I. Overview of Geothermal Energy Geothermal energy (from the Greek words geo [earth] and therme [heat], thus 'earth heat' energy) is a domestic energy resource with cost, reliability, and environmental advantages over conventional energy sources. Energy from this source comes from the renewable source of heat from deep in the Earth (diagram: A). Heat is brought up to near the surface by thermal conduction (diagram: B) and magma. This heat heats ground water to form hydrothermal resources (naturally occurring hot water/steam in fissures [dia ....