Partitioned solar pond collector/storage system

Abstract

This paper presents an analysis of the performance of a partitioned solar pond as a large-scale solar energy collection and long-term storage system for power production, as well as other applications. The absorption of solar radiation as it passes through the pond water is considered and an evaluation is made of the resulting temperature and heat fluxes at various levels in the pond during its year-round operation by solving the Fourier heat conduction equation, with appropriate boundary conditions, in different zones of the pond. This evaluation, combined with energy balance considerations, enables an expression for the transient rate at which heat can be retrieved—in order to keep the temperature of the convective zone constant—to be derived. Numerical calculations, corresponding to solar heat flux and atmospheric air temperature measurements carried out in New Delhi during 1974, are made and the optimisation of the sizes of the non-convective and convective zones in the pond is investigated. Optimal heat retrieval efficiencies of 42%, 33·5%, 29·5% and 26·5% are predicted at extraction temperatures of 40°C, 60°C, 80°C and 100°C, respectively. However, the load levelling improves as the non-convective zone is oversized. A phase difference of about 30 to 45 days is also noted between the incident solar flux and the heat retrieved when the size of the non-convective zone is near its optimum. The efficiency of the solar-pond system for converting solar energy into mechanical work is also studied. This efficiency is found to increase with collection temperature and to tend to level off at collection temperatures above 90°C.