Photovoltaic Thermal Unit Research Articles

Integration of concentrated multi-junction solar cells with small-scale organic rankine cycle

In this paper, concentrated photovoltaic system using multiple (four) multi-junction solar cells with a refractive system for a single point focus Fresnel lens was developed to achieve high performance in terms of optical efficiency, uniformity (Peak average ratio value) and compactness. Geometric concentration ratio, F-number, focal length and height of homogenizer were investigated showing that at Geometric concentration ratio of 400×, F-number of 1.12, focal length of 632.5 mm and height of homogenizer of 50 mm, the concentrated photovoltaic achieves an optical efficiency and Peak average ratio value of 79.6% and 1.52 respectively. Active cooling was simulated in order to ensure effective operation of the multi-junction solar cells (operating temperature < 110 °C) and to investigate the potential of exploiting the heat generated in the cells to operate an Organic Rankine Cycle to maximize the overall solar energy conversion efficiency. An Organic Rankine Cycle system with a target 1 kW power output is studied at different operating conditions and working fluid in order to be integrated with the Concentrated Photovoltaic Thermal system. Various configurations for integrating the Concentrated Photovoltaic Thermal units with the Organic Rankine Cycle working at various operating conditions and working fluids were investigated. Results showed that the integrated system with surface area of 16.8 m2, Organic Rankine Cycle system using R245fa can produce 6.17 kW of electricity with overall energy conversion efficiency of 46.57%. The developed system has the potential to provide the required electricity for buildings in Saudi Arabia which enjoys abundant solar radiation.

Comparison of the performance of different designs of a combined system consisting of a photovoltaic thermal unit and a sensible rotary heat exchanger

Steady-state energy and exergy evaluation are performed on two designs of a hybrid building integrated photovoltaic thermal (BPT) unit and a thermal wheel (SRX). The working principles of these designs in summer are similar such that the warm outside air is precooled by exchanging heat with air coming out of the building in SRX and then enters the building. Also, other outlet air from SRX passes through the BPT unit and cools PV modules, boosting their efficiency. The working principle of the design A in winter are that the outside air is preheated by receiving heat from the building exhaust air in SRX and then preheated again by passing through the BPT system. The design B works in the same way in winter, with the air passing through the BPT system first and then the SRX. The outcomes revealed that the annual total rate of thermal energy, electrical energy and thermal exergy outputs of the design A are 23183.4 kW h, 5994 kW h, 261.6 kW h, respectively, while these values for the design B are respectively 22785.2 kW h, 6030. 6 kW h and 243 kW h. In addition, it was found that the overall energy/exergy performance of design A is better/worse than design B.

Improving Thermal Distribution in Water-Cooled PV Modules and Its Effect on RO Permeate Recovery

Among the most notable emerging hybrid technologies for water treatment are those that combine reverse osmosis (RO) membrane systems with alternative energy sources such as solar photovoltaic (PV). Solar PV modules can enable systems disconnected from the electricity grid, and in some locations can also be used for water heating as photovoltaic-thermal (PVT) units, a process in which water removes heat from the PV module, increasing its electrical generation efficiency. When combined with RO, the higher temperature feed water can increase RO permeate flux, improving recovery but decreasing the rejection of dissolved salts. Although the decrease in efficiency of PV modules at higher temperatures is a well-known issue, this is usually under conditions of uniform temperature. However, the temperature distribution in water-cooled PV modules is usually not uniform and, given the anisotropy of the distribution and electrical connection of the PV cells in the module, this factor has not been the focus of much study. In this context, a PVT unit that focuses on increasing the output water temperature with a high global heat transfer coefficient will not necessarily be the most electrically efficient system. This study experimentally assesses several proposed heat-exchange configurations for PVT systems where the PV modules are cooled by forced convective water flow. A simulation model of PVT performance is then validated and used to predict the productivity of the PVT-RO coupling, both in terms of electrical generation and permeate flux of the hybrid system under different conditions. The results suggest that water-cooled PV modules have several potential applications for off-grid and remote water treatment, as well as water transportation systems.

Experimental study of the effect of sheet-and-sinusoidal tube collector on the energetic and exergetic performance of a photovoltaic-thermal unit filled with biologically synthesized water/glycerol-silver nanofluid

The focus of this experimental work is on assessing the energetic and exergetic performance of a photovoltaic-thermal unit equipped with a sheet-and-sinusoidal tube collector (PVTW). The performance metrics of the unit are compared with those of the PV panel without cooling and a photovoltaic-thermal unit equipped with a sheet-and-plain tube collector (PVTP). The considered heat transfer fluid is the biologically prepared water/glycerol-silver nanofluid. The experiments are carried out for different mass flow rates of nanofluid (20, 40, 60 and 80 kg/h) and volume concentrations of silver nanoadditives (0, 0.50 and 1%). Both the PVTW and PVTP units showed better energetic and exergetic performances at higher mass flow rates (ṁnf) and nanoadditive concentrations (φ). Moreover, for all the examined cases, it was found that the performance metrics of the PVTW unit is superior to those of the PVTP unit. The overall energy and exergy efficiencies of the PVTW unit were respectively in the range of 67.86–80.57% and 13.8–14.49%, while these intervals for the PVTP unit were 61.34–70.85% and 13.63–14.16%. Therefore, it was found that the overall energy and exergy efficiencies of the PVTW unit is 9.11–15.51% and 1.12–2.59% higher than those of the PVTP unit.

