Solar Power Plant System Research Articles

Technical challenges and future direction for high-efficiency metal hydride thermal energy storage systems

Recently, there has been increasing interest in thermal energy storage (TES) systems for concentrated solar power (CSP) plants, which allow for continuous operation when sunlight is unavailable. Thermochemical energy storage materials have the advantage of much higher energy densities than latent or sensible heat materials. Furthermore, thermochemical energy storage systems based on metal hydrides have been gaining great interest for having the advantage of higher energy densities, better reversibility, and high enthalpies. However, in order to achieve higher efficiencies desired of a thermal storage system by the US Department of Energy, the system is required to operate at temperatures >600 °C. Operation at temperatures >600 °C presents challenges including material selection, hydrogen embrittlement and permeation of containment vessels, appropriate selection of heat transfer fluids, and cost. Herein, the technical difficulties and proposed solutions associated with the use of metal hydrides as TES materials in CSP applications are discussed and evaluated.

Numerical analysis on an industrial-scaled solar updraft power plant system with ambient crosswind

Existing research indicated that the ambient crosswind (ACW) has very complex influences on the SUPPS both through the chimney outlet and collector inlet as demonstrated by numerical analysis from the Spanish prototype. But what influence exert ACW through chimney outlet and collector inlet independently on the overall performance of SUPPS is still unclear. In this research, two geometrical models are constructed for numerical simulation on industrial-scale SUPPS in the vicinity of 10 MW. In model 1, ACW acts on both chimney outlet and collector inlet; in model 2, ACW acts only on the chimney outlet. Fluid flow, heat transfer and power output performances of SUPPS are investigated and discussed. It is found that, the negative effect of ACW only occurs at the collector inlet, with cold ambient air into the collector resulting in changing of fluid distribution and deterioration of buoyant driving force, whereas the positive effect occurs at the chimney outlet, with strong ACW passing by the chimney outlet causing entrainment of buoyant airflow within the chimney outlet. To avoid deterioration and to improve the overall performance of SUPPS, effective measures can be taken to prevent ACW from entering the collector inlet and also to induce beneficial effects of high altitude strong ACW blowing across the chimney outlet.

A Novel Lab-scale Solar Reactor for Kinetic Analysis of Non-volatile Metal Oxides Thermal Reductions

Thermal reduction of metal oxides is of primary interest within the R&D field of solar driven thermochemistry, because it is frequently involved in processes such as thermochemical cycles for hydrogen production or in thermochemical energy storage systems for solar thermal power plants. A lab-scale solar reactor has been designed to test and analyze solar-driven reduction of non-volatile metal oxides arranged in a packed bed. The test bed allows monitoring of oxygen evolution to determine the reaction rate. Experimental tests with Mn2O3, Mn3O4 and CeO2 have been carried out and the performance of each reaction has been analyzed. Total conversion is obtained for Mn2O3 reduction. However, only some zones of the Mn3O4 and CeO2 samples achieve reaction temperature. Different types of sample-holders have been used to hold the particles packed-bed, in order to enhance the conversion. The high influence of the irradiance distribution on the sample surface is demonstrated by a testMn3O4 reduction.

Thermocline thermal storage systems for concentrated solar power plants: One-dimensional numerical model and comparative analysis

Concentrated solar power plants have attracted increasing interest from researchers and governments all over the world in recent years. An important part of these plants is the storage system which improves dispatchability and makes the plant more reliable. In this paper, a one-dimensional transient mathematical model for a single-tank thermocline thermal energy storage system is presented. The model used temperature dependent correlations to obtain the thermophysical properties for the heat transfer fluid and considered heat loss through the tank wall. The effect of variation in important system parameters like the type of heat transfer fluid, the storage temperature difference and the cycle cut-off criterion on system performance was investigated. The results suggest that two important aspects for assessing the performance of the system are the cyclic behaviour of the system and the time required to attain equilibrium conditions. These aspects directly influence the discharge capacity and discharge power of the storage system, and therefore play an essential role in understanding the start-up characteristics of the system and provide an insight regarding the availability of storage when designing the power cycle for concentrated solar power applications. It was also observed that the cycle durations and the time required to attain cyclic conditions are highly sensitive to not only the storage temperature difference, but also the cut-off temperature difference.

