Geothermal heating. Greenhouses being heated by geothermal energy. Hot water from below the ground is piped into the greenhouses, which are used for growing tomatoes. Steam is rising from the warm waters. This is at Fludir, Iceland. Iceland lies on the boundary between two tectonic plates (on which the continents are carried), and as such is very geologically active. Geothermal energy is non-polluting and inexhaustible, making it an environmentally friendly source of energy.