Thursday, February 20, 2014

Solar Thermal Desalination

Article Source & Photo Credit: The New York Times, 2.16.14

Renewable Energy Source: Solar Energy
Polluted near-surface groundwater sometimes found in agricultural areas apparently can be desalinated and purified to acceptable levels for various productive reuses. This article reports that some entrepreneurs are accomplishing this by using solar energy without the intermediate step of generating photovoltaic electricity.

WaterFX: a San Francisco area startup company.
The founders of this startup company seek to develop solar thermal desalination technology that is commercially viable and scalable for different applications. Working with a water district in the Central Valley, their efforts are funded by the State of California. The initial installation, a $1 million plant (solar array shown in photo above), " removing impurities... at half the cost of traditional desalinization, according to Aaron Mandell, a founder of WaterFX."

Off-the-Shelf Solar Array Unit and Equipment
"The parabolic-shaped [solar energy] receiver is a standard unit made by a Colorado company called SkyFuel for solar thermal power plants. It uses a reflective film rather than expensive mirrors to focus the sun on tubes containing mineral oil that are suspended over the solar array... As the oil warms to 248 degrees, the heat is piped into refurbished, 1960s-era evaporators to generate steam. The steam then condenses fresh water and separates the salts and heavy metals. The cycle is repeated to further concentrate the brine.

WaterFX relies on... a heat pump of its own design. The pump recycles excess steam for reuse through a chemical process rather relying on an electricity-driven compressor. 'It cuts the number of solar collectors you need roughly in half,' Mr. Mandell said...

[Also] WaterFX can purify water using half as much energy... [compared to traditional desalination.]"

Energy storage allows desalination 24 hour a day.
"During the pilot project, WaterFX produced 14,000 gallons of purified water a day... [A larger-scale] version of the plant, set to be built this year on 31 acres of land, will produce 2,200 acre-feet [of water] a year... The company will store excess heat generated by the solar array in molten salt to allow the plant to operate 24 hours a day... Mr. Mandell said WaterFX currently produces an acre-foot of water for $450."

Multi-Source Community Water Supply Systems
"The desalinated water [from WaterFX] is of bottled-water quality, purer than what is needed for irrigation... Michael Hanemann, a professor of agricultural and resource economics at the University of California, Berkeley, called desalinization a hedge against future shortages and the rising price of water. 'It’s a form of insurance,' he said. 'The issue isn’t turning over your whole water supply to desalinization but adding to it.'"

Solar Thermal vs. Reverse Osmosis Desalination
"Professor Hanemann... noted that traditional desalinization plants carried high capital costs as they were often built as backup sources of water and operated infrequently. A solar thermal desalinization plant that runs continuously and relies on free sunlight for fuel could make the technology more competitive, he said.

Standard desalinization plants rely on membranes to filter out salt and other impurities from seawater. The process, called reverse osmosis, is expensive. Membranes must be periodically replaced, and forcing seawater through them is energy-intensive, with electricity typically accounting for around a third of operating costs...

Brent Giles, a senior analyst at Lux Research, said solar thermal desalinization’s competitiveness with reverse osmosis remained to be seen. He noted that contaminated water like that found in the Central Valley contained far less salt than seawater and required less energy to purify."

Process By-Products: recycle & reuse -- & proper disposal
The recycled water, in various levels of purity, from essentially wastewater is clearly a reuse that is a valuable and marketable product. It's not clear from this report if the other by-product elements removed or created by this recycling process are good for productive reuse -- or simply waste. Is there currently an expense amount, per acre-foot of recycled water, for toxic waste disposal?

DO MORE with less...
Can't we just USE LESS? Of course we can do what might be called 'water conservation measures' -- and we should conserve our precious water! Nonetheless, I'm concerned that in the case of consecutive annual droughts, that alone may not be enough


On Topic:
"Solar Desalination Gives California Water District More Freshwater," WSJ, 2.18.14


GIVE ME A MOMENT a lifestyle
Subscribe FREE (see: upper right column) for new posts. Reader-referred topics are welcomed and considered. Comments here are disabled. Readers may contact the blogger by email:

Post No. 203

Apologies for any unwelcome and distracting Google audio clip advertising that might pop up here