Investigation of the Load-Following Capability of CSP Plants

Abstract

The increasing penetration of PV and wind energy in several markets is forcing the power plants (both fossil and renewable) to operate with a high level of flexibility. In this scenario, the load-following capability of CSP power plants can play a fundamental role. The Thermal Energy Storage (TES) system allows exploiting solar energy after sunset and adjusting the power output according to the power demand variability. The paper aims to investigate different CSP plant configurations operating in island-mode to fulfill the power demand of a mid-size town located in the Upington region (South Africa). The power block is based on a steam Rankine cycle with superheated steam temperature 550°C, coupled with a molten salt direct storage system. Two solar fields are compared: Parabolic Trough Collectors (PTCs) and Central Receiver System (CRS). In order to analyze the load-following capability, two different electric loads (with the same annual energy demand of 360 GWh) are considered: the first one is typical of an industrial city, whilst the second one is the power demand pattern of a residential district. A numerical model of the two selected CSP technologies has been developed with the software Trnsys® and the optimization tool GenOpt. The simulation results show that the CSP plant based on CRS exhibits a higher load-following capability: both industrial and residential power demands are met with a lower aperture area and lower investment costs. The PTCs result to be affected by a strong efficiency variation between summer and winter: the load-following capability is good for the residential load profile, whilst is poor for the flat industrial load.