Performance analysis of a novel hydrogen production system incorporated with hybrid solar collector and phase change material

In this technical article, a novel experimental setup is designed and proposed to produce a hydrogen by using solar energy. This system comprises a hybrid or photovoltaic Thermal (PVT) solar collector, Hoffman's voltameter, heat exchanger unit and Phase Change Material (PCM). The effect of PCM and mass flow rate of water on the hybrid solar collector efficiency and hydrogen yield rate is studied. This experimental results clearly showed that by adding the thermal collector with water, decreases PV module temperature by 20.5% compared with conventional PV module. Based on the measured values, at 12.00 and 0.011 kg/s mass flow rate, about 33.8% of thermal efficiency is obtained for water based hybrid solar collector. Similarly, by adding Paraffin PCM to the water based thermal collector, the maximum electrical efficiency of 9.1% is achieved. From this study, the average value of 17.12% and 18.61% hydrogen yield rate is attained for PVT/water and PVT/water with PCM systems respectively.     

Maximising the energy output of a PVT air system

Simultaneously generating both electricity and low grade heat, photovoltaic thermal (PVT) systems maximise the solar energy extracted per unit of collector area and have the added benefit of increasing the photovoltaic (PV) electrical output by reducing the PV operating temperature. A graphical representation of the temperature rise and rate of heat output as a function of the number of transfer units NTUs illustrates the influence of fundamental parameter values on the thermal performance of the PVT collector. With the aim of maximising the electrical and thermal energy outputs, a whole of system approach was used to design an experimental, unglazed, single pass, open loop PVT air system in Sydney. The PVT collector is oriented towards the north with a tilt angle of 34°, and used six 110 Wp frameless PV modules. A unique result was achieved whereby the additional electrical PV output was in excess of the fan energy requirement for air mass flow rates in the range of 0.03–0.05 kg/s m². This was made possible through energy efficient hydraulic design using large ducts to minimise the pressure loss and selection of a fan that produces high air mass flow rates (0.02–0.1 kg/s m²) at a low input power (4–85 W). The experimental PVT air system demonstrated increasing thermal and electrical PV efficiencies with increasing air mass flow rate, with thermal efficiencies in the range of 28–55% and electrical PV efficiencies between 10.6% and 12.2% at midday.     

Utilizing the multi-objective particle swarm optimization for designing a renewable multiple energy system on the basis of the parabolic trough solar collector

Today, to preserve fossil resources, mankind has to search for new ways to respond to its ever-increasing energy needs. In this study, a hybrid system of energy and the use of a parabolic trough solar collector to attract solar radiation was investigated to produce clean electricity, cooling, and hydrogen from thermodynamic and economic aspects. The designed system consisted of a parabolic trough solar collector, organic Rankine cycle, lithium-bromide absorption refrigeration cycle, and proton exchange membrane electrolysis system. The evaporator input temperature, turbine inlet temperature, solar radiation intensity, mass flow rate of collector and parabolic trough collector surface area were set as decision variables and the effect of these parameters on system performance and system exergy loss were investigated. The objective functions of this research were exergy efficiency and cost rate. In order to optimize this system, multi-objective particle swarm optimization algorithm was employed. Optimization results with particle swarm optimization indicated that the best rate of exergy efficiency is 3.12% and the system cost rate is 16.367 US$ per hour, at the same time. The system is capable of producing 15.385 kW power, 0.189 kg/day hydrogen and 56.145 kW cooling in its optimum condition. The results of sensitivity analysis showed that increasing mass flow rate at the collector, temperature at the evaporator inlet, and temperature at the turbine inlet have positive effect on the performance of the proposed system.     

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.     

Thermodynamic analysis of a new renewable energy based hybrid system for hydrogen liquefaction

In this paper, a parametric study of the triple effect absorption cooling system (TEACS) integrated with solar photo-voltaic/thermal (PV/T), geothermal, and Linde–Hampson cycle is conducted. The effect of different operating parameters on the COPs, ratio ‘n’, amount of hydrogen gas pre-cooled, amount of hydrogen liquefied, and utilization factor of the integrated system are studied. It is found that when mass flow rate of air increases the energetic and exergetic COPs decrease in an exponential form from 2.6 to 1.9, and 0.4 to 0.3, respectively. The amounts of hydrogen gas pre-cooled and hydrogen liquefied decrease from 0.39 kg/s to 0.32 kg/s and 0.082 kg/s and 0.066 kg/s, respectively with increase in mass flow rate of air. Moreover, the amounts of hydrogen gas pre-cooled and hydrogen liquefied decrease from 0.42 to 0.27, and 0.088 to 0.066, respectively with increase in mass flow rate of geothermal. In addition, energetic and exergetic utilization factors of integrated system decrease from 0.059 to 0.037, and 0.21 and 0.13, respectively with increase in mass flow rate of geothermal.     

