Exergetic analysis and performance evaluation of parabolic dish Stirling engine solar power plant

In this communication, a 50 MW_e design capacity parabolic dish Stirling engine solar power plant (PDSSPP) has been modeled for analysis, where 2000 units of parabolic dish Stirling engine each having capacity of 25 kW_e were considered to get desired capacity. An attempt has been made to carry out the energetic and exergetic analysis of different components of a solar power plant system using parabolic dish collector/receiver and Stirling engine. The energetic and exergetic losses as well as efficiencies for typical PDSSPP under the typical operating conditions have been evaluated. Variations of the efficiency of Stirling engine solar power plant at the part‐load condition are considered for year‐round performance evaluation. The developed model is examined at location Jodhpur (26.29°N, 73.03°E) in India. It is found that year‐round energetic efficiency varies from 15.57% to 27.09%, and exergetic efficiency varies from 16.83% to 29.18%. The unit cost of electric energy generation (kW_eh) is about 8.76 Indian rupees (INR), with 30 years life span of the plant and 10% interest rate on investment. Copyright © 2012 John Wiley & Sons, Ltd.     

Development and performance analysis of a new solar tower and high temperature steam electrolyzer hybrid integrated plant

In this article, an extensive thermodynamic performance assessment for the useful products from the solar tower and high-temperature steam electrolyzer assisted multigeneration system is performed, and also its sustainability index is also investigated. The system under study is considered for multi-purposes such as power, heating, cooling, drying productions, and also hydrogen generation and liquefaction. In this combined plant occurs of seven sub-systems; the solar tower, gas turbine cycle, high temperature steam electrolyzer, dryer process, heat pump, and absorption cooling system with single effect. In addition, the energy and exergy performance, irreversibility and sustainability index of multigeneration system are examined according to several factors, such as environment temperature, gas turbine input pressure, solar radiation and pinch point temperature of HRSG. Results of thermodynamic and sustainability assessments show that the total energetic and exergetic efficiency of suggested paper are calculated as 60.14%, 58.37%, respectively. The solar tower sub-system has the highest irreversibility with 18775 kW among the multigeneration system constituents. Solar radiation and pinch point temperature of HRSG are the most critical determinants affecting the system energetic and exergetic performances, and also hydrogen production rate. In addition, it has been concluded that, the sustainability index of multigeneration suggested study has changed between 2.2 and 3.05.     

Performance assessment of parabolic dish and parabolic trough solar thermal power plant using nanofluids and molten salts

The present study has been conducted using nanofluids and molten salts for energy and exergy analyses of two types of solar collectors incorporated with the steam power plant. Parabolic dish (PD) and parabolic trough (PT) solar collectors are used to harness solar energy using four different solar absorption fluids. The absorption fluids used are aluminum oxide (Al₂O₃) and ferric oxide (Fe₂O₃)‐based nanofluids and LiCl‐RbCl and NaNO₃‐KNO₃ molten salts. Parametric study is carried out to observe the effects of solar irradiation and ambient temperature on the parameters such as outlet temperature of the solar collector, heat rate produced, net power produced, energy efficiency, and exergy efficiency of the solar thermal power plant. The results obtained show that the outlet temperature of PD solar collector is higher in comparison to PT solar collector under identical operating conditions. The outlet temperature of PD and PT solar collectors is noticed to increase from 480.9 to 689.7 K and 468.9 to 624.7 K, respectively, with an increase in solar irradiation from\ 400 to 1000 W/m². The overall exergy efficiency of PD‐driven and PT‐driven solar thermal power plant varies between 20.33 to 23.25% and 19.29 to 23.09%, respectively, with rise in ambient temperature from 275 to 320 K. It is observed that the nanofluids have higher energetic and exergetic efficiencies in comparison to molten salts for the both operating parameters. The overall performance of PD solar collector is observed to be higher upon using nanofluids as the solar absorbers. Copyright © 2015 John Wiley & Sons, Ltd.     

