What a difference a month makes. Back in June, the California Farm Bureau Federation reported that local officials were still a bit iffy over the prospects for scaling up a relatively small, demonstration-scale solar desalination plant for the water-starved San Joaquin Valley. We have no idea what changed their minds, but just last week the desalination plant’s developer, WaterFX, announced plans for bouncing the project up to a commercial-scale facility capable of producing 1.6 billion gallons of fresh water per year.
Solar Desalination: That Was Then…
Commercial solar desalination could make a huge difference in California’s ability to maintain a viable agriculture sector under drought conditions. Conventional desalination involves huge amounts of energy, and solar energy provides a low-cost, sustainable way to reclaim otherwise unusable water.
In 2014, we took note when WaterFX cranked up its HydroRevolution solar desalination demonstration facility. The project, built for the Panoche Water and Drainage District, actually kills two birds with one stone. In addition to solar desalination, it involves a cost-effective system for reclaiming the huge quantities of salt generated by conventional desalination systems.
Fast forward to June 2015, and we find a mention of the plant in the Ag Alert, the weekly bulletin of the aforementioned California Farm Bureau Federation.
As described by Ag Alert assistant editor Kate Campbell, the solar desalination demonstration has its roots in an agreement by the region’s agriculture industry to reduce the discharge of salts and other pollutants, which seep through a complex tile drainage system into the San Joaquin River.
With the state of California in an ongoing drought, the water reclamation aspect of the project has given it new urgency.
In her article dated June 24, Campbell cites an official from Panoche, who seems to be pretty convinced that the WaterFX project, among others, will remain in the pilot phase for the next few years.
…This Is Now
So much for continuing the pilot phase for several years. Barely three weeks later, in a press release dated July 15, WaterFX announced that the solar desalination facility would make the jump from pilot to full commercialization, and the Panoche Drainage District had this to say:
Given the trend of highly uncertain inputs from the Delta, we need to develop a reliable supply of water in the Central Valley. This is a sustainable solution that can provide a substantial amount of additional water. After seeing the results from the demonstration plant by WaterFX™, we’re eager to get the HydroRevolutionSM plant online quickly and optimistic about seeing others replicate what we’re doing here…
Including its solar collectors, the expanded plant will be built on a 35-acre site, with the potential to scale up to 70 acres. WaterFX notes that the footprint compares favorably to the region’s conventional irrigation drainage management system, which encompasses about 6,000 acres.
How It Works
In conventional desalination systems, salty brine is forced through a membrane at high pressure, which accounts for the high energy use. In contrast, the WaterFX solar desalination system works on evaporation. It’s the same basic principle behind open-air lagoons, but the WaterFX process is much faster and integrates a system for capturing the evaporated water rather than letting it drift into the atmosphere.
The secret sauce is a modular unit that WaterFX calls Aqua4, which acts like an “engineered aquifer.”
WaterFX claims that the Aqua4 combination of solar energy and advanced absorption, enables it to evaporate and distill water 30 times more efficiently than natural evaporation.
Aqua4 is composed of off-the-shelf components, including a 400-kilowatt trough-shaped solar collector, which is used to heat mineral oil. The oil is then piped to a heat pump to ramp up efficiency, and the heat goes on to operate the distiller.
With an integrated thermal energy storage system, Aqua4 can operate continuously, whether or not the sun is shining.
As for the problem of brine disposal, the efficiency of the system enables it to produce relatively small quantities of highly concentrated brine, which is a much more efficient platform for resource recovery than large quantities of diluted brine.
WaterFX expects that gypsum, calcium compounds, magnesium salts, selenium, nitrates, and boron are among the recoverable substances from reclaimed brine.
Onwards & Upwards For Solar Desalination
Aside from recovering drainage water from agricultural sites, California is also eyeballing the vast potential of solar-powered seawater recovery. The state’s Carlsbad solar-enabled desalination plant, now under construction, will be the largest of its kind in the western hemisphere.
For the record, Saudi Arabia is building the largest solar desalination plant in the world, including a special filtering component to address the jellyfish issue.
An emerging technology I’m keeping an eye on is a fuel cell–based desalination system that partly offsets its energy consumption by generating electricity from wastewater.
Another interesting solar desalination project is Sahara Forest, which aims to use solar energy as part of an integrated desalination system for inland desert agriculture.
Image: HydroRevolution system, via WaterFX.
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