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.     

Performance assessment of an integrated PV/T and triple effect cooling system for hydrogen and cooling production

In this paper we study an integrated PV/T absorption system for cooling and hydrogen production based on U.A.E weather data. Effect of average solar radiation for different months, operating time of the electrolyzer, air inlet temperature and area of the PV module on power and rate of heat production, energy and exergy efficiencies, hydrogen production and energetic and exergetic COPs are studied. It is found that the overall energy and exergy efficiency varies greatly from month to month because of the variation of solar radiation and the time for which it is available. The highest energy and exergy efficiencies are obtained for the month of March and their value is 15.6% and 7.9%, respectively. However, the hydrogen production is maximum for the month of August and its value is 9.7 kg because in august, the solar radiation is high and is available for almost 13 h daily. The maximum energetic and exergetic COPs are calculated to be 2.28 and 2.145, respectively and they are obtained in the month of June when solar radiation is high for the specified cooling load of 15 kW.     

非晶硅太阳能光伏/光热空气集热器性能对比实验研究

文章设计了新型非晶硅太阳能PV/T空气集热器,该空气集热器能够解决传统太阳能PV/T热水器在高温波动情况下,晶硅电池热应力大的问题,同时避免了冬季管道发生霜冻的现象。文章通过实验对比,分析了非晶硅太阳能PV/T空气集热器、单独非晶硅光伏电池和传统太阳能空气集热器的能量效率和[火用]效率的差异。分析结果表明:非晶硅太阳能PV/T空气集热器的平均热效率为45.70%,比传统太阳能空气集热器的平均热效率降低了约25.88%;当空气质量流量增大至0.048 kg/s时,非晶硅太阳能PV/T空气集热器中的非晶硅光伏电池的平均电效率高于单独非晶硅光伏电池,它们的平均电效率分别为4.70%,4.54%;非晶硅太阳能PV/T空气集热器的总[火用]效率高于传统太阳能空气集热器的热[火用]效率和单独非晶硅光伏电池的电[火用]效率,非晶硅太阳能PV/T空气集热器总[火用]效率最大值为7.14%。文章的分析结果为非晶硅太阳能PV/T空气集热器的推广提供了参考。     

Energy and exergy analysis of a latent heat storage system with phase change material for a solar collector

Analysis of energy and exergy has been performed for a latent heat storage system with phase change material (PCM) for a flat-plate solar collector. CaCl₂·6H₂O was used as PCM in thermal energy storage (TES) system. The designed collector combines in single unit solar energy collection and storage. PCMs are stored in a storage tank, which is located under the collector. A special heat transfer fluid was used to transfer heat from collector to PCM. Exergy analysis, which is based on the second law of thermodynamics, and energy analysis, which is based on the first law, were applied for evaluation of the system efficiency for charging period. The analyses were performed on 3 days in October. It was observed that the average net energy and exergy efficiencies are 45% and 2.2%, respectively.     

太阳能驱动的固体氧化物电解池制氢系统性能研究

采用太阳能驱动电解水制氢是实现将太阳能转换为氢能来存储的最佳方式。该文提出一种采用光伏、光热协同驱动固体氧化物电解池（SOEC）进行高温蒸汽电解的制氢系统。建立各子系统数学模型,选取北京地区夏至日气象参数,分析太阳辐照度对制氢系统的性能影响,最后对整个系统进行能量及火用分析。结果表明,电流密度和温度是影响SOEC工作的重要因素。在电流密度较大的情况下升高温度,将有利于提高电解效率。耦合太阳能后系统最大能量及火用效率分别达到19.1%和20.3%。火用分析结果表明系统最大有用功损失发生在光电转换过程,火用损比例为87%。提升光电效率,将成为提高太阳能-氢能转换效率的关键。     

复合抛物面聚光太阳能PV/T系统的实验研究

设计并搭建了CPC低倍聚光太阳能PV/T单通道空气系统实验台,对不同工作环境下聚光PV/T系统的热电性能进行了实验研究。实验研究结果显示:在聚光条件下,系统的各表面温度随光照强度的增加而升高,随下部通道入口空气流速的增加而降低。聚光PV/T系统的最大输出功率可达到60W,比对应相同电池面积平板系统最大输出功率高20W。聚光PV/T系统的各效率随光照强度增加而增大,系统的最大电效率为11%,最大热效率为70%,最大火用效率为16%,比单纯发电时最大火用效率提高约5%。实验获得了一批新的有价值的实验数据,为聚光太阳能光伏光热系统的进一步研究提供了依据。     

