A thermal energy storage system that utilizes a thermoelectric heat pump as a power-to-heat technology to reach elevated temperatures by charging the storage system itself has been engineered by researchers in Spain.

The system is composed of a thermoelectric heat pump, an electric resistance component and a thermal energy storage cycle that relies on an open cycle with air as a heat transfer fluid. The fan is positioned at the cycle's air inlet, and the pushed air is then heated by the heat pump, which uses thermoelectric modules with complementing electric resistance.

A prototype was constructed and tested under 45 scenarios with different voltages in the resistor, storage inlet temperature and airflow rates. The voltages applied were 4 V, 6 V, 8 V or 10 V, and the inlet temperatures were in the 120° C to 200° C range. The system was operated with airflow rates of 13 m³/hour to 23 m³/hour.

Under the highest airflow rate tested, 655.5 W of heat can be generated with a coefficient of performance of 1.35 and an increase in airflow temperature from the ambient to 113.1° C. Inclusion of the thermoelectric heat pump into the charging process of a thermal energy storage system based on electrical resistances boosted the energy conversion efficiency by 15% and 30% for energy storage temperatures between 120° C and 200° C.

The system developed by researchers from the Public University of Navarre, National Renewable Energy Centre of Spain and the Industry Association of Navarra and described in Applied Thermal Engineering may achieve an overall efficiency of 112.6% at 135° C.