Why is geothermal energy considered a renewable resource?
The heat of the Earth self-replenishes and so is considered renewable.
Geothermal energy refers to energy that is captured from the Earth's crust ( geo referring to Earth and thermal referring to heat). This can be done a few ways:
- the ground, for the first 10 feet or so, is a near constant temperature of 10 C - 16 C degrees. This can be used to cool and heat buildings by using a heat pump,
- hot water from hot springs can be used for heating buildings or heating water,
- steam from hot springs can spin turbines, making electricity
A renewable resource is:
- something of economic value
- that can be replaced or replenished
(the link below also adds that the replacement period must be equal to or less than the time it took to harvest the resource in the first place. I don't know that I agree with that aspect of their definition - it takes years to replace a forest that can be harvested in the course of days.)
Some resources have an endless supply and don't require effort to be replenished (and thus referred to as "self-replenishing", such as solar energy) while others require effort to replenish (such as planting trees to regrow a forest that had been harvested for wood).
Because there is an infinite supply of heat from the Earth and it requires no effort to replenish, it is , it is considered self-replenishing, and therefore renewable.