纳米流体太阳能电热联产系统性能研究

提出了一种具有选择性吸收功能的直接吸收式油基纳米流体太阳能电热联产系统,采用油基二氧化钛纳米流体匹配硅光伏电池板以实现对太阳辐射的分波段利用.通过求解辐射传递方程和能量守恒方程,分析了该系统在不同聚光强度和工质循环速率条件下的工作性能.通过与传统电热联产系统中光伏模块工作温度、循环流体出口温度、光热转换效率,以及光电转换效率的比对,验证了该系统能够在维持良好的光伏电池热管理的同时获得相对高品位热能收集.结果表明,在入射光强小于200 kW/m2工况下,该系统中的光伏电池板的工作温度能够维持在330K以下,其系统总的有效输出能相较于采用导热油作为循环工质的传统电热联产系统可实现16％ ～58％的效率提升.     

Thermal management of metal hydride hydrogen storage using phase change materials for standalone solar hydrogen systems: An energy/exergy investigation

This paper reports on an energy/exergy analysis of a standalone solar-hydrogen system with a metal hydride (MH) system thermally managed using a phase change material (PCM). This is a self-contained thermal management arrangement that stores the heat released from the MH unit, when it is being charged and transfers it back to the MH while discharging hydrogen. The first and second laws of thermodynamics were used to develop a mathematical model in MATLAB to simulate this system and quality its performance from the energy and exergy viewpoints. The model was then applied on a passive standalone house, with ～3.8 MWh/year electricity demand, located in southeast Australia. The exergy efficiencies of the solar PV, electrolyser, fuel cell and the whole solar hydrogen system were found to be 6.5%, 88%, 50.6%, and 3.74%, respectively. The paper also provides the detailed entropy generation and exergy analysis on the MH hydrogen storage unit together with its PCM-based thermal management arrangement. The results show that the annual entropy generation, exergy destruction and exergy efficiency of the MH hydrogen storage unit were 173 Wh/K, 51.5 kWh, and 98.8%, respectively.     

Enhanced generation of hydrogen,power, and heat with a novel integrated photoelectrochemical system

Hydrogen is an essential component of power-to-gas technologies that are needed for a complete transition to renewable energy systems. Although hydrogen has zero GHG emissions at the end-use point, its production could become an issue if non-renewable, and pollutant energy and material resources are used in this step. Therefore, a crucial step for the fully developed hydrogen economy is to find alternative hydrogen production methods that are clean, efficient, affordable, and reliable. With this motivation, in this study, an integrated and continuous type of hydrogen production system is designed, developed, and investigated. This system has three components. There is a solar spectral splitting device (Unit I), which splits the incoming solar energy into two parts. Photons with longer wavelength is sent to the photovoltaic thermal hybrid solar collector, PV/T, (Unit II) and used for combined heat and power generation. Then the remaining part is transferred to the novel hybrid photoelectrochemical-chloralkali reactor (Unit III) for simultaneous H₂, Cl₂, and NaOH production. This system has only one energy input, which is the solar irradiation and five outputs, namely H₂, Cl₂, NaOH, heat, and electricity. Unlike most of the studies in the literature, this system does not use only PV or only a photoelectrochemical reactor. With this approach, solar energy utilization is maximized, and the wasted portion is minimized. By selecting PV/T rather than PV, the performance of the panels is maximized because recovering the by-product heat as a system output in addition to electricity, and the PV/T has less waste and higher efficiency. The present reactor does not use any additional electron donors, so the wastewater discharge is only depleted NaCl solution, which makes the system significantly cleaner than the ones available in the literature. The specific aim of this study is to demonstrate the optimum operating parameters to reach the maximum achievable production rates and efficiencies while keeping the exergy destruction as little as possible. In this study, there are four case studies, and in each case study, one decision variable is optimized to get the desired performance results. Within the selected operating parameter range, all performance criteria (except exergy destruction) are normalized and ranked for proper comparison. The maximum production rates and efficiencies with the least possible exergy destruction are observed at the operating temperature of 30 °C. At 30 °C, 4.18 g/h H₂, 127.55 g/h Cl₂, 151 W electricity, and 716 W heat are produced with an exergy destruction rate of 95.74 W and 78% and 30% energy and exergy efficiencies, respectively.     

