What We've Learned About Geothermal Energy

Geothermal energy, basically directly accessing the Earth's inner furnace, offers the promise of clean, universally available energy. The potential to cut emissions and wean us from fossil fuels is tremendous. On the other hand, we've learned a lot about geothermal energy in the last few years, not all of it attractive.

The old way of harvesting geothermal energy was tapping into a porous layer of earth, like sandstone, that was underlain by a hot granitic type of bedrock. The sandstone acted as a sort of sponge, holding the hot water as it heated and keeping it available for use. It was also easy to drill into.

But layers of sandstone sitting atop layers of granite don't happen everywhere. So traditional geothermal drilling is kind of a niche energy source.

A new approach involves drilling directly into the lower, hotter granitic rock that you can find pretty much everywhere around the world if you drill down far enough. The more accessible formations are in areas that are tectonically active, around volcanoes and fault zones. But they offered the promise of universality if we could get the techniques worked out.

Since granite is not known for its porosity, water is not present in these formations, Neither are the pathways for the water to get heated. The solution was to drill down to the granite, and then create a fracture. Using a camera, they can determine which direction the fracture propagated, and then drill another hole to meet the other end of it. If you pump cold water down one hole, you could receive hot water (or more likely steam) out of the other. But it didn't turn out that cleanly.

Fracturing rock at this depth and scale, it turns out, allowed other formations to shift in the area. This caused earthquakes. A few years ago, geothermal drilling outside Basel, Switzerland, set off a magnitude 3.4 earthquake. Smaller quakes continued for months after the project was stopped. The environmental review for a demonstration project in California stated that minor earthquakes would result, but no significant damage would occur. We will never know since that project was abandoned last year after the drilling contractor repeatedly broke bits in attempting to drill into the granite.

So the bloom is off the rose. Does that mean we should not pursue geothermal energy? Not so much. Consider the problems presented by our continued dependence on fossil fuels, the unresolved issue of nuclear waste, the destructiveness of hydropower dams. The fact is that ALL forms of energy have drawbacks. The goal is not to find the panacea, the goal is to find energy with the least impacts.

The message we are getting from the geothermal world is that geothermal energy is a bit harder and more expensive than expected, and that better safeguards - like restricting drilling to non-tectonically active areas until the technology is better understood - need to be put in place.

And on a broader scale the message is - as if we need to hear it again - that reducing our energy demand through energy efficiency is the best route to curbing climate change, remaining globally competitive, and building a sustainable society. The cheapest kilowatt-hour remains the one you don't buy.

Paul Birkeland lives in Seattle, WA, US, and develops Strategic Energy Management Systems for government, commercial, and industrial organizations through Integrated Renewable Energy.