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The Vast, Maddening Promise of Enhanced Geothermal Systems

31 May
Diagram of EGS with numeric labels. 1:Reservoi...

Image via Wikipedia

Geothermal power is the red-headed stepchild of renewable energy.

Unlike wind, solar, and biofuels, it rarely makes headlines or stirs up controversy. Politicians and pundits never hail geothermal as the Next Big Thing and often fail to even mention it when speechifying on the importance (or, depending on their political slant, boondoggle) of green energy. The average citizen, meanwhile, doesn’t even know what geothermal energy is, beyond the suspicion that it has something to do with volcanoes and Old Faithful.

Here’s the thing about geothermal, though: it is, by far, the most promising renewable source for big time, base load, continuous (i.e. not intermittent, like wind and solar) energy. Dig down deep enough pretty much anywhere on earth and you’ll find dry rocks heated by the decay of radioactive minerals and by heat radiating from the earth’s molten core are ubiquitous. Tapping the vast, virtually endless amounts of heat stored in these rocks could (at least theoretically) help solve many, if not most, of our energy problems. In a report published by MIT, geologists and other scientists estimate that the United States alone contains 200,000 exajoules of recoverable geothermal energy–2000 times the amount of primary energy the country consumes annually.

How to harvest this bounteous resource?

The basic idea, known as enhanced geothermal systems (EGS) is simple: find a bunch of hot rock within drilling range, sink a couple of wells, pump water down at high pressure to open a network of fissures within the rock, then cold water through the fissures to absorb heat, send the water back up through the second well, transfer its heat to a liquid with a relatively low boiling point, and use the resulting steam to power electricity generating turbines.

So … what are we waiting for, you may ask. Dig the wells! Pump the water! Let’s start using the planet’s in-exhaustible store of heat to make clean, emission-free electricity!

Yes, let’s … but before we do, there’s just one thing to consider: after more than 30 years of enhanced geothermal research and development, beginning with the Fenton Hill project at Los Alamos National Lab in New Mexico in the mid ‘70s, scientists are still a little shaky on how best to make the elegantly simple idea of EGS work in the field. This isn’t to say that the technology doesn’t work; it does. Scientists know beyond a doubt that you can use subterranean hot rocks to produce net energy. But they don’t know how to make EGS work as efficiently as possible every time, everywhere. Because, as the MIT report documents in fine-grained detail, when you start messing around with hot, dense rock buried several thousand feet in the earth’s mantel, there’s no telling what might happen.

For example, engineering the a network of fissures and cracks is no cakewalk. Ideally, the fracture system channels the water toward the extraction well, up through which the now hot water returns to the surface to give up its valuable heat. But as researchers have learned over the past several decades, giant slabs of rock tend to have minds of their own when it comes to fracturing. Almost all large rocks have fused networks of cracks and fissures already in place; forcing pressurized water down to re-open the system often has unpredictable and unintended consequences, such as broadening the network so much that the water meant to absorb and return heart to the surface spreads out and seeps away.

Geothermal engineers have made progress since the ‘70s. Advances in drilling, fracturing techniques, and mapping and monitoring what’s happening deep underground have helped inch the technology forward. Small-scale commercial projects are operating in France and Germany, and dozens of other pilot projects are in the works around the world.

Still, EGS is a long way from realizing its huge potential. What needs to happen for EGS to take the next step, to scale up and become a true power player in the global energy game? I’ll tackle that question in my next post. Stay tuned.

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Unappetizing Geothermal Tidbit

5 Apr
Indians at dedication (LOC)

Image by The Library of Congress via Flickr

I’m researching a chapter on geothermal energy and came across this historical note about the history of The Geysers (the largest collection of geothermal power plants in the world, located in northern California):

Long before the region was developed as a power plant, its geothermal hot springs and bubbling mud pools were used by Native Americans as a source of healing. For example, The Wappo Indians “mixed sulphur salt  with the ashes of burnt stalks of cow parsnip and ate this with acorn bread, ‘presumably for medical purposes.’”  I love the ‘presumably’ part. I guess there’s a chance the Wappo just liked how this combination of ingredients tasted … but I doubt it.

Visiting The Geysers

26 Aug

I just returned from northern California, where I’d gone to tour The Geysers–an area two hours north of San Francisco that’s home to several geothermal power plants owned by the Calpine Corporation.  Unlike wind and solar, geothermal plants are largely invisible, hidden away in remote areas, much like coal power plants.  And, of course, the source of energy–geothermal steam–comes from underground, so there’s not much to actually see.

The power plants themselves, though, are fascinating.  Here are some pictures from my visit.

Here’s a geothermal well–pretty much just an insulated tube stuck into the ground up through which steam comes rushing.

The steam snakes through a series of pipes that runs throughout The Geysers.  These pipes condense steam from nearby wells and send it to one of the small power plants.

Inside the plant, the steam is used to run a turbine to generate electricity. It’s the same principle at work at a coal-fired power plant.  Except in a geothermal plant there are no CO2 emissions. An average plant at the Geysers makes about 75MW of electricity, which is sent to the local grid.

Once the steam has been used to spin the turbine, it’s condensed into water and sent here, where the water cools and is sent back to the wells to generate more steam.

Two guys who work at one of the plants. Most geothermal plants at The Geysers are “one-man plants,” meaning that there’s only only operator on hand at a time.  That speaks to the basic simplicity of how a geothermal plant works.

Gas mixed in with the steam is scrubbed before being either burned off or allowed to dissipate into the atmosphere.  This is sulfur harvested from geothermal gas.  The plant sells it as fertilizer material.

A Long view of one of the plants.

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