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 wisely about water issues, and so his concerns about the amount of water used for 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 the flat panels on a neighbor’s roof that are used to heat water. This photovoltaic 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 almost certainly passive solar heaters, not photovoltaic (PV). I have one of these systems on my roof. If it’s generating electricity I’d sure like to know where that power is going.

And as far as PV not being commercially feasible, Glennon might want to talk with some of the tens of thousands of homeowners and businesses in the US using grid-tied PV (we’re far behind Germany and Japan in this 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 he asks supporters of solar power to consider the amount of water needed to 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 plant consumes 500 gallons of water per MWh (gal/MWh) of electricity generated. 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 plant consumes about 200 gal/MWh. A water-cooled parabolic trough plant consumes about 800 gal/MWh.”

Water intensive parabolic troughs have dominated the CSP field. But many in the solar industry see an industry shift to power towers. And many existing natural gas plants are the simple-cycle variety that use more water. Companies still 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. As writer 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 be included, but as a part of the overall energy “footprint.” And the same goes for all sources of energy.

I’ll happily join Glennon and Barnett in demanding that water use be considered in regulating energy sources — as long as these new regulations aren’t limited to solar power. (Glennon gives a nod in this more 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’t produce — green house gases. Using natural gas as an energy source in the United States, on the other hand, emits 6.7 metric tons of methane annually according to a DOE study, making it the largest single contributor to human-caused methane emissions. (And because methane’s effect on global warming is 23 times greater than that of CO2, this is the equivalent of 154 tons of carbon dioxide.)

So, while I quibble over some parts of  his argument, I recognize that Glennon’s op-ed is an important reminder that this time we need to get 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 for far too long. What’s needed isn’t just a non-GHG emitting energy source. We need to change our attitude. We need to see energy, including solar, in a new, more thoughful light.

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3 thoughts on “Seeing solar in a different light

  1. Thank you for shining light on an under-reported issue. Not only do we not ask/understand/report true water demand for coal, nuclear, etc., we don’t yet understand it for biofuels. It is difficult for me as a journalist to report on the water/energy nexus without reliable water data for all energy sources. Bigger picture, we can’t make informed decisions about our energy future without good data on actual water demand and actual costs — both financial and ecological.

  2. Last year, the National Energy Technology Laboratory released a study pointing out that instituting carbon capture and sequestration would increase the water consumption of coal-fired power plants. Under one scenario in the study, adding carbon sequestration to new and existing plants would increase the electric power sector’s water consumption by nearly 50 percent. If, however, we are obtaining 20 percent of our electricity from wind by 2030, the electric power sector’s consumption would fall 17 percent.

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