Exergetic Analysis of a Solar Thermal Power Plant

The study of heat loss and exergy loss distribution in the power plant system plays a very important role in improving the efficiency of the system. In this paper, a dynamic simulation model of the 5MW solar thermal power system is established. Then, the simulation test with the actual data in a solar thermal power plant is carried out, and we analyze the heat and the exergy loss of the system. The results show that, the heat loss of the condenser is the largest, up to 72%. To increase the thermal efficiency of the system, the energy-saving research for the condenser should be pay attention to. The solar collector field has the most of exergy loss in the system, accounting for approximately 89%. From the exergy efficiency perspective, the solar collector system has huge potential for energy- saving. The thermal efficiency and exergy efficiency of a solar thermal power plant system increases as the load increases, full-load operation of the unit should be maintained as much as possible.

Numerical analysis on the solar updraft power plant system with a blockage

Ambient crosswind has complicated influence on the performance of the solar updraft power plant system (SUPPS) both via the collector inlet and via the chimney outlet. To overcome the negative impact of strong ambient crosswind on the performance of a 50kW SUPPS model with the same dimensions as the prototype in Manzanares, Spain through the collector inlet, a 2m high blockage was circularly set a few meters away from the collector inlet. A geometrical model including the SUPPS and its outside ambience was built, and the mathematical models to describe the fluid flow, heat transfer and output power of the whole system were further developed. The pressure, temperature and velocity distribution of the air in the ambience and SUPPS together with the output power of the SUPPS were analyzed. The numerical simulation results revealed that after being set a blockage in front of the collector inlet, the negative influence of ambient crosswind on the performance of the SUPPS has been overcome to a great extent.

Effect of Step-Change Radiation Flux on Dynamic Characteristics in Tower Solar Cavity Receiver

The heat flux on the inner surface of the tower solar thermal power plant system will show the characteristics of noncontinuous step change, especially in nonnormal and transient weather conditions, which may result in a continuous dynamic variation of the characteristic parameters. Therefore, the research of dynamic characteristics plays a very important role in the operation and the control safely in solar cavity receiver system. In this paper, based on the noncontinuous step change of radiation flux, a non-linear dynamic model is constructed to obtain the effects of the non-continuous step change radiation flux and step change feed water flow on the receiver performance by sequential modular approach. The subject investigated in our study is a 1 MW solar power station constructed in Yanqing county, Beijing, China. This study has obtained the dynamic responses of the characteristic parameters in the cavity receiver such as drum pressure, drum water level, main steam flow, and main steam enthalpy under step change radiation flux. And the influence of step-change feed water flow to the dynamic characteristics has also been analyzed. The results could provide general guidance for security operation and control in solar cavity receiver system.

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

SUMMARY In this communication, a 50 MWe 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 kWe 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 (kWeh) 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.

Exergetic analysis and performance evaluation of parabolic trough concentrating solar thermal power plant (PTCSTPP)

Energetic and exergetic analysis has been carried out for the components of the solar thermal power plant system (parabolic trough collector/receiver and Rankine heat engine). The energetic and exergetic losses as well as efficiencies for typical parabolic trough concentrating solar thermal power plant (PTCSTPP) under the specific operating conditions have been evaluated. Operating pressures for a Rankine heat engine have been optimized for maximum efficiency. It has been found that, the energetic and exergetic efficiencies of PTCSTPP increased by 1.49% and 1.51% with increasing pressure from 90 to 105 bar respectively. Progression of the STPP from the variable load to full load conditions, the year round average energetic efficiency can be increased from 22.01% to 22.62% for the location of Jodhpur, and in case of Delhi, it can be increased from 20.98% to 21.50%. Year round average exergetic efficiency can be increased, from 23.66% to 24.32% for the location of Jodhpur and in case of Delhi, it can be increased from 22.56% to 23.11%. Land areas required for the 50 MWe thermal power plants are 79.2 ha and 118.8 ha respectively for the locations of Jodhpur and Delhi.

