Solar Thermal Power System Research Articles

Thermodynamic performance of a mid-temperature solar fuel system for cooling, heating and power generation

Solar thermal fuel is a promising approach of solar energy utilization, in which concentrating solar energy can drive the hydrocarbon fuel decomposition or steam reforming to produce hydrogen or syngas for generating power through heat engine. In the present, most of solar thermal fuel processes have employed solar heat at above 800°C which needs higher-concentration-ratio solar cavity reactor with higher re-radiation loss, bringing about poor annually average efficiency of solar-fuel-power. Here, a mid-temperature solar thermal fuel system by using chemical looping combustion (CLC) is studied for producing cooling, heating and power. The concentrated solar heat at approximately 350°C is utilized to drive the dimethyl ether fueled-chemical looping combustion with pair of CoO/Co as oxygen carrier. By using the mid-temperature solar heat driving CLC, the low-grade solar heat is upgraded into high-grade chemical energy of metal Co as solar fuel that is further converted into high-temperature thermal energy at 900°C via oxidation of Co and drives a recuperated gas turbine for generating power. The waste heat from the gas turbine can be utilized to produce a double-effect water/lithium bromide absorption chiller for producing the cooling and the heating. The thermodynamic performance of this mid-temperature solar fuel system is analyzed and the effects of several operation parameters such as solar irradiation, production of the solar fuel and pressure ratio are examined. The annually average efficiency of solar-fuel-power can be about 21%, with approximately 5 percentage points higher than that of solar thermal power system. In addition, the reason of the improvement in the performance is revealed by the irreversibility methodology. Our results would be expected to bring a new pathway for the application of solar thermal fuel in the distributed CCHP technology.

Performance analysis of a lunar based solar thermal power system with regolith thermal storage

The manned deep-space exploration is a hot topic of the current space activities. The continuous supply of thermal and electrical energy for the scientific equipment and human beings is a crucial issue for the lunar outposts. Since the night lasts for periods of about 350 h at most locations on the lunar surface, massive energy storage is required for continuous energy supply during the lengthy lunar night and the in-situ resource utilization is demanded. A lunar based solar thermal power system with regolith thermal storage is presented in this paper. The performance analysis is carried out by the finite-time thermodynamics to take into account major irreversible losses. The influences of some key design parameters are analyzed for system optimization. The analytical results shows that the lunar based solar thermal power system with regolith thermal storage can meet the requirement of the continuous energy supply for lunar outposts.

Evolution and feasibility of decentralized concentrating solar thermal power systems for modern energy access in rural areas

The desire of the international community to balance global economic growth against concerns of accelerated CO2 emissions has brought solar technologies into the forefront for meeting increasing energy demands. This manuscript discusses the historical and potential future roles for small-to-medium scale solar thermal technologies in addressing the challenge of leveling energy access standards across countries with widely variable economic resources and consumer needs. Access to modern energy services, such as heating for water, pumping for agricultural irrigation or potable water sources, and an on-demand 24/7 electrical grid, is central to provision of high quality social services, economic growth, and improved quality of life; however, over 1 billion people remain unelectrifi ed globally. Enabling the projected growth in energy demands without relying on fossil fuels requires consideration of the viability of renewable energy technologies to serve these markets; this manuscript provides a discussion of the role of solar thermal energy systems in this capacity. A survey of systems under 1 MW capacity reported in the literature (academic and commercial) was conducted, with projects aggregated by service type (heat, cooling, electricity, or multi-) in the database provided as an appendix to this manuscript. In general, many hardware confi gurations have been explored, with economics driven substantially by supply chain pricing, and no clear winner has emerged. Process heat applications demonstrate economic competitiveness over a wide range of commercial applications; however, early explorations into power generation—or co/tri-generation confi gurations—provide indications that such technologies, while not expected to reach grid-parity tariffs, may in fact provide the most economical pathway to energy delivery in the currently most underserved communities.

