不同热调控策略下太阳能PV/T-PCM系统性能实验研究

通过在太阳能集热器中添加饱和式脂肪酸相变材料,对太阳能光伏光热系统的不同热调控策略开展了实验研究。分析集热器中通水和不通水两种热调控策略对系统能量利用的影响。结果表明：相变材料可有效降低光伏板温度,但两种热调控策略下相变材料存在明显的温度分层现象;与不通水策略相比,通水策略在强化系统换热的同时促进了更多余热的回收,不通水和通水策略的热效率分别为71.3%和77.1%;通水策略可以更加有效地降低光伏板温度,缓解相变材料过热的影响,光电转化效率提高了7.3%。     

Investigation of hydrogen production performance of a reactor assisted by a solar pond via photoelectrochemical process

In this study, the hydrogen production performance of a reactor assisted by a solar pond by photoelectrochemical method is examined conceptually. The main components of the new integrated system are a solar pond, a photovoltaic panel (PV) and a hybrid chlor-alkali reactor which consists of a semiconductor anot, photocathode and cation exchange membrane. The proposed system produces hydrogen via water splitting reaction and also yields the by products namely chlorine and sodium hydroxide while consumes saturated NaCl solution and pure water. In order to increase the efficiency of the reactor, the saturated hot NaCl solution at the heat storage zone (HSZ) of the solar pond is transferred to the anot section and the heated pure water by heat exchanger in the HSZ is transferred to cathode section. The photoelectrode releases electrons for hydrogen production with diminishing the power requirement from the PV panel that is used as a source of electrical energy for the electrolysis. The results confirm that the thermal performance of the solar pond plays a key role on the hydrogen production efficiency of the reactor.     

A turbulent air-flow corrugating photovoltaic model to enhance power output

This paper investigated the influence of the cooling of turbulent blowing air on the photovoltaic (PV) modules using the corrugation technique. The well-known five-parameter diode equation side by side with conservation principles were used to study the effect of corrugating lower PV sides to cool PV's and enhance efficiency. As the main restriction of PV systems is low efficiency that is powerfully counting on its operational temperature, therefore, reducing the operating temperature of PV cells is critical for the PV panel to work. To achieve this aim, a mathematical model describing PV temperatures and efficiency using continuity, momentum, and energy side by side with the Shockley diode equation was built. It was found that the corrugating of lower sides of PV's up to 1 mm in a distance of 20 mm considering turbulent flow conditions considerably reduced temperature and consequently enhanced thermal efficiency from 13% to 15%; the eddy viscosity and Reynolds shear stress increased boundary layer thickness and velocities, so increased the coefficient of heat transfer and consequently electrical power output and thermal efficiency.     

Performance evaluation of photovoltaic/thermal–HDH desalination system

The efficiency of photovoltaic (PV) panel drops with increase in cell temperature. The temperature of the PV panel can be controlled with various cooling techniques. In the proposed work the PV panel is cooled by circulating water and the recovered heat energy is used to run a humidification and dehumidification desalination to produce distilled water from sea water (or) brackish water. This work deals with a detailed analysis of performance of combined power and desalination (Photovoltaic/Thermal–Humidification and Dehumidification) system. A mathematical model of PV/thermal–humidification dehumidification plant was developed and simulations were carried out in MATLAB environment. The performance of photovoltaic/ thermal desalination (Photovoltaic/Thermal–Humidification and Dehumidification) system was investigated under various solar radiation levels (800–1000 W/m²). For each solar radiation level the effect of mass flow rate of coolant water (30–110 kg/h) on water outlet temperature, PV efficiency, PVT thermal efficiency, distilled water production, and plant efficiency was studied. Results show that under each solar radiation level increasing coolant flow rate increases efficiency of PV panel and reduces the plant efficiency. The highest PV efficiency (16.598%) was reached under 800 W/m² at mass flow rate of 110 kg/h and the highest plant efficiency (43.15%) was reached under 800 W/m² at a mass flow rate of 30 kg/h. The maximum amount of distilled water production rate (0.82 L/h) was reached under 1000 W/m² at water mass flow rate of 30 kg/h.     

