> By the straight math this could cover 17% of daily usage If you are heating from room temperature to RT+50C the actual energy extractable (as electricity) f

> By the straight math this could cover 17% of daily usage If you are heating from room temperature to RT+50C the actual energy extractable (as electricity) from that heat is only about 15% of what you put in https://en.wikipedia.org/wiki/Thermal_efficiency https://en.wikipedia.org/wiki/Thermal_efficiency. If you used the energy purely for heating you would in theory get it all back but the low temperature differential would mean in practical terms it would not work fast enough. You also need to factor in loss from conduction.