California welcomed solar thermal technology on a grand scale last week at the Ivanpah plant in the Mojave Desert. It’s a project that’s all about producing clean electricity. But in the state’s agricultural heartland, a much smaller project is using the concentrated power of the sun for a different purpose, and in the long run it might be a more important development.
As highlighted by Todd Woody in the New York Times, water managers are turning to solar to transform saline-heavy drainage water into H2O that farmers can use again to grow crops. A historic drought in California has been national news this year, but drought or not, fresh water has long been one of the state’s biggest challenges.
A San Francisco company called WaterFX has devised the Aqua4 system that has been undergoing testing by the Panoche Water District in the Central Valley town of Firebaugh. The system’s 400-kilowatt solar collectors are a lot like what’s in use at the new Solana Generating Station in Arizona – parabolic troughs that track the sun, focusing energy on a receiver tube that runs the length of the trough. A mineral oil transfer fluid running through the tube carries heat to a distillation system – and to a unit that, as at Solana, uses molten salts to store heat. That means the system as the potential to run around the clock.
The company said in a January press release that in six months in operation, its 6,500 square-foot unit “produced up to 8 gallons per minute of pure water from saline discharge drainage.”
While WaterFX bills its system as being much cheaper than earlier desalination units that ran on conventional fuels and used reverse osmosis, the water is still expensive – $450 for an acre-foot (about 271,000 gallons) vs. the $280 an acre-foot that the Central Valley Project charges, the company told the Times. But this year the Panoche farmers won’t get any water deliveries, making that $450 price tag look a lot better – and, indeed, WaterFX said in January that the Firebaugh system will be expanded this year “to produce 2,200 acre-feet per year.”
To learn more about the Aqua4, here’s an excellent video produced by the company that gives an outline of the system, including a description of how the solids captured in the process can be put to use: