorough analysis to determine the electrical and thermal performance of a PV panel using a PCM with different fin configurations, with results showing that PV panel temperatures could be reduced by 15 °C with a 12-fin configuration, relative to a reference panel without PCM integration or fins. The electrical efficiency of PCM-cooled PV panels with 12-fins, 6-fins, 3-fins and no fins were 5.4 %, 3.4 %, 2.9 % and 1.0 % higher than the reference PV panel, respectively. Similarly, Huang et al. [142] studied PV panel performance by integrating PCMs with different fin configurations. The study showed that the heat transfer rate within the PCM was raised by the use of fins and, subsequently, there was a major temperature drop on the PV panel front surface. With certain fin intervals, convection rates increased and there was a reduction in thermal stratification of the PCM.
就大多数 PCM(包括有机 PCM)而言,虽然这些材料的潜热容量高,因此能量密度大,但热导率却很低。添加高导热材料添加剂可用于提高合适 PCM 的导热率 [130]、[138]、[139]、[140]。Tan 等人[141] 进行了全面分析,以确定使用不同鳍片配置的 PCM 的光伏面板的电气和热性能,结果表明,相对于没有集成 PCM 或鳍片的参考面板,使用 12 鳍片配置的光伏面板温度可降低 15 °C。采用 12 片鳍片、6 片鳍片、3 片鳍片和无鳍片的 PCM 冷却光伏面板的电气效率分别比参考光伏面板高 5.4%、3.4%、2.9% 和 1.0%。同样,Huang 等人[142] 研究了通过不同鳍片配置集成 PCM 的光伏板性能。研究表明,使用鳍片提高了 PCM 内部的热传导率,光伏面板前表面的温度随之大幅下降。在翅片间隔一定的情况下,对流率增加,PCM 的热分层减少。
Rajvikram et al. [143] experimented with a PV panel embedded with a PCM attached to an aluminium plate. From outdoor experiments, a 24–25 % improvement in the PV conversion efficiency was observed compared to the reference panel subjected to no cooling. Rajvikram and Sivasankar [144] proceeded to enhance the heat transfer rate to the PCM with an external heat sink to regulate the temperature. Maximum electrical efficiency of 17 % was reported, which is considered very reasonable. Hasan et al. [145] enhanced the efficiency of a PV-PCM system by employing water circulation through the panel. The stored heat from the PCM was used for hot water for domestic applications. The experiments revealed improvements to both the electrical and thermal efficiencies, of 1.3 % and 41 % (in absolute terms), respectively. Proceeding further, Hasan et al. [146] performed outdoor experiments and simulation analysis with calcium chloride hexahydrate and capric acid-palmitic acid eutectic mixtures as two different PCMs at two different locations for PV cooling (Dublin, Ireland and Vehari, Pakistan). The study evaluated the performance of these PCMs in enhancing the efficiency of PV panels. The results showed that calcium chloride hexahydrate performed better at both locations. Compared to capric-palmitic acid, calcium chloride hexahydrate resulted in a 3–4 °C higher PV temperature drop and 3 % more power generation in Vehari, Pakistan. Comparing the two location climates, it was concluded that PCM-integrated PV systems are more suitable in hot and stable climatic conditions.
Rajvikram 等人[143] 尝试在光伏板上嵌入附着在铝板上的 PCM。从室外实验中观察到,与没有冷却的参考面板相比,光伏转换效率提高了 24-25%。Rajvikram 和 Sivasankar [144]通过外部散热器调节温度,提高了 PCM 的热传导率。据报道,最高电气效率为 17%,这被认为是非常合理的。Hasan 等人 [145] 通过在面板中使用水循环,提高了 PV-PCM 系统的效率。PCM 所储存的热量被用于提供家用热水。实验显示,电能和热能效率分别提高了 1.3% 和 41%(绝对值)。Hasan 等人[146] 进一步使用六水氯化钙和辛酸-棕榈酸共晶混合物作为两种不同的 PCM,在两个不同地点(爱尔兰都柏林和巴基斯坦维哈里)进行了室外实验和模拟分析,用于光伏冷却。研究评估了这些 PCM 在提高光伏电池板效率方面的性能。结果表明,六水氯化钙在这两个地点的表现都更好。与辛-棕榈酸相比,六水氯化钙可使巴基斯坦维哈里的光伏温度下降 3-4 °C,发电量增加 3%。通过比较两地的气候条件,可以得出结论:PCM 集成光伏系统更适合炎热和稳定的气候条件。
Khanna et al. [147] developed a model of a tilted PV-PCM system to identify the temperature of the system in different situations and reported that the electrical efficiency of the PV panel increased, thanks to the PCM integration. The efficiency was further enhanced by increasing the tilt angle due to the larger heat extraction by the PCM and reduced the PV temperature. The study also revealed that heat losses from the top surface of the PV panel decreased at higher wind azimuth angles, and suggested that PCMs with a melting point close to ambient are most appropriate for PV cooling. A schematic of energy flows in a PCM integrated PV panel is shown in Fig. 20.
Khanna 等人[147] 建立了一个倾斜式 PV-PCM 系统模型,以确定系统在不同情况下的温度。由于 PCM 抽取了更多的热量并降低了光伏温度,增加倾斜角度进一步提高了效率。研究还发现,风向方位角越大,光伏板顶面的热损失越小,这表明熔点接近环境温度的 PCM 最适合用于光伏冷却。图 20 显示了 PCM 集成光伏面板中的能量流示意图。
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Fig. 20. Energy flows in the PV-PCM integrated system considered in the study [146].
图 20.研究中考虑的 PV-PCM 集成系统的能量流 [146]。

In related work, Manikandan et al. [148] showed that a significant temperature reduction can be obtained by the integration of suitable PCMs into CPV collectors. Results in this study showed that both the power output and efficiency increased with an increase in concentration ratio and fill volume of PCM. The temperature of the CPV was measured and found to be 55 °C and 32 °C at PCM heights of 0.75 mm and 3 mm, respectively, indicating that additional PCM content (by volume) had the potential to significantly reduce the temperature. PCM integration (at a concentration ratio of 3 and PCM height of 3 mm) resulted in CPV output power and efficiency enhancements of 27 % and 22 %, respectively.
在相关研究中,Manikandan 等人[148] 发现,将合适的 PCM 集成到 CPV 集热器中可显著降低温度。研究结果表明,随着 PCM 浓度比和填充量的增加,功率输出和效率都会提高。在 PCM 高度为 0.75 毫米和 3 毫米时,CPV 的温度分别为 55 ℃ 和 32 ℃。PCM 集成(浓度比为 3,PCM 高度为 3 毫米)使 CPV 输出功率和效率分别提高了 27% 和 22%。
The global annual energy output of PCM-integrated PV panels was analysed by Smith et al. [149]. PCMs with a melting point from 0 °C to 50 °C were examined, to determine suitable PCMs at different locations. Locations with high insolation and reduced annual climate variations were shown to benefit the most by PCM-integrated panels. When employing optimal PCMs, the annual PV energy output in regions such as eastern Africa and South America (e.g., Mexico) increased by 6 %, while in regions such as Southern Asia, the rest of Africa, Central and South America, the Middle East, and the Indonesian archipelago, the energy output increased by 5 %, relative to PV panels without PCM cooling. On the other hand, the annual energy output in more Northern climates, such as Europe, increased between 2 % and 5 %. Fig. 21 shows an energy balance diagram presenting the energy flows in the PV-PCM system presented in the study [149].
Smith 等人[149] 分析了 PCM 集成光伏电池板的全球年发电量。对熔点在 0 °C 至 50 °C 之间的 PCM 进行了研究,以确定适合不同地点的 PCM。结果表明,日照充足、年气候变化较小的地区最受益于集成 PCM 面板。采用最佳 PCM 时,非洲东部和南美洲(如墨西哥)等地区的光伏年发电量增加了 6%,而在南亚、非洲其他地区、中美洲和南美洲、中东和印度尼西亚群岛等地区,与不使用 PCM 冷却的光伏电池板相比,发电量增加了 5%。另一方面,在欧洲等气候较北的地区,年能源产出增加了 2% 到 5%。图 21 显示了研究 [149] 中 PV-PCM 系统的能量平衡图。
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Fig. 21. Energy fluxes in the PV-PCM system presented in the study [149].
图 21.研究 [149] 中介绍的 PV-PCM 系统的能量通量。