Increasing the efficiency of PV panel with the use of PCM

The article presents how to increase electrical efficiency and power output of photovoltaic (PV) panel with the use of a phase change material (PCM). The focus of the work is in experimental setup and simulation heat extraction from the PV panel with the use of TRNSYS software. A modification of PV panel Canadian Solar CS6P-M was made with a phase change material RT28HC. The actual data of cell temperature of a PV panel with and without PCM were given and compared. A simulation of both PV panels in TRNSYS software was performed, followed by the comparison of results with the simulation and experimental actual data. The experimental results show that the maximum temperature difference on the surface of PV panel without PCM was 35.6 °C higher than on a panel with PCM in a period of one day. Referring to experimental results the calculation of the maximum and average increase of electrical efficiency was made for PV-PCM panel with TRNSYS software. Final results of simulation shows that the electricity production of PV-PCM panel for a city of Ljubljana was higher for 7.3% in a period of one year.     

Experimental performance of cooling photovoltaic panels using geothermal energy in an arid climate

In this study, an experimental prototype was built to examine the use of an underground water tank as a heat exchange medium with the soil to reduce photovoltaic (PV) panel operation temperatures and simultaneously improve PV efficiency. Three PV systems were evaluated: a benchmark PV panel without cooling (panel A); a PV panel with water spray cooling (panel B); and a PV panel with evaporative cooling (panel C). The cooling techniques in modules (B) and (C) were used to investigate the effects of underground water on the performance of PV panels in arid conditions. Four cases were devised as follows: spray panel back cooling (I), spray front and back cooling (II), spray front and back cooling using an Arduino controller (III), and repeating case III with different water flow rates (IV). Readings were taken from 9:00 am to 4:00 pm  from May to August. The experimental results showed that the use of underground water spray cooling led to reductions in the temperature of PV panel B, 14°C, 17.6°C, 18.8°C, and 22.7°C for cases I, II, III, and IV, respectively, when compared with the uncooled panel, and efficiency improved by 3.5%, 4.8%, 18%, and 23.1%, respectively.     

Further progress in the research of fin‐based passive cooling technique for the free‐standing silicon photovoltaic panels

The paper deals with a passive air‐based cooling technique of photovoltaic (PV) panels in operating conditions. Cooling technique is done by specific type of using aluminium fins, and its main purpose is to increase the electrical efficiency of the PV panel. An increase in electrical efficiency can be achieved because of temperature degradation effect, where the PV panel yields less power at higher operating temperatures (the PV panel's efficiency can drop by up to 0.5%/°C). To confirm a cooling technique, a medium‐sized PV system was used in a 2‐month experiment. The experiment was done in realistic operating conditions, and all working parameters were thoroughly measured. After the analysis of the data, no significant raise in electrical efficiency was recorded throughout the experiment. A numerical approach was conducted, based on gained experimental data. Developed numerical model gave explanations of experimental results and provided an insight in heat flow through the PV cell. Later on, developed numerical model was used to propose new cooling variations of the fin‐based technique and to further examine the overall potential of air based passive cooling techniques. It was shown that cooling effect by up to 5°C is a realistic expectation for this technique in described operating conditions.     

Experimental investigation on the effect of photovoltaic panel partially and fully submerged in water

This study presents an experimental analysis of improving the thermal, electrical efficiency, and yield of a conventional solar still (CSS). The photovoltaic (PV) efficiency decreases with increase in water depth inside the basin while the still efficiency is higher in the case of fully submerged condition. The maximum water production was about 8 kg/m ²/day with PV under fully submerged condition; and during off‐shine hours the still efficiency was higher when compared with the partially submerged condition. Similarly, with a decrease in water temperature the panel efficiency is increases. The maximum hourly water production with and without the PV was found to be 1.3 and 0.45 kg/m ², respectively. The main outcome of this study is that this mechanism can be used in isolated locations where there is a scarcity of current and distilled water.     

