After a little more than eight months of operation, a pilot plant that uses solar energy to distill contaminated groundwater in the parched farmlands of California's Central Valley has performed so well that at least one expert is seeing a new gold rush on the way.
"We are actually sitting on a wealth of groundwater that just needs treatment," says Dennis Falaschi, manager of the Panoche Water District in the Central Valley. Panoche is host of the state-funded pilot project. "It is a really good treatment process. You are using natural solar energy to treat water."
"In that sense, it is liquid gold. You're converting an unlimited water resource from saltwater to fresh," agrees Aaron Mandell, founder and chairman of WaterFX, the company that built the plant.
Mandell says the demonstration system produces an acre-ft of distilled water for $450. The water is essentially distilled water and of a higher quality than needed for agricultural. It is of a higher cost, too, compared to the $280 per acre-ft that farmers pay now—when water is available. But it is close to the cost of treated water for municipal and industrial water supplies, says Falaschi; if it were to be scaled up to a large number of sites across the Central Valley or elsewhere, the solar stills would not add strain to the electric grid, as would a comparable expansion of reverse-osmosis plants.
WaterFX's Aqua4 solar thermal desalinization plant is built around off-the-shelf technology, including a mirrored parabolic-trough concentrating-solar-power collector made by SkyFuel, Arvada, Colo. The collector is 6 meters wide by 115 m long. Its surface is made of aluminum panels coated with a 4- millimeter-thick polymer mirror film that has a specular reflectance of 94%. There is no glass in the system.
The film, called ReflecTechPLUS, uses silver encased in multiple layers of polymer films, which protect it from ultraviolet radiation and moisture. It has a pressure-sensitive adhesive back with a peel-off release liner for fastening to smooth surfaces. The sheets of the trough are shipped flat and take their curved shape as they are slipped into the mounting frame.
The Aqua4 plant uses the trough to heat to 248ºF mineral oil in a tube suspended in the focus line of the mirror. The oil heats a 10-stage evaporation system that purifies 93% of the input water and then drives an absorption heat pump, created by WaterFX, to recover and reuse the low-grade steam. The remaining 7% of the input water goes into a crystallizing process to extract the remaining salts, chemicals and minerals.
Additionally, a molten-salt solar-heat storage system, backed up by a propane heater, ensures round-the-clock operation.
The process is very different from reverse-osmosis desalinization, which has a 50% recovery rate, adds Mandell. He claims his system achieves a 100% recovery rate, producing water and bags of salt. Beyond California, he sees potential use in many other parts of the nation and world. "It is very common to have saline groundwater in areas of water scarcity," he notes. "There is a correlation."
Plans now are being refined by WaterFX and its engineering partner, ATSI Inc., to build a 50-collector, 2,200-acre-ft-per-year plant in the same location and have it operational by the end of this year. Mandell hopes to spread the technology quickly by making some of it open source and by adopting a business model that encourages others to copy the system. "We see a bigger opportunity on the service application side. We're interested in being more like the SolarCity of water—a new type of utility."
Calif. Gov. Jerry Brown (D) "wants to spend billions of dollars on water tunnels, but it's never going to happen. … By the time you get it through the courts and the environmental reviews, we will all be gone," says Falaschi. "We have run tests on a system that is producing about 40 gallons per minute with excellent results. The treatment can pretty much produce distilled water, and if we wanted to sell the water, we could use the revenue to expand our treatment areas," he says.
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