Hybrid power generation system of solar energy and fuel cells

This paper introduces the methods of integration of solar energy and low-temperature solid oxide fuel cells. On the one hand, we design the system that integrates the solar photovoltaic cells and fuel cells. On the other hand, solar energy is concentrated to heat up the fuel cell and supply the working temperature at hundreds Celsius degrees by Fresnel lens. Then the fuel conversion efficiency is increased because of gain from the solar energy. Moreover, integration of solar thermal energy power system with the fuel is a good method for resolving the instability of solar energy. CHP (combined heat and power) is another aspect to enhance the design hybrid system overall efficiency. Finally, we present a novel device but built on different scientific principle. It can convert solar energy and chemical energy of fuel to electric energy simultaneously within the same device to integrated solar cell and fuel cell from the device level. Copyright © 2016 John Wiley & Sons, Ltd.

First-Principles Study for Thermodynamic Properties of Solid $$\hbox {KNO}_{2}$$ KNO 2 System

To enable us better understand the performance of molten salt energy storage in a solar thermal power system, thermodynamic properties of the solid $$\hbox {KNO}_{2}$$ system at ambient pressure and temperatures between 0 K and 711 K are determined by first-principles simulation based on density functional perturbation theory calculations with plane waves and pseudopotentials. Thermodynamic parameters of the Debye temperature, specific heat capacity at constant volume, phonon transfer speed, phonon mean free path, and phonon thermal conductivity as a function of temperature are estimated. The results show that the calculated phonon thermal conductivity is in good agreement with experimental values, but the calculated specific heat capacity at constant volume is lower than measured values. The isometric specific heat capacity of $$\hbox {KNO}_{2}$$ is $$75.03\,\hbox {J}{\cdot }\hbox {mol}^{-1}{\cdot }\hbox {K}^{-1}$$ , and the phonon thermal conductivity is $$2.37\,\hbox {W}{\cdot }\hbox {m}^{-1}{\cdot }\hbox {K}^{-1}$$ at ambient temperature.

Numerical Investigation of High-temperature Molten Salt Leakage

Abstract As molten salt has been widely used in solar thermal power and nuclear power system, its leakage was an important problem. In this paper, the high-temperature molten salt leakage is simulated by considering the effects of phase change and flow dynamics. During the molten salt leakage process, the liquid molten salt is cooled by the ground and air, so it will solidify, and then a thin solidification layer of molten salt forms. The whole high-temperature molten salt leakage process consists of three subprocesses: spreading process, stable solid front formation process and solidification process after leakage. According to the simulation result, the radius of the leakage opening mainly affects the radius of nitrate solidification layer, while the leakage temperature and the leakage velocity will influence both the radius and thickness of salt layer. Besides, different kinds of molten salt are also considered, and the radius of molten salt solidification layer with SYSU-N1 is smaller than that with Solar Salt.

Economic Evaluation of Shell-and-tube Latent Heat Thermal Energy Storage for Concentrating Solar Power Applications

Abstract The capital cost and thermal performance of shell and tube type latent heat thermal energy storage (LHTES) is analyzed in this paper. In order to get the lowest cost of the shell and tube LHTES, the ideal one dimensional heat transfer model is used. The discharging process of shell and tube LHTES working in solar thermal power tower system and parabolic trough solar thermal power system were numerically simulated using lumped capacitance method. The capital cost of the LHTES was calculated considering different volume ratio of tubes and tube length. The results of the economic analysis shows that the tube and shell LHTES is a promising method to reduce the thermal energy storage cost.