A review on solar-hydrogen/fuel cell hybrid energy systems for stationary applications

There are several methods for producing hydrogen from solar energy. Currently, the most widely used solar hydrogen production method is to obtain hydrogen by electrolyzing the water at low temperature. In this study, solar hydrogen production methods, and their current status, are assessed. Solar-hydrogen/fuel cell hybrid energy systems for stationary applications, up to the present day are also discussed, and preliminary energy and exergy efficiency analyses are performed for a photovoltaic-hydrogen/fuel cell hybrid energy system in Denizli, Turkey. Three different energy demand paths – from photovoltaic panels to the consumer – are considered. Minimum and maximum overall energy and exergy efficiencies of the system are calculated based on these paths. It is found that the overall energy efficiency values of the system vary between 0.88% and 9.7%, while minimum and maximum overall exergy efficiency values of the system are between 0.77% and 9.3% as a result of selecting various energy paths. More importantly, the hydrogen path appears to be the least efficient one due to the addition of the electrolyzer, the fuel cells and the second inverter for hydrogen production and utilization.     

Component exergy analysis of solar powered transcritical CO<Subscript>2</Subscript> rankine cycle system

In this paper,exergy analysis method is developed to assess a Rankine cycle system,by using supercritical CO2 as working fluid and powered by solar energy.The proposed system consists of evacuated solar collectors,throttling valve,high-temperature heat exchanger,low-temperature heat exchanger,and feed pump.The system is designed for utilize evacuated solar collectors to convert solar energy into mechanical energy and hence electricity.In order to investigate and estimate exergy performance of this system,the energy,entropy,exergy balances are developed for the components.The exergy destructions and exergy efficiency values of the system components are also determined.The results indicate that solar collector and high temperature heat exchanger which have low exergy efficiencies contribute the largest share to system irreversibility and should be the optimization design focus to improve system exergy effectiveness.Further,exergy analysis is a useful tool in this regard as it permits the performance of each process to be assessed and losses to be quantified.Exergy analysis results can be used in design,optimization,and improvement efforts.     

Energy and exergy efficiencies of a hybrid photovoltaic–thermal (PV/T) air collector

In this communication, an attempt has been made to evaluate exergy analysis of a hybrid photovoltaic–thermal (PV/T) parallel plate air collector for cold climatic condition of India (Srinagar). The climatic data of Srinagar for the period of four years (1998–2001) has been obtained from Indian Metrological Department (IMD), Pune, India. Based on the data four climatic conditions have been defined. The performance of a hybrid PV/T parallel plate air collector has been studied for four climatic conditions and then exergy efficiencies have been carried out. It is observed that an instantaneous energy and exergy efficiency of PV/T air heater varies between 55–65 and 12–15%, respectively. These results are very close to the results predicted by Bosanac et al. [Photovoltaic/thermal solar collectors and their potential in Denmark. Final Report, EFP Project, 2003, 1713/00-0014, www.solenergi.dk/rapporter/pvtpotentialindenmark.pdf].     

Optimization of a solar photovoltaic thermal (PV/T) water collector based on exergy concept

In this paper, the optimization of a solar photovoltaic thermal (PV/T) water collector which is based on exergy concept is carried out. Considering energy balance for different components of PV/T collector, we can obtain analytical expressions for thermal parameters (i.e. solar cells temperature, outlet water temperature, useful absorbed heat rate, average water temperature, thermal efficiency, etc.). Thermal analysis of PV/T collector depends on electrical analysis of it; therefore, five-parameter current–voltage (I–V) model is used to obtain electrical parameters (i.e. open-circuit voltage, short-circuit current, voltage and current at the point which has maximum electrical power, electrical efficiency, etc.). In order to obtain exergy efficiency of PV/T collector we need exergy analysis as well as energy analysis. Considering exergy balance for different components of PV/T collector, we obtain the expressions which show the exergy of the different parts of PV/T collector. Some corrections have been done on the above expressions in order to obtain a modified equation for the exergy efficiency of PV/T water collector. A computer simulation program has been developed in order to obtain the amount of thermal and electrical parameters. The simulation results are in good agreement with the experimental data of previous literature. Genetic algorithm (GA) has been used to optimize the exergy efficiency of PV/T water collector. Optimum inlet water velocity and pipe diameter are 0.09 m s⁻¹, 4.8 mm, respectively. Maximum exergy efficiency is 11.36%. Finally, some parametric studies have been done in order to find the effect of climatic parameters on exergy efficiency.     

