A temperature threshold evaluation for thermocline energy storage in concentrated solar power plants

Regarding energy storage in concentrated solar power plants, thermocline technology is considered to be a cost effective but less efficient solution than conventional two-tank. However, thermocline storage charge and discharge are usually stopped when the varying outlet temperature reaches an arbitrarily chosen value. It is shown here that the stop of the thermocline charge depends on the overheating risk in the solar collectors, while the stop of the discharge is defined by the steam generator requirements. As a consequence, the temperature thresholds that must be defined by the experimental constraints are dynamic. Using these dynamic thresholds on an experimental setup comprising a 230 kWh thermocline tank and a 150 kWth parabolic trough solar field led to a charge efficiency of 95.7% and a 93.5% discharge efficiency. Thus, the varying outlet temperature of a thermocline storage system is not an issue when integrated in a concentrated solar power plant.