What is geothermal energy?

What is geothermal energy? This is for a homework assignment.

Answer from Green Energy Efficient Homes

Geothermal energy literally means heat from the earth (geo=earth and thermal=heat). There are two main ways in which geothermal energy is used:

1. To generate electricity. In places where there is volcanic activity close to the surface, there may be naturally occurring steam caused by water flowing down through surface rock, encountering hot rock below, and boiling as a result. This steam can be captured and used to drive a turbine. If there is no naturally occurring water in the rock, water can be injected down a bored well to create the necessary steam. While a small amount of toxic gases may be mixed in with the steam that comes up, these toxins can be recaptured and re-injected into the ground so that they don't pose an environmental hazard.

2. To heat and cool buildings. For heating, you are using the heat of the ground to warm a building: a pump circulates a fluid through a loop of tubing underground, and a geothermal heat pump extracts heat from that fluid and uses it to heat a building. For cooling, you are using the fact that below- frost-line temperatures are fairly constant year round, and the fact that heat pumps can move heat from a cooler area to a hotter area, in order to extract heat from your home and pump it into the ground, again using the geothermal heat pump.

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