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.     

Direct use of solar energy for water desalination

Solar energy utilization in three different types of solar desalination systems is considered. The overall efficiency of a typical basin type solar desalination plant is 30 per cent or lower. The major design factors affecting energy utilization are basin temperature, condensing surface temperature and ambient air temperature. Basic reflection and thermal radiation from the evaporating surface and transparent cover are the major sources of heat energy loss in a solar still. The efficiency of a solar desalination plant can be improved by controlling radiation from the plant basin and by the reuse of the latent heat of condensation.     

Energetic and economic investigation of Organic Rankine Cycle applications

The use of organic working fluids for the realization of the so called Organic Rankine Cycle (ORC) has been proven to be a promising solution for decentralized combined heat and power production (CHP). The process allows the use of low temperature heat sources, offering an advantageous efficiency in small-scale applications. This is the reason why the number of geothermal and biomass fired power plants based on this technology have been increased within the last years. The favourable characteristics of ORC make them suitable for being integrated in applications like solar desalination with reverse osmosis system, waste heat recovery from biogas digestion plants or micro-CHP systems. In this paper, the state of the art of ORC applications will be presented together with innovative systems which have been simulated in a process simulation environment using experimental data. The results of the simulation like efficiencies, water production rates or achievable electricity production cost will be presented and discussed.     

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.     

不同太阳能利用区有机朗肯循环工质的选择

为太阳能有机朗肯循环系统(organic Rankine cycle,ORC)合理选择工质需要综合考虑太阳能辐射强度和环境温度的影响。基于建筑热工设计分区和太阳能资源区划标准,将我国分为了11个太阳能利用区。利用太阳能ORC热力学能量流通数学模型,以太阳能ORC系统典型月平均热发电效率最高为原则,为太阳能ORC系统绘制出推荐的工质地图。     

Thermodynamic assessment of modified Organic Rankine Cycle integrated with parabolic trough collector for hydrogen production

Hydrogen is one of the most clean energy carrier and the best alternative for fossil fuels. In this study, thermodynamic analysis of modified Organic Rankine Cycle (ORC) integrated with Parabolic Trough Collector (PTC) for hydrogen production is investigated. The integrated system investigated in this study consists of a parabolic trough collector, a modified ORC, a single effect absorption cooling system and a PEM electrolyzer. By using parabolic trough collector, solar energy is converted heat energy and then produced heat energy is used in modified ORC to produce electricity. Electricity is then used for hydrogen production. The outputs of this integrated system are electricity, cooling and hydrogen. By performing a parametric study, the effects of design parameters of PTC, modified ORC and PEM electrolyzer on hydrogen production is evaluated. According to the analysis results, solar radiation is one of the most important factor affecting system exergy efficiency and hydrogen production rate. As solar radiation increases from 400?W/m² to 1000?W/m², exergy efficiency of the system increases 58%–64% and hydrogen production rate increases from 0.1016?kg/h to 0.1028?kg/h.     

Technical and economical analysis of a solar–geothermal hybrid plant based on an Organic Rankine Cycle

A combined concentrating solar power system and a geothermal binary plant based on an Organic Rankine Cycle (ORC) is analyzed. Given a supercritical ORC, designed for the optimal utilization of an intermediate enthalpy geothermal source, a solar parabolic trough field was included in the plant, introducing an additional high temperature heat source for the cycle and increasing power production. The off-design performance analysis of the power cycle was performed first. An hour-by-hour simulation was then carried out to estimate the yearly production using a detailed solar field model. Finally, a differential economic analysis was performed to determine the cost of the additional electricity generated with the solar source. On the basis of the current cost of solar collectors, levelized costs of electricity of 145-280 €/MWh were obtained depending on the location of the plant: a competitive value with respect to large, stand-alone concentrating solar power plants.     

Performance of S-CO_2 Brayton Cycle and Organic Rankine Cycle(ORC) Combined System Considering the Diurnal Distribution of Solar Radiation

This paper researches the performance of a novel supercritical carbon dioxide(S-CO_2) Brayton cycle and organic Rankine cycle(ORC) combined system with a theoretical solar radiation diurnal distribution. The new system supplies all solar energy to a S-CO_2 Brayton cycle heater, where heat releasing from the S-CO_2 cooler is stored in the thermal storage system which is supplied to the ORC. Therefore, solar energy is kept at a high temperature, while at the same time the thermal storage system temperature is low. This paper builds a simple solar radiation diurnal distribution model. The maximum continuous working time, mass of thermal storage material, and parameter variations of the two cycles are simulated with the solar radiation diurnal distribution model. 10 organic fluids and 5 representative thermal storage materials are compared in this paper, with the mass and volume of these materials being shown. The longer the continuous working time is, the lower the system thermal efficiency is. The maximum continuous working time can reach 19.1 hours if the system provides a constant power output. At the same time, the system efficiency can be kept above 38% for most fluids.     

