Tesla Batteries and Solar Panels Create Energy Islands in Vermont

by Tom Brown

Air conditioners were humming this summer as Central Vermonters sweated through July, the hottest month ever recorded in Vermont.

August has started the same way, and whether you believe these heat waves are the new normal or merely an anomaly, some utilities are already working to reduce the spike in customer bills caused when the New England power grid reaches peak demand.

Green Mountain Power (GMP), the state’s largest electric utility, says it was able to save customers about $500,000 in July by drawing on energy stored in its customers’ home solar storage batteries as well as the company’s storage facilities in Rutland and Panton.

Power companies are charged for the extra energy needed to meet peak demand, the one day each year that the most electricity is used. This year it was August 6 between 5 and 6 pm, surpassing the previous peak of July 5.

In anticipation of peak demand, GMP gave the grid a jolt by sending much of the stored energy from its facilities and more than 610 Tesla batteries in customers’ homes into the system. By reducing its total demand for expensive fossil fuel generation needed to meet the peak period, GMP lowered its share of the money owed to so-called peaker plants, which go online to meet the additional loads, said Josh Castonguay, GMP’s chief innovation officer. Those plants are largely fueled by natural gas, oil, and coal, he said.

“For every megawatt we reduce by using battery storage it just means they need that many fewer megawatts essentially coming from these other energy sources,” Castonguay said.

GMP says it has installed 579 Tesla storage batteries in homes and has a goal of 2,000 by the end of the year. Customers can store energy in those batteries either from their own solar panels or by charging the batteries from the grid. During peak demand the company can draw that stored power to reduce its need to purchase additional supply.

The company also draws from its large solar energy sites in Rutland and Panton. The Panton battery array holds about 4,000 kilowatt hours (kWh) of energy, enough to power seven homes for one month, the company said. The Rutland storage site can supply about 3,700 kWh, or enough to power six homes for a month.

Castonguay said there are plans to bring more stored energy “islands” online and envisions battery storage as a potential replacement for fossil fuel backup generators for businesses and institutions in addition to homes.

The Panton facility, he said for example, could serve as a mini-grid, a self-sustained power source for emergency shelters and other essential services in the event of a sustained power outage.

Green Mountain Power will install a home-sized Tesla Powerwall 2 battery for a $1,500 one-time payment or $15 a month for 10 years ($1,800). Customers may also purchase their own batteries and have them connected them to the GMP system, Castonguay said.

Renewable energy advocates generally support the concept.

“The closer you can keep things to the source the better,” said Austin Davis of Renewable Energy Vermont. “It’s similar to the local food movement in terms of efficiency and distribution costs.”