Geothermal energy has until recently had a
considerable economic potential only in areas where
thermal water or steam is found concentrated at depths
less than 3 km in restricted volumes, analogous to oil
in commercial oil reservoirs. This has changed in the
last two decades with the development of power
plants that can economically utilise lower temperature
resources (around 100°C) and the emergence of
ground source heat pumps using the earth as a heat
source for heating or as a heat sink for cooling,
depending on the season. This has made it possible for
all countries to use the heat of the earth for heating
and/or cooling, as appropriate. It should be stressed
that heat pumps can be used basically everywhere.