Hasan et al. [150] undertook a study to determine the effectiveness of PCMs when integrated within PV panels. Five different PCMs, namely CaCl2·6H2O, paraffin wax, SP22, capric–lauric acid and capric-palmitic acid, were evaluated. Experiments were conducted to determine the key thermal properties of all five PCMs using differential scanning calorimetry (DSC) and the temperature history method (THM). DSC is a standard method used for measuring the thermal properties of small samples of materials, in the range of 3–10 mg. THM is a method that allows the properties of larger samples, up to 40 mg, to be measured. Additionally, THM determines the PCM under-cooling properties — a feature that is not available via the DSC method. The results showed that capric-palmitic acid was the best PCM for the adopted PV panel. Capric-palmitic acid had the highest latent heat and showed the greatest capacity for regulating/controlling the PV cell temperature. Furthermore, in regions where the climate was hot, the temperature of the panel was found to exceed the upper limit of the generally allowable operating temperature range of PV panels (from −40 °C to 80 °C). Operation in these conditions can quickly lead to cell delamination, rapid degradation, physical damage and failure.
Hasan 等人[150] 开展了一项研究,以确定 PCM 集成到光伏电池板中的效果。他们评估了五种不同的 PCM,即 CaCl 2 -6H 2 O、石蜡、SP22、癸酸-月桂酸和癸酸-棕榈酸。实验采用差示扫描量热法(DSC)和温度历史法(THM)确定了所有五种 PCM 的主要热特性。差示扫描量热法是一种标准方法,用于测量 3-10 毫克范围内小材料样品的热特性。THM 是一种可以测量较大样品(最多 40 毫克)特性的方法。此外,THM 还能确定 PCM 的欠冷特性,这是 DSC 方法所不具备的特性。结果表明,癸酸-棕榈酸是所采用的光伏面板的最佳 PCM。癸棕榈酸的潜热最高,调节/控制光伏电池温度的能力最强。此外,在气候炎热的地区,发现面板的温度超过了光伏面板一般允许工作温度范围的上限(从 -40 °C 到 80 °C)。在这种条件下运行会很快导致电池分层、快速降解、物理损坏和失效。
Savvakis et al. [151] analysed two PV/PCM systems, one of which employed RT 27 PCM while the other used RT 31 PCM. These investigations of PV/PCM systems were performed on a 10-Wp PV panel, and it was demonstrated that the peak temperature could be reduced by 6.4 °C and 7.5 °C for 260 g of RT 27 and RT 31, respectively, under hot and sunny Mediterranean conditions. Another approach by Velmurugan et al. [152] emphasised the utilisation of PCMs for thermal management via both convective and radiative means, but with the avoidance of conduction. In this experimental study, a cylindrical tube PCM matrix was utilised which was not kept in direct contact with the rear side of the PV panel. This helped reduce the heat transfer from the PCM to the panel which in turn avoided the abrupt temperature rise that resulted when the PCM was in the liquid state. As a result of this arrangement, the heat was transferred from the PV panel to the PCM matrix only by means of convection and radiation. The optimised spacing between the panel and the PCM matrix was found to be 6 mm and a temperature reduction of 2.5 °C, as well as an increase in the electrical output by 0.2 %, was obtained and reported by the authors compared to a control panel without a PCM.
Savvakis 等人[151] 分析了两个 PV/PCM 系统,其中一个使用 RT 27 PCM,另一个使用 RT 31 PCM。这些对 PV/PCM 系统的研究是在 10 瓦 PV 面板上进行的,结果表明,在炎热和阳光充足的地中海条件下,260 克 RT 27 和 RT 31 的峰值温度可分别降低 6.4 ℃ 和 7.5 ℃。Velmurugan 等人[152] 的另一种方法强调通过对流和辐射两种方式利用 PCM 进行热管理,但避免传导。在这项实验研究中,使用了圆柱管 PCM 矩阵,该矩阵与光伏板后侧没有直接接触。这有助于减少 PCM 向面板的热传导,从而避免 PCM 处于液态时导致的温度骤升。由于采用了这种布置方式,热量只能通过对流和辐射从 PV 面板传递到 PCM 基质。作者发现,光伏板与 PCM 矩阵之间的最佳间距为 6 毫米,与不含 PCM 的对照板相比,温度降低了 2.5 °C,电力输出增加了 0.2%。
An important consideration when using PCM-based solutions is that if the PCM is not chosen appropriately for a particular design and application, this may lead to a deterioration in performance, i.e., an increase in the temperature of a PV panel. This was demonstrated explicitly in the experimental investigations by Bayrak et al. [153], where the utilisation of PCMs resulted in a negative effect on PV panel output power if the PCM temperature was higher than the PV panel surface temperature. Further, Madurai Elavarasan et al. [154] experimentally investigated the characteristics of OM29 PCM for the summer season in Southern India. These experiments proved that OM29 did not reduce the temperature after 9 am since the ambient temperature exceeded the melting point of the PCM and resulted in poor performance. Such research has indicated that for the selection of suitable PCMs, real-time temperature data, in particular, the maximum and average operating temperature of the PV panel surface, along with knowledge of the ambient temperature at the region under consideration are of utmost importance in selecting an appropriate PCM for optimum performance.
在使用基于 PCM 的解决方案时,一个重要的考虑因素是,如果 PCM 的选择不适合特定的设计和应用,可能会导致性能下降,即 PV 面板的温度升高。Bayrak 等人的实验研究[153] 明确证明了这一点,如果 PCM 温度高于 PV 面板表面温度,则使用 PCM 会对 PV 面板的输出功率产生负面影响。此外,Madurai Elavarasan 等人[154] 对印度南部夏季的 OM29 PCM 特性进行了实验研究。这些实验证明,由于环境温度超过了 PCM 的熔点,OM29 在上午 9 点之后无法降低温度,导致性能不佳。这些研究表明,要选择合适的 PCM,实时温度数据,特别是光伏板表面的最高和平均工作温度,以及所考虑地区的环境温度知识,对于选择合适的 PCM 以实现最佳性能至关重要。
In summary, a diverse collection of studies, from which is it difficult to draw consistent, cross-cutting conclusions due to the vast array of collector types, design parameters and application conditions and characteristics, have shown some evidence that PCMs can play a role in enhancing the efficiency of cooling, although the opposite has also been reported in cases where the PCM was not suitable. According to the studies introduced in this section, the melting point of the PCM is the most critical parameter in these applications, as the operating temperature of a PV panel is always slightly higher than the melting point of the PCM. Therefore, it is of importance to select a PCM with a low melting point for effective PV cooling. Of note is that the PCM can only absorb a limited amount of heat. Thus, the heat capacity of the PCM is also an important parameter, which should be large enough to absorb the waste heat in PV panels over a whole day. Therefore, the density and specific heat capacity of the PCM should be carefully considered. Additional heat transfer structures, such as fins, can be used to enhance the heat transfer between the PV panel and the PCM, thus further decreasing the PV temperature. The heat absorbed by the PCM can be further used for downstream thermal demands, e.g., space heating, hot water, etc., which is a promising way to improve the overall efficiency of the solar system and the economic viability of such projects. Additional studies on PV cooling with the use of PCMs are tabulated in Table 5.
总之,由于集热器类型、设计参数以及应用条件和特点多种多样,因此很难从中得出一致的、贯穿各领域的结论。这些研究表明,有证据表明 PCM 可在提高冷却效率方面发挥作用,但也有报告称,在 PCM 不合适的情况下,情况恰恰相反。根据本节介绍的研究,在这些应用中,PCM 的熔点是最关键的参数,因为光伏板的工作温度总是略高于 PCM 的熔点。因此,选择熔点低的 PCM 对于有效冷却光伏非常重要。值得注意的是,PCM 只能吸收有限的热量。因此,PCM 的热容量也是一个重要参数,它应足够大,以吸收光伏电池板一整天的废热。因此,应仔细考虑 PCM 的密度和比热容。可以使用额外的传热结构(如散热片)来增强光伏板和 PCM 之间的传热,从而进一步降低光伏板的温度。PCM 吸收的热量可进一步用于下游热需求,如空间加热、热水等,这是提高太阳能系统整体效率和此类项目经济可行性的一种可行方法。表 5 列出了使用 PCM 进行光伏制冷的其他研究。

Table 5. Summary of research aimed at PV-PCM integrated systems for efficiency enhancement.
表 5.旨在提高 PV-PCM 集成系统效率的研究综述。

