Solar Desalination Could be a Game Changer for California Farms

A solar desalination unit operating in California’s drought-stricken Central Valley uses parabolic mirrors to concentrate sunlight and distill freshwater from salty farm drainage. Photo courtesy of WaterFX.

Let’s be clear from the outset: I’m no fan of conventional desalination.

The idea of using climate-altering fossil fuels to drive an energy-intensive de-salting process that threatens coastal environments in order to produce drinking water that, in most cases, could be secured more cheaply through conservation and efficiency improvements, simply fails to pass the bar of economically sensible, environmentally sound solutions to our water problems.

But now desalination of a very different stripe is under way – not by the sea, but in California’s drought-stricken Central Valley farming region. The project is turning salty, contaminated agricultural drainage into fresh water that can be re-used to irrigate crops.

Powered not by fossil fuels, but by the sun, the technology has the potential to shift the way water is used and managed in parts of the west, where agriculture accounts for 70-80 percent of water use.

Developed by a San Francisco-based company called WaterFX, the solar desalination unit has been piloted in the Panoche Water District in Fresno County. Farmers in the area grow a wide variety of crops, including almonds, asparagus, tomatoes, pistachios, cotton, alfalfa and wheat.

The district is located on the valley’s west side, where farm drainage contains not only high levels of salt, but also selenium, a naturally occurring element that is essential in trace amounts but poisonous at high concentrations.

In the Central Valley and elsewhere in the western United States, irrigation has washed considerable quantities of salt, selenium and other contaminants out of the soil and into drainage water, which has polluted rivers and wetlands, and harmed birds and wildlife.

WaterFX’s “Aqua4” system offers a way of addressing both these critical contamination problems and mounting water shortages.

The technology uses parabolic mirrors to concentrate the sun’s energy, heating a tube that then distills fresh water out of the salty drainage. It’s an age-old process made far more efficient with modern technology. The system can produce 200 acre-feet (65 million gallons) of water per acre of solar collection area, making it, according to WaterFX, the most efficient solar desalination system available.

In addition to the solar collection, absorption and distillation equipment, the system includes a unit to store the solar thermal energy it produces, ensuring round-the-clock operation. It can also reclaim the metals and salts left behind from the distillation process.

During the drought, farmers in the Panoche and other Central Valley irrigation districts have faced cutbacks of 80 percent or more in their water deliveries from the dams and canals operated by the federal Bureau of Reclamation. The possibility of treating and reusing the water they do get to sustain more crop production has obvious appeal. And the districts are under the gun to further curtail the harmful pollution draining off their fields into the San Joaquin River.

The Panoche District has already made moves toward more sustainable production, including the institution of a tiered pricing schedule, where farmers pay more per acre-foot the more water they use. The majority of farms now use highly efficient irrigation systems, mostly drip and micro-sprinklers, to get more crop per drop.

With the ability to treat and reuse their water, farmers can stretch their limited supplies even further.  At a minimum, that could afford an effective hedge against drought.

The modular solar thermal technology converts previously unusable farm drainage into a new, local source of clean water. Photo courtesy of WaterFX.
The modular solar thermal technology converts previously unusable farm drainage into a new, local source of clean water. Photo courtesy of WaterFX.

But WaterFX has bigger plans.

“Our long term goal is to chart a new course towards water independence and reduce the need to import water from finite natural sources,” says Aaron Mandell, co-founder of WaterFX.

Success will depend, of course, on cost and scalability.

Aqua4 is both modular and moveable. A single module occupies 6,500 square feet and can treat 65,000 gallons per day. That basic formula – 10 gallons per square foot per day – is scalable to any size, says Mandell.

The Panoche District will continue piloting and assessing the solar desalination process over the coming years to determine if it is suitable for “scaling up,” district general manager Dennis Falaschi told the publication Ag Alert last month.

Meanwhile, WaterFX is actively moving to scale up. Through a project dubbed HydroRevolution, the company is organizing a community-based fundraising campaign to expand on its work with Panoche and build the Central Valley’s first commercial solar desalination plant.

The goal is to take drainage from 7,000 farm acres in Panoche and other neighboring districts and churn out 5,000 acre-feet (1.6 billion gallons) of clean water per year.

With an estimated 1 million acre-feet of irrigation drainage available for treatment and reuse in the Central Valley, it’s just possible that this new brand of desalination – solar-powered, decentralized and focused on water treatment and reuse – could give farmers and rural communities a sustainable new water source and open up new possibilities for keeping more flow in depleted rivers and streams.

Sandra Postel is director of the Global Water Policy Project, Freshwater Fellow of the National Geographic Society, and author of several books and numerous articles on global water issues.  She is co-creator of Change the Course, the national freshwater conservation and restoration campaign being piloted in the Colorado River Basin.

Sandra Postel is director of the Global Water Policy Project and author of Replenish: The Virtuous Cycle of Water and Prosperity. From 2009-2015, she served as Freshwater Fellow of the National Geographic Society. Sandra is also co-creator of Change the Course, the national water stewardship initiative awarded the 2017 US Water Prize for restoring billions of gallons of water to depleted rivers and wetlands. The recipient of several honorary degrees, she works to bridge science, policy, and practice to promote innovative ways of securing water to meet both human and ecosystem needs.
  • Joseph Rizzi

    For WaterFX if there was a pipeline from the salty Bay water or water from the sea to the inland valley the valley could Desalinate all the water they could get.

