Hybrid photovoltaic/thermal solar systems

We present test results on hybrid solar systems, consisting of photovoltaic modules and thermal collectors (hybrid PV/T systems). The solar radiation increases the temperature of PV modules, resulting in a drop of their electrical efficiency. By proper circulation of a fluid with low inlet temperature, heat is extracted from the PV modules keeping the electrical efficiency at satisfactory values. The extracted thermal energy can be used in several ways, increasing the total energy output of the system. Hybrid PV/T systems can be applied mainly in buildings for the production of electricity and heat and are suitable for PV applications under high values of solar radiation and ambient temperature. Hybrid PV/T experimental models based on commercial PV modules of typical size are described and outdoor test results of the systems are presented and discussed. The results showed that PV cooling can increase the electrical efficiency of PV modules, increasing the total efficiency of the systems. Improvement of the system performance can be achieved by the use of an additional glazing to increase thermal output, a booster diffuse reflector to increase electrical and thermal output, or both, giving flexibility in system design.     

Effect of solar photovoltaic and various photovoltaic air thermal systems on hydrogen generation by water electrolysis

A novel photovoltaic thermal air (PVTa) system with semi length fins in the downstream portion of the air channel was tested experimentally for its performance capability for the generation of hydrogen in the present work. Fins are passive devices used to overcome the main detrimental effect of reduced power output due to photovoltaic panel heating. For this purpose, 2 semi length fin configurations namely longitudinal fin and wavy fin were placed in second half length of the channel in the direction of air flow. To compare the impact of PVTa systems with semi lengthened fins in hydrogen generation, the performance study of PV and PVTa system assisted hydrogen generation were also conducted. The experiments were conducted at the site of Tiruchirappalli district, Tamilnadu state, India having latitude and longitude of 10.82 and 78.70 respectively during March–June 2019 from 9 a.m. to 4 p.m. on clear and sunny days. The results indicated PVTa system with semi length wavy fins yielded maximum generation of hydrogen among the 4 cases of PV assisted hydrogen generation techniques considered. It was observed that downstream located longitudinal and wavy fins provided enhanced PV panel cooling which increased the current supply to the electrolyzer unit. The hydrogen generation rate was 13.5, 12.1, 9.5 and 7.8 ml/min for PVT with wavy fins, longitudinal fins, PVT and PV respectively. Keywords: Solar PV, fins, hydrogen, heat transfer.     

Performance evaluation of solar photovoltaic/thermal systems

The major purpose of the present study is to understand the performance of an integrated photovoltaic and thermal solar system (IPVTS) as compared to a conventional solar water heater and to demonstrate the idea of an IPVTS design. A commercial polycrystalline PV module is used for making a PV/T collector. The PV/T collector is used to build an IPVTS. The test results show that the solar PV/T collector made from a corrugated polycarbonate panel can obtain a good thermal efficiency. The present study introduces the concept of primary-energy saving efficiency for the evaluation of a PV/T system. The primary-energy saving efficiency of the present IPVTS exceeds 0.60. This is higher than for a pure solar hot water heater or a pure PV system. The characteristic daily efficiency η_s* reaches 0.38 which is about 76% of the value for a conventional solar hot water heater using glazed collectors (η_s*=0.50). The performance of a PV/T collector can be improved if the heat-collecting plate, the PV cells and the glass cover are directly packed together to form a glazed collector. The manufacturing cost of the PV/T collector and the system cost of the IPVTS can also be reduced. The present study shows that the idea of IPVTS is economically feasible too.     

Cost and sensitivity analysis for photovoltaic station in Kuwait

A full analysis is shown in this paper for the cost of kWh generated from photovoltaic station located in Kuwait. By using a 21 years weather data for Kuwait, the yearly generated energy was found by proposing the PV station capacity with known panels tilt angle. The cost of kWh generated from PV station was compared with the kWh generated from conventional units in the country. A sensitivity analysis was done to some factors; capital cost per installed PV peak watt, discount rate, and operating peak hours, which affect the cost of kWh production from both PV and conventional units. If the PV station is proposed to be installed in Kuwait, the capital cost per PV installed peak watt must be less than today's prices.     

Cost studies on terrestrial photovoltaic power systems with sunlight concentration

A systems simulation program for comparing the energy costs associated with various alternative concentrating photovoltaic solar systems to energy costs expected with flat arrays is described. The application to linear focus and point focus concentrators is presented in a parameterized way. The results show that concentration offers a distinct cost advantage at high cell costs. However, they also show that concentration has the potential for being a viable alternative to the flat unconcentrated arrays for cell costs as low as $50/m². Also, for a given concentrator cost, cell cost and cell cooling effectiveness, there exists an optimum effective aperture area to cell area ratio. For reasonable projected cell costs, this optimum ratio is below 30 for passively cooled devices and below 60 for actively cooled systems.     