State estimation of a solar direct steam generation mono-tube cavity receiver using a modified Extended Kalman Filtering scheme

State estimation plays a key role in the development of advanced control strategies for Concentrating Solar Thermal Power (CSP) systems, by providing an estimate of process variables that are otherwise infeasible to measure. The present study proposes a state estimation scheme for a once-through direct steam generation plant, the SG4 steam generation system at the Australian National University. The state estimation scheme is a modified Extended Kalman Filter that computes an estimate of the internal variables of the mono-tube cavity receiver in the SG4 system, from a dynamic non-linear model of the receiver. The proposed scheme augments the capabilities of a Continuous-Direct Extended Kalman Filter to deal with the switched nature of the receiver, in order to produce estimates during system start-up, cloud transients and operation of the plant. The estimation process runs at regular sample intervals and happens in two stages, a prediction and a correction stage. The prediction stage uses the receiver model to calculate the evolution of the system and the correction stage modifies the predicted estimate from measurements of the SG4 system. The resulting estimate is a set of internal variables describing the current state of the receiver, termed the state vector. This paper presents a description of the modified Extended Kalman Filter and an evaluation of the scheme using computer simulations and experimental runs in the SG4 system. Simulations and experimental results in this paper show that the filtering scheme improves a receiver state vector estimation purely based on the receiver model and provides estimates of a quality sufficient for closed loop control.

Thermodynamic analysis of an idealised solar tower thermal power plant

In the real solar tower thermal power system, it is widely acknowledged that the thermodynamic irreversibility, such as convective and radiative loss on tower receiver, and thermal resistance in heat exchangers, is unavoidable. With above factors in mind, this paper presents an ideal model of the solar tower thermal power system to analyze the influence of various parameters on thermal and exergy conversion efficiencies, including receiver working temperature, concentration ratio, endoreversible heat engine efficiency and so forth. And therefore the variation of maximum thermal conversion efficiency in terms of concentration ratio and endoreversible heat engine efficiency could be theoretically obtained. The results indicate that raising the receiver working temperature could initially increase both thermal and exergy conversion efficiencies until an optimum temperature is reached. The optimum temperature would also increase with the concentration ratio. Additionally, the concentration ratio has a positive effect on the thermal conversion efficiency: increasing the concentration ratio could raise the conversion efficiency until the concentration ratio is extremely high, after which there will be a slow drop. Lastly, the endoreversible engine efficiency also has significant influence on the thermal conversion efficiency, it will increase the thermal conversion efficiency until it reaches the maximum and optimum value, and then the conversion efficiency will drop dramatically.

Conceptual Design and Analysis of Hydrocarbon-Based Solar Thermal Power and Ejector Cooling Systems in Hot Climates

A combined thermal power and ejector refrigeration cooling cycle is proposed in this paper to harness low-grade solar energy. It explores the possibility of utilizing abundant and low-cost hydrocarbon as the working fluid. Hydrocarbon fluid has been identified as a promising alternative to existing high global-warming-potential (GWP) refrigerants (i.e., HFCs) in next-generation cooling and organic thermal power systems. Several typical alternative refrigerants are evaluated by considering their fundamental thermophysical properties: absolute pressure level, volumetric cooling capacity, surface tension, saturated liquid/vapor density ratio, and kinematic viscosity. Comparing with R1234yf, R1234ze, and R744 (CO2), hydrocarbon refrigerants, such as R290 (propane) and R601 (pentane), do have inherent advantages for either cooling or power generation purposes in hot climates. Fundamental phase stability and transition issues have been considered in designing hydrocarbon ejectors for combined power and cooling cycles operating at high ambient temperature. Thermodynamic energy and exergy analysis has indicated that the proposed stand-alone solar thermal system offers an effective way to sustainable energy production in hot and dry climates.

A Review About Solar Thermal Power Technology and its Use in India

Generally energy is available in two forms i.e. non renewable and renewable energy sources. Several environmental issues are related with the use of conventional energy sources like coal, petroleum and natural gas and different type of advantages or benefits offered by non conventional energy sources like solar, wind and small hydro included. Solar technology from history point of view is very old i.e. from 7th century B.C. to today. But in recent years the attention is more focused on solar energy for generate electricity. Solar energy help us to reduce the use of fossil fuel. Solar technology is a pollution free technology, so this technology is called by green technology. Solar energy can be used in two ways one of which is solar photovoltaic and another one is solar thermal and this paper is based on the review of solar thermal energy and sustainable developments in area of solar thermal power systems in India.

