The main source of this heat is generated from radioactive materials in the crust and mantle, as well as heat from when the earth was formed. At the upper one- to two hundred meters of the crust, solar energy is the main heating source. The resource is basically available everywhere. It is an energy source of the future because it is a renewable, and provides continuous power- and/or heat production regardless of sun, wind or rain. There is a distinction between shallow geothermal systems that extract the energy for heating and cooling through heat pumps, and deep geothermal systems for power generation or direct use of heat. In a sustainable system, the energy extracted from the earth will be restored by heat transfer from surrounding areas. That is why it is considered as a renewable energy source.
In 2010 the worlds geothermal systems produced 67 TWh electricity and 122 TWh heat. Geothermal heat pumps are one of the fastest growing renewable energy technologies. The scientific and technical solutions are at a point where the deep resource can be made commercially viable in areas with or without active hydrothermal resources. IPCC has estimated that the potential of production in 2050 will be 1255 TWh of electricity and 2184 TWh of heat. By developing this science and technology the potential for exploiting the recourses is nearly unlimited.