Performance investigation of the heat pump and power generation integration system

A novel heat pump and power generation integration system (HPPGIS) using solar energy as a low temperature heat source was presented in this study. This system could be operated in both an organic Rankine cycle power generation (ORC‐PG) mode and a reverse Carnot cycle heat pump (RCC‐HP) mode. Compared with a single heat pump and power generation system, this system improved the utilization efficiency of solar energy, thus showing potential for the generation of economic benefits. Contrastive analyses of different working fluids using ORC‐PG and RCC‐HP systems were conducted first, leading to the selection of R142b and R245fa as optimal fluids. Then, an experimental investigation of the system was carried out under different conditions. A heat pump and ORC system model was proposed and validated by comparing experimental and simulated values. The experimental results indicated that the HPPGIS had good feasibility and stability in both modes. In the ORC‐PG mode, HPPGIS had a power output of 1.29 kW and a thermal efficiency of 4.71% when the water inlet temperature of the evaporator was 90.03°C. In the RCC‐HP mode, HPPGIS had a COP of 3.16 and a heat capacity of 33.24 kW when the water outlet temperature of the condenser was 106.23°C.     

Solar heat pump systems for domestic hot water

Vapour compression heat pumps can upgrade ambient heat sources to match the desired heating load temperature. They can offer considerable increase in operational energy efficiency compared to current water heating systems. Solar heat pumps collect energy not only from solar radiation but also from the ambient air. They can operate even at night or in totally overcast conditions. Since the evaporator/collector operates at temperatures lower than ambient air temperature it does not need glazing or a selective coating to prevent losses. Currently, however, they are not used much at all in domestic or commercial water heating systems. In this paper comparison is made of a conventional solar hot water system, a conventional air source heat pump hot water system and a solar heat pump water heating system based on various capital city locations in Australia. A summary is given of specific electricity consumption, initial and operating costs, and greenhouse gas generation of the three systems dealt with in this paper. The ultimate choice of unit for a particular location will depend heavily on the solar radiation, climate and the local price paid for electricity to drive or boost the unit chosen.     

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.     

Volumetric receivers in Solar Thermal Power Plants with Central Receiver System technology: A review

Deployment of the first generation of grid-connected plants for electricity production, based on Solar Thermal Power Plants with Central Receiver System technology using large heliostat fields and a solar receiver placed on the top of a tower, is currently being boosted by the first commercial plants in Spain, PS10, PS20, and Gemasolar.Therefore one of the main goals of solar technology research is the study of existing receivers and development of new designs to minimize heat losses.In this context, volumetric receivers appear to be the best alternative to tube receivers, mainly due to their functionality and geometric configuration. They consist of a porous material that absorbs concentrated radiation inside the volume of a structure and transfers the absorbed heat to a fluid passing through the structure. Solar radiation is first converted into thermal energy or chemical potential, and then at a later stage, into electricity.This volumetric receiver technology has been under development since the early 1990s in various research and development projects. This paper is a chronological review of the volumetric receivers of most interest for electricity production, identifying their different configurations, materials and real and expected results, and pointing out their main advantages and conclusions based on the multitude of international and national projects reports and references.This study also deals with other important issues surrounding the volumetric receiver, such as the basic plant configuration, flow stability phenomenon and the main problems of a windowed design for pressurized receivers.     

