For example, heat energy in the form of hot water generated by solar thermal collectors could be a great thing to inject into the ground loop side of a heat pump. The heat energy would raise the temperature of the water entering the heat pump, and because the heat pump works off of a refrigerant cycle, the higher entering temperature would equate to higher efficiencies. That lets the heat pump work less to provide the same amount of heat, reducing energy consumption, and saving you money.