Simulation and experimental validation of heat transfer in a novel hybrid solar panel

A hybrid solar panel has been invented to integrate photovoltaic (PV) cells onto a substrate through a functionally graded material (FGM) with water tubes cast inside, through which water serves as both heat sink and solar heat collector. Therefore, the PV cells can work at a relatively low temperature while the heat conduction to the substrate can be minimized. Solar panel prototypes have been fabricated and tested at different water flow rates and solar irradiation intensities. The temperature distribution in the solar panel is measured and simulated to evaluate the performance of the solar panel. The finite element simulation results are very consistent with the experimental data. The understanding of heat transfer in the hybrid solar panel prototypes will provide a foundation for future solar panel design and optimization. The finite element model is general and can be extended for different material design and other size of panels.     

Improving Photovoltaic Module Efficiency Using Water Cooling

An effective way of improving efficiency and reducing the rate of thermal degradation of a photovoltaic (PV) module is by reducing the operating temperature of its surface. This can be achieved by cooling the module and reducing the heat stored inside the PV cells during operation. In this paper, long-term performance modeling of a proposed solar-water pumping system is carried out. The system, which is used for irrigation purposes, consists of a PV module cooled by water, a submersible water pump, and a water storage tank. Cooling of the PV panel is achieved by introducing water trickling configuration on the upper surface of the panel. An experimental rig is developed to investigate and evaluate PV module performance with the proposed cooling technique. The experimental results indicated that due to the heat loss by convection between water and the PV panel's upper surface, an increase of about 15% in system output is achieved at peak radiation conditions. Long-term performance of the system is estimated by integrating test results in a commercial transient simulation package using site radiation and ambient temperature data. The simulation results of the system's annual performance indicated that an increase of 5% in delivered energy from the PV module can be achieved during dry and warm seasons.     

一种新型全铝扁盒式PV/T热水系统

将单晶硅光伏电池与全铝扁盒式太阳能热水器集热板通过特殊工艺粘结起来,制成了一套自然循环式光伏光热一体化(PV/T)系统,在利用太阳能发电的同时提供热水。于04年7月-10月在合肥地区进行了室外实验,测试并讨论了该系统以不同水量和不同初始水温运行时的光电光热性能。结果表明,当m/Ac>80kg/m2时,这种PV/T热水系统的发电效率在10.15%左右,热效率在50%左右,光电光热总效率可以达到60%左右,光电光热综合性能效率可以达到70%左右。相对于单纯的光伏系统或自然循环式太阳能热水系统,这种PV/T热水系统具有占地面积小、综合效率高等优点。     

Use of TRNSYS for modelling and simulation of a hybrid pv–thermal solar system for Cyprus

This paper deals with the modelling and simulation of a hybrid photovoltaic–thermal (PV/T) solar energy system. This is a combined system consisting of a normal PV panel at the back of which a heat exchanger with fins is embedded. The advantage of this type of system is that the PV panel operates at a lower temperature, thus more efficiently, and also hot water is produced at the same time as electricity. The PV system consists of a series of PV panels, a battery bank and an inverter whereas the thermal system consists of a hot water storage cylinder, a pump and a differential thermostat. The system is modelled using TRNSYS, which is a transient simulation program and typical meteorological year (TMY) conditions for Nicosia, Cyprus. The main component of the TRNSYS deck file constructed for this purpose is Type 49, accompanied by other additional components required for the model. The results show that the optimum water flow rate of the system is 25 l/h. The hybrid system increases the mean annual efficiency of the PV solar system from 2.8% to 7.7% and in addition covers 49% of the hot water needs of a house, thus increasing the mean annual efficiency of the system to 31.7%. The life cycle savings of the system is Cy£790.00 and the pay-back time is 4.6 years.     