Novel non-concentrating solar collector for intermediate-temperature energy capture

Tremendous research efforts have been conducted studying the capturing and conversion of solar energy. Solar thermal power systems offer a compelling opportunity for renewable energy utilization with high efficiencies and excellent cost-effectiveness. The goal of this work was to design a non-concentrating collector, capable of reaching stagnation temperatures above 250°C and fluid outlet temperatures under flow above 200°C at 1000W/m2 solar irradiance. The study provides a detailed description of the methods and materials for construction of non-concentrating, high-temperature, evacuated solar collectors, the output fluid temperature depending on the input flow rate of working fluid in a low-flow rate, high-temperature regime, and an analytical description of the heat transfer between the collector and the working fluid. Temperature gains compared to ambient far above 200°C were possible under solar irradiance of 1000W/m2 with collector efficiencies of 30% and more. For a temperature gain of 227°C (fluid outlet temperature 253°C), the collector efficiency was 30%, and for a temperature gain of 214°C (fluid outlet temperature 240°C), the collector efficiency was 49%. This result opens up many new uses for non-concentrating solar collectors in fields such as power generation, fuel reforming, and catalysis.

Numerical Investigation of Nitrate Leakage and Migration in the Soil after Rainfall

Nitrate salt is important heat transfer and storage medium in solar thermal power system, but nitrate salt leakage and pollution in groundwater is seldom investigated. In this paper, the nitrate salt leakage and migration in the soil after rainfall are simulated and analyzed. During the nitrate leakage process, the liquid nitrate will solidify, and then a thin solidification layer of nitrate forms. According to the simulation result, the radius of the leakage opening mainly affects the radius of nitrate solidification layer, while the leakage velocity will influence the radius and thickness of salt layer. During the nitrate migration process after rainfall, the nitrate will gradually migrate to the groundwater, and the final migration domain of nitrate in the soil will be mainly determined by the radius of nitrate solidification layer.

Automatic Generation Control of an Organic Rankine Cycle Solar–Thermal/Wind–Diesel Hybrid Energy System

AbstractThe organic Rankine cycle solar–thermal power system is a promising concept for the distributed energy market. The present work investigates the automatic generation control of an autonomous hybrid energy system based on organic Rankine cycle solar–thermal technology. Any mismatch between the active power generation and consumption in the hybrid energy system manifests itself as a frequency deviation from the nominal system frequency. To confront the frequency excursion problem, the present work considers automatic generation control, in which the controllers’ parameters are optimized by using particle swarm optimization (PSO). The performance of each controller is compared with its genetic algorithm (GA)‐optimized counterpart with respect to its ability to capture the frequency variation in the proposed hybrid energy system. The simulation results reveal that the performance of the PSO‐optimized controller is better than its GA‐optimized counterpart in terms of settling time and overshoot in deviation of frequency.

The limits to solar thermal electricity

The potential and limits of solar thermal power systems depend primarily on their capacity to meet electricity demand in mid-winter, and the associated cost, storage and other implications. Evidence on output and costs is analysed. Most attention is given to central receivers. Problems of low radiation levels, embodied energy costs, variability and storage are discussed and are found to set significant difficulties for large scale solar thermal supply in less than ideal latitudes and seasons. It is concluded that for solar thermal systems to meet a large fraction of anticipated global electricity demand in winter would involve prohibitive capital costs.

A review of available methods for the alignment of mirror facets of solar concentrator in solar thermal power system

In the concentrated solar power system, the mirror facets of the solar concentrator have to be aligned correctly in order to obtain an optimally focused solar flux at the receiver. In mirror assembly, therefore, it is necessary to develop an accurate, inexpensive and fast measurement method to facilitate the installation and operation of the solar concentrator. In this paper, the available methods for the mirror facet alignment are reviewed. Three kinds of methods including on-sun single mirror facet alignment, mechanical alignment and optical alignment are reviewed in detail. The advantages and disadvantages of these methods are analyzed and discussed. Finally, some future developments are considered. 2014 Elsevier Ltd.