High-efficiency integrated multijunction photovoltaic/electrolysis systems for hydrogen production

In this study, two integrated PV/electrolysis systems were studied. An integrated PV/electrolysis device is a device where the PV system and the electrolyser are combined into a single system. In the case studied here, the areas of the PV device and the electrolyzer are identical. Multijunction photovoltaic (PV)/electrolysis configurations were investigated, and a high solar-to-hydrogen conversion efficiency cell demonstrated. The energy diagram of the configuration has been evaluated and exemplified with n/p, n/p-GaInP/GaAs(Pt)/KOH electrolyte and triple-junction p–i–n a-Si(Pt)/KOH electrolyte photovoltaic/electrolysis cells. The efficiency of the cells was determined based on the short-circuit photocurrent. Measurements were obtained both indoors under 100-mW/cm² insolation, and outdoors. For the a-Si system, a 7.8% solar-to-hydrogen conversion efficiency was demonstrated. For the GaAs/GaInP₂ system, the solar-to-hydrogen conversion efficiency was over 16%.     

小型太阳能光伏直流车载冰箱的实验性能研究

设计了一个小型太阳能光伏直流车载冰箱实验系统,实验验证了该系统各部件工作时的匹配性能,并测试了系统工作时的电流、冰箱温度、负载功率、蓄电池电压等数据,最后对各部分能耗进行了分析。实验结果表明：该装置能稳定运行,可满足实际冷藏要求;在完全无日照情况下,冰箱可连续运行34 h。     

Aspects and improvements of hybrid photovoltaic/thermal solar energy systems

Hybrid photovoltaic/thermal (PV/T or PVT) solar systems consist of PV modules coupled to water or air heat extraction devices, which convert the absorbed solar radiation into electricity and heat. At the University of Patras, an extended research on PV/T systems has been performed aiming at the study of several modifications for system performance improvement. In this paper a new type of PV/T collector with dual heat extraction operation, either with water or with air circulation is presented. This system is simple and suitable for building integration, providing hot water or air depending on the season and the thermal needs of the building. Experiments with dual type PV/T models of alternative arrangement of the water and the air heat exchanging elements were performed. The most effective design was further studied, applying to it low cost modifications for the air heat extraction improvement. These modifications include a thin metallic sheet placed in the middle of the air channel, the mounting of fins on the opposite wall to PV rear surface of the air channel and the placement of the sheet combined with small ribs on the opposite air channel wall. The modified dual PV/T collectors were combined with booster diffuse reflectors, achieving a significant increase in system thermal and electrical energy output. The improved PV/T systems have aesthetic and energy advantages and could be used instead of separate installation of plain PV modules and thermal collectors, mainly if the available building surface is limited and the thermal needs are associated with low temperature water or air heating.     

Uniqueness verification of direct solar spectral index for estimating outdoor performance of concentrator photovoltaic systems

To analyze the impact of a direct spectral distribution of the solar spectrum on the outdoor performance of concentrator photovoltaic (CPV) systems, an index for the direct spectral distribution is needed. Average photon energy (APE), the average energy of a photon in the direct solar spectrum, is one of these indexes. In this contribution, the uniqueness of APE to the direct solar spectral distribution is statistically analyzed to assure that an APE value uniquely yields the shape of a direct solar radiation spectrum. The results have exhibited the uniqueness of the direct normal solar spectrum with each APE value, in which the standard deviations are quite small. Short-circuit current density of the InGaP/InGaAs/Ge triple-junction solar cell in the CPV system is additionally calculated using the direct spectral irradiance with different APE values. It is revealed that APE is a useful index to describe the direct spectral distribution to evaluate the outdoor performance of the CPV systems.     

Electrification using solar photovoltaic systems in Nepal

Historically, the rural population of Nepal has been meeting their energy needs from traditional sources like fuel wood and other biomass resources. Only about 44% of the total population has access to grid electricity. Because of country’s rough and mountainous topography, high cost of grid extension, and low and scattered population density, constructing some big power plants (e.g. large hydropower) can not meet the electricity needs of all people, especially those living in rural areas. Distributed generation of electricity, using environment friendly solar photovoltaic (PV) systems, might be one of the reliable alternatives for urban as well as rural electrification. This article begins with a general overview of energy resources in Nepal. Present status and perspectives of solar PV sector have also been discussed. Benefit cost and breakeven analyses of solar PV systems in Nepalese urban areas have been carried out. The breakeven year has been calculated between 2027 and 2036 for PV systems with system life time between 40 and 25 years, respectively. It has been concluded that the solar PV systems are not the economic solutions for grid connected urban areas in Nepal. On the other hand, this article concludes that the rural electrification projects should not be decided on the basis of mere monetary benefits, rather many social aspects should be considered, and in this case, there are not convincing alternatives to solar PV systems for electrification in many rural villages in Nepal.     

