Researchers at the University of California Advanced Solar Technologies Institute (UC Solar) at the University of California, Merced (US) have developed an external compound parabolic concentrator — or XCPC — that may be a solar-powered desalination solution in California’s ongoing drought and help provide usable water for farmlands.
The innovative solar technology, which will be presented at the 2015 UC Solar Research Symposium in San Francisco on 16 October, could help make water desalination cheaper, more accessible and cleaner.
A prevalent issue with using reclaimed irrigation water in an attempt to alleviate water shortage in California’s agriculture is the accumulation of salt. Irrigation water adds salt to the soil, and each time it is reused, it gets saltier. In fact, salinization is a growing problem worldwide, aggravated by the excessive use of fertilizers.
“Desalination produces usable water and a stream of waste brine to be disposed,” says UC Solar Director Roland Winston. In Central Valley, California, waste water disposal is restricted. The cleanest option is to evaporate the brine, which requires boiling temperatures. “Our XCPC boils water efficiently at low cost,” says Winston, adding that with the water content removed, the residue can be readily taken away and may have value, like providing selenium, which has semiconducting properties, and other minerals.
“Our external compound parabolic concentrator concentrates sunlight to produce high temperature, much higher than needed to boil water and to make steam,” the researcher describes his team’s innovation. “The concentrator is formed by non-imaging optics, which tracks the sun. There are no moving parts.”
UC Solar’s XCPC has a several advantages over previous desalination systems. “Other solar technology for high temperature requires tracking and more cost,” Winston says. What’s more, he further explains that tracking systems require bright, direct sunlight, while his concentrator can use “most of the sky” — from hazy to partly cloudy conditions, etc.
XCPC solar thermal arrays elsewhere in the world
Eventually, the XCPC could contribute not only to a solution in fighting California’s drought and resulting water shortage but also to the widespread use of solar energy around the world. “Being more efficient and more affordable, we have demonstrations in China, India and Mongolia,” Winston says, pointing out that the photos here show a traditional ger in the US embassy, Ulaanbaatar, Mongolia, with an XCPC solar thermal array.
The expert says the XCPC’s technology translates to applications other than desalination. “We are already working with a food laboratory in Albany, California, to process fruits and vegetables.”
The next step for Winston and his team in this research endeavor? “We participate in an exciting ARPA-E project to produce electricity and high temperature from sunlight at the same time.”