Applied Thermal Engineering
Research Paper
Dynamic coupled thermal-and-electrical modelling of sheet-and-tube hybrid photovoltaic/thermal (PVT) collectors
IlariaGuarracino a AlexanderMellor b Nicholas J.Ekins-Daukes b Christos N.Markides a
Highlights
bull; A fully dynamic, 3-D numerical model of a PVT collector is presented.
bull; High-resolution weather data and hot-water demand data are used in the simulation.
bull; The use of PV cells with reduced emissivity for PVT applications is introduced.
Abstract
In this paper we present a dynamic model of a hybrid photovoltaic/thermal (PVT) collector with a sheet-and-tube thermal absorber. The model is used in order to evaluate the annual generation of electrical energy along with the provision of domestic hot-water (DHW) from the thermal energy output, by using real climate-data at high temporal resolution. The model considers the effect of a non-uniform temperature distribution on the surface of the solar cell on its electrical power output. An unsteady 3-dimensional numerical model is developed to estimate the performance of such a collector. The model allows key design parameters of the PVT collector to vary so that the influence of each parameter on the system performance can be studied at steady state and at varying operating and atmospheric conditions. A key parameter considered in this paper is the number of glass covers used in the PVT collector. The results show that while the thermal efficiency increases with the additional glazing, the electrical efficiency deteriorates due to the higher temperature of the fluid and increased optical losses, as expected. This paper also shows that the use of a dynamic model and of real climate-data at high resolution is of fundamental importance when evaluating the yearly performance of the system. The results of the dynamic simulation with 1-min input data show that the thermal output of the system is highly dependent on the choice of the control parameters (pump operation, differential thermostat controller, choice of flow rate etc.) in response to the varying weather conditions. The effect of the control parameters on the system#39;s annual performance can be captured and understood only if a dynamic modelling approach is used. The paper also discusses the use of solar cells with modified optical properties (specifically, reduced absorptivity/emissivity) in the infrared spectrum, which would reduce the thermal losses of the PVT collector at the cost of only a small loss in electrical output when the selective coating is applied.
Keywords Photovoltaic/thermal systems Hybrid PVT Solar collectors System performance Domestic energy demand
1. Introduction
Hybrid photovoltaic/thermal (PVT) collectors are devices for the conversion of solar radiation into electrical and thermal energy simultaneously. This solution is particularly interesting in residential applications, where a demand for electricity exists alongside one for low temperature heat. Liquid (water) PVT systems are interesting in cold climate regions such as the UK – the location chosen for this study – where the demand of heating and domestic hot water is almost constant during the year. It is predicted in Refs. [1,2] that a PVT system with a 15thinsp;m2 collector area designed for a 3-bedroom house in the UK can cover up to 36% of the demand for hot water and up to 51% of the demand for electricity based on a four-member family.
