Geothermal energy is getting heat (thermal) from the ground (geo). Many people are familiar from heat being harvested from surface hot springs (Chena Hot Springs outside of Fairbanks uses direct hot water pools for tourism/baths- but also utilizing a system with various chemical fluids to create electricity). Yet heat from the ground can also be harvested sub surface. Hot reservoirs of pooled water along faults can be tapped and the water used directly, or the water can be drawn to turbines. Areas under the ground where there are hot dry rocks can be utilized. Even volcanic areas can yield heated fluids.
These types of extractions are fairly capital intensive and may be operated by state/nationally owned enterprises, or possibly private corporations (such as in the SW U.S. where major oil companies had divisions to extract heat). But for the local home owner or resident who does not have a surface spring of water bubbling up on their property, there are a couple ways to access heat from the ground.
Ground source heat pumps can be operated at a single home dwelling, or large industrial/commercial buildings. And there are a couple of ways. One is to dig a very large, wide trench to drop horizontal and flexible tubing and then bury it. Or to drop a well casing down and put a pump in. In these systems, hot water is not drawn up, but rather a fluid is circulated IN the piping….The key then- the next post’s subject- is how to transfer the heat from the ground!