Nature of work  工作性质PCM used  使用的 PCMEfficiency enhancement  提高效率Observation/remark  意见/评论Ref.  参考文献
Experimental  实验性Paraffin wax RT42  石蜡 RT42Electrical efficiency increased by 7.7 %
电气效率提高了 7.7
BICPV-PCM integrated system resulted in an average temperature reduction of the PV panel by 3.8 °C in contrast to a naturally ventilated PV panel.
与自然通风的光伏板相比,BICPV-PCM 集成系统使光伏板的平均温度降低了 3.8 °C。
[136]
Experimental and numerical
实验和数值
Paraffin wax RT27  石蜡 RT27  -Usage of PCM with internal fins gave better temperature regulation on the PV surface compared to the usage of a single flat aluminium plate. The fins also reduced thermal stratification in the PCM, and thereby enhanced the overall system performance and efficiency.
与使用单一平面铝板相比,使用带有内部翅片的 PCM 可以更好地调节光伏表面的温度。鳍片还减少了 PCM 中的热分层,从而提高了整个系统的性能和效率。
[142]
Experimental and numerical
实验和数值
Paraffin wax RT25  石蜡 RT25  -PV front temperature maintained below 36.4 °C for 80 min by using PCM with a melting point of 32 °C under solar irradiance condition of 1000 W/m2 and an ambient temperature of 20 °C, in a system with fins.
在太阳辐照度为 1000 W/m 2 和环境温度为 20 °C 的条件下,在带鳍片的系统中使用熔点为 32 °C 的 PCM,80 分钟内光伏前沿温度保持在 36.4 °C 以下。
[155]
Experimental  实验性Petroleum jelly  凡士林Electrical efficiency increased by 21 %
电气效率提高 21
Petroleum jelly has better performance in BIPV applications. The average power and efficiency of the PV panel with PCM located on a concrete roof increased by 23 % and 21 % relative to a PV panel without PCM.
凡士林在 BIPV 应用中具有更好的性能。与不含 PCM 的光伏板相比,位于混凝土屋顶上的含 PCM 的光伏板的平均功率和效率分别提高了 23% 和 21%。
[156]
Experimental  实验性Paraffin wax RT35  石蜡 RT35The peak temperature of the PV-PCM panel was 11 °C lower compared to the conventional PV panel for a time of 4 h.
在 4 小时内,PV-PCM 面板的峰值温度比传统 PV 面板低 11 °C。
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Experimental and numerical
实验和数值
Paraffin wax RT42  石蜡 RT42Average efficiency increased by 6.6 % in January and 5.2 % in April
1 月份平均效率提高了 6.6%,4 月份提高了 5.2
PV-PCM performance varied with the season. During summer, due to the high ambient temperature, the PCM remained in the liquid state for most of the time, whereas, during winter the PCM was mostly solid. On average, the PCM resulted in a PV temperature drop of 10.5 °C, which led to an increase in the power output of the system by 5.9 %.
PV-PCM 的性能随季节而变化。在夏季,由于环境温度较高,PCM 大部分时间处于液态,而在冬季,PCM 大部分时间处于固态。平均而言,PCM 使光伏温度下降了 10.5 °C,从而使系统的功率输出增加了 5.9%。
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Numerical  数字Paraffin wax  石蜡An average efficiency enhancement of 2.1 % observed
观察到平均效率提高了 2.1
The electricity generation efficiency of PV-MEPCM integrated system (microencapsulated PCM (MEPCM) with a melting point of 30 °C and PCM layer thickness of 3 cm) was a little over 19 %, which was 2.0 % higher than the efficiency of an equivalent standalone PV cell (no PCM).
光伏-MEPCM 集成系统(微胶囊 PCM,熔点为 30 °C,PCM 层厚度为 3 厘米)的发电效率略高于 19%,比同等独立光伏电池(无 PCM)的效率高 2.0%。
[159]
Experimental  实验性Paraffin wax RT55 with Al2O3 as nanoparticle
以 Al 2 O 3 作为纳米粒子的石蜡 RT55
System output increased by 13 %
系统产出增加 13
PCM was suspended with 2 % Al2O3 nanoparticles to enhance the heat conduction. Integration of the BIPV panel with the PCM increased its average efficiency by 14 % relative to a PV panel without PCM.
PCM 中悬浮有 2% 的 Al 2 O 3 纳米粒子,以增强热传导。与不含 PCM 的 PV 面板相比,集成了 PCM 的 BIPV 面板的平均效率提高了 14%。
[160]
Experimental  实验性Lauric acid  月桂酸Maximum efficiency enhancement of 14 % achieved at a flow rate of 4 L/min
流量为 4 升/分钟时,效率最大提高 14
PVT-PCMs were more economical and attractive in the long run than standalone PV. The payback time of the PVT-PCM collector and standalone PV panel are 4 and 6 years, respectively.
从长远来看,PVT-PCM 比独立的 PV 更经济、更有吸引力。PVT-PCM 集热器和独立光伏板的投资回收期分别为 4 年和 6 年。
[161]
Experimental  实验性Inorganic Glauber salt (Na2SO4·10H2O)
无机芒硝(Na 2 SO 4 -10H 2 O)
Electrical efficiency increased by 10 %
电气效率提高 10
BIPV-PCM system showed a lower peak instantaneous temperature than a PV panel, which increased the electrical conversion efficiency. Experiments showed that the integrated system reduced the surface temperature by 8 °C and increased the efficiency of the system by 10 % relative to a conventional PV panel.
BIPV-PCM 系统的峰值瞬时温度低于光伏板,从而提高了电能转换效率。实验表明,与传统的光伏板相比,集成系统的表面温度降低了 8 °C,系统效率提高了 10%。
[162]

