Everyone knows that Minnesota is the Land of 10,000 Lakes. Soon, some of the smaller ones could be used to generate electricity by storing wind-generated energy for use during periods of high power demand.
According to a study released Friday by the University of Minnesota Duluth's Natural Resources Research Institute (NRRI), ponds in Minnesota's Iron Range that were created from water-filled pit mines could be used to harness wind energy and better integrate it into Minnesota's power grid.
Using a pumped-hydro storage process, excess late-night wind energy would be used to pump water uphill from the water-filled pits to a higher-elevation holding pond. Then, during periods of high power demand, the process would be reversed; water would be released back into the pond it came from, thus generating energy by turning hydro turbines as it flows downhill.
For every 100 megawatts used to pump the water upward, this process could generate nearly 80 megawatts through the hydro turbines, according to the U of M. To put those numbers in context, one megawatt of wind energy generates enough power for 225 to 300 households to use in a year.
Minnesota utilities have invested heavily in wind power, a variable-energy resource whose output doesn't always match customer energy requirements. Pumped-hydro storage would allow utilities to stockpile excess power when it is not needed by customers and then return it to the power grid when there's high demand.
The state has good reason to look for ways to boost its wind energy production: Minnesota's Renewable Energy Standard requires that electric utilities supply 12 percent of energy for Minnesota consumers from renewable sources by 2012, 20 percent by 2020, and 25 percent by 2025. Minneapolis-based Xcel Energy, Inc., the state's largest utility, must derive 30 percent of its sales from renewable energy by 2020.
The researchers who conducted the study are optimistic about using a pumped-hydro storage process in Minnesota.
"The altered landscape of the Iron Range makes it ideal for this purpose," Don Fosnacht, NRRI director and the study's lead investigator, said in a statement. "There are over 100 mining pits, and those near ridges or cliffs would provide the necessary water reservoir prospects to allow the concept to be practically implemented."