Concentrated Solar Power (CSP) plants are usually coupled with Thermal Energy Storage (TES) in order to increase the generation capacity and reduce energy output fluctuations and the levelized cost of the energy. In Direct Steam Generation (DSG) CSP plants, a popular TES option relies on steam accumulation. This conventional option, however, is constrained by temperature and pressure limits, and delivers saturated or slightly superheated steam at low pressure during discharge, which is undesirable for part-load turbine operation. However, steam accumulation can be integrated with sensible-heat storage in concrete to provide high-temperature superheated steam at higher pressures. The conventional steam accumulation option and the integrated concrete-steam option are presented, analysed and compared in this paper. The comparison shows that the integrated option provides more storage capacity by utilizing most of the available thermal power in the solar receiver. Further, the integrated option delivers higher power output with enhanced thermal efficiency for longer periods when the power plant is solely operating using the stored thermal energy. An application to the 50 MW Khi Solar One CSP plant, based on solar tower and in operation in South Africa, is proposed.
Keywords renewable/green energy resources, advanced energy technologies, thermal energy storage