6. Utilisation of nanoparticle suspensions (nanofluids)
6.纳米颗粒悬浮液(纳米流体)的利用

In this section, the use of nanofluids for convective heat transfer enhancement is emphasised. Although the cost of nanofluids is generally high, their use can allow higher heat transfer rates (fluxes) compared to other forced convection cooling techniques. Therefore, nanofluids can significantly reduce the temperature of PV panels compared to other cooling technologies and thus, enhance PV efficiency. On the other hand, the employment of nanofluids has faced some controversy and challenges more recently, and a remaining crucial element that needs to be considered carefully concerns the limitations related to their use in practice and any proposed solutions in applications of interest. Typical issues involve agglomeration, separation, loss of performance, limited lifetimes and high maintenance costs, but also issues relating to safety and environmental implications that are non-trivial [163].
本节将强调使用纳米流体来增强对流传热。虽然纳米流体的成本普遍较高,但与其他强制对流冷却技术相比,使用纳米流体可以获得更高的热传导率(通量)。因此,与其他冷却技术相比,纳米流体可显著降低光伏板的温度,从而提高光伏效率。另一方面,纳米流体的应用最近也面临着一些争议和挑战,需要仔细考虑的一个关键因素是纳米流体在实际应用中的局限性,以及在相关应用中提出的任何解决方案。典型的问题包括团聚、分离、性能损失、有限的使用寿命和高昂的维护成本,以及与安全和环境影响有关的非同小可的问题 [163]。
Abu-Rahmeh [164] investigated the operating performance of a PV panel using various cooling techniques, namely natural-convection passive cooling, fins, water and nanofluid cooling. The authors demonstrated an electrical efficiency enhancement of up to ∼ 3 % (relative to a benchmark case without nanoparticles) could be achieved by using a nanofluid (0.04 % wt. TiO2/water) as a cooling medium. Gangadevi et al. [165] also performed an experiment to cool a PV panel using a nanofluid (Al2O3). The ordinary PV temperature rose to 70 °C which in turn curtailed the lifespan of PV panels. But, with 2 % wt. of Al2O3/water (nanofluid), the temperature decreased to 36 °C. From the results, it was concluded that, with 2 % wt. of Al2O3/water (nanofluid), the overall efficiency increased to 58 % which was higher than those cooled with water and 1 % wt. of Al2O3/water (nanofluid). Sardarabadi et al. [166] investigated the performance of a PV panel when cooling it using a nanofluid coolant combined with PCM integration. An experimental study was conducted using ZnO/water nanofluid and PCM for cooling the PV panel. The results showed that, with the PCM/nanofluid as a cooling medium, the electrical output was increased by 13 % compared to a conventional PV panel. The simultaneous use of both nanofluid and PCM in the cooling system increased the overall exergy efficiency by more than 23 % compared to the conventional PV panel.
Abu-Rahmeh [164] 研究了使用各种冷却技术(即自然对流被动冷却、翅片、水和纳米流体冷却)的光伏板的运行性能。作者证明,使用纳米流体(0.04% 重量的 TiO 2 /水)作为冷却介质,可实现高达 ∼ 3% 的电气效率提升(相对于无纳米颗粒的基准情况)。Gangadevi 等人[165] 也进行了使用纳米流体(Al 2 O 3 )冷却光伏板的实验。普通光伏温度上升到 70 °C,这反过来又缩短了光伏板的使用寿命。但是,使用 2% 重量的 Al 2 O 3 /水(纳米流体)后,温度降至 36 °C。从结果中可以得出结论,使用 2 % 重量的 Al 2 O 3 /水(纳米流体)时,总效率提高到 58 %,高于用水和 1 % 重量的 Al 2 O 3 /水(纳米流体)冷却的效率。Sardarabadi 等人 [166] 研究了使用纳米流体冷却剂结合 PCM 集成冷却光伏板的性能。实验研究使用 ZnO/水纳米流体和 PCM 冷却光伏板。结果表明,使用 PCM/纳米流体作为冷却介质,与传统的光伏板相比,电力输出增加了 13%。在冷却系统中同时使用纳米流体和 PCM,与传统的光伏板相比,整体能效提高了 23% 以上。
Stalin et al. [167] investigated experimentally the effect of a nano-PCM (CuO with paraffin wax) on the performance of PV panels. Results showed that with the integration of the nano-PCM, the peak temperature of the PV panel can be reduced by 49 °C (32 %). The results also showed that thanks to the nano-PCM, the daily PV panel efficiency increased by 8.5 %. Karaaslan and Menlik [168] numerically investigated the performance of PV-T collectors with mono- and hybrid-nanofluids, and showed that enhancements in the thermal efficiency with a hybrid nanofluid (CuO + Fe/water) of 2.0 % and 5.4 % compared to a mono-nanofluid (CuO/water) and base fluid (pure water), respectively. It was also observed that the electrical efficiency was 11.4%, 11.5% and 11.6% when utilising pure water, the mono-nanofluid and the hybrid-nanofluid as the working fluid. Sohani et al. [169] performed an analysis of a PV-T system using different nanofluids namely Al2O3, TiO2, and ZnO to determine the most suitable nanofluid based on reliability, efficiency, energy, economic and environmental criteria. From this study, it was concluded that the PV-T system based on the ZnO nanofluid had the best performance in terms of annual energy production and average electrical and thermal efficiencies of 633 kWh, 15 %, and 48 %. Jamil et al. [170] also studied PV panels integrated with different types of nanoparticles integrated with PCM (PT-58), and demonstrated experimentally that peak temperature reductions of 9.9 °C and 5.0 °C can be achieved with 0.5 wt% of graphene nanoplatelets-PCM and PV-PCM panel compared to a conventional reference PV panel.
Stalin 等人[167] 通过实验研究了纳米 PCM(含石蜡的氧化铜)对光伏板性能的影响。结果表明,在集成了纳米 PCM 后,光伏板的峰值温度可降低 49 °C(32%)。结果还显示,由于采用了纳米多相催化还原剂,光伏板的日效率提高了 8.5%。Karaaslan 和 Menlik [168]对使用单一和混合纳米流体的 PV-T 集热器的性能进行了数值研究,结果表明,与单一纳米流体(CuO/水)和基础流体(纯水)相比,混合纳米流体(CuO + Fe/水)的热效率分别提高了 2.0% 和 5.4%。研究还发现,使用纯水、单一纳米流体和混合纳米流体作为工作流体时,电气效率分别为 11.4%、11.5% 和 11.6%。Sohani 等人 [169] 使用不同的纳米流体(即 Al 2 O 3 、TiO 2 和 ZnO)对光伏-T 系统进行了分析,以根据可靠性、效率、能源、经济和环境标准确定最合适的纳米流体。研究得出结论,基于 ZnO 纳米流体的 PV-T 系统在年发电量、平均电效率和热效率(633 kWh、15 % 和 48 %)方面表现最佳。Jamil 等人[170] 还研究了集成了不同类型纳米粒子和 PCM(PT-58)的光伏面板,实验证明,与传统参考光伏面板相比,0.5 wt% 的石墨烯纳米颗粒-PCM 和 PV-PCM 面板的峰值温度可分别降低 9.9 °C 和 5.0 °C。
Ghadiri et al. [171] proceeded further to consider the use of nanofluid cooling in PV-T collectors, by investigating the effect of ferrofluid (Fe3O4-water) as a coolant on the performance of a PV-T collector using different weight concentrations. Fig. 22 shows a diagram of the ferrofluid-cooled PV-T system in this study. The results from this experimental campaign revealed that the thermal and electrical efficiencies of the ferrofluid-cooled PV-T system applying an alternating magnetic field with a frequency of 50 Hz can be enhanced in relative terms by around 55 % and 5.7 % relative to a conventional water-cooled PV-T system at a solar irradiance of 1100 W/m2. Also focussing on PV-T collectors, Aberoumand et al. [172] experimentally found that the performance of a PV-T system with Ag/water nanofluid as the cooling medium showed significant enhancement in the thermal, electrical, and exergy efficiencies of the collector. The schematic of this PV-T cooling system is shown in Fig. 23. Another experiment on PV-T cooling with PCM and nanofluid circulation to enhance heat transfer and raise overall efficiency was reported by Al-Waeli et al. [173]. This PV-T PCM-nanofluid system increased the electrical efficiency from 9.9 % to 14 % compared to a conventional water-cooled PV-T system, while also increasing the thermal efficiency from 35 % to 72 %.
Ghadiri 等人[171]进一步考虑了在 PV-T 集热器中使用纳米流体冷却的问题,研究了使用不同重量浓度的铁流体(Fe 3 O 4 -水)作为冷却剂对 PV-T 集热器性能的影响。图 22 显示了本研究中铁流体冷却 PV-T 系统的示意图。实验结果表明,在太阳辐照度为 1100 W/m 2 时,应用频率为 50 Hz 的交变磁场的铁液冷却 PV-T 系统的热效率和电效率相对于传统的水冷 PV-T 系统分别提高了约 55% 和 5.7%。同样针对 PV-T 集热器,Aberoumand 等人 [172] 通过实验发现,使用 Ag/water 纳米流体作为冷却介质的 PV-T 系统在集热器的热效率、电效率和能效方面都有显著提高。该 PV-T 冷却系统的示意图如图 23 所示。Al-Waeli 等人[173] 报道了另一项利用 PCM 和纳米流体循环来增强传热和提高整体效率的 PV-T 冷却实验。与传统的水冷 PV-T 系统相比,这种 PV-T PCM 纳米流体系统将电效率从 9.9% 提高到 14%,同时将热效率从 35% 提高到 72%。
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Fig. 22. Schematic of the PV-T system with nanofluid as tested in the study [171].
图 22.研究 [171] 中测试的带有纳米流体的 PV-T 系统示意图。

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Fig. 23. Schematic of PV-T system with nanofluids used in the study [172].
图 23.研究中使用的带有纳米流体的 PV-T 系统示意图 [172]。

Nanofluids diversify the research, innovation and development opportunities for improving the efficiency of PV panels, as well as the application opportunities of the technology, however, non-trivial challenges remain that are linked to the use of nanoparticles. For example, Rostami et al. [174] proposed a novel configuration for cooling PV panels in which CuO nanofluids and water were used as coolants and in which high-frequency ultrasound waves were utilised as a part of the solution to atomise the CuO nanofluid and water, acting to resolve a common problem that arises when using nanofluids. When using 0.8 w/v of nanofluid, an increase in the maximum power of close to 50 % was reported, however, such solutions are associated with added costs and operational/design complexity that need to be considered. A list of studies using different nanofluids suitable for cooling PV is provided in Table 6.
纳米流体为提高光伏电池板的效率提供了多样化的研究、创新和发展机会,也为该技术的应用提供了机会,然而,与纳米粒子的使用相关的挑战依然存在。例如,Rostami 等人[174] 提出了一种用于冷却光伏板的新型配置,其中使用了氧化铜纳米流体和水作为冷却剂,并利用高频超声波作为解决方案的一部分,使氧化铜纳米流体和水雾化,从而解决了使用纳米流体时出现的常见问题。据报道,当使用 0.8 w/v 的纳米流体时,最大功率提高了近 50%,然而,这种解决方案会增加成本和操作/设计复杂性,需要加以考虑。表 6 列出了使用适合光伏冷却的不同纳米流体进行的研究。

Table 6. Summary of research aimed at nanofluid/nanoparticle-cooled PV systems for efficiency enhancement.
表 6.旨在提高效率的纳米流体/纳米粒子冷却光伏系统研究综述。

Nature of work  工作性质Nanofluid/Nanoparticle used
使用的纳米流体/纳米粒子
Efficiency enhancement  提高效率Observation/remark  意见/评论Ref.  参考文献
Experimental  实验性Al2O3With 2 wt% Al2O3/water nanofluid, the electrical, thermal and overall efficiencies of the PV-T system were improved by 13 %, 45 %, and 58 % compared to water
使用 2 wt% Al 2 O 3 / 水纳米流体,与水相比,PV-T 系统的电效率、热效率和总体效率分别提高了 13 %、45 % 和 58 %。
Al2O3/water nanofluid cooling resulted in a temperature reduction of PV panel by 36 °C.
Al 2 O 3 /水纳米流体冷却使光伏板的温度降低了 36 °C。
[165]
Experimental  实验性ZnO/water  氧化锌/水13 % electrical and48 % thermal
13 % 电能和 48 % 热能
PV-T collector with PCM and nanofluid had a 23 % higher exergy efficiency relative to PV only system.
与单纯的光伏系统相比,带有 PCM 和纳米流体的 PV-T 集热器的能效提高了 23%。
[166]
Experimental  实验性Ferrofluid (Fe3O4/water)
铁流体(Fe 3 O 4 /水)
With a 3 wt% concentration of nanofluid, the total efficiency of the system enhanced by about 45 %
纳米流体浓度为 3 wt%时,系统的总效率提高了约 45
Electrical efficiency increased by nearly 4.8 % when using a ferrofluid with distilled water.
使用含蒸馏水的铁流体时,电气效率提高了近 4.8%。
[171]
Experimental  实验性Ag/waterHybrid PV-T system with nanofluid exergy efficiency improved by 50 % and 30 % compared to PV with no cooling and with water cooling
采用纳米流体的光伏-T 混合系统的能效分别比无冷却和水冷光伏系统提高了 50% 和 30
With turbulent flow and 4 % wt. of nanofluid, the PV panel power output increased by about 35 % and 10 % compared to PV panels without cooling and with water cooling, respectively.
在湍流和 4% 重量的纳米流体的作用下,光伏电池板的输出功率与无冷却和水冷的光伏电池板相比,分别提高了约 35% 和 10%。
[172]
Experimental  实验性SiC/water  碳化硅/水6.6 % electrical and38 % thermal
6.6 % 电能和 38 % 热能
PV-T system gave electrical power of 121 W while, for PV panel, it was 61 W. Maximum thermal energy gain of the hybrid system was 72 % greater than PV-T with the PCM water system.
PV-T 系统的电功率为 121 W,而 PV 面板的电功率为 61 W。混合系统的最大热能增益比 PV-T 和 PCM 水系统高 72%。
[173]
Numerical  数字Ag/waterThermal, electrical and overall exergetic efficiency improved by 1.7 %, 12 % and 14 %, respectively
热效率、电效率和总体能效分别提高了 1.7%、12% 和 14
PV-T nanofluid system with optimised thermal and optical properties produced 1.3 MWh/m2 of high-grade exergy in a year with the lowest exergy payback time of 2 years. The hybrid system also showed the potential to prevent 448 kg of CO2(eq)/m2 emissions per year.
具有优化热学和光学特性的 PV-T 纳米流体系统在一年内产生了 1.3 MWh/m 2 的高能量,最低的能耗回收期为 2 年。该混合系统还显示出每年可减少 448 千克 CO 2 (eq)/m 2 排放的潜力。
[175]