Low-grade heat conversion into power using organic Rankine cycles – A review of various applications

An organic Rankine cycle (ORC) machine is similar to a conventional steam cycle energy conversion system, but uses an organic fluid such as refrigerants and hydrocarbons instead of water. In recent years, research was intensified on this device as it is being progressively adopted as premier technology to convert low-temperature heat resources into power. Available heat resources are: solar energy, geothermal energy, biomass products, surface seawater, and waste heat from various thermal processes. This paper presents existing applications and analyzes their maturity. Binary geothermal and binary biomass CHP are already mature. Provided the interest to recover waste heat rejected by thermal devices and industrial processes continue to grow, and favorable legislative conditions are adopted, waste heat recovery organic Rankine cycle systems in the near future will experience a rapid growth. Solar modular power plants are being intensely investigated at smaller scale for cogeneration applications in buildings but larger plants are also expected in tropical or Sahel regions with constant and low solar radiation intensity. OTEC power plants operating mainly on offshore installations at very low temperature have been advertised as total resource systems and interest on this technology is growing in large isolated islands.     

Simulation analysis of cooling methods of an on‐board organic Rankine cycle exhaust heat recovery system

Energy saving and emission reduction of engines were taken seriously, especially for vehicular diesel engines. Exhaust heat recovery based on organic Rankine cycle (ORC) system has been considered as an effective approach for improving engine fuel economy. This article presents the investigation of water or air cooling method for an ORC exhaust heat recovery system on a heavy‐duty truck through simulations. The models of the truck engine and the ORC system were developed in GT suite, and the integration system model was developed in the Simulink environment. The validity of the models was verified experimentally. The performance of the vehicular engine with ORC system using water or air cooling method was comparatively analyzed. The simulation results indicated that the water cooling method is more suitable for the vehicular ORC system than air cooling method. The relation between benefit and penalty of the ORC system and cooling system was discussed. The operating condition of the cooling system was confirmed having significant effects on the combined system performance, especially the fan speed. The performance improvement of the engine with the use of ORC system was further evaluated under different engine operating conditions and ambient temperatures. Lower ambient temperature had positive effects on the engine fuel economy. The mass flow rate of exhaust gas for heat recovery should be regulated for better performance under high ambient temperature.     

Performance and design optimization of a low-cost solar organic Rankine cycle for remote power generation

Recent interest in small-scale solar thermal combined heat and power (CHP) power systems has coincided with demand growth for distributed electricity supplies in areas poorly served by centralized power stations. One potential technical approach to meeting this demand is the parabolic trough solar thermal collector coupled with an organic Rankine cycle (ORC) heat engine.The paper describes the design of a solar organic Rankine cycle being installed in Lesotho for rural electrification purpose. The system consists of parabolic though collectors, a storages tank, and a small-scale ORC engine using scroll expanders.A model of each component is developed taking into account the main physical and mechanical phenomena occurring in the cycle and based on experimental data for the main key components.The model allows sizing the different components of the cycle and evaluates the performance of the system. Different working fluids are compared, and two different expansion machine configurations are simulated (single and double stage).     

Dynamic modelling of a solar hydrogen system for power and ammonia production

A new configuration of solar energy-driven integrated system for ammonia synthesis and power generation is proposed in this study. A detailed dynamic analysis is conducted on the designed system to investigate its performance under different radiation intensities. The solar heliostat field is integrated to generate steam that is provided to the steam Rankine cycle for power generation. The significant amount of power produced is fed to the PEM electrolyser for hydrogen production after covering the system requirements. A pressure swing adsorption system is integrated with the system that separates nitrogen from the air. The produced hydrogen and nitrogen are employed to the cascaded ammonia production system to establish increased fractional conversions. Numerous parametric studies are conducted to investigate the significant parameters namely; incoming beam irradiance, power production using steam Rankine cycle, hydrogen and ammonia production and power production using TEGs and ORC. The maximum hydrogen and ammonia production flowrates are revealed in June for 17th hour as 5.85 mol/s and 1.38 mol/s and the maximum energetic and exergetic efficiencies are depicted by the month of November as 25.4% and 28.6% respectively. Moreover, the key findings using the comprehensive dynamic analysis are presented and discussed.     

Thermodynamic analysis and optimization of a solar-driven regenerative organic Rankine cycle (ORC) based on flat-plate solar collectors

This paper presents a regenerative organic Rankine cycle (ORC) to utilize the solar energy over a low temperature range. Flat-plate solar collectors are used to collect the solar radiation for their low costs. A thermal storage system is employed to store the collected solar energy and provide continuous power output when solar radiation is insufficient. A daily average efficiency is defined to evaluate the system performance exactly instead of instantaneous efficiency. By establishing mathematical models to simulate the system under steady-state conditions, parametric analysis is conducted to examine the effects of some thermodynamic parameters on the system performance using different working fluids. The system is also optimized with the daily average efficiency as its objective function by means of genetic algorithm under the given conditions. The results indicate that under the actual constraints, increasing turbine inlet pressure and temperature or lowering the turbine back pressure could improve the system performance. The parametric optimization also implies that a higher turbine inlet temperature with saturated vapor state could obtain the better system performance. Compared with other working fluids, R245fa and R123 are the most suitable working fluids for the system due to their high system performance and low operation pressure.     

