Dynamic simulation of integrated rock-bed thermocline storage for concentrated solar power

• Published in: Solar energy Vol. 110; pp. 830 - 842
• Main Authors: Mertens, Nicolas, Alobaid, Falah, Frigge, Lorenz, Epple, Bernd
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01-12-2014; Elsevier; Pergamon Press Inc
• Subjects: Applied sciences; Concentrated solar power; Dynamic simulation; Electric power plants; Electrical engineering. Electrical power engineering; Electrical power engineering; Energy; Energy. Thermal use of fuels; Exact sciences and technology; Heat transfer; Mathematical models; Natural energy; Non classical power plants; Photovoltaic power plants; Power plants; Pressure loss; Rock-bed thermal storage; Simulation; Solar energy; Solar thermal conversion; Solar thermal power plants; Theoretical studies. Data and constants. Metering; Transport and storage of energy; Concentrated solar power; Rock-bed thermal storage; Dynamic simulation; Pressure loss; Performance evaluation; Costs; Packed bed; Thermal energy storage; Thermocline; Modeling; Discharge charge cycle; Optimization; Rock bed; Energy supply; Air flow; Warm air; Photovoltaic power plant; Solar power plant; Regenerator; Solar energy; Dynamic model; Mathematical model; Heat transfer; Industrial power plant
• ISSN: 0038-092X; 1471-1257
• DOI: 10.1016/j.solener.2014.10.021

•First study of electrical efficiency for application of air/rock-bed thermal storage to CSP.•Heat discharged at 120°C below design temperature is still useful for steam generation.•Compressor work should be considered in the selection of storage geometry.•Electrical efficiency penalty amounts to 3.7 % points for the charge and discharge cycle.
In contrast to wind and photovoltaic, concentrated solar power plants can be equipped with thermal energy storage in order to decouple intermittent energy supply and grid feed-in. The focus of this study is the technical evaluation of a cost-efficient storage concept for solar tower power plants. Consisting of a quartzite-rock bed that is charged with a hot air flow and discharged by cold air counter-flow, the storage essentially operates like a regenerator. For such systems, the discharge temperature typically declines with time. Furthermore, the use of a randomly packed bed results in considerable pressure loss. In order to describe the relevant flow and heat transfer mechanisms in rock beds used for thermal storage, a mathematical model written in the modelling language Modelica is developed and validated. Good agreement with experimental data from literature is obtained. With the aid of the validated model, a rock-bed thermal storage for application in a semi-industrial scale solar power plant (1.5MWel) is designed and optimised with respect to electrical efficiency of the plant during the charge and discharge cycle. The storage capacity is equivalent to four hours of full-load operation. Results show that compressor work should be considered directly in the selection of packed-bed geometry in order to minimise the efficiency penalty of storage integration in the solar plant.