Exergetic analysis of solar concentrator aided natural gas fired combined cycle power plant

This article deals with comparative energy and exergetic analysis for evaluation of natural gas fired combined cycle power plant and solar concentrator aided (feed water heating and low pressure steam generation options) natural gas fired combined cycle power plant. Heat Transfer analysis of Linear Fresnel reflecting solar concentrator (LFRSC) is used to predict the effect of focal distance and width of reflector upon the reflecting surface area. Performance analysis of LFRSC with energetic and exergetic methods and the effect, of concentration ratio and inlet temperature of the fluid is carried out to determine, overall heat loss coefficient of the circular evacuated tube absorber at different receiver temperatures. An instantaneous increase in power generation capacity of about 10% is observed by substituting solar thermal energy for feed water heater and low pressure steam generation. It is observed that the utilization of solar energy for feed water heating and low pressure steam generation is more effective based on exergetic analysis rather than energetic analysis. Furthermore, for a solar aided feed water heating and low pressure steam generation, it is found that the land area requirement is 7 ha/MW for large scale solar thermal storage system to run the plant for 24 h.     

Comparative energy,exergy and exergo-economic analysis of solar driven supercritical carbon dioxide power and hydrogen generation cycle

Parabolic dish solar collector system has capability to gain higher efficiency by converting solar radiations to thermal heat due to its higher concentration ratio. This paper examines the exergo-economic analysis, net work and hydrogen production rate by integrating the parabolic dish solar collector with two high temperature supercritical carbon dioxide (s-CO₂) recompression Brayton cycles. Pressurized water (H₂O) is used as a working fluid in the solar collector loop. The various input parameters (direct normal irradiance, ambient temperature, inlet temperature, turbine inlet temperature and minimum cycle temperature) are varied to analyze the effect on net power output, hydrogen production rate, integrated system energetic and exergetic efficiencies. The simulations has been carried out using engineering equation solver (EES). The outputs demonstrate that the net power output of the integrated reheat recompression s-CO₂ Brayton system is 3177 kW, whereas, without reheat integrated system has almost 1800 kW net work output. The overall energetic and exergetic efficiencies of former system is 30.37% and 32.7%, respectively and almost 11.6% higher than the later system. The hydrogen production rate of the solarized reheat and without reheat integrated systems is 0.0125 g/sec and 0.007 g/sec, accordingly and it increases with rise in direct normal irradiance and ambient temperature. The receiver has the highest exergy destruction rate (nearly 44%) among the system components. The levelized electricity cost (LEC) of 0.2831 $/kWh with payback period of 9.5 years has proved the economic feasibility of the system design. The increase in plant life from 10 to 32 years with 8% interest rate will decrease the LEC from (0.434-0.266) $/kWh. Recuperators have more potential for improvement and their cost rate of exergy is higher as compared to the other components.     

Exergetic optimization for solar heat receiver with heat loss and viscous dissipation

The exergetic efficiency of heat receiver in solar thermal power system is optimized by considering the heat loss outside the receiver and fluid viscous dissipation inside the receiver. The physical models of heat loss and pumping power consumption for solar heat receiver are first proposed, and associated exergetic efficiency is further induced. As the flow velocity rises, the pumping power consumption and heat absorption efficiency significantly rises, and the maximum absorption efficiency and optimal incident energy flux also increase. Along the flow direction of solar receiver, the exergy flux increment and the flow exergy loss almost linearly increase, while the exergetic efficiency varies very slowly at high flow velocity. According to the exergetic efficiency loss from flow viscou’s dissipation, the exergetic efficiency of solar heat receiver will first increase and then decrease with the flow velocity. Because of the coupling effects of heat absorption efficiency and exergetic efficiency from fluid internal energy, the exergetic efficiency of solar heat receiver will approach to the maximum at proper inlet temperature. As a result, the exergetic efficiency of solar heat receiver will reach the maximum at optimal inlet temperature, incident energy flux and flow velocity.     

