<Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> <P> Geothermal heating is the direct use of geothermal energy for heating some applications . Humans have taken advantage of geothermal heat this way since the Paleolithic era . Approximately seventy countries made direct use of a total of 270 PJ of geothermal heating in 2004 . As of 2007, 28 GW of geothermal heating capacity is installed around the world, satisfying 0.07% of global primary energy consumption . Thermal efficiency is high since no energy conversion is needed, but capacity factors tend to be low (around 20%) since the heat is mostly needed in the winter . </P> <P> Geothermal energy originates from the heat retained within the Earth since the original formation of the planet, from radioactive decay of minerals, and from solar energy absorbed at the surface . Most high temperature geothermal heat is harvested in regions close to tectonic plate boundaries where volcanic activity rises close to the surface of the Earth . In these areas, ground and groundwater can be found with temperatures higher than the target temperature of the application . However, even cold ground contains heat, below 6 metres (20 ft) the undisturbed ground temperature is consistently at the Mean Annual Air Temperature and it may be extracted with a heat pump . </P> <Table> Top countries using the most geothermal heating in 2005 <Tr> <Th> Country </Th> <Th> Production PJ / yr </Th> <Th> Capacity GW </Th> <Th> Capacity Factor </Th> <Th> Dominant applications </Th> </Tr> <Tr> <Td> China </Td> <Td> 45.38 </Td> <Td> 3.69 </Td> <Td> 39% </Td> <Td> bathing </Td> </Tr> <Tr> <Td> Sweden </Td> <Td> 43.2 </Td> <Td> 4.2 </Td> <Td> 33% </Td> <Td> heat pumps </Td> </Tr> <Tr> <Td> USA </Td> <Td> 31.24 </Td> <Td> 7.82 </Td> <Td> 13% </Td> <Td> heat pumps </Td> </Tr> <Tr> <Td> Turkey </Td> <Td> 24.84 </Td> <Td> 1.5 </Td> <Td> 53% </Td> <Td> district heating </Td> </Tr> <Tr> <Td> Iceland </Td> <Td> 24.5 </Td> <Td> 1.84 </Td> <Td> 42% </Td> <Td> district heating </Td> </Tr> <Tr> <Td> Japan </Td> <Td> 10.3 </Td> <Td> 0.82 </Td> <Td> 40% </Td> <Td> bathing (onsens) </Td> </Tr> <Tr> <Td> Hungary </Td> <Td> 7.94 </Td> <Td> 0.69 </Td> <Td> 36% </Td> <Td> spas / greenhouses </Td> </Tr> <Tr> <Td> Italy </Td> <Td> 7.55 </Td> <Td> 0.61 </Td> <Td> 39% </Td> <Td> spas / space heating </Td> </Tr> <Tr> <Td> New Zealand </Td> <Td> 7.09 </Td> <Td> 0.31 </Td> <Td> 73% </Td> <Td> industrial uses </Td> </Tr> <Tr> <Td> 63 others </Td> <Td> 71 </Td> <Td> 6.8 </Td> <Td> </Td> <Td> </Td> </Tr> <Tr> <Th> Total </Th> <Th> 273 </Th> <Th> 28 </Th> <Th> 31% </Th> <Th> space heating </Th> </Tr> </Table>

Where does the heat from geothermal energy come from