PVT systems operate mostly under dynamic conditions, particularly where the solar irradiance fluctuates due to cloud coverage. However, most previous studies undertaken with the aims of evaluating the suitability and of assessing the potential of this technology (such as Ref. [1]) were based on quasi-steady approaches, wherein the PVT collector is assumed to operate in steady state, while other system components with a larger thermal mass – such as the hot-water tank – have a dynamic response to the time-varying inputs. A few studies (such as Ref. [3] 全文共89265字，剩余内容已隐藏，支付完成后下载完整资料
平板和管混合光伏/热（PVT）收集器的热电动态耦合模型
作者：Ilaria Guarracino , Alexander Mellor , Nicholas J. Ekins-Daukes , Christos N. Markides
本文亮点：
提出了一种PVT的全动态、三维数值模型。
模拟过程中使用高精确度的天气数据和热水需求数据。
介绍了PVT应用中降低发射率的光伏电池的使用情况。
摘要
本文提出了一种平板和管式吸热器混合光伏/热（PVT）集热器的动态模型。该模型采用高精确度的实时气候数据，用以评估电能年发电量随着生活热水（DHW）提供的热能输出，并考虑了太阳能电池表面的非均匀温度分布对其输出功率的影响。建立了一个非定常三维数值模型来估算这种集热器的性能。该模型允许PVT收集器的关键设计参数变化，以便在稳态、不同操作和大气条件下研究每个参数对系统性能的影响。本文考虑的一个关键参数是PVT收集器中使用的玻璃罩的数量。如预期的那样，结果表明随着附加玻璃的热效率的提高，由于液体的温度升高和光损耗增加，电效率降低。本文还表明，在评估系统的年度性能时，使用动态模型和高精确度的真实气候数据是至关重要的。用1分钟输入数据的动态仿真结果表明，系统的热输出功率在应对天气变化时是高度依赖于控制参数的选择（水泵运行，微分恒温控制器、流量等的选择）。只有使用动态建模方法，才能捕捉和理解控制参数对系统年度性能的影响。本文还讨论了在红外光谱中使用具有改进的光学特性（特别是降低吸收率/发射率）的太阳能电池，这种太阳能电池在选择涂层时只会损失少量的电输出，从而减少PVT收集器的热损失。
关键词：光伏/热系统 混合型PVT 太阳能集热器 系统性能 民用能源需求
1 介绍
1 。 jiegrave;介 shagrave;o绍
Hybrid photovoltaic/thermal (PVT) collectors are devices for the conversion of solar radiation into electrical and thermal energy simultaneously. This solution is particularly interesting in residential applications, where a demand for electricity exists alongside one for low temperature heat. Liquid (water) PVT systems are interesting in cold climate regions such as the UK – the location chosen for this study – where the demand of heating and domestic hot water is almost constant during the year. It is predicted in Refs. [1,2] that a PVT system with a 15thinsp;m2 collector area designed for a 3-bedroom house in the UK can cover up to 36% of the demand for hot water and up to 51% of the demand for electricity based on a four-member family.
混合光伏/热（PVT）收集器是同时将太阳辐射转换为电能和热能的装置。这种解决方案在住宅应用中尤其有趣，因为那里的电力需求与低温热同时存在。寒冷气候地区，液态（水）PVT系统是有趣的，比如该研究所选择的地点——英国那里一年内供暖和生活热水的需求几乎是不变的。据文献[ 1,2 ]预测，一个15平方米的集热器面积thinsp;设计在英国的三居室的房子PVT系统可以覆盖到36%的热水需求，高达51%的基于四个成员的家庭的电力需求。
