However, as fitting as the PV electric hot water system is for coastal communities, what makes the SURE HOUSE model even more desirable is the coupling with a high efficiency heat pump as a secondary source of energy. Generally, when you need to resort to a secondary heat source, the next line of defense is a traditional resistance coil that draws a large amount of electric energy to heat water. Instead, in the SURE HOUSE system, this backup device is a highly efficient heat pump triggered only when the sun cannot provide enough energy to keep the water temperature above a certain set point. The heat pump consists of a loop containing a fluid with a high thermal capacity, giving it the ability to store a great amount of energy. This energy is then easily transferred to the hot water tank due to the high surface area of the loop before it is sent back to the heat pump to be reheated. Even when in heat pump mode, our hot water system will still use 70% less energy than a standard electric hot water heater.