Second-Law Analysis of Solar Collectors With Energy Storage Capability

Abstract

This is an analytical and numerical study of the exergy that can be delivered by a solar collector installation with temporary energy storage capability. In the first part of the study, the method of variational calculus is used to show that under conditions of time-dependent inlet and outlet flow rates, the total exergy delivered by the installation is maximum when the collector temperature is maintained at an optimum constant level throughout the insolation period. More realistic models of solar collectors with storage capability are analyzed in the second and third parts of the study. In each of the models considered, the analysis shows that the relative timing of the filling and discharge processes has a significant effect on the total exergy delivered by the installation. The main conclusion of the study is that the daily regime of operation of the collection/storage installation can be selected by design in order to maximize the harvesting of solar exergy per unit of collector area.