光伏光热一体化组件性能实验探究与分析

通过搭建PV/T一体化组件性能测试实验台,测试在不同进口水温、不同一体化组件倾角和不同流量时PV/T一体化组件的热、电效率。结果表明,在进口水温30℃工况下一体化组件拥有最优的热效率值和输出电功率值,其日总热效率为35.97%,对应的输出电功率范围为29.40~30.51 W;45°倾角放置的一体化组件可接收到较多的太阳辐照度,且具有最优的光热性能,对应的日总热效率为32.65%;流量85 L/h工况下一体化组件拥有最优的热效率值,对应的日总热效率值为25.89%,串联50Ω电阻时组件的输出电功率随流量的增大而增大,但变化较小,流量120 L/h工况下一体化组件拥有最优的输出电功率值,对应的输出电功率值范围为24.02~29.19 W。     

Experimental analysis of photovoltaic thermal system assisted with nanofluids for efficient electrical performance and hydrogen production through electrolysis

In this study the influence of the nanofluid in the photovoltaic thermal system (PVT) has been examined experimentally. The nanoparticles zinc oxide (ZnO) dispersed in the base fluid water at the concentration of 0.25 %wt. A series of experimental tests were conducted between 9:00 A.M. to 16:00 P.M. ZnO nanofluids passed through the PVT panel at various mass flow rates. To increase the thermal efficiency and performance of the PVT, instead of using plain water, nanofluids were introduced. The parameters such as output power, surface temperature, fluid outlet temperature, thermal efficiency, and electrical efficiency were examined at the different mass flow rates such as 0.008 kg/s, 0.010 kg/s, and 0.012 kg/s. Added to above, the proposed photovoltaic thermal system was also assisted in producing hydrogen by electrolysis process. Polymer electrolyte membrane (PEM) has been used to generate the hydrogen via electrolysis. With the use of nanofluids, the electrical efficiency and thermal efficiency were increased owing to the reduction in the cell temperature. Introduction of the nanofluids at the optimal mass flow rate helps the panel to produce higher electrical output. The hydrogen yield rate was also increased by the use of nanofluids. Among the different mass flow rate, 0.012 kg/s reported maximum thermal efficiency of 33.4% with the hydrogen production rate of 17.4 ml/min. Based on the extensive observed results procured, photovoltaic thermal systems can be a promising candidate for the production of hydrogen using PEM electrolyzer.     

Performance evaluation of photovoltaic–thermosyphon system for subtropical climate application

The rapid development and sales volume of photovoltaic (PV) modules has created a promising business environment in the foreseeable future. However, the current electricity cost from PV is still several times higher than from the conventional power generation. One way to shorten the payback period is to bring in the hybrid photovoltaic–thermal (PVT) technology, which multiplies the energy outputs from the same collector surface area. In this paper, the performance evaluation of a new water-type PVT collector system is presented. The thermal collection making use of the thermosyphon principle eliminates the expense of pumping power. Experimental rigs were successfully built. A dynamic simulation model of the PVT collector system was developed and validated by the experimental measurements, together with two other similar models developed for PV module and solar hot-water collector. These were then used to predict the energy outputs and the payback periods for their applications in the subtropical climate, with Hong Kong as an example. The numerical results show that a payback period of 12 year for the PVT collector system is comparable to the side-by-side system, and is much shorter than the plain PV application. This is a great encouragement in marketing the PVT technology.     

Heat transfer augmentation in a hybrid microchannel solar cell

This paper considers experimental investigations on a hybrid microchannel solar cell, which is designed as an attractive technology for PV cooling systems. The proposed unit combines two elements: a microchannel and a photovoltaic–thermal module. Experiments were performed at indoor condition. In order to remove heat from the PV module, water was used as a single-phase working fluid. Water flowed through series of microchannels with a hydraulic diameter of 0.667 mm. In the studied range of Re number, detailed parametric investigation and energy evaluation were carried out for various fluid flow rates. The output power of the PV/T panel was compared with that of the conventional photovoltaic panel having no arrangement for heat removal. An excellent cooling performance was found from experiments so that the cell maximum power was marginally improved above 30%.     