Empirical investigation of a photovoltaic-thermal system with phase change materials and aluminum shavings porous media

Since a high photovoltaic panel (PV) temperature impacts the electrical output power, especially in tropical countries, the use of some cooling methods such as fluid flows, phase change materials (PCMs), and porous media has been suggested as an attractive option. In this study, these methods are integrated experimentally; a novel low-cost porous medium is developed using aluminum shavings, considered as waste materials in some industries, to increase the thermal conductivity of the phase change material. Then, the combination of this porous medium with salt hydrate is added to the water-based photovoltaic-thermal (PV/T) system; the electrical, thermal, and exergy efficiencies of the units are measured in July and December. The results of this research show that the photovoltaic-thermal unit, integrated with phase change material and porous medium, would have a high cooling performance by reducing the average temperature of the photovoltaic panel. The 24 °C reduction would augment the electrical efficiency by 2.5%, compared to solo PV, in the warm month. Also, it is found that, by using a porous medium, the melting time of the phase change material decreases by about 19%–25%. This method yields a maximum of 4.34% exergy efficiency improvement, compared to the single photovoltaic unit.

Experimental evaluation of energy and exergy performance of a nanofluid-based photovoltaic/thermal system equipped with a sheet-and-sinusoidal serpentine tube collector

The chief goal of this survey is about comprehensively examine a photovoltaic-thermal (PVT) system with a sheet-and-sinusoidal serpentine tube collector (PVT-S) experimentally from the perspective of energy, exergy and entropy generation. The results are compared with those of the PV module deprived of cooling and the PVT unit accompanied by a sheet-and-plain serpentine pipe collector (PVT-P). A water based nanofluid (NF) containing magnetite nanoadditives is considered as a coolant. The effects of volume concentration of nanoadditives (ϕ), NF mass flow rate (m˙nf), amplitude of the sinusoidal serpentine tube (a), and wavelength of the sinusoidal serpentine tube (w) on the performance metrics of the PVT unit are considered. The outcomes declared that the combined use of sinusoidal serpentine tube and NF leads to augmentation of energetic and exergetic performances of the PVT unit. According to the results, the first-law thermal, electrical and overall efficiencies of the PVT-S unit are 20.67–30.63%, 1.94–2.32% and 8.83–18.28% bigger than those of the PVT-P unit, respectively. In addition, the second-law thermal, electrical and overall efficiencies of the PVT-S unit are 10.56–26.68%, 1.94–2.32% and 2.44–4.57% greater than those of the PVT-P unit, respectively. Moreover, it was demonstrated that the increase of ϕ and m˙nf and the decrease of w result in an increment of performance features of the studied PVT units. Furthermore, it was found that among the entire the items considered in the survey, the best energetic and exergetic performances and the lowest entropy generation rate belongs to the NF-based PVT-S unit at ϕ=2%, m˙nf=80 kg/h, a=5 mm and w=60 mm.

Development of a composite PVT panel with PCM embodiment, TEG modules, flat-plate solar collector, and thermally pulsing heat pipes

An integrated, multi-layered, composite photovoltaic thermal (PVT) module consisting of a multitude of stand-alone mini PVT cartridges was developed and a prototype was tested. Individual PVT cartridges consist of several sandwiched layers with photovoltaic cells, TEG units, packed-bed PCM layer for thermal storage, and thermally controlled heat pipes with dynamic control. These cartridges may be easily removed from the master PVT casing and re-installed for repair, inspection, and replacements. When cartridges are installed, the composite PVT module is completed by adding a flat-plate collector layer on the top. An internal array of pulse-control heat pipes maintains the total exergy output (power and heat) at a maximum by adjusting the heat flux. This PVT panel design eliminates the need for external thermal storage, pumping of the PVT coolant, and associated parasitic losses. PVT technology is made more energetically and exergetically rational as an economic asset for decarbonizing the environment. In such a configuration, it represents the solar equivalent of a conventional cogeneration system with a bottoming cycle. This paper summarizes the technological evolution of the new composite PVT system and provides examples of its use. Pilot-scale tests have shown that the Rational Exergy Management Model efficiency is about 25% more than a conventional PVT system and the total net electrical power output per unit solar insolation area is more than 30%. Total exergy output (power and heat) is twice as much as a conventional PVT unit in a typical summer month. The results obtained are discussed with further evolutionary recommendations. The importance of exergy-levelized unit panel cost is put forth to provide a basis for the fundamental procedure for a dedicated, well-accepted, and stand-alone PVT test method for the rating of system performance.

