Geothermal Energy: Pros and Cons

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?

Pros

• Almost entirely emission free


• Zero carbon


• 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

Cons

• Prime sites are very location-specific


• Prime sites are often far from population centers


• Losses due to long distance transmission of electricity


• Water usage


• 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.

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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

[Image credit: Eyeline-imagery: Flickr Creative Commons]

RP Siegel, PE, is the President of Rain Mountain LLC. He is also the co-author of the eco-thriller Vapor Trails, the first in a series covering the human side of various sustainability issues including energy, food, and water in an exciting and entertaining format. Now available on Kindle.

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