Maybe it's time for Maine to change its license-plate slogan (currently "Vacationland") to something more energetic and 21st century, like... "Humongous-Battery Land." A Canadian startup has announced its intention to build what's essentially a giant battery where the decommissioned Maine Yankee nuclear power plant used to be.

Their plan, which has some impressive backing, is to blast giant caverns out of the bedrock 600 meters below and then, during times of peak electricity demand, divert water from the Black River into the caverns, which would power electric turbines on the way down. When demand is low, meanwhile, excess electricity would be used to operate the turbines in reverse, pumping water back out of the caverns. Because the power generated at a hydroelectric plant is proportional to the height the water travels, and because the Maine project would be twice the height of the tallest hydroelectric dam in the world, this underground hydro plant could generate a huge amount of electricity. It would have a capacity of 1000 megawatts, and could run at full bore for six to eight hours before its storage caverns were full.

Utilities already need—and pay a premium for—on-demand "peaking power," but they're going to need a lot more of it if intermittent power sources like wind and solar are going to become a bigger part of their electricity portfolios. Right now a lot of that peaking power comes from natural-gas turbines, which are less carbon-intensive than coal power plants, but hardly the clean energy source that the natural gas industry makes them out to be. It would be much better to store electricity from wind or solar during times when supply exceeds demand and put that electricity back into the grid when supply is tight.

There are a lot of novel ideas for ways to store large amounts of energy from the electric grid—as kinetic energy in flywheels, in compressed air in underground caverns, or even in large banks of batteries. But pumping water back uphill at hydroelectric plants is something that's relatively cheap and that's been done for a number of years on a commercial scale. The problem is that it's only possible at a limited number of sites—places where it's possible to build two reservoirs right next to each other. Creating a short-term reservoir deep underground is one way to get around this problem. It's the sort of massive undertaking that could go horribly wrong, but if it went right—and if it could be replicated—it'd be a big step towards a renewable-electricity future.

--Rob Inglis, High Country News