Comparative life cycle assessment of thermal energy storage systems for solar power plants

Abstract The present work compares the environmental impact of three different thermal energy storage (TES) systems for solar power plants. A Life Cycle Assessment (LCA) for these systems is developed: sensible heat storage both in solid (high temperature concrete) and liquid (molten salts) thermal storage media, and latent heat storage which uses phase change material (PCM). The aim of this paper is to analyze if the energy savings related to the stored energy of the different systems are enough to balance the environmental impact produced during the manufacturing and operation phase of each storage system. Some hypothetical scenarios are studied using LCA methodology to point out the differences between each TES system. The system based on solid media, due to his simplicity, shows the lowest environmental impact per kWh stored of all three systems compared. In addition, the liquid media (molten salts) shows the highest impact per kWh stored because it needs more material and complex equipment.

Energy management in solar thermal power plants with double thermal storage system and subdivided solar field

In the paper, two systems for solar thermal power plants (STPPs) are devised for improving the overall performance of the plant. Each one attempts to reduce losses coming from two respective sources. The systems are simulated and compared to a reference STPP. They consists on: (a) a double thermal energy storage (DTS) with different functionalities for each storage and (b) the subdivision of the solar collector field (SSF) into specialised sectors, so that each sector is designed to meet a thermal requirement, usually through an intermediate heat exchanger. This subdivision reduces the losses in the solar field by means of a decrease of the temperature of the heat transfer fluid (HTF). Double thermal energy storage is intended for keeping the plant working at nominal level for many hours a day, including post-sunset hours. One of the storages gathers a fluid which is heated up to temperatures above the nominal one. In order to make it work, the solar field must be able to overheat the fluid at peak hours. The second storage is the classical one. The combination of both allows the manager of the plant to keep the nominal of the plant for longer periods than in the case of classical thermal energy storage. To the authors’ knowledge, it is the first time that both configurations are presented and simulated for the case of parabolic through STPP with HTF technology. The results show that, if compared to the reference STPP, both configurations may raise the annual electricity generation (up to 1.7% for the DTS case and 3.9% for the SSF case).

Thermal‐fluid flow within innovative heat storage concrete systems for solar power plants

Purpose – The purpose of this paper is to describe an experience of R&D in the field of new technologies for solar energy exploitation within the Italian context. Concentrated solar power systems operating in the field of medium temperatures are the main research objectives, directed towards the development of a new and low‐cost technology to concentrate the direct radiation and efficiently convert solar energy into high‐temperature heat.Design/methodology/approach – A multi‐tank sensible‐heat storage system is proposed for storing thermal energy, with a two‐tanks molten salt system. In the present paper, the typology of a below‐grade cone shape storage is taken up, in combination with nitrate molten salts at 565°C maximum temperature, using an innovative high‐performance concrete for structures absolving functions of containment and foundation.Findings – Concrete durability in terms of prolonged thermal loads is assessed. The interaction between the hot tank and the surrounding environment (ground) is co...

Sensitivity of long-term performance simulations of solar energy systems to the degree of stratification in the thermal storage unit

This paper investigates the sensitivity of the long-term performance simulations of solar energy systems to the degree of stratification in both liquid and packed-bed storage units. The degree of stratification is controlled by the number of nodes used in a finite-difference approximation of the storage system temperature distribution. Short- and long-term simulations of typical water heating and solar thermal power plant systems are conducted. The results indicate that the long-term performance of these systems is far less sensitive to the number of nodes used to represent the degree of stratification than expected based on short-term simulations or experimental data. An explanation is offered for this non-intuitive result. Copyright © 2007 John Wiley & Sons, Ltd.

System and components design of a sodium heat transfer circuit for solar power plants

Abstract The first part of the paper briefly compares the characteristic properties of different heat transfer fluids to show the advantages of sodium; the second part details design features of a small sodium heat transfer system, including the main components comprising receiver, steam generator, pumps, vessels, etc., on the basis of the CRS solar power plant at Almeria, Spain (IEA-SSPS Project); the final part indicates aspects of the scaling-up of such systems for larger solar power plants.