The core of the Earth, some 4,000 miles beneath its surface, is a fiery morass of superheated gas and molten rock which exists at roughly 7200 degrees Fahrenheit. That temperature is maintained by the decay of radioactive particles located within the Earth’s core. Technically, one could say that geothermal power is a form of nuclear power, though with far different implications from nuclear power as we know it, since these reactions occur in a containment vessel with walls thousands of miles thick. Even so, we still get things like uranium and radon gas, seeping up to the surface.
Moving away from the core, the temperature cools down to the point where it might be 1500 degrees, fifty miles down and 3-400 degrees, three to four miles below the surface. Since the Earth is not at all uniform, these results will vary. There will be some places where the crust is thinner than others, which means the hotter temperatures will be closer to the surface. Hot springs, geysers and, of course, volcanoes can often be found in these places. The Earth’s crust varies from roughly 20 to 40 miles thick as measured from the surface. (It is thinner beneath the sea.)
The amount of thermal energy contained in the Earth’s crust is enormous. Experts estimate it at an equivalent of 79 million billion barrels of oil, or roughly 15,000 times more than estimated worldwide oil reserves. And unlike oil, much of that heat is continually replenished. The hydrothermal resource base (found in hot springs, etc.) has been estimated at 100,000 MW or more.
Geothermal resources vary from location to location, but as new technologies emerge that are capable of utilizing lower temperatures, geothermal power will become more widespread. Iceland, already generates more than 25 percent of its energy from geothermal.
A major new project was recently announced in Kenya.
So how do you produce electricity from this abundant source? It actually almost as simple as drilling a hole in the ground, sending water down, having steam come up and running that steam through a turbine. There are of course many nuances. You can see a nice presentation here.
Geothermal power, like solar thermal power, can also be harnessed for low intensity heat at shallower depths, which can be used for space and water heating and cooling.
So what are some of the pros and cons?
Almost entirely emission free
The process can scrub out sulfur that might have otherwise been released
No fuel required (no mining or transportation)
Not subject to the same fluctuations as solar or wind
Smallest land footprint of any major power source
Virtually limitless supply
Inherently simple and reliable
Can provide base load or peak power
Already cost competitive in some areas
Could be built underground
Some level of geothermal energy available most places
New technologies show promise to utilize lower temperatures
Prime sites are very location-specific
Prime sites are often far from population centers
Losses due to long distance transmission of electricity
Sulfur dioxide and silica emissions
High construction costs
Drilling into heated rock is very difficult
Minimum temperature of 350F+ generally required
Care must be taken to manage heat and not overuse it
All in all, this is a very positive balance. There is certainly a lot of potential here and one would expect to see a growing number of systems emerging around the world in places where the resource is abundant.
What about other energy sources?
Pros and Cons of Wind Power
Pros and Cons of Fusion Power
Pros and Cons of Tar sands oil
Pros and Cons of Solar Heating and Cooling
Pros and Cons of Concentrating Solar Power
Pros and Cons of Solar photovoltaics
Pros and Cons of Natural Gas
Pros and Cons of Fuel Cell Energy
Pros and Cons of Biomass Energy
Pros and Cons of Combined Heat and Power
Pros and Cons of Clean Coal
Pros and Cons of Algae Based Biofuel
Pros and Cons of Liquid Flouride Thorium Power
Pros and Cons of Tidal Power
Pros and Cons of Nuclear Energy