I wrote about a ‘simple’ device that provides pure water for villages of a thousand or so in developing nations. But, now, instead of converting humidity in the air for water uses on land, solar technology has been adapted- and expanded- to make it relevant and critical to America… for our farms.

The San Joaquin Valley is a big agricultural resource for our country. And, that is among the places hard hit by our current drought conditions. We’ve already heard that the Central Valley Project is not providing enough water this year. But, what I had not realized is that part of this area has billions of gallons of waters in aquifers below the surface. You know there’s a caveat, thought- it’s in terrible condition.

That subsurface water is replete with salt, selenium, and multitudes of heavy metals. Not the sort of thing that can be used for growing crops. It’s why many of the crops in the Panoche Water District are all highly salt-resistant varieties: almonds, tomatoes, cotton, wheat, asparagus, pistachios and alfalfa.

Now, a start up, WaterFX, may have a solution. A $1 million solution. They’ve just erected a 377 foot solar array. No, it is NOT being used for our electric grid. Instead, it’s powering a thermal desalination plant. This makes sense for in this location because there is plenty of available sunshine- and unused land.

Oh, I know you’ve heard about reverse osmosis (membrane technology) facilities producing pure water from brackish and polluted sources. But, that process needs lots of energy. And, it produces a fair amount of highly concentrated waste. There’s far less waste (and, it’s possible, but not highly economical, to leave only a salt residue) from thermal desalination plants- which means more water for use. This one is purifying the water at half the cost of conventional processes.

WaterFx employs a SkyFuel (Colorado) parabolic solar receiver designed for solar power plants. What makes this different is that the receiver has reflective films, rather than mirrors (more expensive), that beam the sun’s power onto mineral oil within tubes. The only proprietary equipment WaterFX provides as part of its system is the heat pump. Instead of using electricity to run the compressor, it employs the steam through a chemical process. This cuts the energy demand by about 1/2- a critical factor to the process’ success.

The solar reflector uses mineral oil  (which can be heated to higher temperatures than water), so no pressurized facilities would be needed.  (Water boils at 100 C  [212 F]), heating the water to higher temperatures would require higher pressures.). That keeps capital costs low.

This hot mineral oil (on the order of 120 C [248 F] is fed to evaporators that produce steam from the polluted ground waters- and steam is virtually pure water. (The cycle is repeated to further concentrate the brine, the fluid left after the [pure water as] steam escapes.)

The WaterFx pilot plant yielded some 14000 gallons of water daily. Impressive, but not very useful for farming.  So, now, they are putting the finishing touches on a full-scale 31 acre facility- to yield 2200 acre-feet of water annually.   (Sorry, folks, that’s how agriculture determines water needs and usage.)  An acre-foot of water is just what it sounds like- the amount it would take to cover an acre of land with a foot of water- about 325,000 gallons.

As you can see, this plant will yield 2 million gallons of water a day (MGD).  It will also produce water all day long, since the excess heat of the day will be stored in molten salt arrays.  The hot salt will heat the mineral oil when there is no solar irradiation.

Even so, the process is not cheap. Assuming the Central Valley Project is providing water, the water cost is $ 280 an acre-foot. This plant will produce the water for $ 450. But, if you have no water available, that’s a pretty cheap price.

And, right now, the Panoche Water District is providing no water to farmers, which is down (you think?) from last year’s 20% allocation and two year’s ago 40% levels. (This is not an isolated case- the California State Water Project just cut off 750,000 acres of farmland from water allocations. Look for your food prices to rise- rapidly!)

So, the WaterFX solution solves two problems- the water availability one, which is huge. The second benefit is the eradication of the growing salt contamination of agricultural land- which has been forcing farmers to let some 100,000 acres in the Valley lie fallow (as unusable). The old process of pumping the saltwater from the ground to the San Joaquin Valley is no longer acceptable, since it pollutes that body of water.

WaterFX is not the only company considering this solution. SunDrop Farms converts seawater to potable water for greenhouse crops in Australia.

My guess is if the economics and reliability prove out (as I expect), these two firms will be joined by many others.