A Review on the Heat Pipe Photovoltaic/Thermal(PV/T) System

The Photovoltaic/thermal(PV/T) system combines the conventional PV panel with solar collector into one integrated system, which could achieve the function of generating power and providing thermal energy at the same time. Recently, it has become the most promising solar system for building applications. Most of the PV/T systems use water as the coolant, which could cause freezing problem in winter. To overcome this problem, the heat pipe PV/T system is developed to provide electrical and thermal energy stably without the seasonal barrier. Although some published review works have involved this type of PV/T system, they just stated a simple introduction on it, acting as a small part of their works. This paper focuses on the heat pipe PV/T system independently and provides a comprehensive and in-depth analysis of its performance. Firstly, the structure and operational principles of the heat pipe PV/T module and system are introduced concisely. Then the features and performance of different types of heat pipe PV/T systems, i.e., integral heat pipe, loop heat pipe, and pulsating heat pipe PV/T system, are presented and analyzed. This is followed by the review on the performance of the systems which combine heat pipe PV/T module and other devices. Finally, the research gaps in this field are identified, and some future research trends and directions are recommended.     

Efficient single glazed flat plate photovoltaic-thermal hybrid collector for domestic hot water system

This paper deals with the design of a single glazed flat plate Photovoltaic-Thermal (PV-T) solar collector. First, the thermal and electrical performances of several single glazed flat plate PV-T concepts based on water circulation are investigated, using a simple 2D thermal model, then different ways of improvement are presented. It mainly consists in focusing on the heat transfer between PV cells and fluid, and also on the optical properties of materials. Thus, the most appropriate concept configuration has been identified and suitable material properties have been selected. A prototype collector has been designed, built and tested. A high thermal efficiency was reached at zero reduced temperature. For this level of thermal efficiency, the corresponding electrical efficiency has is lower than efficiency of a standard PV panel using the same technology. However, this solar PV-T collector is reaching, in these standard conditions, the highest efficiency level reported in the literature.     

管式PV/T水冷装置的对流传热性能分析与效能实验

针对PV/T的研究主要以实验方法为主缺乏理论依据的问题,利用管道液体对流传热理论,对PV/T水冷装置的热吸收能力和传热时延进行了初步分析,研究了流速对装置性能的影响。通过设计U型管水冷PV/T进行模型实验,表明了在功能方面,PV/T既可以实现太阳能的热利用,也可以降低组件温度,从而提高光伏发电效率。在性能方面,PV/T的热吸收能力受流速的影响很大,需要平衡热吸收能力与水泵驱动功率之间的矛盾。     

一种多功能光伏发电系统的可行性研究

通过在光伏组件的背面连接了一个热电转换模块,形成一个光伏一热电混合模块,从而将光伏组件工作过程中产生的废热转换成电能的同时又降低了光伏组件的温度,进而提高了光电转换效率。将光伏一热电模块与百叶有效结合,从而实现了室内采光、通风及节约空间等多种功能。同时,为了提高光伏组件的入射太阳辐射,引入了可调节的抛物型双面聚焦板,减少了太阳能电池板的面积,从而减少了太阳能发电的成本。     

无盖板型水冷式PV/T模块光电/光热综合性能实验研究

无盖板PV/T组件相比于盖板式PV/T组件有更高的光电转换效率,在电能输出方面的优势明显。基于此,提出一种无盖板型水冷式PV/T模块,并搭建由光伏对比模块、水冷式PV/T模块以及无冷却水循环的PV/T对比模块构成的实验平台开展对比实验,研究温度、流量对无盖板PV/T模块电、热转换效率的影响。结果表明,在水冷作用下,PV/T模块的光伏组件温度显著降低,与PV/T对比模块相比发电效率提升11.54%;环境平均温度为21.7 ℃、平均辐照度650 W/m²的测试条件下,流量0.12 m³/h时模块的电效率为17.44%,热效率为19.80%,综合效率达到65.69%,考虑到循环泵消耗的电能,表面积1.93 m²的水冷式PV/T模块全天可存储有效能3.72 MJ。     

Performance improvement study of an integrated photovoltaic system for offshore power production

