Heat takes up the largest part of the energy demand within a household and storing household energy in the form of heat is more cost effective than in a battery. To assure a constant heat supply using only intermittent power sources, Borg has developed a thermal battery that can provide a household with up to two weeks worth of heat and hot water. In addition, by connecting to and (autonomously) steering i.e. the heat pump or other power/heat generator, this technology enables homeowners to make use of flexible energy prices, charging the battery when power is cheap, and using the stored heat when prices are high.