Performance of optimized solar central receiver systems as a function of receiver thermal loss per unit area

Recent efforts in solar central receiver research have been directed toward high-temperature applications. Associated with high-termperature processes are greater receiver thermal losses due to thermal radiation and convection. This article examines the performance of central receiver systems having optimum heliostat fields and receiver aperture areas as a function of receiver thermal loss per unit area. The results address the problem of application optimization, where the receiver design, temperature and consequently thermal loss per unit area may vary. A reasonable range of values for the primary independent variable L (the average thermal loss per unit area of receiver aperture) and a reasonable set of design assumptions were first established. Heliostat field analysis and optimization required a detailed computational analysis. Results are discussed for tower focal heights of 150 and 180 m. Values of L ranging from 0.04 to 0.50 MW per square meter were considered, roughly corresponding to working fluid temperatures in the range of 650–1650°C. As L increases over this range, the receiver thermal efficiency and the receiver interception factor decrease. The optimal power level drops by almost half, and the cost per unit of energy produced increases by about 25% for the base case set of design assumptions. The resulting decrease in solar subsystem efficiency (relative to the defined annual input energy) from 0.57 to 0.35 is about 40% and is a significant effect. Unoptimized systems would experience an even greater degradation in cost-effectiveness.     

Energy and exergy analyses of an integrated solar‐based desalination quadruple effect absorption system for freshwater and cooling production

In this paper, a novel integrated solar photovoltaic thermal absorption desalination system for freshwater and cooling production is proposed and analyzed thermodynamically. Ammonia–water pair is considered as a working fluid for the absorption system. Effect of average solar radiation for different months, time period of solar radiation availability in Abu Dhabi, salinity of seawater, and temperature of the seawater on energetic and exergetic COPs, production rate of freshwater, and overall performance of the system are investigated under different operating conditions. It is found that energetic and exergetic COPs, production rate of freshwater, energetic and exergetic utilization factors, and performance ratios vary greatly from one month to another because of the dynamic variation in solar radiation and its time of availability. The highest amount of freshwater is produced in the month of July as calculated to be 152 kg/h for a collector area of 100 m² and solar power of 4.8 kW. The highest energetic and exergetic COPs and utilization factors are also obtained for the month of July. Moreover, the highest performance ratio is found to be 0.056 as obtained in the month of July when solar radiation intensity is highest as available for more than half of a day. Copyright © 2012 John Wiley & Sons, Ltd.     

Comparative energetic and exergetic performance analyses for coal-fired thermal power plants in Turkey

The purpose of this study is to analyze comparatively the performance of nine thermal power plants under control governmental bodies in Turkey, from energetic and exergetic viewpoint. The considered power plants are mostly conventional reheat steam power plant fed by low quality coal. Firstly, thermodynamic models of the plants are developed based on first and second law of thermodynamics. Secondly, some energetic simulation results of the developed models are compared with the design values of the power plants in order to demonstrate the reliability. Thirdly, design point performance analyses based on energetic and exergetic performance criteria such as thermal efficiency, exergy efficiency, exergy loss, exergetic performance coefficient are performed for all considered plants in order to make comprehensive evaluations. Finally, by means of these analyses, the main sources of thermodynamic inefficiencies as well as reasonable comparison of each plant to others are identified and discussed. As a result, the outcomes of this study can provide a basis used for plant performance improvement for the considered coal-fired thermal power plants.     

