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Sci Tech    H4'ed 12/19/14

Solar Desalination: Surviving Water's Coming Armageddon

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For thousands of years, billions have lived in areas requiring conversion of water or contaminated water to potable form, particularly in the arid Middle East. Sanskrit and Greek writings listed at least three methods of creating drinking water: exposing it to the sun (solar), filtering it through charcoal, sand, or clay (distillation), or by boiling [28]. Aristotle conducted a distillation experiment in 350 BCE [29].

As population quadrupled in the U.S. after World War II, so did outcries for converting foul water to fresh by water districts, municipalities, agriculture, and industry. By 1952 Congress passed the Saline Water Act. It offered $1,416,000,000 (today's value) for developing larger desalination installations [30]. Until recently, all have been dependent on membranes separating water from salt and other contaminants as fossil-fuel and nuclear-energy powers a process emitting clouds of carbon into the atmosphere, and high risks of nuclear storage [31].

Additionally, if discharge is "recaught" and reprocessed, equipment suffers further increases in fouling and corrosion [32]. Constant reprocessing affects water's taste and eventually makes it alkaline, as a National Geographic writer noted about Israel's non-stop recycling operations [33]. Water needs to rest.

Equipment is ruinously expensive and requires constant cleansing and replacements, as well as enormous installations to house it and, equally, enormous sources of nearby oceans, rivers, or lakes [32]. Costs are still so high that only Arab kingdoms, other wealthy nations, or companies can meet them.

For example, the San Diego County Water Authority faces paying $2,257 per acre-foot per year (average: $2,000) to a private desalination company (Poseidon Resources)--passing that sum--and operating overhead--to water bills of 1,300,000 customers [34]. That's because immense energy--1,000 pounds per square inch [4]--yields 1,000 gallons of freshwater at most fossil-fuel installations, but burns at least 14 kilowatt-hours of electricity [35].

Twenty years ago the average world price of fossil-fuel water was about $5 for 264 gallons (one cubic meter). True, U.S. prices in 2013 dropped to 29 for 264 gallons, but have provided only 1% of drinkable water globally [36].

Because some 300,000,000 people today rely on desalinated water, it explains why by 2013 more than 17,000 non-solar plants existed by 2013--not counting those accompanying every fossil-fuel fracking operation. A collective 21,120,000,000 gallons per day was produced for 150 water-short countries, including the U.S. Dozens more are on the drawing boards [33]. Even so, it won't be long before most nations, especially those inland, will be forced to let millions die of thirst or disease from polluted water as is happening to the Great Lakes from pesticide/synthetic fertilizer runoff [38].

UNESCO's desalination expert conceded improvements in membrane materials and energy-recovering devices, but admitted that the fossil-fuel process has plateaued [39].

Solar Desalination to the Rescue: Simple, Cheap, and Available

Yet all is hardly lost, thanks to the recent and spectacular rise of solar desalination systems around the world--coastal or inland--possibly because of the environment movement and recycling emphasis of the last 20 years. Sunshine covers the Earth freely. One signal of this booming market was the DuPont company quitting the membrane business in 2004 [40].

The sun's colossal heating power (thermal energy) is Earth's oldest energy source. From food preparation, it evolved in the 7th-century BCE to people using a crude magnifying glass to make fire and destroy ants. In 212 BCE, Greek mathematician Archimedes applied the same principle to bronze shields against Rome's armies and destroyed its fleet at Syracuse [41].

First attempts at direct solar desalination was explained in 1609 by Italy's Giambattista della Porta [42]. By 1816, Scotland's Robert Stirling added the sun's energy to industrial use for powering electrical engines. Twenty years later in France, Edmond Becquerel boosted that power by exposing electrodes in a selenium solution to sunlight. The photovoltaic cell was born [43].

Then came an 1880 silver strike near Las Salinas in northern Chile. It drew hundreds of prospectors to that desert area, including Charles Wilson, an American. Instead of digging for silver, he cashed in on thirsty miners with solar power to convert mines' saltpeter discharges into potable water. He leased 50,000 square feet and bought a few supplies on credit: a 5,000-gallon tank, wood to frame 64 "troughs," glass, and a windmill for power. At 1 per gallon, he earned what today would be $45,460 on a peak day. The still served thousands for 40 years until water was piped in [44, 45]. Its resemblance to today's solar panels is uncanny. As an historian described the 1882 operation--and the "Father of Solar Distillation":

"[The system] pumped brine from the ground using a windmill to fill long, shallow troughs. Wilson's plant had each trough permanently roofed with a low, A-frame made of glass panels. The vapor-laden air, much hotter than the outside atmosphere, condensed when it came in contact with the cooler glass. The glass clouded up. Droplets formed, coalesced and trickled down the sloping glass ceiling into collecting grooves that led to [the] freshwater storage tank" [45].

Solar desalination proved itself in the mid-1960s on four Greek islands, one producing eight to 33 gallons of potable water per day. It then took off. By 1985, California had 345 solar plants serving farms and towns [46].

Solar desalination's simplicity does not require much equipment nor huge installations or overhead, and has none of fossil-fuel's desalination drawbacks except for brine collection. Energy is free and pumps are driven by wind and/or photovoltaic energy. So overhead is minimal and production sufficient [47].

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Dr. Ellis is the principal of Ellis & Associates, LLC, a writers group in Portland OR, a nominee for a Pulitzer Prize in history in 2004 (The Moving Appeal), and a former journalism professor at Louisiana's McNeese State University and Oregon State (more...)
 
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