Exergetic optimization of a solar photovoltaic thermal (PV/T) air collector

In this paper, an exergetic optimization has been developed to determine the optimal performance and design parameters of a solar photovoltaic thermal (PV/T) air collector. A detailed energy and exergy analysis has been carried out to calculate the thermal and electrical parameters, exergy components, and exergy efficiency of a typical PV/T air collector. The thermal and electrical parameters of a PV/T air collector include solar cell temperature, back surface temperature, outlet air temperature, open‐circuit voltage, short‐circuit current, maximum power point voltage, maximum power point current, etc. An improved electrical model has been used to estimate the electrical parameters of a PV/T air collector. Furthermore, a new equation for the exergy efficiency of a PV/T air collector has been derived in terms of design and climatic parameters. A computer simulation program has been also developed to calculate the thermal and electrical parameters of a PV/T air collector. The results of numerical simulation are in good agreement with the experimental measurements noted in the previous literature. Moreover, the simulation results obtained in this paper are more precise than the one given by the previous literature, and the new exergy efficiency obtained in this paper is in good agreement with the one given by the previous literature. Finally, exergetic optimization has been carried out under given climatic, operating, and design parameters. The optimized values of inlet air velocity, duct length, and the maximum exergy efficiency have been found. Parametric studies have been also carried out. Copyright © 2010 John Wiley & Sons, Ltd.     

Energy and exergy analysis of novel solar bi‐ejector refrigeration system with injector

Energy and exergy balances were done on a novel solar bi‐ejector refrigeration system with R123, whose circulation pump is replaced by an injector. The analysis result of the novel system was compared with that of the original one. The effect of operation condition on system energy efficiency, exergy efficiency and exergy loss was analyzed, and the dynamic performance of a designed solar bi‐ejector refrigeration system was also studied. The comparative results indicate that under the same operating condition, the novel system and the original system have equal energy efficiency, exergy efficiency and exergy loss, and the only difference between them is the exergy losses of the generators and the added injector. The other conclusions mainly include: the solar collector has the largest exergy loss rate of over 90% and for the bi‐ejector refrigeration subcycle, the ejector has the largest exergy loss rate of about 5%; the total exergy loss changes inversely proportional to the evaporation temperature and positively proportional to the condensation temperature; when the other parameters are fixed, there exists an optimum generation temperature, at which the overall energy and exergy efficiencies are both the maximum and the total exergy loss is the minimum. The study points out the direction for optimizing the novel solar bi‐ejector refrigeration system. Copyright © 2009 John Wiley & Sons, Ltd.     

A review on energy and exergy analysis of solar dying systems

Solar energy is a clean, abundant and freely available renewable energy sources. Energy and exergy analysis of solar thermal devices has drawn considerable interest among the researchers across the world. Solar drying is the promising option to utilize low grade energy to dry agricultural produces. Exergy analysis is a tool to access the efficient usage of solar energy. It is the property of the system, which gives the maximum power that can be distracted from the system when it is brought to a thermodynamic equilibrium state from a reference state. Using exergy analysis, based on the first and second laws of thermodynamics, it is possible to infer the true potential of different kinds of energies. In this paper, a holistic approach on energy and exergy analysis of solar dryer with case studies has been made.     

