It depends on the ambient temperature. Heat pumps can obtain a coefficient of performance of about 2.5 in very cold conditions (-20 C) or as much as 5 in warmer

It depends on the ambient temperature. Heat pumps can obtain a coefficient of performance of about 2.5 in very cold conditions (-20 C) or as much as 5 in warmer conditions (+5 C). In theory, you could get even better performance by using a heat pump during the day to melt calcium chloride hexahydrate (mp 29 C = 84 F), and then freezing it at night to recover the stored energy. But now your system cost is even higher, since you need a ton of calcium chloride.