hugrave;n混 heacute;合 guāng光 fuacute;伏 / regrave;热 （ P V T ） shōu收 jiacute;集 qigrave;器 shigrave;是 toacute;ng同 shiacute;时 jiāng将 tagrave;i太 yaacute;ng阳 fuacute;辐 shegrave;射 zhuǎn转 huagrave;n换 weacute;i为 diagrave;n电 neacute;ng能 heacute;和 regrave;热 neacute;ng能 de的 zhuāng装 zhigrave;置 。 zhegrave;这 zhǒng种 jiě解 jueacute;决 fāng方 agrave;n案 zagrave;i在 zhugrave;住 zhaacute;i宅 yigrave;ng应 yograve;ng用 zhōng中 yoacute;u尤 qiacute;其 yǒu有 qugrave;趣 ， yīn因 wegrave;i为 nagrave;那 lǐ里 de的 diagrave;n电 ligrave;力 xū需 qiuacute;求 yǔ与 dī低 wēn温 regrave;热 toacute;ng同 shiacute;时 cuacute;n存 zagrave;i在 。 zagrave;i在 yīng英 guoacute;国 děng等 haacute;n寒 lěng冷 qigrave;气 hograve;u候 digrave;地 qū区 ， yegrave;液 tagrave;i态 （ shuǐ水 ） P V T xigrave;系 tǒng统 shigrave;是 yǒu有 qugrave;趣 de的 — — gāi该 yaacute;n研 jiū究 suǒ所 xuǎn选 zeacute;择 de的 digrave;地 diǎn点 — — niaacute;n年 negrave;i内 gōng供 nuǎn暖 heacute;和 shēng生 huoacute;活 regrave;热 shuǐ水 de的 xū需 qiuacute;求 jī几 hū乎 shigrave;是 bugrave;不 biagrave;n变 de的 。 jugrave;据 weacute;n文 xiagrave;n献 yugrave;预 cegrave;测 。 [ 1 , 2 ] ， yī一 gegrave;个 1 5 piacute;ng平 fāng方 mǐ米 de的 jiacute;集 regrave;热 qigrave;器 miagrave;n面 jigrave;积 thinsp; shegrave;设 jigrave;计 zagrave;i在 yīng英 guoacute;国 de的 sān三 jū居 shigrave;室 de的 faacute;ng房 zi子 P V T xigrave;系 tǒng统 kě可 yǐ以 fugrave;覆 gagrave;i盖 dagrave;o到 3 6 % de的 regrave;热 shuǐ水 xū需 qiuacute;求 ， gāo高 daacute;达 5 1 % de的 jī基 yuacute;于 sigrave;四 gegrave;个 cheacute;ng成 yuaacute;n员 de的 jiā家 tiacute;ng庭 de的 diagrave;n电 ligrave;力 xū需 qiuacute;求 。
PVT systems operate mostly under dynamic conditions, particularly where the solar irradiance fluctuates due to cloud coverage. However, most previous studies undertaken with the aims of evaluating the suitability and of assessing the potential of this technology (such as Ref. [1]) were based on quasi-steady approaches, wherein the PVT collector is assumed to operate in steady state, while other system components with a larger thermal mass – such as the hot-water tank – have a dynamic response to the time-varying inputs. A few studies (such as Ref. [3]) did take into account the dynamic response of the collector but did not go as far as estimating the temperature gradients on the PV module and the dynamic analysis is limited to a daily simulation. Similarly, in the studies reported in Refs. [4–6], dynamic analyses of PVT collectors were also preformed but without an accompanying discussion of the interaction of the collector with other system components. Some recent experimental and numerical studies on the dynamic performance of PVT systems for DHW applications can be found in Refs. [7,8] where the demand of hot water was a daily or hourly average input.
PVT系统主要在动态条件下工作，特别是在太阳辐射由于云层覆盖而波动的情况下。然而，以往的研究大多以适宜性评价的目的和评价该技术的潜力（如参考文献[ 1 ]）是基于准稳态的方法，所述的PVT收集器假设工作在稳定的状态，而具有更大的热容量–如热水罐–必须时变输入动态响应其他系统组件。一些研究（如参考文献3）确实考虑了收集器的动态响应，但没有估算PV模块上的温度梯度，动态分析仅限于日常模拟。同样，在文献[ 4 - 6 ]报道的研究中，PVT收集器的动态分析也预先建立，但没有伴随的集电极与其他系统组件的相互作用的讨论。在DHW应用PVT系统动态性能的一些最近的实验和数值模拟研究可以在文献[7,8]中发现，热水需求量是每天或每小时的平均输入。
