To Store Renewable Energy, Try Freezing Air

By John Fialka,E&E News

The system that supplies clean electricity to Vermont is not exactly a model of Yankee ingenuity.

In 2011, the state adopted a plan to get 90% of its power from renewable sources by 2050. That led to a surge of wind-generated power from the northeastern part of the state and an expansion of solar.

But transmission lines in this sparsely populated part of Vermont have such low capacity that much of the renewable energy is often unavailable because the lines are too congested. The state was deprived of another form of emission-free power in 2014 when an aging nuclear power plant called Vermont Yankee was permanently shut down.

So what can Vermont do?

A British company called Highview Power proposes a novel solution: a storage system that uses renewable electricity from solar or wind to freeze air into a liquid state where it can be kept in insulated storage tanks for hours or even weeks.

The frozen air is allowed to warm and turn itself back into a gas. It expands so quickly that its power can spin a turbine for an electric generator. The resulting electricity is fed into transmission lines when they are not congested.

"Vermont has transmission issues," explained Salvatore Minopoli, vice president of Highview's USA affiliate. "It's a situation that many places in the U.S. are dealing with where renewable energy is being deployed more and more. It's power that's intermittent. They need something to balance their system out."

Minopoli said that "the longer duration of your energy storage, the more economical it is for a Highview system," rather than using big electric storage batteries.

For years, utilities have tried other non-battery approaches. One is pumped storage, where utilities use electricity to pump water uphill when power is cheap, and then let it flow down through a generator, creating electric power when it is more expensive.

Some utilities even pump air into played-out natural gas fields, compressing it to spin turbines when it's released. But Minopoli pointed out that the Highview approach doesn't need hills or abandoned gas fields. It can be built on a 2-acre site almost anywhere.

He says the ideal place for installing what Highview calls its "liquid air energy storage system," or LAES, is the site of an abandoned coal-fired power plant. There are many in the United States.

"That's where we project our biggest growth," Minopoli said, noting that old power stations still have the abandoned transmission lines connecting them to the regional power grid.

In December, Highview issued a press release suggesting that its first U.S. storage facility might be located in northern Vermont, where it could capture and store as much as 400 megawatt-hours of electricity that might not otherwise be used.

That gave a shock to some U.S. experts. Jason Burwen, vice president of the U.S. Energy Storage Association, said that size of facility would be "on a par with the largest grid energy storage projects under development today." He said it would be the equivalent electricity needed "to powering perhaps 50,000 residences for eight hours."

"Numerous companies are competing to bring to market a variety of new energy storage technologies to meet the needs of the electric system, and Highview Power would be breaking out," Burwen added.

Indeed, a U.S. energy consulting firm, Wood Mackenzie, predicts that various forms of energy storage in the United States will break out, growing from an estimated $645 million market in 2019 to $5.4 billion by 2024. IBM recently announced it has developed a large electric storage battery for power plants that is bigger and safer than traditional lithium-ion batteries now used by utilities (Climatewire, Dec. 19, 2019).

Exactly where Highview's first facility might be installed, however, is going to take further negotiations. Those can be complicated and lengthy in the utility business.

Kerrick Johnson, vice president of strategic innovation for Vermont Electric Power Co. (VELCO), which manages Vermont's electricity transmission system, said that after three conversations with Highview, its LAES technology remains an "option."

"It's an intriguing technology and holds some promise, but the jury is very much still out over whether this project makes sense for VELCO or Vermont in this particular context," he said.

VELCO, whose owners include 17 small Vermont generating companies, has also been considering buying more transmission lines to ease congestion. It has also been talking to electric battery suppliers about storage alternatives.

Johnson explained that an economic depression in the area attracted developers to assemble parcels for a large wind turbine farm. There is also hydroelectric power and rooftop and community solar arrays.

"So there is a lot of energy that wants to get out of that system with skinny wires," Johnson said.

In a memo sent to Highview last month, VELCO's senior planning engineer, Hantz Presume, said the company wants more information on the cost and efficiency of liquid air storage and its long-term management needs. He acknowledged, however, that Vermont still faces a problem that needs a solution. "There is no headroom for additional renewable generation," he said.

Part of VELCO's impasse is created by federal regulators, who encourage wholesale electricity suppliers to be competitive. But states like Vermont want to meet long-term renewable energy goals that may require more spending.

"This is a federal and state policy collision," Johnson said.

Reprinted from Climatewire with permission from E&E News. E&E provides daily coverage of essential energy and environmental news at www.eenews.net.