Development and thermodynamic assessment of a novel solar and biomass energy based integrated plant for liquid hydrogen production

In this paper, a combined power plant based on the dish collector and biomass gasifier has been designed to produce liquefied hydrogen and beneficial outputs. The proposed solar and biomass energy based combined power system consists of seven different subplants, such as solar power process, biomass gasification plant, gas turbine cycle, hydrogen generation and liquefaction system, Kalina cycle, organic Rankine cycle, and single-effect absorption plant with ejector. The main useful outputs from the combined plant include power, liquid hydrogen, heating-cooling, and hot water. To evaluate the efficiency of integrated solar energy plant, energetic and exergetic effectiveness of both the whole plant and the sub-plants are performed. For this solar and biomass gasification based combined plant, the generation rates for useful outputs covering the total electricity, cooling, heating and hydrogen, and hot water are obtained as nearly 3.9 MW, 6584 kW, 4206 kW, and 0.087 kg/s in the base design situations. The energy and exergy performances of the whole system are calculated as 51.93% and 47.14%. Also, the functional exergy of the whole system is calculated as 9.18% for the base working parameters. In addition to calculating thermodynamic efficiencies, a parametric plant is conducted to examine the impacts of reference temperature, solar radiation intensity, gasifier temperature, combustion temperature, compression ratio of Brayton cycle, inlet temperature of separator 2, organic Rankine cycle turbine and pump input temperature, and gas turbine input temperature on the combined plant performance.     

Energy,exergy, exergo-economic and exergo-environmental analyses of solar based hydrogen generation system

The present study focuses on the energy, exergy, exergo-economic, and exergo-environmental analyses of the solar-assisted multi-generation system. The multi-generation system consists of parabolic trough solar collector, regenerative power plant, double-effect absorption chiller system, proton exchange membrane electrolyzer, and multi-stage flash desalination plant. In the regenerative power plant, liquid petroleum gas (LPG) based boiler is implemented. The propane (C₃H₈) is used as the fuel in the boiler combustion chamber. The thermal and exergetic efficiencies of the power cycle are observed to be 41.08% and 23.26%, respectively. The electrical power of 1.384 MW is produced by the low-pressure turbine. Whereas, the thermal COP and exergetic COP are observed and maintained in the range of 1.28 to 0.22, respectively. The liquid hydrogen is produced by the PEM electrolyzer with the thermal and exergetic efficiencies of 60.83% and 64.65%, respectively. Furthermore, the exergo-economics and exergo-environmental analyses have also been conducted and all the parameters have been analyzed and concluded through graphs and tables.     

Exergetic analysis of a solar thermal power system

This communication presents a second law analysis based on an exergy concept for a solar thermal power system. Basic energy and exergy analysis for the system components (viz. parabolic trough collector/receiver and Rankine heat engine, etc.) are carried out for evaluating the respective losses as well as exergetic efficiency for typical solar thermal power systems under given operating conditions. It is found that the main energy loss takes place at the condenser of the heat engine part, whereas the exergy analysis shows that the collector–receiver assembly is the part where the losses are maximum. The analysis and results can be used for evaluating the component irreversibilities which can also explain the deviation between the actual efficiency and ideal efficiency of a solar thermal power system.     

对太阳能热发电走向成功之路的思考

从理论方面对降低太阳能热发电投资成本的方式进行了分析,认为可通过扩大规模来降低投资成本,依靠扩大发电系统的规模和优化镜场设计来提高太阳能热发电系统的光电转换效率;碟式和点聚焦菲涅耳聚光系统的光热转换效率高,竞争力较强。当采用超大功率蒸汽轮机时,可使发电系统的规模扩大10倍、热电转换效率提高25%;按照光学效率和接收器热效率均达到92%计算,碟式聚光系统的光热转换效率可达到84.64%,而塔式聚光系统的光热转换效率为57.73%,前者比后者提高了46.62%,使碟式太阳能热发电系统的光电转换效率比塔式太阳能热发电系统的提高了83.3%,从而使碟式太阳能热发电系统的总投资成本比塔式太阳能热发电系统的下降了45.4%,共用跟踪系统使其总投资成本又下降了4.8%,再加上碟式太阳能热发电系统的中发电系统规模扩大10倍,最终,碟式太阳能热发电系统的总投资成本可比塔式太阳能热发电系统的降低75.2%。在不考虑材料和制造技术方面进步的情况下,太阳能热发电的上网电价可从目前的1元/kWh降至约0.25元/kWh,使太阳能热发电成为未来有竞争力的主要能源技术。     

