This is not really the same. Malta seems to use a heat pump to produce reservoirs of both hot and cold material. This allows to produce electricity via a carnot

This is not really the same. Malta seems to use a heat pump to produce reservoirs of both hot and cold material. This allows to produce electricity via a carnot process with very high efficiency (theoretically 100% because while the carnot process that produces electricity has an efficiency <1, the heat pump can have a carnot efficiency of >1). In practice they might get to 70% efficiency or so. Sunamp.com seems to be just ohmic heating for thermal usage of excess electricity.