One new idea for storing energy, and helping the grid use more wind and solar power, is about as unflashy as it gets. It involves turning a lot of electric heaters on and off really fast.
Demonstrations from Hawaii to Pennsylvania to the eastern banks of Canada are showing that a "fleet" of water or space heaters can act as a sort of fast-acting sponge that absorbs extra electricity on the grid, especially wind power.
The idea is both simple and extremely complex. A handful of companies are rolling out wireless controllers that work with existing water heaters -- that's the easy part -- and building "virtual power plants" that may make a crowd of heaters as responsive as a traditional power plant.
Those who have developed and studied the technology say it's just about the cheapest form of energy storage there is, though it lacks some crucial abilities that are found in batteries. And the kinks are still being worked out.
A four-year test is wrapping up in the Maritime provinces of Canada (New Brunswick, Nova Scotia and Prince Edward Island). There, 16 or 17 megawatts of heaters in homes and businesses are storing energy in tandem with the forecast output from wind turbines. New Brunswick now gets 8 percent of its electricity from wind.
"If every water heater in North America becomes capable of storing energy, you have a huge battery," said Michel Losier, a program director at NB Power, the primary utility for New Brunswick. "I think what we're demonstrating is that this works."
The emerging term for this technology is the grid-integrated water heater (GIWH). The unit's controller is connected to the Internet or to a cell network, and it switches the heat on or off very quickly, even in microseconds. A connected space heater works in much the same way. Meanwhile, the customer's water (or air) remains consistently hot.
In the U.S., a leading player is Battelle, the giant nonprofit research group, which plans to spin off a GIWH business "very, very soon," said spokesman TR Massey. Another is Steffes Corp. of North Dakota, whose mainstay business is building oil tanks for the fracking industry.
The biggest opportunity in the U.S. is the country's 40 million or 50 million electric water heaters. Many are concentrated in the Pacific Northwest, where electricity rates are cheap, and in the South, where rural communities rely on electric heaters because they have no gas lines, said Dan Flohr, the founder of Sequentric, a GIWH startup that is collaborating with Battelle.
Canada has those water heaters and also a lot of electric space heaters, which store heat in ceramic bricks. Both bricks and water can store heat for long periods. That means the heating can occur any time of day.
A hundred water heaters are undergoing tests at Hawaiian Electric Co. (HECO). They are part of a simulation that has them soaking up power from wind farms when the turbines produce more power than the grid can use, according to Earle Ifuku, director of HECO's demand response division.
HECO's eventual plan is to have the water heaters smooth the output from wind farms so the utility can turn its attention to the even more unpredictable output from the state's many rooftop solar installations.
In a different pilot project in Pennsylvania, water heaters were used for "frequency regulation," or keeping the grid in the narrow frequency band where it's stable.
Internet-connected water heaters were installed last year at two buildings on the campus of PJM Interconnection, which oversees the grid in 13 Eastern states. At two-second intervals, they determined whether to heat water based on signals from other power plants and users. PJM participated in a similar test last year in Washington, D.C., with 30 water heaters.
"I was surprised how quickly they can respond," said Scott Baker, a PJM engineer.
However, there are important ways in which a GIWH is not as flexible as a battery, Baker said. A heater fleet can absorb power but can't send it back to the grid, like a battery can. Where the problem is congestion -- a choke point where wires simply can't accommodate any more electrons -- batteries can be placed at strategic points, while water heaters can't.
Such limitations mean GIWHs don't meet the rules for incentive programs for energy storage in the country's two largest markets, California and New York, Flohr said.
In fact, many of today's water heaters are already radio-controlled, but in a more blunt fashion. Since the 1970s, utilities have offered rebates and giveaways for water heaters that the utility can turn off for a few hours at a time on the hottest summer days or coldest winter days, when overall electricity demand is high.
The new generation of fast-response, Internet-enabled water heaters may find their way into homes with incentives like this.
But that day may still be a way off. The controllers and the platforms are still expensive. As with any new technology platform, competing standards are creating confusion and slowing things down.
"It works, but it's a bit clunky yet," said Losier of NB Power. "It's going to take some time."