Improvement of PV module optical properties for PV-thermal hybrid collector application

Photovoltaic-thermal collectors (or PV-T collector) are hybrid collectors where PV modules are integrated as an absorber of a thermal collector in order to convert solar energy into electricity and usable heat at the same time. In most of the cases, the hybrid collectors are made by the superposition of a PV module on the thermal absorber of a solar collector. In this paper, the approach is different and is to analyze thermal and optical properties related to both PV and solar thermal functions in order to identify an optimum combination leading to a maximum overall efficiency. Indeed, although these two functions do not exploit the same range of radiation wavelengths, thermal and PV functions are not so complementary due to photo-conversion thermal dependency. In this context, an alternative PV cell lamination has been developed with increased optical and thermal performance. The improvements were evaluated around 2 mA/cm² in terms of current density in comparison to a standard module encapsulation. Based on this technique, a real size PV-T module has been built and tested at Fraunhofer solar test facilities. The results show a global efficiency of the PV-T collector above 87% (79% thermal efficiency plus 8.7% electrical efficiency, based on the absorber area).     

Comparative study to use nanofluid ZnO and CuO with phase change material in photovoltaic thermal system

In this study, the simultaneous use of nanofluid and phase changing material as a coolant for photovoltaic fluid collector system and its effects are investigated experimentally. Two types of nanofluid are taken for the consideration, that is, ZnO and CuO, which are water‐based fluid. The experiments are performed in five different types of photovoltaic thermal system conventional: PT, PVT (ZnO), PVT (CuO), PCM medium (PVT/PCM/ZnO), and PCM medium (PVT/PCM/CuO). The results are obtained for surface temperature, energy, and thermal efficiency, and it is compared with each other. Further, the effect of the nanofluid as the effective alternative for pure deionized water is measured. From the results, it is evident that the PVT/PCM/CuO system minted 15% high electric output compared with convention module. Furthermore, the addition of the CuO nanofluid increases the thermal output significantly up to 8% for PVT and 12% for PCM without energy consumption. It also found that the nanofluid increases the overall energy efficiency of the system compared with convention PV.     

Exergoeconomic analysis of glazed hybrid photovoltaic thermal module air collector

In this paper, an exergoeconomic analysis has been carried out and on the basis of this analysis it has been concluded that in terms of energy saving the glazed hybrid photovoltaic thermal (PVT) module air collector offers a greater potential compared to PV module. The experimental validation for glazed hybrid PVT module air collector has also been performed and it has been observed that there is a good agreement between the theoretical and experimental values with correlation coefficient in range of 0.96–0.99 and root mean square percentage deviation in range of 2.38–7.46. The experiments have been carried out on clear days during the month July 2010 to June 2011. For the validation of theoretical results with experimental results, a typical day of winter month (December 08, 2010) and summer month (April 11, 2011) has been considered. An experimental uncertainty for December and April month is 11.6% and 2.1% respectively. The annual overall thermal energy and exergy gain are 1252.0 kWh and 289.5 kW h respectively. The annual net electrical energy savings by glazed hybrid PVT module air collector is 234.7 kW h.     

Thermal modeling of a combined system of photovoltaic thermal (PV/T) solar water heater

In this paper, an integrated combined system of a photovoltaic (glass–glass) thermal (PV/T) solar water heater of capacity 200 l has been designed and tested in outdoor condition for composite climate of New Delhi. An analytical expression for characteristic equation for photovoltaic thermal (PV/T) flat plate collector has been derived for different condition as a function of design and climatic parameters. The testing of collector and system were carried out during February–April, 2007. It is observed that the photovoltaic thermal (PV/T) flat plate collector partially covered with PV module gives better thermal and average cell efficiency which is in accordance with the results reported by earlier researchers.     

基于相变微胶囊悬浮液的太阳能光伏热系统的研究进展

在太阳能光伏热系统中,光伏电池温度过高会导致太阳能发电效率下降。相变微胶囊悬浮液(MEPCMS)是一种潜热型功能性流体,将其作为冷却介质用于太阳能光伏热系统可以有效降低光伏电池温度,提高系统的能量利用率。针对相变微胶囊易泄露、导热性差等问题提出了改性方法,使其具有光热转换功能并提升了综合性能。基于性能评价指标分析了太阳能光伏热系统性能的影响因素。结果发现,流速、浓度和太阳辐照量是影响MEPCMS在太阳能光伏热系统中换热性能的关键因素。适当增加MEPCMS浓度和流速能提高工质的换热性能,在降低光伏板温度的同时增加太阳辐照量和系统热电产量,但需结合太阳辐照量大小合理匹配工质的浓度和流速。未来研究方向可集中在提升MEPCMS在太阳能光伏热系统中的换热性能、探究运行参数和太阳辐照量之间的匹配关系、优化集热器结构、利用其蓄热性解决太阳能间歇性等方面。     

The performance of a cylindrical solar water heater

A cylindrical solar water heater is designed and manufactured in the Department of Mechanical Engineering, University of Bahrain. It consists of a cylindrical tube made from high quality glass having a length of 0.8, 0.14 m outer diameter and a thickness of 6 mm. A copper coil tube in the shape of spiral rings, with the tube inner diameter of 2 mm and outer diameter of 3.175 mm, painted black, serves as a collector to the incident solar energy on the cylinder wall. The thermal performance was evaluated extensively throughout the months of March and April 2002; a maximum temperature difference of 27.8 °C between inlet and outlet of the solar water heater at a mass flow rate of 9 kg/h was achieved. The efficiency of the cylindrical solar water heater was calculated. The maximum value during the experimental period was found to be 41.8%. This reveals a good capability of the system to convert solar energy to heat which can be used for heating water. An economic analysis has reveals that the cylindrical solar water heater compared with the flat plate collector is cost effective.     

