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.