On the improvement of annual performance of solar thermal power plants through exergy management

SUMMARY Advancing in the learning curve of solar thermal power plants (STPP) requires detailed analysis for reducing exergy losses in the energy conversion chain. This requirement should be applied to any configuration proposed for the solar field and the power block. The aim of this work is to perform this type of analysis for two ways of structuring the power plant. The first plant structure consists of a subdivision of the solar collector field into specialized sectors with specific goals conveying different requirements in temperature. The second plant structure is based on a dual thermal energy storage system with a defined hierarchy in the storage temperature. The subdivision of the solar field into different sectors reduces the exergy losses in the heating process of the working fluid. Moreover, the average temperature of the heat transfer fluid in the solar field decreases when it is compared to the conventional solar field, reducing this way the exergy losses in the collectors. The dual thermal energy storage system is devised for keeping the exergy input to the power block at its nominal level for long periods of time, including post-sunset hours. One of the storage systems gathers a fluid heated up to temperatures above the nominal value and the second one is the classical one. The combination of both allows the manager of the plant to keep the nominal operation of the plant for longer periods than in the case of classical system. Numerical simulations performed with validated models are the basis of the exergy analyses. The configurations are compared to a reference STPP in order to evaluate their worth. Furthermore, the behaviour of the configurations is analysed to study the irreversibility of the included devices. Special attention is paid to the storage systems, as they are a key issue in both plant structures. Copyright © 2013 John Wiley & Sons, Ltd.