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.     

Heat transfer enhancement of concentrated solar absorber using hollow cylindrical fins filled with phase change material

A concentrated solar absorber with finned phase change materials was experimentally studied using a Scheffler type parabolic dish concentrator. The absorber's inner surface was fixed with hollow cylindrical containers filled with phase change material (PCM) for heat transfer augmentation. The absorber's selected PCM was acetanilide (Melting point of 116 °C)—the cylindrical capsules protruding into the fluid side to create turbulence and mixing and acting as fins. The absorber surface temperature was observed to be about 130–150 °C during the outdoor tests while passing fluid through the absorber. The fluid flow rate varied from 60 to 100 kg/h during the outdoor experiments. The peak energy and exergy efficiency of parabolic dish collector (PDC) at the fluid flow rate of 80 kg/h with PCM integrated solar absorber was found to be about 67.88% and 6.96%, respectively. The integration of cylindrical PCM containers resulted in more heat transfer augmentation in the solar absorbers. The optimized solar absorber could be suitable for various applications like steam generation, biomass gasification, space heating, and hydrogen generation.     

Performance improvement of PV/T solar collectors with natural air flow operation

The electrical efficiency of a photovoltaic system drops as its operating temperature rises and PV cooling is necessary. The photovoltaic/thermal (PV/T) system is a relatively recent type of solar collector where a circulating fluid of lower temperature than PV module extracts heat from it, cooling the module to improve its output power while the solar pre-heated fluid provides sensible heat. In the present work, air cooling of a commercial PV module configured as PV/T air solar collector by natural flow is presented, where two low cost modification techniques to enhance heat transfer to air stream in the air channel are studied. The considered methods consist of thin metal sheet suspended at the middle or fins attached to the back wall of the air-channel to improve heat extraction from the module. A numerical model was developed and validated against the experimental data obtained from outdoor test campaigns for both glazed and unglazed PV/T prototype models studied. The validation results show good agreement between predicted values and measured data and thus could be used to study analytically the performance of these PV/T air collectors with respect to several design and operating parameters. The modified systems present better performance than the usual type and will contribute to better performance of integrated PV systems for natural ventilation applications in buildings, both space cooling and heating.     

A parametric study of a renewable energy based multigeneration system using PEM for hydrogen production with and without once-through MSF desalination

The importance of renewable energy compared to fossil fuels is increasing due to growing energy demand and environmental challenges. Multi-generation systems use one or more energy sources and produce several useful outputs. The present study aims at investigating and comparing solar energy based multi-generation systems with and without once-through MSF desalination unit from the thermodynamic point of view. Firstly, hydrogen, electricity, and hot water for space heating and domestic usage are produced using the system, which consists of a parabolic trough collector, an organic Rankine cycle (ORC) and a PEM electrolyzer and heat exchanger as sub-systems. The performance of the entire system is evaluated from the energetic and exergetic points of view. Various parameters affecting hydrogen production rate and efficiency values are also investigated with the thermodynamic model implemented in the Engineering Equation Solver (EES) package. The system can produce hydrogen at a mass flow rate of 20.39 kg/day. The results of the study show that the energy and exergy efficiency values of the ORC are calculated to be 16.80% and 40% while those for the overall system are determined to be 78% and 25.50%, respectively. Secondly, once-through MSF desalination unit is integrated to the system between ORC evaporator and heat exchanger producing domestic hot water in the solar cycle in order not to affect hydrogen production rate while thermodynamic values are compared. Fresh water production capacity of the system is calculated to be at a volumetric flow rate of 5.74 m³/day with 10 stages.     

新型管板式太阳能PV/T集热器光热特性研究与优化

为提高太阳能光伏/光热（PV/T）集热器全年运行效率,提出一种新型管板式太阳能PV/T集热器结构,并针对该集热器光热传递与光电转换过程进行分析,建立水和空气同时运行时的二维非稳态传热数学模型;在验证模型可靠性的基础上,模拟研究空气流道高度和空气流量等设计参数对PV/T集热器光热、光电特性的影响。结果表明,空气流道高度为15 mm时,PV/T集热器光电光热综合性能效率最佳;在所研究的工况下,该集热器的光电光热综合性能效率为0.84~0.87。