Thermodynamic analysis of solar photovoltaic cell systems

The thermodynamic characteristics of solar photovoltaic (PV) cells are investigated from a perspective based on exergy. A new efficiency is developed that is useful in studying PV performance and possible improvements. Exergy analysis is applied to a PV system and its components, and exergy flows, losses and efficiencies are evaluated. Energy efficiency is seen to vary between 7% and 12% during the day. In contrast, exergy efficiencies, which incorporate the second law of thermodynamics and account for solar irradiation exergy values, are lower for electricity generation using the considered PV system, ranging from 2% to 8%. Values of “fill factors” are determined for the system and observed to be similar to values of exergy efficiency.     

An assessment of electrolytic hydrogen production by means of photovoltaic energy conversion

Photovoltaic-powered electrolysis is studied by using an analytical system-simulation model. Available experimental results are compared with the results of the analytical simulation and, further, the computational model is used to establish a model-driven electrolysis experiment. The input for the analytical model includes real weather data recorded on an annual basis at two different locations. The results include information on the system efficiency, power-matching conditions, annual system output and a cost evaluation of the solar hydrogen product.     

Combined photovoltaic and solar thermal systems for facade integration and building insulation

Most photovoltaic (PV) facades are built as curtain facades in front of thermally insulated buildings, with air ducts in between. This causes additional costs for support structure and installation, while heat dissipation from the solar cells is often not optimal. Measurements carried out are facing both concerns: integration of a thermal insulating layer (which meets the latest German heat-preserving regulation, WSV 95) into the PV facade, plus additional cooling by active ventilation or water flow. Active ventilation at conventional curtain PV facades allows a reduction of cell operating temperatures of 18 K, resulting in an 8% increase in electrical energy output at an airspeed of about 2 m/s. Cell temperatures increase by 20.7 K at thermal insulating PV facade elements (TIPVE) without cooling, which causes a 9.3% loss of electrical yield, but installation costs can be reduced by 20% (all related to a conventional PV curtain plus a heat-insulating facade at a building). HYTIPVE, a hybrid thermal insulating PV facade element combined with a water cooling system, which could also serve for heating up water, lowers the operating cell temperature by 20 K and increases electrical yield by 9% (compared with conventional curtain PV facades). Further economic investigations of such a HYTIPVE, including its operational costs and substitution effect, related to the electrical and thermal yield, are in progress.     

Comparative performance analysis of solar powered supercritical-transcritical CO2 based systems for hydrogen production and multigeneration

CO₂ based power and refrigeration cycles have been developed and analyzed in different existing studies. However, the development of a CO₂ based comprehensive energy system and its performance analysis have not been considered. In this study, the integration of a CO₂ based solar parabolic trough collector system, a supercritical CO₂ power cycle, a transcritical CO₂ power cycle, and a CO₂ based cascade refrigeration system for hydrogen production and multigeneration purpose is analyzed thermodynamically. This study aims to analyze and compare the difference in the thermodynamic performance of comprehensive energy systems when CO₂ is used as the working fluid in all the cycles with a system that uses other working fluids. Therefore, two comprehensive energy systems with the same number of subsystems are designed to justify the comparison. The second comprehensive energy system uses liquid potassium instead of CO₂ as a working fluid in the solar parabolic trough collector and a steam cycle is used to replace the transcritical CO₂ power cycle. Results of the energy and exergy performance analysis of two comprehensive energy systems showed that the two systems can be used for the multigeneration purpose. However, the use of a steam cycle and potassium-based solar parabolic trough collector increases the comprehensive energy systems’ overall energy and exergy efficiency by 41.9% and 26.7% respectively. Also, the use of liquid potassium as working fluid in the parabolic trough collectors increases the absorbed solar energy input by 419 kW and 2100 kW thereby resulting in a 23% and 90.7% increase in energetic and exergetic efficiency respectively. The carbon emission reduction potential of the two comprehensive energy systems modelled in this study is also analyzed.     

Cost and optimal feed-in tariff for small scale photovoltaic systems in China

China has recently become a dominant player in the solar photovoltaic (PV) industry, producing more than one-third of the global supply of solar cells in 2008. However, as of 2008, less than 1% of global installations were based in China. Recently, the government has stated its grand ambitions of expanding the share of electricity derived from solar power. As part of this initiative, policy makers are currently in the process of drafting a feed-in tariff policy to support the development of the solar energy market. In this paper, we aim to calculate what the level of such a tariff should be. We develop a closed form equation for the cost of PV, and use forecasts on prices of solar systems to derive an optimal feed-in tariff, including a digression rate. The focus is on the potential of residential and small scale commercial solar PV installations. We show that the cost of small scale PV in China has decreased rapidly during the period 2005–2009. Our analysis also shows that optimal feed-in tariffs vary widely between regions within China, and that grid parity could be reached in large parts of the country depending on the expected escalation in electricity prices.     

