Design of a direct thermal oil based thermocline thermal energy storage for a concentrating solar power plant

Abstract

Thermal Energy Storage (TES) systems are widely used in commercially operating Concentrating Solar Power (CSP) plants to allow for on-demand electrical power generation. Usually the TES used in these large-scale plants is of the well proven, two-tank, indirect molten salt based type. This paper presents an alternative TES technology that is suitable for small to mid-scale plants; with the design of the direct, thermal oil-based thermocline TES being explained in detail. In this paper special attention has been given to the challenges associated with initiating and maintaining the thermocline and to describe the design issues encountered during the project. The paper shows that by mastering the design challenges an optimized utilization factor of 86% is realistically achievable in normal operation, whilst the thermal efficiency of the storage is ca. 96%. The high levels of efficiency achieved through this type of storage result in reduced costs as the required volume of Heat Transfer Fluid (HTF) and amount of steel used in construction are minimized.