4.2 Active indirect concept for TES with two tanks

Active indirect systems have further two designs for TES integration into CSP plants with the options of two tanks and single tank for storage. In such systems, materials to store thermal energy are different than the heat transfer fluid (HTF). An example of active indirect system with two-tank storage is shown in Figure 3 [13]. At the start of the charging/discharging cycle, TES material is stored in a cold tank, while HTF is moving in the flow path of solar collector, thermodynamics cycle, and heat exchanger. During charging, TES material is pumped from the cold tank to a hot tank through the heat exchanger where it absorbs heat from HTF and stored into the hot tank. The TES is pumped back to the cold tank during discharging in which the materials return heat to the HTF through heat exchanger. Hence, TES material and HTF are totally different and are not mixed with each other during the process.