Experimental and Numerical Study of the Heat Transfer Characteristics in Solar Thermal Absorber Tubes with Circumferentially Non-uniform Heat Flux

This paper presents experimental and numerical studies of the turbulent heat transfer in solar thermal absorber tubes. The absorber tube is a significant component in a solar thermal power system. However, the tube heat transfer performance is different than with other tubes, only half of the circumference surface of the absorber tube is heated with the non-uniform heat flux and the other half is insulated. The non-uniform heat flux on an absorber tube can be up to 1.5MW/2 and generates significant temperature difference and thermal stress. The present study uses the experimental and computational fluid dynamics to reveal the turbulent convective heat transfer performance in the solar absorber tube within the range of Reynolds number from1.0×104 to 3.5×104. The results show that the temperature distribution of fluid and tube wall is very uneven in axial, radial and circumferential direction. The temperature of inner tube wall is an important parameter for preventing the decomposition of heat transfer fluid. The Dittus-Boelter equation is still applicable to calculate the heat transfer in a circular tube with non-uniform heat flux, but it is not suitable to calculate the wall temperature distribution in this condition. The wall temperature distribution of a circular tube with non-uniform heat flux varies with the circular angle of cross section, and this study presents the correlation.

Performance Evaluation of a Small Scale Modular Solar Trigeneration System

In order to improve the efficiency of solar thermal power (STP) system, a novel modular system combining cooling, heating, and power generation (CCHP) is proposed and introduced in this work. This modular CCHP system can simultaneously provide 10 kW electricity, −15~5°C coolant, and 60°C hot water to meet the requirements of cooling, heating, and electricity in a general family or other fields. The flow chart and working process of the modular system are introduced, based on which the energy and exergy efficiencies at the CCHP and STP operation modes are primarily evaluated and discussed. The results show that when the output electricity is constant, the overall efficiencies of energy and exergy of the system operating at the CCHP mode are 9.37 times and 2.62 times as big as those of the system operating at the STP mode, respectively. Thus, the modular solar thermal CCHP system can improve the energy and exergy efficiencies. Furthermore, calculation shows that both the overall energy and exergy efficiencies decrease with increase of inlet vapor temperature at given inlet vapor pressure, but both the efficiencies increase with increase of inlet vapor pressure at given inlet temperature.

Survey of Properties of Key Single and Mixture Halide Salts for Potential Application as High Temperature Heat Transfer Fluids for Concentrated Solar Thermal Power Systems

In order to obtain high energy efficiency in a concentrated solar thermal power plant, more and more high concentration ratio to solar radiation are applied to collect high temperature thermal energy in modern solar power technologies. This incurs the need of a heat transfer fluid being able to work at more and more high temperatures to carry the heat from solar concentrators to a power plant. To develop the third generation heat transfer fluids targeting at a high working temperature at least 800 ℃, a research team from University of Arizona, Georgia Institute of Technology, and Arizona State University proposed to use eutectic halide salts mixtures in order to obtain the desired properties of low melting point, low vapor pressure, great stability at temperatures at least 800 ℃, low corrosion, and favorable thermal and transport properties. In this paper, a survey of the available thermal and transport properties of single and eutectic mixture of several key halide salts is conducted, providing information of great significance to researchers for heat transfer fluid development.

Solar Thermal Power System Augmented with LHP

The present work reports the study of the bubble formation dynamics in the compensation chamber (CC) of the evaporator in Loop Heat Pipes. A series of experiments were conducted at different heat loads and bubbles in the CC were visualized. Bubbles diameter, frequency and velocity were measured and correlated against heat loads. Temperatures were measured at various locations and heat transfer coefficient was calculated. Performance of the LHP evaporator was evaluated at different heat loads.