Seeing Solar In A Different Light

Is Solar Power Dead in the Water?

That’s the reductionist headline for a more nuanced op-ed published recently in the WaPo by Robert Glennon.

Glennon is a professor of law and public policy at the University of Arizona and the author of an excellent new book,  Unquenchable: America’s Water Crisis and What to Do About It. He writes widely and wiselyabout water issues, and so his concerns about the amount of water usedfor Concentrated Solar Power (CSP) deserve serious consideration.

Early on in the piece, Glennon seems a bit confused about solar technology.

“Most people think of solar power as theflat panels on a neighbor’s roof that are used to heat water. Thisphotovoltaic system directly converts the sun’s waves into electricity.But so far, it’s not commercially feasible.”

If they’re flat panels on the roof heating water, they’re almostcertainly passive solar heaters, not photovoltaic (PV). I have one ofthese systems on my roof. If it’s generating electricity I’d sure liketo know where that power is going.

And as far as PV not being commercially feasible, Glennon might wantto talk with some of the tens of thousands of homeowners and businessesin the US using grid-tied PV (we’re far behind Germany and Japan inthis regard) with a total capacity of over a gigawatt of electricity —enough to power approximately 750,000 homes.

Beyond these missteps, however, Glennon is right on the mark when heasks supporters of solar power to consider the amount of water neededto produce electricity by CSP.

Glennon’s op-ed is a reminder that, this time, we need to get it right.

IMHO, Glennon paints a slightly worse picture of CSP than it deserves. For example, he writes:

“…CSP uses four times as much water as a natural gas plant and twice as much as a coal or nuclear plant.”

If you read the government study he cites, however, CSP’s water usage is not quite so bad. According to the study:

“A typical coal plant or nuclear plantconsumes 500 gallons of water per MWh (gal/MWh) of electricitygenerated. This is similar to the water consumption by a power tower.”

A power tower, pictured below, is a kind of CSP that uses mirrors to concentrate sunlight onto a single point.

Power Tower

Power Tower

The study continues:

“A combined-cycle natural gas plantconsumes about 200 gal/MWh. A water-cooled parabolic trough plantconsumes about 800 gal/MWh.”

Water intensive parabolic troughs have dominated the CSP field. But many in the solar industrysee an industry shift to power towers. And many existing natural gasplants are the simple-cycle variety that use more water. Companiesstill build them and plan for more.

So, yes, when generating electricity, the most water-intensive CSP plants use more water than the do the least water-intensive natural gas plants.

But this doesn’t include the water used in extracting natural gas; millions of gallons of water are required to get a single well producing gas.

Glennon focuses on water in his piece, and for good reason. Aswriter and author Cynthia Barnett observes in her wonderful book, Mirage: Florida and the Vanishing Water of the Eastern US,water is too often left out of environmental equations. Water should beincluded, but as a part of the overall energy “footprint.” And the samegoes for all sources of energy.

I’ll happily join Glennon and Barnett in demanding that water use beconsidered in regulating energy sources — as long as these newregulations aren’t limited to solar power. (Glennon gives a nod in thismore inclusive direction near the end of his essay.)

It’s also worth remembering that solar power is enjoying a renaissance at the moment because of what it doesn’tproduce — green house gases. Using natural gas as an energy source inthe United States, on the other hand, emits 6.7 metric tons of methaneannually according to a DOE study,making it the largest single contributor to human-caused methaneemissions. (And because methane’s effect on global warming is 23 timesgreater than that of CO2, this is the equivalent of 154 tons of carbondioxide.)

So, while I quibble over some parts of  his argument, I recognizethat Glennon’s op-ed is an important reminder that this time we need toget it right; we need to use solar power mindfully. We need to ask questions of solar that we failed to ask about coal, nuclear, petroleum and gas.

Glennon points to an obvious truth that has somehow eluded us forfar too long. What’s needed isn’t just a non-GHG emitting energysource. We need to change our attitude. We need to see energy,including solar, in a new, more thoughful light.



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