Does solar energy have a water problem? That’s the question I tried to address in this story (sub. req. sorta) over at the day job:
Look at any map of U.S. solar energy resources, and you will see a band stretching from southern New Mexico across Arizona and into California that shows promise.
Solar energy advocates see a strip of clean, green power growing up in the region.
But if you think closely about what the map is saying, as Arizona water expert Chris Brooks points out, you will see something else. The potential for a solar bonanza is happening in the driest part of the nation. And solar energy, in its most cost-effective form, uses water.
“You need to put it someplace where the sun shines, and a lot of those places tend to be dry.” said Brooks, a Tucson hydrologist and lawyer who writes the Watering the Desert blog.
But it turns out not to be as interesting a problem as I think it has been made out to be, for a couple of reasons:
Experts note there is nothing special about this particular version of the energy-water debate. Many other sources of electricity, especially coal and nuclear power, use large quantities of water for power plant cooling, just as the new solar plants do.
In New Mexico, in fact, the biggest water hog on the new energy horizon is a big new coal plant proposed for northwestern New Mexico. Meanwhile, solar advocates point to alternative types of sun-fueled power plants they say can produce electricity while cutting back on the amount of water consumed.
In other words, there’s nothing terribly special about solar energy. It’s just teh one we’re currently talking the most about. And the tradeoffs are relatively straightforward. You can use less water, it just reduces your plant’s efficiency, essentially making it more expensive per kilowatt hour of power.
I think that analysis leaves one or two things out, though you may have addressed them in your piece at the other site.
One is that many of the proposed solar projects are slotted for locations where there’s no existing power plant to retire, such as the Amargosa Valley proposal.
The other is that at least in the Mojave, the water isn’t used as much for cooling as for mirror washing. It may be that engineers can come up with clever designs for self-dusting mirrors, but there are certain times of the year when that dust and ambient moisture (which does in fact exist in the Mojave) combine to form a rather opaque mud on exposed surfaces. A layer of that would cut efficiency of a concentrating solar plant a bit more than most operators would be comfortable with.
Of course, if you buy out a desert alfalfa farmer and put concentrating solar on her quarter-section, the plant would have a net negative water consumption. And as you say, people are indeed working on CSP designs that would use less water.
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