The system supplying Vermont with clean electricity is not exactly a Yankee ingenuity model.
The state adopted a plan in 2011 to obtain 90% of its power from renewable sources by 2050. This led to an increase in wind-generated power from the state’s northeastern part and solar expansion.
But in this sparsely populated part of Vermont, transmission lines have such low capacity that much of the renewable energy is often unavailable due to too much congestion on the lines. In 2014, when an ageing nuclear power plant named Vermont Yankee was permanently shut down, the state was deprived of another source of emission-free power.
A British company called Highview Power is proposing a new solution: a storage system that uses solar or winds renewable electricity to freeze air into a liquid state where it can be stored for hours or even weeks in insulated storage tanks.
The frozen air will warm up and turn back into a flame. It extends so rapidly that, for an electric generator, its strength will spin a turbine. If they are not congested, the resulting power is pumped into transmission lines.
“Vermont has issues of transmission,” Salvatore Minopoli, vice president of the US branch of Highview, explained. “It’s a problem that many areas in the U.S. are struggling with where renewable energy is gradually being deployed. It’s electricity that’s intermittent. They have to have something to balance their system out.” Minopoli said that “the longer duration of your energy storage, the more cost-effective it is for a Highview system,” rather than using large electric storage batteries.
Many non-battery solutions have been attempted by utilities for years. One is pumped storage, where utilities use energy when power is cheap to pump water uphill, and then let it flow through a turbine, generating electricity when it is more costly.
Highview issued a press release in December stating that its first U.S. storage facility could be built in northern Vermont, where it could collect and store as much as 400 megawatt-hours of electricity that could not be used otherwise.
Several U.S. experts were surprised by that. U.S. Vice President Jason Burwen Energy Storage Association said the capacity of the plant would be “on par with today’s largest grid energy storage projects under construction.” He said it would be the equivalent electricity needed “to power maybe 50,000 homes for eight hours.”