It is customary to say that the least expensive energy is that which one does not consume, by isolating correctly his house. This is true, but it is also renewable energy that can be used to heat or produce electricity: solar energy and wind energy. Thus, the sun's rays can be used either to heat the sanitary water, or to participate in the heating of the house via solar thermal panels. The solar water heater is efficient, quiet, easy to install, simple to maintain. Photovoltaic power generation is very profitable. Photovoltaic panels provide free electricity that can now be self-consumed or reinjected into the network (or even stored). The domestic wind turbine can provide electricity on isolated sites or participate in the energy needs of the house. Finally, the heat pump can produce 3 to 4 times more energy than it consumes.
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