Characteristics analysis of the photovoltaic thermal heat pump system on refrigeration mode: An experimental investigation

Photovoltaic thermal heat pump technology stands for the combination of solar heat pump technology and a photovoltaic system, which has the characteristics of tri-generation (heating, cooling, and electricity) to meet the building's energy requirement. In this paper, the dual-use photovoltaic thermal heat pump system was used and investigated experimentally with an emphasis on the refrigeration mode, which with the feature of the novel roll-bond photovoltaic thermal unit working as condenser directly. Moreover, renewable energy such as solar radiation and long-wave radiation are the main energy source of this system. The experimental investigation of the system comprising; 4 roll-bond photovoltaic thermal units, 1 horsepower heat pump unit and 600 L ice storage tank was carried out. The performance evaluation method and uncertainty analysis of the system was proposed and implemented along with the examination on the refrigeration performance and operating characteristics of the system. The results indicate that the proposed photovoltaic thermal heat pump system can achieve the refrigeration for building space cooling demand in summer with high performance and long-term stable operation. This study could provide a valuable reference for the photovoltaic thermal heat pump multi-generation system design and large-scale practical application in northern China.

Experimental study of Phase Change Material influence on different models of Photovoltaic-Thermal collectors

In this work we evaluate the experimental behaviour of several photovoltaic-thermal panels (PVT) and its energy performance after adding a layer of phase change material (PCM) inside the panel. In order to assess the energy dependency with the heat absorber, different materials and geometries have been considered, whose results were compared to a traditional sheet-and-tube copper absorber. Glazed and unglazed configurations were also explored in each model.PVT panels were exposed to exposed to the sun during the hours of maximum irradiance and subjected to different working conditions to properly evaluate their thermal performance. Results showed a slightly variation in the electrical generation but a great difference in the thermal performance between glazed and unglazed configuration. Regarding the heat absorber, higher thermal performance was found in the aluminum configuration rather than the polymeric case, but similar production with regard to the electrical generation. Attending to the PCM, results did not show a significant thermal improvement but a better distribution of the heat production, reaching to generate up to 30% of maximum thermal power after removing sun exposure.Although further works are needed to analyze the long-term effect of the PCM on photovoltaic-thermal units, this study provides experimental information of the PCM and its real performance when working with different heat absorber units.

Experimental investigation on the tri-generation performance of roll-bond photovoltaic thermal heat pump system during summer

Photovoltaic thermal heat pump system has gained much popularity in the recent research field, which generally refers to the integration of photovoltaic and solar assisted heat pump to meet the various building energy demand. In this paper, dual-use roll-bond photovoltaic thermal heat pump system employing new roll-bond photovoltaic thermal unit has been proposed and investigated experimentally. The system operation principles and the design method of the main components are introduced in more details. A mathematical model of each component of the system is developed according to distributed and lumped parameter models. The tri-generation performance evaluation method of the unit and system is also proposed. The experimental investigation on the tri-generation performance of the system is carried out simultaneously, in terms of the heating, cooling and power supply capacity. Through analysis, it is evident that the proposed system has the potential to provide space cooling, hot water, and electricity for buildings with high efficiency and long-term stable working condition. Furthermore, the detailed performance parameters analysis has been carried out. The results demonstrate that the roll-bond photovoltaic thermal heat pump system is practically feasible and has a large potential for building energy conservation.

Simulation of the performance of a solar concentrating photovoltaic-thermal collector, applied in a combined cooling heating and power generation system

The aim of this study is evaluating the performance of a combined cooling, heating, and power generation system (a trigeneration), composed of a concentrating photovoltaic-thermal unit, coupled with a water-ammonia absorption chiller. In the presented design, an ammonia-water absorption refrigeration cycle with 5 kW of cooling capacity is considered as a part of the trigeneration system. Also, a concentrating photovoltaic-thermal device, equipped with a linear Fresnel collector, is employed as the heat source. The performance of the system is modeled and simulated using TRNSYS. Furthermore, in case of replacing the concentrating collector by a conventional one, the performance of the cycle is investigated. It is revealed that, with the conventional collector type, the system could not provide enough thermal energy for the refrigeration cycle. The annual average of the electrical efficiency of the designed collector and trigeneration system are 12.8% and 58.01%, respectively. By investigating the produced energy from the presented unit, it is concluded that this system could be employed as the heating and cooling source of a typical residential building. However, the electrical energy demand of the building cannot be fully supplied with the presented design, and 6030 kWh of the electrical energy must be provided from the grid.

