Another interesting strategy is the use of solar-assisted systems. For example solar assisted heat pump heating system is a way for reducing the electricity consumption due to the increase of the COP in the heat pump. These systems can be used for domestic hot water or for space heating. You can use flate plate collectors or thermal photovoltaics or various combinations. You can check the next studies for taking ideas: http://www.sciencedirect.com/science/article/pii/S0196890416303703 http://www.sciencedirect.com/science/article/pii/S1359431116308882