Alternative Energy

Published on September 25th, 2009 | by Jennifer Lance


Solar’s Thirst for Water Concerns Desert Residents

In the move toward renewable energy, solar energy advocates in desert areas may be facing a “dirty detail”. Across the desert, large solar arrays are being planned, but residents are beginning to wonder just how much water these solar plants will require. Developers downplay the water usage as only needed to “to run the office bathrooms and wash the arrays of panels a couple of times a year”, but the Las Vegas Sun reports this may be misleading.

Photo by ken lundDesert solar arrays use precious water resources for cleaning panels.

Desert solar arrays use precious water resources for cleaning panels.

How often do solar panels need to be washed? This lazy off-grid homeowner rarely cleans her panels, but the loss from dust on photovoltaic (PV) panels can result in as much as a 3% decreased efficiency. The Las Vegas Sun explains:

Most photovoltaic arrays are cleaned with tap water sprayed with a hose or from a water truck. So solar array managers have to add in the cost of labor, truck rental and gasoline. In a water-starved desert, the additional consideration is how much of the region’s most critical natural resource will wind up evaporating or dripping into the desert.

Specific details for planned solar arrays and their water usage in the Nevada desert include:

The array planned for Primm, for example, is expected to annually require at least as much water as 10.5 average Las Vegas households. NexLight North and NexLight South, which have been combined in the first industrial-scale solar photovoltaic array planned the Bureau of Land Management land in Nevada, would need to truck in about 6.8 million gallons of water a year, developers reported in planning documents. That’s enough, they say, to clean the thousands of acres of solar panels about twice a year.

Do the cleaning needs of solar panels mean we should abort such projects? Probably not, but we need to consider the water requirements of desert arrays, where in the wettest month the average rainfall is only 0.69 inches. Mother Nature is not going to keep PV panels clean in these arid regions, and in fact precipitation may make the situation worse. Bob Boehm, director of UNLV’s Center for Energy Research, explains:

A really good rainstorm means you don’t need to worry about washing your panels for a while, but if you get this typical Las Vegas rainstorm with tons of wind and dust and forty-five drops of rain, that’s the worst kind of thing. It just plasters the dirt to the panel.

Nevada is not alone if facing the concerns of water demands from solar arrays. Arizona Water Resource asks:

One of the sunniest states in the country, Arizona is poised to become the North American capital of solar power. But does the semi-arid state have adequate water resources for large-scale solar energy production? Further, would producing solar energy largely for export out of state be a wise use of those water resources?

The answer is not clear, and it depends on where the solar array is to be located and what sort of production facility is being built. According to the Sierra Club, if the plant is to be located in an undisturbed desert area that requires pumping groundwater, than the answer is no. If the PV plant is replacing agricultural land that is already using large amounts of water, than a solar plant will conserve this precious resource. Case by case analysis must be conducted when selecting solar locations in desert areas.

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