太阳能中温集热利用制蒸汽系统性能研究

构建了一套供热功率为310kW的太阳能中温集热利用制蒸汽系统,建立了系统主要模块——太阳能集热器与热変换器的热力学模型,研究了变工况下太阳辐射强度、凝水回收比、环境温度对系统效率和供热功率的影响,探讨了不同运行参数条件下集热温度与系统性能之间的关系。研究结果表明:增大辐射强度对系统性能提升显著;回收凝水对系统效率的影响不大,但对制热功率的提升较为明显;系统性能随环境温度升高呈先上升后下降的趋势;系统存在最佳集热温度,最佳集热温度随辐射强度和环境温度的增大而升高。     

Parametric analysis and yearly performance of a trigeneration system driven by solar‐dish collectors

Solar‐driven polygeneration systems are promising technologies for covering many energy demands with a renewable and sustainable way. The objective of the present work is the investigation of a trigeneration system, which is driven by solar‐dish collectors. The examined trigeneration system includes an organic Rankine cycle (ORC), which operates with toluene, and an absorption heat pump, which operates with LiBr/H₂O. The absorption heat pump is fed with heat by the condenser of the ORC, which operates at medium temperature levels (120°C to 150°C). The absorption heat pump produces both useful heat at 55°C and cooling at 12°C. The ORC produces electricity, and it is fed by the solar dishes. The examined ORC is a regenerative cycle with superheating. The total analysis is performed with a developed model in Engineering Equation Solver (EES). The system is investigated parametrically for different ORC heat‐rejection temperatures, different superheating levels in the turbine inlet, and various solar‐beam irradiation levels. Furthermore, the system is investigated on a yearly basis for the climate conditions of Athens (Greece) and for Belgrade (Serbia). It is found that the yearly system energy and exergy efficiencies are 108.39% and 20.92%, respectively, for Athens, while 111.38% and 21.50%, respectively, for Belgrade. The values over 100% for the energy efficiency are explained by the existence of a heat pump in the examined configuration. For both locations, the payback period is found close to 10 years and the internal rate of return close to 10%. The final results indicate that the examined configuration is a highly efficient and viable system, which operates only with a renewable energy source.     

Economic appraisal of small-scale solar organic Rankine cycle operating under different electric tariffs and geographical conditions

In the present paper, the economic feasibility of small-scale solar organic Rankine cycle power applications which are assisted with auxiliary gas heaters is investigated. The system is analyzed using three different capacities of ORC system with R-245fa (35, 65, and 110 kWe) in combination with solar water heating system (SWHS) using three models. Flat plate, compound parabolic and evacuated tube solar collectors were used to generate heat with overall heat transfer coefficient (F_RU_L) of 4.35, 1.57, and 2.23 W/m². K respectively. System Advisor Model (SAM) is used to simulate the solar water heater system and optimize the tilt angle, collector area, volume of storage tank and capacity of auxiliary heater under the climatic conditions of Abu Dhabi, New Delhi, Larnaca, Madrid and Munich. The simulation results revealed that the evacuated tube and the compound parabolic collectors performed better than the flat plate collectors. The economic analysis showed that Solar ORC Power Plant is economically and technically feasible with all types of the thermal collectors in Famagusta/Larnaca, Munich and Madrid where the electricity tariff is higher than other cities. Levelized cost of energy (LCOE) is calculated using mathematical model and it ranges between 0.07 and 0.2 USD/kWh based on the plant capacity and type of thermal collectors. Moreover, the profit increase as the plant capacity increase where SIR is 1.05, 1.71, and 2.10 for 35, 65, and 110 kW plant capacity SORC with CPC. A sensitivity analysis is also performed to investigate the effect of operating hours, electricity tariff, ORC unit cost and ORC unit type on the feasibility of the system. According to the results, the electricity tariff and operating hours are the most important parameters because they have a large effect and Play important role on the economic feasibility of the system.