Do not cease talking about the limited reserves of fossil fuels. Energy crisis predicted since the mid-nineteenth century. One of the solutions proposed in those days, Lord Kelvin, does not lose relevance and today. Theoretical background "multiplier heat" flow from operations Carnot. These days, the unit for clean energy for heating said heat pump.
At its core, the heat pump does not differs from the refrigeration unit. It also carries heat from the body with a low temperature to a body with higher temperature. Refrigerator cools the food and the heat energy released into the environment. The main function of the heat pump is heating. It takes energy from the environment and gives her a room at a higher temperature level. The main advantage of the heat pump over other heating systems lies in the fact that for the production of 5 kW of heat energy it needs to be spent (mostly for driving the compressor) 1 1,5 kW of electrical energy. This does not contradict the law of conservation of energy, since the missing kilowatts of heat pump takes from the environment. Air at any temperature has a reserve of thermal energy. It needs to be cooled a few degrees to pick up this heat. Surface and ground water are more stable