7. Combined, integrated photovoltaic-thermal designs
7.光伏与热能结合的一体化设计

Hybrid PV-T collectors and systems recover waste heat from PV cells and complement the electrical power output of these cells by providing an additional thermal output, thereby generating both electrical and thermal energy outputs from the same collector. In a conventional PV-T solar collector, a coolant (often water or air) flows typically below the PV cells, and removes heat from the cells; if designed to improve electrical performance, the system can be operated to lower their operating temperature [176], [177]. A typical PV-T arrangement, with a water circuit and hot water tank, is shown in Fig. 24. The heat obtained from such a hybrid system can be utilised in many applications for domestic space heating, hot water supply, swimming pool heating, etc. [178]; it can also be upgraded with heat pumps, converted to cooling, or even used for secondary power generation [179], [180]. Potential advantages of using PV-T systems include: (i) dual-energy outputs (electrical and thermal) from the same area and system, (ii) the occupation of less space compared to standalone equivalent to PV and solar-thermal systems for the same delivered energy outputs, (iii) lower system costs compared to standalone equivalent systems, and (iv) alleviation of thermal degradation of the PV cells, and thereby, life enhancement.
PV-T 混合集热器和系统可回收光伏电池的余热,并通过提供额外的热输出来补充这些电池的电力输出,从而从同一个集热器中产生电能和热能输出。在传统的 PV-T 太阳能集热器中,冷却剂(通常是水或空气)通常在光伏电池下方流动,并带走电池中的热量;如果设计用于提高电气性能,系统可降低其工作温度 [176],[177]。图 24 显示了一个典型的 PV-T 布置,带有水回路和热水箱。从这种混合系统中获得的热量可用于家庭空间供暖、热水供应、游泳池加热等多种应用[178];也可用于其他用途[179]。[178];也可以通过热泵进行升级,转换为制冷,甚至用于二次发电[179],[180]。使用 PV-T 系统的潜在优势包括(i) 从同一区域和系统输出双重能量(电能和热能),(ii) 与独立的等效光伏和光热系统相比,在输出相同能量的情况下占用的空间更少,(iii) 与独立的等效系统相比系统成本更低,以及 (iv) 缓解光伏电池的热退化,从而延长使用寿命。
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Fig. 24. Photograph of solar water heating system with PV-T collectors [181].
图 24.采用 PV-T 集热器的太阳能热水系统照片[181]。

Rosli et al. [182] examined PV-T systems experimentally by using two different working fluids, i.e., air and water. It was stated that the water-cooling technique was cost-efficient, and yielded better efficiency than the air-cooling technique. The PV-T systems using water and air as the coolant were 8 % and 5 % more expensive than plain polycrystalline PV panels, however, if the piping and circulating pump costs are also included, then the overall cost increases by 10 % and 8 %, respectively. Tonui and Tripanagnostospoulos [183] investigated the operating performance of air-based PV-T collectors and their experimental results gave a good agreement with theoretical predictions. Generally, PV-T/air systems are used in agriculture, industrial and other applications. A series of experiments were designed so as to enhance the PV-T/air collector performance by attaching thin metallic sheets (TMSs) or fins at the rear side of the air channels. TMSs inserted in the middle of the air channel at the back of the collector doubled the removal of heat compared to a normal panel with a single-pass air channel. Fins connected to the back wall of the air channel increased the temperature of outlet air and thus, increased the extracted heat. The experiments concluded that fins provide better cooling performance in high altitude regions; whereas TMSs can be used in low altitude regions as well as offer a wall shading effect.
Rosli 等人[182]通过使用两种不同的工作流体,即空气和水,对 PV-T 系统进行了实验研究。结果表明,水冷却技术具有成本效益,且效率优于空气冷却技术。使用水和空气作为冷却剂的 PV-T 系统的成本分别比普通多晶光伏板高 8% 和 5%,但如果将管道和循环泵的成本也计算在内,则总成本将分别增加 10% 和 8%。Tonui 和 Tripanagnostospoulos [183] 研究了基于空气的光伏-T 集热器的运行性能,他们的实验结果与理论预测十分吻合。一般来说,PV-T/空气系统用于农业、工业和其他应用领域。为了提高光伏-T/空气集热器的性能,我们设计了一系列实验,在空气通道的后侧安装薄金属片(TMS)或翅片。插入集热器后部空气通道中间的 TMS 与单通道空气通道的普通面板相比,散热量增加了一倍。连接到空气通道后壁的翅片提高了出口空气的温度,从而增加了提取的热量。实验得出结论,翅片在高海拔地区具有更好的冷却性能;而 TMS 可用于低海拔地区,并具有墙面遮阳效果。
Also in related work, Noro and Lazzarin [184] studied a PV-T system for a typical 77 m2 two-stage Italian house in Venice, Rome and Crotone. The unglazed PV-T collector was able to cover 72 % and 41 % of the domestic electricity and heat demands of the house in Rome, while the discounted payback period (DPP) was estimated to be around 9–13 years. Furthermore, Metwally et al. [185] developed two cooling models of PV panels namely: (i) an active cooling system using thermoelectric generators, and (ii) a hybrid cooling system using the thermoelectric generator and PCM. They showed that the electrical power generation of the system can be enhanced up to 20 % at irradiation flux of 760 W/m2 and 30% at 1150 W/m2, using hybrid cooling. Sudhakar et al. [186] also experimented on PV panels using a hybrid cooling technique incorporating PCM (OM35) and water cooling, and showed that PV cooling techniques involving top to bottom water circulation with PCM give optimum performance with a decrease in average temperature by 5.4 °C, an increase in energy production by 12 %, an electrical efficiency enhancement of 12 %, a peak overall exergy output of 26 %, and an exergy efficiency enhancement of 8 %.
在相关工作中,Noro 和 Lazzarin [184] 还研究了威尼斯、罗马和克罗托内典型的 77 m 2 两级意大利房屋的光伏-T 系统。无釉 PV-T 集热器能够满足罗马房屋 72% 和 41% 的家庭用电和用热需求,而投资回收期 (DPP) 估计约为 9-13 年。此外,Metwally 等人[185] 还开发了两种光伏板冷却模型,即:(i) 使用热电发电机的主动冷却系统;(ii) 使用热电发电机和 PCM 的混合冷却系统。他们的研究表明,使用混合冷却系统,在辐照通量为 760 W/m 2 时,系统的发电量可提高 20%;在辐照通量为 1150 W/m 2 时,系统的发电量可提高 30%。Sudhakar 等人[186]还利用 PCM(OM35)和水冷混合冷却技术对光伏电池板进行了实验,结果表明,采用 PCM 从上到下水循环的光伏冷却技术可获得最佳性能,平均温度降低 5.4 °C,发电量提高 12%,电效率提高 12%,总体放能输出峰值提高 26%,放能效率提高 8%。
Srimanickam et al. [187] considered a PV-T collector with V-baffled channels. Their experimental apparatus is shown in Fig. 25. The PV cells were cooled by air which was forced to pass through the rear surface of the collector. The study recorded hourly variations of thermal efficiency, equivalent thermal efficiency and overall thermal efficiency. To understand the characteristics of a PV-T system using aluminium substrate instead of glass, an experiment was performed by Pang et al. [188] in which cooling is accomplished by natural air in one case and forced water circulation in another case. The results showed that the electrical efficiency obtained using the aluminium substrate was almost 20 % higher than that obtained using a glass substrate. Though the cost was high, aluminium gave a better lifetime and flexibility to the collector compared to glass. Chauhan et al. [189] simulated the performance of a PV-T/air system under the weather conditions of four different cities in India (i.e., New Delhi, Jodhpur, Bangalore and Srinagar). The simulation results showed that both the electricity and thermal outputs of the PV-T collector in Jodhpur were nearly twice of those in New Delhi. Another experiment was conducted for four configurations of solar air collectors (glass to glass PV panel with and without duct; glass to Tedlar PV panel with and without duct) in New Delhi. The results revealed that PV panels with a duct could achieve annual average electrical efficiencies reaching 10 %, which was 6.8 % higher (in relative terms) than the panel configurations without a duct [190].
Srimanickam 等人[187] 考虑了一种带有 V 型障板通道的 PV-T 集热器。他们的实验装置如图 25 所示。光伏电池由强制穿过集热器后表面的空气冷却。研究记录了热效率、等效热效率和总热效率每小时的变化。为了了解使用铝基板代替玻璃的光伏发电系统的特性,Pang 等人进行了一项实验[188],其中一种情况是通过自然空气冷却,另一种情况是通过强制水循环冷却。结果表明,使用铝基板获得的电气效率比使用玻璃基板高出近 20%。虽然成本较高,但与玻璃相比,铝能为集热器提供更好的使用寿命和灵活性。Chauhan 等人[189] 模拟了光伏-T/空气系统在印度四个不同城市(即新德里、焦特布尔、班加罗尔和斯利那加)天气条件下的性能。模拟结果表明,焦特布尔的 PV-T 集热器的发电量和热输出量几乎是新德里的两倍。另一项实验针对新德里的四种太阳能空气集热器配置(有管道和无管道的玻璃对玻璃光伏板;有管道和无管道的玻璃对 Tedlar 光伏板)进行。结果显示,有导管的光伏板的年平均电效率可达 10%,比没有导管的光伏板配置高出 6.8%(相对值)[190]。
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Fig. 25. Experimental arrangement used by Srimanickam et al. [187].
图 25.Srimanickam 等人使用的实验装置[187]。

