Using Wind to Extract Fresh Water
Researchers at Texas Tech are teaming up with General Electric (GE) to try to optimize what is in theory an ideal marriage: using wind turbines to power water-desalination plants. That way, many water-deprived areas could ultimately obtain clean drinking water in a sustainable way. And wind-turbine farms could gain a place to use excess electricity on high-wind days.
It may sound straightforward, but it’s a tricky task: the water-desalination process envisioned for the project–known as reverse osmosis–operates best at stable, continuous rates. And that’s difficult to achieve when the electricity source is variable. The technology goal is a control unit that can keep the desalination plant running as stably as possible, store some power at certain times, sell some to the grid at peak times, and also pump water to and from the system as necessary.
Within several years, the Texas Tech researchers hope to erect a 1.5 megawatt turbine that will power a desalination plant capable of supplying water to the town of Seminole, TX, which has about 10,000 residents. A 1.5 megawatt wind turbine, generating full power and supplying electricity to a reverse-osmosis unit, could generate about 1,500 cubic meters of clean water per hour from brackish supplies. (Ocean water is saltier and would yield less fresh water.) GE hopes the project–one in a handful of similar R&D initiatives around the world–will yield a commercial product capable of meeting the demands of municipal water suppliers.
The project will get started in early 2007 with a scaled-down test model at Texas Tech that uses a very small, five kilowatt wind turbine.
Supplies of fresh water around Lubbock, a windy but dry area in west Texas, are running out fast. The vast Ogallala aquifer–which sits under eight Great Plains states–is being exhausted by farms, businesses, and homes far faster than it can be naturally replenished. “We are now looking at a potentially serious water problem in west Texas,” says Andy Swift, director of the wind-science engineering center at Texas Tech. “That aquifer is simply being drained faster than it recharges. It could be bled dry within 50 years.” Beneath the Ogallala aquifer, there is a brackish aquifer at depths of 1,000 to 2,000 feet that these states may have to tap.
In a reverse-osmosis system, brackish or salt water is pumped against one side of a special membrane. Fresh water passes slowly through the membrane, with the brinier water staying behind. A lot of electricity is required to pump the brackish or salt water into the system, maintain water pressure against the membranes, and, finally, pump the resulting fresh water to water towers to meet demand.
The key goal is keeping costs reasonable. “We do know you can bring [wind power and desalination] together, but can you bring down the cost of the system?” asks Minesh Shah, the project leader at GE Global Research, in Niskayuna, NY. “To be able to bring down capital, energy, and life-cycle costs, we need to be smarter in how we operate. It’s all about the energy-management system for these two integrated products. We look at it as energy sustainability and water sustainability.”
Any excess wind power could be sold to the power grid during peak times, when–in some regions–electricity fetches higher prices. “You would be making a real-time decision as to how the output of the wind turbine is going to be used: to deliver electricity to the grid, or to run the reverse-osmosis unit,” says Swift.
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