Influence of different operation strategies on transient solar thermal power plant simulation models with molten salt as heat transfer fluid

Abstract

One of the advantages of solar thermal power plants (STPPs) with molten salt as heat transfer fluid is the direct storage system. This means that the thermal energy collected by the solar field and the electric power generation can be fully decoupled. The plant operator must therefore make the daily decision when to start-up or to shut-down the power block (PB). Normally, the solar field of these STPPs is overdesigned which leads to dumping of solar energy during days with high solar radiation, due to the inability of the hot tank and the PB to consume all the collected thermal energy. The PB must therefore start as soon as possible to prevent excessive dumping of solar energy. Contrarily, on days with low solar radiation, the PB should not start too early to prevent a second start-up on this day, because of a low hot tank level. In order to operate within these counter bounds, a fixed and a dynamic operation strategy are proposed. The so-called solar-driven strategy serves as a reference. Using this strategy, the PB operates whenever the solar field is online. The two proposed operation strategies are compared to the reference strategy by means of a transient STPP simulation model. Using the dynamic operation strategy, the annual unnecessary PB start-ups and the auxiliary heater thermal energy for anti-freeze protection are decreased, whereas the annual net electricity is increased.