  • Sandra Firl

    Very interesting article and concept. My question is what happens to the pollutants taken out of the water? Are they useable in some way, or will they need to be stored somewhere for an indefinite length of time.

    Is Solar desalinization a viable process for human consumption? How much per acre ft will it cost to run?

    • Solar desalination is certainly viable and is a growing industry, but is more expensive and energy intensive. Conventional desalination is on the order of four times more expensive than the solar desalination process described in my article. Check out the WaterFX website for more information on the process. My understanding is that the salts and other constituents in the drainage water can be reclaimed and marketed.

  • Fuad Bateh

    Does Aqua4 have application for the desalination of sea water, as well as wastewater highlighted in your article. What would be the CAPEX and OPEX for the 6,500 square feet unit? And are there any economies of scales if the system was designed to 700,000 square feet which is the equivalent of space being utilized in the Gaza Strip for a designed 55 MCM SWRO desalination plant?

  • Fuad Bateh

    What are the CAPEX and OPEX for the 6,500 Square ft unit? Does Aqua4 have application for seawater desalination? Are there any economies of scale for building up to 700,000 square ft unit which is the design space for a 55 MCM SWRO desalination facility planned for the Gaza Strip?

    • Thank you for your questions. For more on the technical details, I suggest you contact WaterFX directly. There’s a contact page at their website where you can send a query. I link to their website in my post. All the best, Sandra

  • Hydrophylic

    This technology sounds promising. However, I’ve yet to see a detailed explanation on the disposal of the waste by-products. They say that the by-products “can” be sold. This is re-used ag runoff and likely has many toxic compounds in it, some natural, some not. Considering the volume of water that is claimed can be cleaned, that would mean a correspondingly large amount of by-product. If these by-products can’t be sold, then they very likely would have to be disposed of as hazardous waste.
    I think the public needs a better description and economic analysis of the by-product issue before they jump on this bandwagon.

  • Laschober Gerhard

    Gerhard Laschober
    Austria, email: gml@aon.at

    Innovativ obtaining drinking water from atmospheric humidity – favoured by CLIMATE CHANGE

    The objective is to find a way for hot, dry regions to tap into an almost endless source of water through capillary condensation of the humidity in the cooler layers of the atmosphere further away from the earth’s surface. The process we have developed will allow this vast resource to be tapped for drinking water as follows:
    A hybrid balloon, connected with the earth’s surface with a rope of variable length, would be filled with helium gas and equipped with a balloon chamber filled with hot air. This balloon would then be sent up to the higher, colder layers of the earth’s atmosphere with an attached three-chamber transport container of porous material suitable for capillary condensation. The balloon would be driven into the atmosphere by the hot air would be heated by the waste heat emanating from these porous material. Analogous to the heat emanating from the porous material, the ambient air will be blown into the already cooled porous material in the transport chambers. As the balloon continues to climb higher into the atmosphere, further ventilation will blow cooler air with higher relative humidity into the cooled porous material. This material would then capture the moisture through capillary condensation. After the porous material in the helium-filled balloon is saturated with moisture, it is brought back to the earth’s surface to the water recovery system. The water recovery system will regenerate the porous material by heating it up to more than 300°C by using parabolic mirrors to capture the sun’s rays. This heating will cause the moisture to be released in the form of steam where it will be passed through a water condenser system that condenses the steam and releases it as liquid. The porous material, now heated, but also free of moisture, is then used as described to heat the hot air to send the balloon into the air again. The balloons are sent up, the porous material absorbs the moisture, the balloon returns to the surface and the water is extracted is a process that would repeat constantly.
    Sending the porous material into the upper atmosphere and bringing it back again is inexpensive with the use of hot air and helium gas. The primary energy for the operation of the water extraction plant on the earth’s surface will be solar rays captured by parabolic mirrors. Solar rays captured by parabolic mirrors will heat the water condensation system with zeolite water cooling technology. This inexpensive, low-wear cooling technology is suitable for mass production as shown in the self-cooling liquid container.
    Settlement areas and industrial zones in warm, dry and sunny areas with water shortages would be the best places for this new form of obtaining drinking water. Drinking water harvest is possible by single balloon or several balloons in the balloon terminal.
    For more information, please write gml@aon.at.
    Gerhard Laschober

  • Justin Roberts

    It’s ironic that this article is about potential feasibility of solar desalination to alleviate CA’s drought problems, but doesn’t take the important step of linking CA’s drought to our country’s dependence on dirty energy, (which is a huge reason to take solar seriously). We urgently need to have a real, continued dialogue about the root cause of these sorts of problems.

    And more needs to be done than just switching to renewables. Recently saw sonme ideas posted at the bottom of this web pg, that outline ways folks get involved in addressing global warming from home. We need to all own this problem, we’re in it together… http://bit.ly/1huMEsO

  • Peter de Groot

    WaterFX is nailing a big problem with a fairly simple, proven water desalination technology based on the principle of condensation.
    For this location in California, it’s the best solution to turn brackish water into water suitable for irrigation. However different situations will need different approaches and technologies. Find an overview of such solar water desalination technologies here:
    Decentralized solar water desalination is now economical in many countries worldwide. Picking the right technology for each unique situation is the key for a successful desalination project.

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