MILLER-McCUNE: The Empowering Power of Ice
Blocks of ice are joining molten salt and compressed air as ways to deliver yesterday's energy when it's wanted today.
By David Richardson
02.08.10
Just when most of the country has “had it up to here” with ice, a coalition of publicly run electric utilities in Southern California say it has plans to cool the state’s energy problems by making even more.
The Southern California Public Power Authority announced last month it plans to construct a 53 megawatt energy storage project over the next two years to store power — in blocks of ice.
David Walden, energy systems manager for the authority, said on-peak power demand is the one of the biggest problems facing the region’s electric utilities. He told Miller-McCune that power purchased during peak hours is not only “expensive,” but that the generators “typically dispatched within the industry to meet peak demand are the most inefficient units that we have.”
In a press release, the authority said its new project will “permanently reduce California’s peak energy demand by shifting as much as 64 gigawatts of on-peak electrical consumption to off-peak periods.” How? By switching off air conditioners and instead, using thousands of tons of ice to cool commercial space.
The authority plans to deploy an energy storage system called Ice Bear, developed by Windsor, Colo.-based Ice Energy. The units will be distributed among 1,500 rooftop and commercial air conditioners over the authority’s 7,000-square-mile service area. Tied in to normal rooftop air conditioners, Ice Bear units will be used to freeze hundreds of gallons of water nightly, when demand for power, and its price, are lower.
During torrid working hours when air conditioners are the major draw on California’s power grid, Ice Bear switches off air conditioning and circulates the warm air from the building’s interior over special panels chilled by melting ice. The resulting cool air is then pumped through the ventilation system back into the building.
Once the ice is completely melted, which Ice Energy said takes about six hours, the air conditioning system switches back into normal operation and the cycle starts again. By that time, the power authority said, the peak-load period will have passed, resulting in less strain on the power grid and “an overall 8% efficiency advantage” for the customer.
Shifting energy generation away from demand has become more common, especially with renewable sources that can’t produce on demand. Solar projects, for example, may use molten salt or compressed air to release the sun’s energy once it’s gone down. Other projects have called for pumping water into upstream reservoirs at night when rates are cheaper, then letting it gush through hydroelectric facilities during peak hours.
Ice Energy, for its part, likens its product to using a battery, but without heavy metals or noxious chemicals.
Much of California’s historical summer electricity shortfalls have occurred on hot days when air conditioners suck up to a third of the state’s electricity and either generation or transmission can’t keep up. Meanwhile, climate change, not surprisingly, is expected to make the pinch worse.
Bill Carnahan, the authority’s executive director, said the project “is a convenient and cost-effective solution for managing peak demand. By using storage to change how — and more importantly when — energy is consumed by air conditioning, we can offset enough peak demand in the region to serve the equivalent of 10,000 homes.”
This isn’t the Ice Energy’s first foray into California, having worked on much smaller scales with the Pacific Gas and Electric Company’s “Shift and Save” program since 2007, and the city of Redding since last summer.
Walden said signing up for the program is relatively simple. “We do all the installation,” he said. Customers need only provide an access agreement similar to that used for any other piece of utility equipment, such as a transformer or meter.
“The system is compatible with 85% of existing air conditioning units,” he said. And cooling with ice made overnight consumes less electricity than running air conditioners during the day, “partly because it’s cooler at night, and partly because the small compressors used to make ice are more efficient than the larger compressors used on commercial air conditioners.” He added that air conditioners’ life spans increase because they aren’t on as much.
Walden said the authority has been using the system on its own buildings “for over five years. … There’s a lot of history behind the product showing that it works.”