Guarracino et al. [191] developed a dynamic 3-D model of a hybrid PV-T collector with a sheet-and-tube thermal absorber. The outcomes revealed that the electrical and thermal outputs of the PV-T system strongly depended on the collector structure (glazing or unglazing), pump operation, differential thermostat controller, and choice of flow rate. The results also showed that the thermal efficiency can be increased by 10 % when ideally decreasing the emissivity of the solar cell from 0.9 to 0. Guarracino et al. [192] experimentally studied the performance characteristics of non-concentrating PV-T collectors under outdoor conditions. The outcomes showed that for the commercial PV-T collector tested, improvements to the thermal contact between PV cells and thermal absorber resulted in a 6–8 % increase in electrical efficiency and a 10 °C decrease in PV temperature. Herrando et al. [193] developed a model to study the performance of a hybrid PV-T collector for providing electricity and hot water. The outcomes showed that a PV-T system was able to save 16 tonnes of CO2 over the lifetime, which was relatively 36 % higher than a PV-only system. A further study [194] presented 26 different options of absorber exchanger designs for hybrid PV-T solar collectors and compared these to a reference sheet-and-tube PV-T collector. It showed that a PV-T collector featuring a polycarbonate flat-box design achieved a higher thermal performance compared to the reference collector (with a 4 % higher optical efficiency and 15 % lower heat-loss coefficient) and achieved a reduction in weight by 9 % and lowered the investment cost by 21 %.
Guarracino 等人[191] 建立了一个带有片管式热吸收器的混合光伏-T 集热器的动态三维模型。研究结果表明,PV-T 系统的电力和热能输出在很大程度上取决于集热器的结构(上釉或不上釉)、泵的运行、差动恒温控制器以及流量的选择。Guarracino 等人[192] 通过实验研究了室外条件下非聚光光伏-T 集热器的性能特征。结果表明,对于测试的商用 PV-T 集热器,改进 PV 电池和热吸收器之间的热接触可使电效率提高 6-8%,PV 温度降低 10 °C。Herrando 等人[193] 建立了一个模型,研究光伏-T 混合集热器在提供电力和热水方面的性能。研究结果表明,PV-T 系统在整个生命周期内可节约 16 吨二氧化碳 2 ,比纯 PV 系统高出 36%。另一项研究[194]介绍了 26 种不同的 PV-T 混合太阳能集热器吸收器交换器设计方案,并将这些方案与参考的板管式 PV-T 集热器进行了比较。研究表明,与参考集热器相比,采用聚碳酸酯平板箱设计的 PV-T 集热器实现了更高的热性能(光学效率提高了 4%,热损失系数降低了 15%),重量减轻了 9%,投资成本降低了 21%。
Herrando et al. [195] examined the performance of a polymeric flat-box PV-T collector design and the performance of solar in combination with heat and power systems. The investigated systems displaced 1.65, 3.87 and 1.54 tons of CO2 per year in London, Athens and Zaragoza, respectively. A further simulation study by the same group [196], using 3-D finite element and computational fluid dynamics showed that a hybrid PV-T system has the potential on average to cover around 50 % of total space heating and domestic hot water demand and around 87 % of total electricity demand. Also, another model was constructed to find out the techno-economic performance of a solar combined cooling, heating and power (S-CCHP) system based on hybrid PV-T collectors [197]. Kianifard et al. [198] modelled, designed and fabricated a novel PV-T collector in which the water was used as a heat collector in the serpentine half pipe instead of a full circular cross-section. The key highlight of using the half pipe was that it highly reduced the thermal resistances. The results showed that the thermal and electrical efficiency of the proposed model was 10–13 % and 0.4–0.6 % higher than the models of conventional collectors.
Herrando 等人[195] 研究了聚合物平板箱式 PV-T 集热器设计的性能以及太阳能与热电系统结合的性能。在伦敦、雅典和萨拉戈萨,所研究的系统每年分别减少 1.65、3.87 和 1.54 吨二氧化碳 2 。同一研究小组使用三维有限元和计算流体动力学进行了进一步的模拟研究[196],结果表明,光电-热混合系统平均可满足约 50% 的空间供暖和生活热水总需求,以及约 87% 的电力总需求。此外,还构建了另一个模型,以了解基于光伏-热电混合集热器的太阳能冷热电三联供系统的技术经济性能[197]。Kianifard 等人[198] 模拟、设计和制造了一种新型 PV-T 集热器,其中水被用作蛇形半管的集热器,而不是全圆截面的集热器。使用半管的主要亮点是极大地降低了热阻。结果表明,与传统的集热器相比,所提出模型的热效率和电效率分别高出 10-13% 和 0.4-0.6%。
Ramos et al. [199] examined a hybrid PV-T system for combined heating, cooling and power provision for a metropolitan environment. The outcomes showed an overall efficiency of 70 % or higher with electrical efficiencies up to 15–20 % and thermal efficiencies over 50 %. Herrando et al. [200] also studied the performance of an integrated PV-T collector and heat pumps system for supplying domestic hot water, space heating and electricity to households. The outcomes showed that, in locations of Rome and Paris, the system covered more than 74 % of the domestic hot water, 100 % of the space heating and over 25 % of the electricity of households. Wang et al. [201] presented a hybrid PV-T collector for a sports centre application in Italy based on thermodynamic analysis of a solar combined heating and power system. It showed that 38 % of the electricity demand was contented and, also, the system covered 24 % of space heating demand and 58 % of the swimming pool and hot water heating demand. Mellor et al. [202] performed an experiment to enhance the thermal efficiency of hybrid PV-T collectors with minimum loss of electrical efficiency. The solar cells were coated with a spectrally-selective low-emissivity coating to reduce radiative thermal loss, and a nanotextured rear reflector was used to improvise the absorption of the near-infrared part of the solar spectrum for heat generation. A 20 % improvement in thermal efficiency could be achieved if the incident radiation was effectively absorbed and changed into useful heat.
Ramos 等人[199] 研究了一种光伏-热电混合系统,该系统可为大都市环境提供供热、制冷和供电。研究结果表明,该系统的总体效率为 70% 或更高,其中电能效率高达 15-20%,热能效率超过 50%。Herrando 等人[200] 还研究了光伏-T 集热器和热泵集成系统的性能,该系统可为家庭提供生活热水、空间供暖和电力。研究结果表明,在罗马和巴黎,该系统覆盖了 74% 以上的家庭热水、100% 的空间供暖和 25% 以上的家庭用电。Wang 等人[201]根据太阳能热电联产系统的热力学分析,为意大利的一个体育中心介绍了一种光伏-热电混合集热器。研究表明,该系统满足了 38% 的电力需求,还满足了 24% 的空间供热需求以及 58% 的游泳池和热水供热需求。Mellor 等人[202]进行了一项实验,旨在提高光伏-太阳能混合集热器的热效率,同时将电能效率损失降至最低。他们在太阳能电池上镀了一层光谱选择性低辐射涂层,以减少辐射热损耗,并使用纳米扭曲后反射器来提高对太阳光谱近红外部分的吸收,以产生热量。如果入射辐射被有效吸收并转化为有用的热量,热效率可提高 20%。
Golzari et al. [203] experimentally presented a method to enhance the efficiency of a PV-T system by electro-hydrodynamics. It was found that the Corona wind enhanced the heat transfer coefficient of the system by 65 % while increasing the thermal efficiency of the system by 28 %. Based on the exergy concept (energy balance of different components), Sobhnamayan et al. [204] optimised a solar PV-T water system. Both exergy analyses, as well as energy analyses, were needed to obtain the exergy efficiency of a PV-T collector. The expressions were obtained for exergy of different parts of the PV-T collector, to obtain the exergy balance for different components of a PV-T collector. Some adjustments were made to modify the equations of exergy efficiency of the PV-T water collector and an advanced computer simulation program was developed to calculate the electrical and thermal efficiency parameters. The exergy efficiency of the PV-T water collector system optimised by a genetic algorithm reached 11 %.
Golzari 等人[203] 通过实验提出了一种利用电流体力学提高光伏发电系统效率的方法。研究发现,电晕风将系统的传热系数提高了 65%,同时将系统的热效率提高了 28%。Sobhnamayan 等人 [204] 基于放能概念(不同组件的能量平衡),优化了太阳能光伏-水系统。要获得 PV-T 集热器的放能效率,需要进行放能分析和能量分析。对 PV-T 集热器不同部分的放能进行了表达,以获得 PV-T 集热器不同部分的放能平衡。对 PV-T 水收集器的放能效率方程进行了一些调整,并开发了一个先进的计算机模拟程序来计算电能和热能效率参数。通过遗传算法优化的 PV-T 集水器系统的能效达到了 11%。
