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Sunday, June 28, 2009
Solar Plant Water Usage A Concern
By John Fleck
Copyright © 2009 Albuquerque Journal
Journal Staff Writer
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.
"It's beginning to be a big concern," said Sandia National Laboratories energy-water expert Mike Hightower.
With large-scale solar barely out of the starting gate in New Mexico, the issue hasn't drawn much attention here. But elsewhere in the west, especially in Nevada and California, solar plants have become caught up in water politics.
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 any conversation about a new source of energy, whether it is land converted to growing crops for biofuels, solar power or more conventional power plants, water needs to be part of the discussion, said Sandia's Hightower.
"In reality," Hightower said in an interview, "what the debate should be about is sustainability."
Solar energy's water consumption stems from the use of what is largely the same technology used in coal and nuclear power plants. Heat is used to boil water and drive a steam turbine. Water is used for cooling, and some evaporates in the process.
Thus, for example, the two big coal plants in northwestern New Mexico that provide much of our electricity consume nearly as much water as the entire city of Albuquerque's water consumption, according to data from the New Mexico Office of State Engineer.
The current technology of choice for solar power, large fields of mirrors that concentrate the sun's heat to drive a turbine, operate much the same way.
The first test of the issue here in New Mexico is happening near the New Mexico-Texas border, where a plant being developed by California startup eSolar for El Paso Electric will use a field of mirrors to shine the sun's light at a collector atop a central tower.
Caitlin Cieslik-Miskimen, a spokeswoman for eSolar, said the plant can be built with available water supplies in the area. Cieslik-Miskimen would not reveal water consumption numbers. A calculation by Hightower, based on publicly available data on the project, suggests its annual water consumption could be about the same as 2,000 to 3,000 typical households use in a year.
Meanwhile, New Mexico's second large-scale solar power plant, planned for the state's northeast corner, avoids the water problem by using a different technology. Tri-State Generation and Transmission Association is working with Arizona-based First Solar Inc. to build a power plant that uses photovoltaic panels.
Photovoltaic panels turn sunlight directly into electricity, requiring no cooling water. The tradeoff: They are more expensive than using mirrors to drive a turbine.
PNM, the utility that serves Albuquerque and much of the rest of New Mexico, is also looking at photovoltaic panels to meet its state-mandated solar power requirements, according to Greg Nelson, who heads the utility's renewable energy program. Low water consumption is also a marketing point for Stirling Energy Systems, a company working with Sandia National Laboratories scientists to develop a new type of solar power plant they hope to begin deploying across the West in coming years.
Wind power is also a winner in the water consumption derby, consuming essentially zero water, said Craig O'Hare, who tracks renewable energy projects for the state of New Mexico.
To the extent water consumption becomes a problem, power plant developers, whether using solar energy or traditional fuels, also have the option of shifting to a technology called "dry cooling" that uses far less water — an option also being used for conventionally fueled power plants in water-short regions.
The tradeoff is efficiency. Dry-cooled plants generate less electricity from a given amount of sunlight or fuel, driving up cost.
PNM, for example, used dry cooling to save water at its Afton natural gas plant in southern New Mexico. The plant is a hybrid that sometimes uses water and, when conditions are favorable, sometimes uses dry cooling, explained Michael Greene, who tracks water consumption for the utility.
These days, Greene said, water consumption is "one of the first things we talk about" when company officials discuss new energy sources.
Water problems also have played a major role in the debate over Desert Rock, a large coal-fired generating station on the Navajo Nation near Farmington. Faced with strong opposition, the plant's developers switched from water cooling to a partially dry-cooled design, said project spokesman Frank Maisano. With little water available in the area, what water they do need will be pumped from a deep, non-potable aquifer rather than using surface water, Maisano said.
With water a major issue for many sources of electricity, the issue should not be seen as a deal-killer for a solar boom in New Mexico, said solar advocate Jason Marks, a member of the state's Public Regulation Commission.
"It's a serious issue that needs to be looked at," Marks said in an interview. "I don't think it's an insurmountable barrier."
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