Sustainable energy is one of the main options for resolving energy problems and climate change issues. Solar energy is one of the main promising renewable energy sources, which can be captured and converted to electrical energy through photovoltaic (PV) panels. In the open literature, it is shown that having two PV panels integrated into a back‐to‐back configuration placed on naturally reflective surfaces provides the potential of doubling the total power produced by a single‐faced PV panel with the appropriate location and orientation. This paper presents a case study of two‐PV panel systems for offshore power production. The relevance to offshore has the water surface as the reflective surface to produce power from the back facing panel. The city of Ottawa in Canada is selected as the location for a case study. Various conditions and operating parameters are considered in assessing the performance of the proposed system, including solar radiation intensity, system orientation, time of year in terms of months, and the variations in parameters throughout the day. The assessment of the proposed system is carried out through modeling and simulating the proposed double PV panels in the COMSOL Multiphysics software. It is found that the minimum improvement in the total power production over the single face conventional PV is 38% in January for the east‐facing PV front face. For the two PV systems, the optimal overall power production for the various time conditions and orientations, at the specified location, is found to be the north orientation of the PV panel. In this case, the power it produces is 89% of that of the east orientation. A similar trend is observed for the single‐faced PV panel, where the north‐facing PV provides 62% of what it could produce in the east‐facing orientation.     

Effect of hybrid nanofluids mixture ratio on the performance of a photovoltaic thermal collector

Solar photovoltaic-thermal (PV/T) collectors, are hybrid collectors used to convert solar radiation into usable thermal and electrical energy. Recently, the field of research on PV/T is has focused on improving the efficiency of the PV/T collector by replacing the conventional heat transfer fluids (HTFs) with nanofluids. This article investigates the effect of hybrid nanofluids mixture ratio on the useful energy and overall efficiency of a PV/T collector operating with Al₂O₃-ZnO water nanofluid as the HTF. Experiments to measure the thermophysical properties of the hybrid nanofluids were conducted for various temperatures, volume concentrations, and mixture ratios, furthermore, accurate correlation models were proposed. Metrological data and energy output readings collected from the PV solar farm at Cyprus International University were used to validate our model. The study observed that at the optimum mixture ratio (0.47 of Al₂O₃ in the hybrid), the electrical, thermal, and exergy efficiencies of the PV/T collector are 13.8%, 55.9%, and 15.13% respectively. Also, the cell temperature drops by 21% when the mass flow rate is 0.1 kg/s as compared to when it is 0.01 kg/s. Finally, the study concludes that by using the Al₂O₃-ZnO hybrid nanofluid an overall peak thermal efficiency of 91% can be attained, and this represents a 34% enhancement in the collector's performance when compared to water.     

Performance investigation of transparent photovoltaic-thermal collector with horizontal oscillating and rectangular spiral flow patterns

Efficiency drop due to increase in photovoltaic (PV) module operating temperature creates a huge difference between the projected and actual electricity generated in large power plants. As a solution to this problem Photovoltaic-Thermal (PV/T) collector, with PV at top and thermal collector at the bottom has been developed. PV/T can cool the PV as well as generate low-temperature thermal energy. This article presents a comparative experimental study of two newly developed PV/T collector having transparent solar panel with copper tube absorber arranged in rectangular spiral (PV/T-RS) and horizontal oscillating (PV/T-HO) configurations. The PV/T collectors are experimentally evaluated under outdoor conditions at Indian Institute of Technology Guwahati. The developed PV/T's are compared in terms of electrical and thermal efficiencies. The PV/T-RS is found to be better as compared to PV/T-HO in terms of electrical output, whereas reverse result is reported in case of thermal output. The average electrical and thermal efficiency was found to be 11.2% ± 0.95% and 57.11% ± 2.94% for PV/T-RS. The calculated average thermal efficiency of PV/T-HO (63.6% ± 2.94%) is found to be 11.4% more as compared to PV/T-RS. The overall exergetic efficiency for PV/T-RS and PV/T-HO was found to be in the range 11.8%-16.2% ± 3.18% and 9.7%-15.25% ± 3.18%, respectively.