. Farshchimonfared et al. [205] examined the electrical and thermal performance of a PV-T air collector system. The authors optimised the performance of the system with channel depth, mass flow rate of air per unit collector area and diameter of an air distribution duct. The results showed that the optimum channel depth value varies between 0.09 and 0.026 m and the optimum air distribution duct diameter varies between 0.3 and 0.5 m for the considered system. It is also observed that the optimum depth increases with both an increase in length to width ratio and in collector area.
.Farshchimonfared 等人[205] 研究了 PV-T 空气集热器系统的电气和热性能。作者根据通道深度、单位集热器面积的空气质量流量和空气分配管道的直径对系统性能进行了优化。结果表明,对于所考虑的系统,最佳通道深度值在 0.09 至 0.026 米之间,最佳空气分配管道直径在 0.3 至 0.5 米之间。此外还发现,最佳深度随着长宽比和集热器面积的增加而增加。
Gagliano et al. [206] investigated the performance of conventional solar thermal plants (photovoltaics plus solar collector) and compared results with hybrid PV-T systems. The results showed that hybrid PV-T systems allowed a relative increase of exergy efficiency between 10 % and 15 % compared to a PV-only system in three cities, namely Catania, Split and Freiburg. Buonomano et al. [207] examined the technical and economic feasibility of PV-T collectors and compared the results with a conventional PV panel. The PV panel electrical efficiency was 18 %, which was greater than that of the PV-T collector, which was 12 %. However, the overall efficiency of the PV-T collector was 26 % greater than that of the PV panel which only had the electrical output.
Gagliano 等人[206] 研究了传统太阳能热发电厂(光伏加太阳能集热器)的性能,并将结果与光伏-热混合系统进行了比较。结果表明,在卡塔尼亚、斯普利特和弗莱堡这三个城市,与纯光伏系统相比,光伏-热电混合系统的能效相对提高了 10% 至 15%。Buonomano 等人[207] 研究了 PV-T 集热器的技术和经济可行性,并将结果与传统的 PV 面板进行了比较。光伏板的电气效率为 18%,高于 PV-T 集热器的 12%。然而,PV-T 集热器的总体效率比仅有电力输出的光伏板高 26%。
Dannemand et al. [208] designed and investigated the operational behaviour of a solar PV-T assisted heat pump system to meet electrical and domestic heating demands. The hybrid system had an electrical efficiency of more than 14 % throughout the testing period. During summer, the PV-T system completely covered the domestic hot-water demand. However, during less sunny periods, the hot water tank had to be recharged by the brine-water heat pump to fulfil the hot water demand. Lebbi et al. [209] focussed on improving the energy performance of the PV-T system using a bi-fluid cooling approach, i.e., air and water which were used to cool the front and rear side of the PV cells, respectively. At a global solar irradiance of 650 W/m2, the resulted improvement was about 5.7 % in electrical efficiency and an average temperature reduction of up to 15 °C was obtained. Further, the overall energy efficiency of the experimented system was found to be 85 %.
Dannemand 等人[208] 设计并研究了太阳能光伏-热泵辅助系统的运行特性,以满足电力和家庭供热需求。在整个测试期间,该混合系统的电气效率超过 14%。在夏季,PV-T 系统可完全满足生活热水需求。然而,在阳光不那么充足的时期,热水箱必须通过盐水热泵来补水,以满足热水需求。Lebbi 等人[209]采用双流体冷却方法,即用空气和水分别冷却光伏电池的正面和背面,重点改善了光伏-T 系统的能源性能。在全球太阳辐照度为 650 W/m 2 时,电能效率提高了约 5.7%,平均温度降低了 15 °C。此外,实验系统的总体能源效率为 85%。
Aste et al. [210] conducted a combined experimental and modelling investigation of a PV-T system at three geographical (and climatic) locations, namely Paris, Milan and Athens. Their annual results showed that the overall efficiency of the PV-T collector was 33 %, 36 % and 41 % in Paris, Milan and Athens, respectively. According to annual irradiation on a horizontal plane, the thermal efficiency upsurges progressively from Paris to Milan to Athens. In the hybrid system, the achieved electrical efficiencies were 14 % in Paris, also 14 % in Milan, and 13 % in Athens. Liang et al. [211] designed and developed a hybrid PV-T solar collector with a 20-mm-thick graphite layer attached below the sheet-and-tube thermal absorber. The backplane of the PV-T collector had a 16.7 °C lower temperature than the standalone PV panel at a solar irradiance of around 1000 W/m2. The daily average electrical efficiency of the PV-T collector was 6.5 %, which is higher than that of the standalone PV panel of 5.2 %.
Aste 等人[210]对巴黎、米兰和雅典三个地理(和气候)位置的光伏-T 系统进行了实验和建模相结合的调查。他们的年度结果显示,巴黎、米兰和雅典的 PV-T 集热器总效率分别为 33%、36% 和 41%。根据水平面的年辐照度,从巴黎到米兰再到雅典,热效率逐步上升。在混合系统中,巴黎的发电效率为 14%,米兰为 14%,雅典为 13%。Liang 等人[211]设计并开发了一种 PV-T 混合太阳能集热器,在板管式热吸收器下面附有 20 毫米厚的石墨层。在太阳辐照度约为 1000 W/m 2 时,PV-T 集热器背板的温度比独立的光伏板低 16.7 °C。PV-T 集热器的日平均电气效率为 6.5%,高于独立光伏板的 5.2%。
Ebrahimi et al. [212] investigated both the efficiency and cost of 11 different PV-T systems with different working fluids (water and air), thermal absorbers (round and rectangular tubes), PV materials (mono-crystalline, poly-crystalline and amorphous Si) and glazing structures (single and double glazing). An analytical network process (ANP) was used to find the best design partially for Asia. They concluded that the best design is a non-concentrating, non-glazed design using water as the working fluid, based on the assumption that the electricity and thermal energy are of the same value for the decision-maker.
Ebrahimi 等人[212]研究了 11 种不同 PV-T 系统的效率和成本,这些系统具有不同的工作流体(水和空气)、热吸收器(圆形和矩形管)、光伏材料(单晶、多晶和非晶硅)和玻璃结构(单层和双层)。分析网络过程(ANP)被用来为亚洲找到最佳的局部设计。他们得出的结论是,基于电能和热能对决策者具有相同价值的假设,最佳设计是使用水作为工作流体的非聚光、非玻璃设计。
Spectral splitting is another promising approach for PV thermal management for electrical, thermal and combined generation applications [213], [214], [215]. PV cells are only effective to a part of the solar spectrum, while the rest of the spectrum has to be dissipated as waste heat in the PV cells. For example, Si solar cells are not able to electrically utilise the infrared spectrum (λ > 1100 nm) and also have very low efficiency in the ultraviolet spectrum range (λ <  400 nm). The diagram of a fluid-based spectral splitting PV-T collector is shown in Fig. 26 [216]. The channel above the PV cells is filled with flowing liquid, which can selectively absorb the unusable spectrum in advance, thus reducing the waste heat in PV cells. The rest of the spectrum, which is electrically effective to the PV cells, passes through the liquid filter channel. The flowing liquid filter acts as both the optical filter and the heat transfer fluid. Nanofluids have attracted particular attention as they are effective and suitable for spectral splitting PV-T collectors. Taylor et al. [214] developed a mathematical model to design nanofluid-based filters to match different solar cells. Common nanoparticles for the spectral splitting nanofluids include Ag/SiO2, Ag/TiO2, Au/SiO2, ZnO etc. [213], [214], [217], while common base fluids include water, glycol, Therminol heat transfer oil, etc. An ideal optical filter can absorb ∼ 25 % and ∼ 38 % of the incident solar energy that is electrically unusable to Si and CdTe solar cells [218]. A recent review article by Huang et al. [216] and Liang et al. [217] summarised the development of spectral splitting PV-T technologies based on different nanomaterials.
光谱分割是另一种有前途的光伏热管理方法,可用于电、热和联合发电应用 [213]、[214]、[215]。光伏电池只对部分太阳光谱有效,其余光谱则必须作为废热在光伏电池中耗散。例如,硅太阳能电池无法利用红外光谱(λ > 1100 纳米),在紫外光谱范围(λ < 400 纳米)内的效率也非常低。图 26[216]所示为基于流体的分光光伏-T 集热器示意图。光伏电池上方的通道中充满了流动的液体,它可以提前选择性地吸收不可用的光谱,从而减少光伏电池中的废热。其余对光伏电池有效的光谱则通过液体过滤通道。流动的液体过滤器既是光学过滤器,又是传热液体。纳米流体因其有效且适用于分光光伏集热器而备受关注。Taylor 等人 [214] 建立了一个数学模型,用于设计基于纳米流体的过滤器,以匹配不同的太阳能电池。光谱分离纳米流体的常见纳米粒子包括 Ag/SiO 2 、Ag/TiO 2 、Au/SiO 2 、ZnO 等。[213], [214], [217],而常见的基液包括水、乙二醇、Therminol 导热油等。理想的光学滤光片可以吸收 25% 和 38% 的入射太阳能,这些太阳能对硅和碲化镉太阳能电池来说是不可用的[218]。Huang 等人[216]和 Liang 等人[217]最近发表的一篇综述文章总结了基于不同纳米材料的分光光伏发电技术的发展情况。
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Fig. 26. Diagram of fluid-based spectral splitting PV-T collector [216].
图 26.基于流体的分光光伏-T 集热器示意图 [216]。