太阳能PV/T系统电热输出性能及其Matlab仿真研究

建立了太阳能PV/T(Photovoltaic/Thermal)系统的热电模型,编制了Matlab程序,采用迭代法对电热参数进行耦合求解。研究了PV/T系统在呼和浩特不同季节下的热电效率,电池温度和性能曲线的变化,通过与实验数据对比,验证了该模型具有较高的精度。实验结果显示了环境温度、风速、入射辐射量对太阳能PV/T系统热、电以及综合性能的影响:PV/T系统夏季的日平均电效率、热效率及正午组件最大功率分别为14.1%、34.5%和180.8 W,冬季的日平均电效率、热效率及正午组件最大功率分别为16.1%、24.8%和190.3 W。     

A method for estimating the performance of photovoltaic systems

A method is presented for predicting the long-term average performance of photovoltaic systems having storage batteries and subject to any diurnal load profile. The monthly-average fraction of the load met by the system is estimated from array parameters and monthly-average meteorological data. The method is based on radiation statistics, and utilizability, and can account for variability in the electrical demand as well as for the variability in solar radiation.     

Life cycle analysis for future photovoltaic systems using hybrid solar cells

Global climate change concerns have lead to growing demand for renewable energy sources (RES). However the viability of these sources is critically dependent on environmental, economic and technological considerations. This paper focuses on the environmental aspect of future photovoltaic (PV) systems which are assessed through life cycle analysis (LCA). Previous LCA studies on commercially available PV systems are reviewed. The sustainable evaluation methods used in these studies are also discussed. These methods are applied to the hybrid quantum dot (QD)-based solar cells currently under development within a project between the University of Manchester and Imperial College London. The aim of this project is to develop affordable solar cells with efficiencies up to 10% for micro-generation applications. Presently hybrid QD-based solar cells are not commercially fabricated; therefore the study is mostly based on very small laboratory-scale production. For easy comparability 10% conversion efficiency and 25 years lifetime are initially assumed. Lower conversion efficiencies and shorter lifetimes likely to initially characterise emerging PV technologies such as the hybrid QD-based solar cells are discussed. Comparable criteria for sustainability of electricity-generating systems namely net energy ratio (NER), energy pay-back time (EPB-T) and CO₂ emissions per unit generated during lifetime are found to be lower than current commercially available PV modules.     

Utilisation of solar photovoltaic pumping for aeration systems in aquaculture ponds

This research pertains to solar photovoltaic (PV) pumping for aeration of aquaculture ponds and evaluates it economically. A stand-alone photovoltaic aeration system based on recycling of water at 10 cm under the water surface, at the surface (0 cm) and above the surface (30 cm) on a perforated tray was evaluated. The effect of pump discharges (35, 50, 65 L/min) on standard oxygen transfer rate (SOTR) and standard aeration efficiency (SAE) was investigated. Results revealed that the daily averages of PV energy output, PV efficiency and load energy were 0.844 kWh/d, 9.87% and 0.615 kWh/d, respectively, at 65 L/min and 42.7°C PV temperature. Water flow upward at 30 cm over the perforated tray in the radial direction proved to be better since it gave an opportunity for the exchange of gaseous between the water and the atmosphere. The SOTR and SAE for the third position were 0.025 kgO₂/h and 0.1 kgO₂/kW h, respectively.     

Review of hydrogen production with photovoltaic electrolysis systems

Of vital importance for the increasing share of nonfossil primary energy in energy supply systems is the development and economic availability of a new chemical energy carrier, which offers large-scale and long-term storage of thermal and electrical energy, the main products of nonfossil primary energy conversion. The potential of H₂ for the extensive utilization of solar energy is of particular importance. Characteristics and performance of H₂ production by means of photovoltaic solar energy conversion and water electrolysis are studied and discussed. Experimental results of a small system consisting of a polycrystalline solar cell generator, water electrolysis and power conditioning are compared with calculated results of a system simulation model. The stationary and dynamic behaviour of system and components and the efficiency and performance of power conditioning are investigated. For an optimized and reliable operation of photovoltaic electrolyzer systems, the behaviour of electrolysis at part-load and overload, the start-up and shut-down behaviour, corrosion and degradation effects are important aspects. The status and further improvements of advanced electrolysis are discussed, as well as results of system analysis studies for future large-scale solar H₂ production.