Experimental investigations of hybrid PV/Spiral flow thermal collector system performance using Al2O3/water nanofluid

In this paper, the PV/T (Photovoltaic thermal unit) system is investigated experimentally to examine the thermal, electrical and overall efficiency by circulating Al2O3/water nanofluid of 1wt% and 2wt% with an optimum flow rate of 40L/H. The overall efficiency of PVT system is largely influenced by various factors such as heat due to photovoltaic action; energy radiated at the infrared wavelength of the solar spectrum, solar irradiance, mounting structure, tilt angle, wind speed direction, Ambient temperature and panel material composition. However, the major factor is considered in this study to extract the heat generated in the PV panel by using nanofluid as a coolant to increase the overall system efficiency. Therefore, the result shows that by using 2 wt% Al2O3/water nanofluid the electrical efficiency, thermal efficiency and overall efficiency of the PVT system enhanced by 13%, 45%, and 58% respectively compared with water.

Experimental and numerical study of metal-oxides/water nanofluids as coolant in photovoltaic thermal systems (PVT)

In this study, the use of metal-oxides/water nanofluids as coolants in photovoltaic thermal units (PVT) is investigated experimentally and numerically. The considered nanoparticles include Aluminum-oxide (Al2O3), Titanium-oxide (TiO2) and Zinc-oxide (ZnO) all dispersed in deionized water as base fluid, with 0.2% by weight (wt%). To investigate the reliability of the measurements, an uncertainty analysis is performed for the experimental data. The t-statistic indicator is used to verify that the results of the numerical model are statistically significant. The electrical efficiency for the PVT system is calculated based on the measured temperature of the photovoltaic surface and the fluid outlet. The energy balance equations for various parts of the PVT system are solved using numerical simulations. Both numerical and experimental results show that the TiO2/water and ZnO/water nanofluids present a better performance in terms of the electrical efficiency compared to that of the Al2O3/water nanofluid and deionized water. In terms of the thermal performance of the system, the ZnO/water nanofluid is found to have the highest thermal efficiency compared to deionized water and the other two nanofluids. Finally, the numerical model is used to investigate the effect of nanoparticles mass fraction, ranged from 0.05 to 10wt%, on electrical and thermal performance of the PVT system.

Experimental investigation of a PVT system performance using nano ferrofluids

In this paper, the effects of ferrofluids as a coolant on the overall efficiency of a PVT (photovoltaic thermal unit) system are experimentally investigated. The fluids considered in the experiment are distilled water and a ferrofluid (Fe3O4-water) with 1% and 3% concentrations by weight (wt%). The experiments were performed in indoor conditions under two constant solar radiations (1100W/m2 and 600W/m2) using a solar simulator. Due to the unique characteristic behavior of ferrofluids, their rheological and thermophysical properties can be changed under an external magnetic field. The ferrofluids in this study were placed under constant and alternating magnetic fields in the cooling section in order to investigate the effect of both types of magnetic fields on the overall efficiency of a PVT system. The results show that by using a 3wt% ferrofluid, the overall efficiency of the system improved by 45% and when an alternating magnetic field with 50Hz frequency was applied, the overall efficiency increased to about 50% compared to that of the distilled water as coolant fluid. The overall exergy output of the system with and without ferrofluids, was also compared with that of the PV system with no collector. It was observed that by adding a thermal collector to a PV system and using a 3wt% ferrofluid under an alternating magnetic field, the total exergy can be increased as high as 48W.

Experimental investigation of the effects of silica/water nanofluid on PV/T (photovoltaic thermal units)

In this research, the effects of using nanofluid as a coolant on the thermal and electrical efficiencies of a PV/T (photovoltaic thermal unit) are experimentally studied. Coolant fluids in the experiments are pure water and silica (SiO2)/water nanofluid 1% and 3% by weight (wt%). A brief uncertainty analysis is performed which shows that the measurements are sufficiently accurate. By converting the output electrical energy of the PV/T system into an equivalent thermal energy, it is found that the overall energy efficiency for the case with a silica/water nanofluid of 1 wt% is increased by 3.6% compared to the case with pure water. When using the silica/water nanofluid of 3 wt%, however, the increase is 7.9%. The thermal efficiency of the PV/T collector for the two cases of 1 wt% and 3 wt% of silica/water nanofluids are increased by 7.6% and 12.8%, respectively. The total exergy of the PV/T system, with and without nanofluids, is also compared with that of the PV system with no collector. It is observed that by adding a thermal collector to a PV system, the total exergy for the three cases with pure water, 1 wt% silica/water nanofluid, and 3 wt% silica/water nanofluid is increased by 19.36%, 22.61% and 24.31%, respectively.