Thermoeconomic analysis of household refrigerators

This study deals with thermoeconomic analysis of household refrigerators for providing useful insights into the relations between thermodynamics and economics. In the analysis, the EXCEM method based on the quantities exergy, cost, energy and mass is applied to a household refrigerator using the refrigerant R134a. The performance evaluation of the refrigerator is conducted in terms of exergoeconomic aspects based on the various reference state temperatures ranging from 0 to 20°C. The exergy destructions in each of the components of the overall system are determined for average values of experimentally measured parameters. Exergy efficiencies of the system components are determined to assess their performances and to elucidate potentials for improvement. Thermodynamic loss rate‐to‐capital cost ratios for each components of the refrigerator are investigated. Correlations are developed to estimate exergy efficiencies and ratios of exergy loss rate‐to‐capital cost as a function of reference (dead) state temperature. The ratios of exergy loss rates to capital cost values are obtained to vary from 2.949 × 10^?4 to 3.468 × 10^?4 kW USThis study deals with thermoeconomic analysis of household refrigerators for providing useful insights into the relations between thermodynamics and economics. In the analysis, the EXCEM method based on the quantities exergy, cost, energy and mass is applied to a household refrigerator using the refrigerant R134a. The performance evaluation of the refrigerator is conducted in terms of exergoeconomic aspects based on the various reference state temperatures ranging from 0 to 20°C. The exergy destructions in each of the components of the overall system are determined for average values of experimentally measured parameters. Exergy efficiencies of the system components are determined to assess their performances and to elucidate potentials for improvement. Thermodynamic loss rate‐to‐capital cost ratios for each components of the refrigerator are investigated. Correlations are developed to estimate exergy efficiencies and ratios of exergy loss rate‐to‐capital cost as a function of reference (dead) state temperature. The ratios of exergy loss rates to capital cost values are obtained to vary from 2.949 × 10^?4 to 3.468 × 10^?4 kW US$^?1. The exergy efficiency values are also found to range from 13.69 to 28.00% and 58.15 to 68.88% on the basis of net rational efficiency and product/fuel at the reference state temperatures considered, respectively. It is expected that the results obtained will be useful to those involved in the development of analysis and design methodologies that integrate thermodynamics and economics. Copyright © 2006 John Wiley & Sons, Ltd.     

First and second law analyses to an energetic valorization process of biogas

The limitations in the world sources of energy are being mitigated by the exploitation of renewable forms and by increases in the efficiency of energy utilization. Exergy analysis is a useful method for the design, evaluation, and improvement of energy systems, that uses conservation of mass and conservation of energy principles, together with the second law of thermodynamics.This study covers first and second law analyses of a cogeneration system run with the biogas produced in a landfill. Such plant produces useful electrical and thermal energies, while protecting the environment from greenhouse emissions. The objectives were to identify locations where major irreversibilities occur, to evaluate their magnitudes, and to assess the energy and exergy efficiencies of the global system and of its constituent units.The results show that the overall-plant first law efficiency is 37.9% and the exergy efficiency is 36.2%, which is far from the thermodynamic ideal limit. The internal combustion engine and one of the radiators are the most inefficient units, as judged by the parameters degree of thermodynamic perfection and exergy destruction quotient. The main potential for improvement in the plant is the harnessing of the energy in the exhaust gases.     

Experimental investigation of energy and exergy efficiency of masonry-type solar cooker for animal feed

The performance of a masonry animal feed solar cooker was evaluated in terms of energy and exergy. It is a low-cost cooker made of cement, bricks, glass covers and a mild steel absorber plate. The energy and exergy efficiencies of the animal feed solar cooker were experimentally evaluated. The energy output of this cooker ranges from 1.89 to 49.4 kJ, whereas the exergy output ranges from 0.11 to 2.72 kJ during the same time interval. The energy efficiency of the cooker varies between 1.12% and 29.78%, while the exergy efficiency varies between 0.07% and 1.52 % during the same period.     

Exergy modeling of a new solar driven trigeneration system

In this paper, exergy modeling is used to assess the exergetic performance of a novel trigeneration system using parabolic trough solar collectors (PTSC) and an organic Rankine cycle (ORC). Four cases are considered: electrical-power, cooling-cogeneration, heating-cogeneration, and trigeneration. In this trigeneration system a single-effect absorption chiller is utilized to provide the necessary cooling energy and a heat exchanger is utilized to provide the necessary heating energy. The trigeneration system considered is examined using three modes of operation. They are: solar mode during the low-solar radiation time of the day, solar and storage mode during the high-solar radiation time of the day, and storage mode during night time. The storage mode is operated through the heat collected in a thermal storage tank during the solar and storage mode. The exergy efficiencies and exergy destruction rates are examined under the variation of the ORC evaporator pinch point temperature, ORC pump inlet temperature, and turbine inlet pressure. This study reveals that the maximum electrical-exergy efficiency for the solar mode is 7%, for the solar and storage mode is 3.5%, and for the storage mode is 3%. Alternatively, when trigeneration is used, the exergy efficiency increases noticeably. The maximum trigeneration-exergy efficiency for the solar mode is 20%, for solar and storage mode is 8%, and for the storage mode is 7%. Moreover, this study shows that the main sources of exergy destruction rate are the solar collectors and ORC evaporators. Therefore, careful selection and design of these two components are essential to reduce the exergy destructed by them and, thus, increase the exergy efficiencies of the system.