In summary, PV-T systems provide a useful thermal output that can be used for multiple purposes, and to obtain higher overall efficiency. PV-T collector designs have relied on a combination of cooling/thermal management techniques, e.g., air/water cooling, fins, PCMs, etc., to enhance heat transfer, while nanofluids have also been used to enhance performance. Highlights from a range of studies on PV-T collectors and systems, in terms of thermal and electrical performance, are listed in Table 7.
总之,PV-T 系统可提供有用的热输出,可用于多种用途,并获得更高的整体效率。PV-T 集热器设计依赖于冷却/热管理技术的组合,如空气/水冷却、翅片、PCM 等,以增强热传递,同时纳米流体也被用于增强性能。表 7 列出了一系列关于 PV-T 集热器和系统的研究在热性能和电性能方面的亮点。

Table 7. Summary of research aimed at PV cooling and efficiency enhancement when part of a hybrid PV-T collector system.
表 7.针对光伏冷却和提高光伏-T 混合集热系统效率的研究综述。

Nature of work  工作性质Fluid used  所用流体Efficiency enhancement  提高效率Observation/remark  意见/评论Ref.  参考文献
Experimental and numerical
实验和数值
Air  空气Highest overall efficiency achieved was 61–62 %, by a PV-T air glazed type collector with a finned back wall
带有翅片后墙的 PV-T 空气玻璃型集热器的最高总效率为 61-62
The analytical results show that both high flow rates and small channel depths result in higher electrical efficiency and thermal output and may be suggested for efficient PV-T/air systems. However, this results in higher pressure drops and increased operating running costs of the system.
分析结果表明,高流速和小通道深度都能带来更高的电气效率和热输出,可用于高效的光伏-空气系统。不过,这会导致压降增大,增加系统的运行成本。
[183]
Experimental and numerical
实验和数值
Air  空气Fin integrated system gave the highest efficiency improvement followed by TMS system, ranging from 12 % to 20 %
翅片集成系统的效率提高幅度最大,其次是 TMS 系统,从 12 % 到 20 % 不等
PV-T based air circulation reduced PV panel temperature by a minimum of 5 °C. The results show that fin systems are suitable for high latitude regions (more heating) where the high heat gain is exploited in winter, whereas TMS systems are more suitable for low latitude regions and tropical countries to maximise both the improved heat gain and the wall shading effect.
基于 PV-T 的空气循环可将光伏板温度降低至少 5 °C。结果表明,翅片式系统适用于高纬度地区(供暖较多),在冬季可利用高得热量,而 TMS 系统更适用于低纬度地区和热带国家,可最大限度地提高得热量和墙体遮阳效果。
[219]
Experimental  实验性Air  空气With HRV, the overall efficiency of the PV-T collector was 38 % which included 15 % and 23 % electrical and mechanical efficiency, respectively
使用 HRV 后,PV-T 集热器的总效率为 38%,其中电气和机械效率分别为 15% 和 23%。
Heat recovery ventilated recovery systems can be coupled with air-type PV-T for enhancing build environment performance.
热回收通风回收系统可与空气型 PV-T 相结合,以提高建筑环境性能。
[220]
Experimental  实验性Air  空气Thermal and electrical efficiencies increased by 40 % and 2.4 %, respectively, when the air flow rate per unit collector area increased from 0.01 to 0.07 kgs-1m−2
当单位集热器面积的空气流速从 0.01 kgs -1 m −2 增加到 0.07 kgs -1 m −2 时,热效率和电效率分别提高了 40 % 和 2.4 %。
Exergy analysis is not an encouraging approach for investigating PV-T systems used for space heating.
对于研究用于空间供热的光伏发电-热电联产系统来说,进行能耗分析并不是一种令人鼓舞的方法。
[221]
Experimental and numerical
实验和数值
Air  空气An increase in air flow rate from 0.008 to 0.016 (kgs−1) was associated with thermal, electrical and overall efficiencies improvements of 23 %, 14 % and 22 %
空气流速从 0.008 增加到 0.016(千克 −1 )时,热效率、电效率和总体效率分别提高了 23%、14% 和 22%。
Uniform distribution of air on a PV panel prevents local excessive temperature on the panel. Using a concentrator with a reflector wall or increased air flow increases overall system efficiency by 41 % and 22 %, respectively.
光伏电池板上均匀分布的空气可防止电池板局部温度过高。使用带反射墙的聚光器或增加空气流量,可使系统的整体效率分别提高 41% 和 22%。
[222]
Experimental  实验性Water  Compared to a conventional PV panel, the average power of the PV-T collector tested here was 5.5 % higher
与传统的光伏板相比,这里测试的 PV-T 集热器的平均功率高出 5.5
The overall power output of a PV-T system is higher due to the raise of its voltage because of the lower operating temperature of the PV cell. The electric power produced by conventional PV and PV-T systems is 61.7 W and 65.1 W, respectively.
由于光伏电池的工作温度较低,电压升高,因此 PV-T 系统的总功率输出较高。传统光伏系统和 PV-T 系统产生的电能分别为 61.7 W 和 65.1 W。
[223]
Experimental and numerical
实验和数值
Water  With the tested hybrid PV-T system, 13 % and 53 % improvements of electrical and thermal efficiencies were obtained which compete well with the traditional system
通过测试光伏-热混合系统,电能效率和热能效率分别提高了 13% 和 53%,与传统系统相比毫不逊色。
The experimental results show the capacity of the hybrid system to produce about 20 L of water at 80 °C in a day with improved electrical efficiency.
实验结果表明,混合动力系统能够在 80 °C 的温度下每天生产约 20 升水,同时提高了电能效率。
[224]
Experimental and numerical
实验和数值
Air  空气Overall system efficiency above 45 % was achieved
系统整体效率超过 45
It is observed that, during winter, low flow rate air circulation systems perform better as high air temperature differences can be achieved. However, during summer, high flow rate systems achieve a lower operating temperature of a PV cell.
据观察,在冬季,低流速空气循环系统的性能更好,因为可以实现较高的空气温差。然而,在夏季,高流速系统可实现较低的光伏电池工作温度。
[225]
Experimental and numerical
实验和数值
Water  Maximum overall thermal and exergy efficiencies obtained were 34 % and 15 %, respectively
获得的最高总体热效率和放热效率分别为 34 % 和 15 %。
The experimental results show that, with the copper PV-T base water heating system, the electrical efficiency of the system reduces with a temperature rise. Due to better heat transfer between the PV cell and the flowing fluid, the maximum overall thermal energy of the proposed copper base PV-T collector is higher than that of the conventional Tedlar base PV-T collector.
实验结果表明,使用铜基 PV-T 水加热系统时,系统的电效率会随着温度的升高而降低。由于光伏电池和流动液体之间的传热效果更好,拟议的铜基 PV-T 集热器的最大总热能高于传统的 Tedlar 基座 PV-T 集热器。
[226]
Experimental and simulation
实验和模拟
Air and Water  空气和水The daily rate of thermal gain and daily overall electrical gain is 2.5 % and 5.2 % higher for an aluminium base PVT-TEC water collector and opaque PVT-TEC water collector, respectively