As everyone knows, California is enduring its worst drought in its history as a state. Gov. Brown has ordered residences and business to cut water use by 25 percent. So why are farmers in California’s Central Valley paying to get rid of hundreds of billions of gallons of water a year? It turns out that there’s sufficient water in the state’s Central Valley. The problem is, because of the high mineral content of the soil, the water runoff is much too salty, and that salinity harms both farmland and the ecosystem as a whole.
But early next year, construction will begin on a desalination plant in Fresno County, powered completed by solar thermal technology, which will create enough freshwater from Central Valley water to irrigate 2000 acres of farmland. WaterFX, a company founded by Aaron Mandell, has developed a concentrated solar still (CSS) system it calls Aqua4. The basic technology of stills has been around for centuries. But the proposed still in Fresno County will allegedly be thirty times more efficient than normal evaporation techniques, and it will be the largest renewable-powered desalination plant in the U.S.
The plant – which will utilize only local water, sparing the cost of transporting it via aqueducts from elsewhere – will have five purposes:
- To purify the local water into fresh water;
- To preserve the minerals (e.g., gypsum, selenium, boron) filtered out of the water, so they can be repurposed as usable products (e.g., sheetrock, semiconductors);
- To eliminate fossil fuel use in the desalination process;
- To save costs, as Mandell estimates that Aqua4 only costs one-fourth as much as the usual (reverse osmosis) method of desalination;
- To avoid the brine-filled runoff common to other desalination methods, which is environmentally harmful.
The technology of the Aqua4 array involves a solar “collector,” a large curved surface of coated aluminum that acts as a mirror. The collector focuses the sun’s rays on a pipe that carries the water and turns it into steam. The steam is captured, cooled, then condensed, purifying the water and leaving the minerals as residue. The heat that the system generates can then be stored to help run the plant.
A successful pilot project was carried out in the Panoche Water District, close to the Fresno County border. When the actual commercial project is completed in Fresno County, it will have a 24 MW field of solar collectors, enough to generate an estimated 5 million gallons of purified water per day. And since the technology is modular, it is completely scalable. Mandell predicts that small farms might someday have their own solar desalination mini-plants, based on this technology.
“This is going to be a much more sustainable approach to farming in water scarce regions like California,” Mandell was quoted as saying. “And this is a model that can be replicated around the world.”
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