A solar-driven combined cycle power plant

The main results of a feasibility study of a combined cycle electricity generation plant, driven by highly concentrated solar energy and high-temperature central receiver technology, are presented. New developments in solar tower optics, high-performance air receivers and solar-to-gas turbine interface, were incorporated into a new solar power plant concept. The new design features 100% solar operation at design point, and hybrid (solar and fuel) operation for maximum dispatchability. Software tools were developed to simulate the new system configuration, evaluate its performance and cost, and optimize its design. System evaluation and optimization were carried out for two power levels. The results show that the new system design has cost and performance advantages over other solar thermal concepts, and can be competitive against conventional fuel power plants in certain markets even without government subsidies.     

A novel combined biomass and solar energy conversion-based multigeneration system with hydrogen and ammonia generation

In the present study, an innovative multigeneration plant for hydrogen and ammonia generation based on solar and biomass power sources is suggested. The proposed integrated system is designed with the integration of different subsystems that enable different useful products such as power and hydrogen to be obtained. Performance evaluation of designed plant is carried out using different techniques. The energetic and exergetic analyses are applied to investigate and model the integrated plant. The plant consists of the parabolic dish collector, biomass gasifier, PEM electrolyzer and hydrogen compressor unit, ammonia reactor and ammonia storage tank unit, Rankine cycle, ORC cycle, ejector cooling unit, dryer unit and hot water production unit. The biomass gasifier unit is operated to convert biomass to synthesis gaseous, and the concentrating solar power plant is utilized to harness the free solar power. In the proposed plant, the electricity is obtained by using the gas, Rankine and ORC turbines. Additionally, the plant generates compressed hydrogen, ammonia, cooling effect and hot water with a PEM electrolyzer and compressed plant, ammonia reactor, ejector process and clean-water heater, respectively. The plant total electrical energy output is calculated as 20,125 kW, while the plant energetic and exergetic effectiveness are 58.76% and 55.64%. Furthermore, the hydrogen and ammonia generation are found to be 0.0855 kg/s and 0.3336 kg/s.     

Simulation and analysis of the central cavity receiver’s performance of solar thermal power tower plant

Solar central receiver, which plays a dominant role in the radiation–heat conversion, is one of the most important components in the solar tower plants. Its performance can directly affect the efficiency of the entire solar power generation system. In this study, an integrated receiver model for full range operation conditions was proposed in order to simulate and evaluate the dynamic characteristics of a solar cavity receiver. It mainly couples the radiation–heat conversion process, the determination of convective heat transfer coefficient, the temperature computation of receiver walls and the calculation and analysis of the thermal losses. Based on this model, the dynamic characteristics of the solar cavity receiver were tested by encountering a sudden solar radiation disturbance. In addition, the thermal loss was also calculated and analyzed with different wind conditions. The results indicated that the parameters of the receiver had a significant variation under the sharp disturbance of DNI if no control rules were imposed. The wind conditions can obviously affect the thermal losses and the value reaches its maximum when the wind blows from the side of the receiver (α = 90°). In order to verify the validity of this model, the simulation results were used to compare the design points under the same input conditions, and the results showed that simulation data had a good agreement with design data.     

Solar tower power plant in Germany and future perspectives of the development of the technology in Greece and Cyprus

Since the 80s power production with solar thermal power plants has been a way to substitute fossil fuels. By concentrating direct solar radiation from heliostats very high temperatures of a thermal fluid can be reached. The resulting heat is converted to mechanical energy in a steam cycle which generates electricity.High efficiencies and fast start-up are reached by using air as a heat medium, as well as using porous ceramic materials as solar receiver of the concentrated sunlight.In Germany the construction of a 1.5 MW_e solar tower power plant began in 2008. It is operational since December 2008 and started production of electricity in the spring of 2009.In Greece and Cyprus, countries with high solar potential, the development of this competitive solar thermal technology is imperative, since it has already been implemented in other Mediterranean countries.     

Geothermal and solar energy–based multigeneration system for a district

In this study, parabolic trough collector with an integrated source of geothermal water is used with regenerative Rankine cycle with an open feedwater heater, an electrolyzer, and an absorption cooling system. The absorption fluids used in the solar collectors were Al₂O₃‐ and Fe₂O₃‐based nanofluids. Detailed energetic and exergetic analyses are done for the whole system including all the components. A comparative analysis of both the used working fluids is done and plotted against their different results. The parameters that are varied to change the output of the system are ambient temperature, solar irradiance, the percentage of nanofluids, the mass flow rate of the geothermal well, the temperature gradient of the geothermal well that had an effect on the net power produced, and the outlet temperature of the solar collector overall energetic and exergetic efficiencies. Other useful outputs by this domestic integrated multigeneration system are the heating of domestic water, space heating (maintaining the temperature at 40°C‐50°C), and desalination of seawater (flash distillation). The hydrogen production rate for both the fluids diverges with each other, both producing average from 0.00490 to 0.0567 g/s.     

Central collector solar energy receivers

Central receivers for use with power-generating equipment require compact boiler and superheater designs to effectively concentrate the solar heat input and to improve system power cycle efficiency. Solar thermal collectors employ a central receiver that must be compact to effectively utilize the high concentration ratios of sunlight energy. The demonstration of lightweight, long-life receiver designs is a technology issue that must be resolved if the concept is to be attractive for power generation. The receiver must be lightweight to minimize the cost of the supporting tower structure. Current applied aerospace technology in compact steam boilers and rocket thrust chamber designs can be directly applied to the design and fabrication of solar central receivers.This technology recently has been applied to a compact steam generator that uses liquid oxygen and natural gas, propane or fuel oil. The compact steam generator permits a 300:1 size reduction in boiler and superheater size. This paper discusses the application of the compact steam generator technology to the design and fabrication of central receivers for solar-energy-powered electrical powerplants. Receiver designs are discussed for tower-mounted applications where size and weight are important. The heat flux rates necessary for central solar receivers are nearly identical to the design hear fluxes for the compact steam generator. Fabrication of the central receiver is discussed as well as design details and applicable materials.     

Solar-driven high temperature hydrogen production via integrated spectrally split concentrated photovoltaics (SSCPV) and solar power tower

Hydrogen production can be achieved via combined concentrated photovoltaic (CPV) and concentrated solar power (CSP) in which concentrated radiation is spectrally split and then converted in a photovoltaic receiver and a thermal absorber. This study thus proposes an innovative solar process design integrating both thermal and quantum components of solar energy while providing a complete assessment of its global performance to demonstrate its practical interest. A stand-alone solar-to-hydrogen path was modeled and numerically simulated, which was both electrically and thermally supplied by a solar power generation unit to feed the electrolyzer power utilization unit with enhanced solar-to-hydrogen conversion efficiency. Following balance of plant (BoP), the heliostat field and cavity receiver were designed to match the entire system in which the receiver only intercepts a definite range of infrared wavelength while the rest is converted by separately insulated PV cells. Moreover, dichroic reflectors and optimum cutoff wavelength were applied to fulfill separate optimization and heat load reduction of each solar cell. Finally, the solid oxide electrolysis cell (SOEC) was designed to utilize the generated thermal and electrical power appropriately. In best case scenario, a solar-to-hydrogen conversion efficiency of 36.5% was achieved under 899 W/m² direct normal irradiance (DNI) and 1000 suns concentration. The solar plant outputs at this operating point were 850 g/h H₂ and 6754 g/h O₂. Further improvement in efficiency can be achieved through alignment in regard to the site location and annual insolation variation.