Stabilization of the outflow temperature of a packed-bed thermal energy storage by combining rocks with phase change materials

•Encapsulated phase-change material (PCM) placed on top of packed-bed thermal storage.•1.3% of PCM by volume sufficient to stabilize outflow temperature during discharging.•Charging–discharging efficiency not affected by addition of phase-change material.

A new thermal energy storage (TES) configuration for concentrated solar thermal power is proposed for stabilizing the outflow temperature of a packed bed of rocks during discharging. This concept is based on the combination of sensible and latent heat storage by adding a relatively small amount of phase change material (PCM) to the top of the bed. Transient simulations solving the energy conservation equations for fluid, solid, and molten phases show that the outflow temperature during discharging can be kept constant around the PCM melting temperature, thereby eliminating the inherent temperature drop of TES based on sensible heat storage only. A PCM volume of only 1.33% of the total storage volume is sufficient to accomplish stabilization, corresponding to 4.4% of the total thermal energy stored as latent heat.