P V T xigrave;系 tǒng统 zhǔ主 yagrave;o要 zagrave;i在 dograve;ng动 tagrave;i态 tiaacute;o条 jiagrave;n件 xiagrave;下 gōng工 zuograve;作 ， tegrave;特 bieacute;别 shigrave;是 zagrave;i在 tagrave;i太 yaacute;ng阳 fuacute;辐 shegrave;射 yoacute;u由 yuacute;于 yuacute;n云 ceacute;ng层 fugrave;覆 gagrave;i盖 eacute;r而 bō波 dograve;ng动 de的 qiacute;ng情 kuagrave;ng况 xiagrave;下 。 raacute;n然 eacute;r而 ， yǐ以 wǎng往 de的 yaacute;n研 jiū究 dagrave;大 duō多 yǐ以 shigrave;适 yiacute;宜 xigrave;ng性 piacute;ng评 jiagrave;价 de的 mugrave;目 digrave;的 heacute;和 piacute;ng评 jiagrave;价 gāi该 jigrave;技 shugrave;术 de的 qiaacute;n潜 ligrave;力 （ ruacute;如 cān参 kǎo考 weacute;n文 xiagrave;n献 [ 1 ] ） shigrave;是 jī基 yuacute;于 zhǔn准 wěn稳 tagrave;i态 de的 fāng方 fǎ法 ， suǒ所 shugrave;述 de的 P V T shōu收 jiacute;集 qigrave;器 jiǎ假 shegrave;设 gōng工 zuograve;作 zagrave;i在 wěn稳 digrave;ng定 de的 zhuagrave;ng状 tagrave;i态 ， eacute;r而 jugrave;具 yǒu有 gegrave;ng更 dagrave;大 de的 regrave;热 roacute;ng容 liagrave;ng量 – ruacute;如 regrave;热 shuǐ水 guagrave;n罐 – bigrave;必 xū须 shiacute;时 biagrave;n变 shū输 rugrave;入 dograve;ng动 tagrave;i态 xiǎng响 yigrave;ng应 qiacute;其 tā他 xigrave;系 tǒng统 zǔ组 jiagrave;n件 。 yī一 xiē些 yaacute;n研 jiū究 （ ruacute;如 cān参 kǎo考 weacute;n文 xiagrave;n献 3 ） quegrave;确 shiacute;实 kǎo考 lǜ虑 le了 shōu收 jiacute;集 qigrave;器 de的 dograve;ng动 tagrave;i态 xiǎng响 yigrave;ng应 ， dagrave;n但 meacute;i没 yǒu有 gū估 suagrave;n算 P V moacute;模 kuagrave;i块 shagrave;ng上 de的 wēn温 dugrave;度 tī梯 dugrave;度 ， dograve;ng动 tagrave;i态 fēn分 xī析 jǐn仅 xiagrave;n限 yuacute;于 rigrave;日 chaacute;ng常 moacute;模 nǐ拟 。 toacute;ng同 yagrave;ng样 ， zagrave;i在 weacute;n文 xiagrave;n献 bagrave;o报 dagrave;o道 de的 yaacute;n研 jiū究 zhōng中 。 [ 4 - 6 ] ， P V T shōu收 jiacute;集 qigrave;器 de的 dograve;ng动 tagrave;i态 fēn分 xī析 yě也 yugrave;预 xiān先 jiagrave;n建 ligrave;立 ， dagrave;n但 meacute;i没 yǒu有 bagrave;n伴 suiacute;随 de的 jiacute;集 diagrave;n电 jiacute;极 yǔ与 qiacute;其 tā他 xigrave;系 tǒng统 zǔ组 jiagrave;n件 de的 xiāng相 hugrave;互 zuograve;作 yograve;ng用 de的 tǎo讨 lugrave;n论 。 zagrave;i在 D H W yigrave;ng应 yograve;ng用 P V T xigrave;系 tǒng统 dograve;ng动 tagrave;i态 xigrave;ng性 neacute;ng能 de的 yī一 xiē些 zuigrave;最 jigrave;n近 de的 shiacute;实 yagrave;n验 heacute;和 shugrave;数 zhiacute;值 moacute;模 nǐ拟 yaacute;n研 jiū究 kě可 yǐ以 zagrave;i在 weacute;n文 xiagrave;n献 zhōng中 fā发 xiagrave;n现 。 [ 7 , 8 ] ， regrave;热 shuǐ水 xū需 qiuacute;求 liagrave;ng量 shigrave;是 měi每 tiān天 huograve;或 měi每 xiǎo小 shiacute;时 de的 piacute;ng平 jūn均 shū输 rugrave;入 。
Taking the dynamics of the system into account is of fundamental importance when the weather conditions change rapidly. The present paper, in fact, shows that a dynamic model, together with the use of real weather and DHW demand data, is required in order to accurately estimate the energy output of the PVT system. It will be demonstrated, based on both types of model, that quasi-steady solutions dev
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