Vermont's 110-Megawatt Virtual Power Plant Delivered 90 in July

Green Mountain Power dispatched 90 megawatts from batteries, EV chargers and other customer-side equipment during Vermont's early July heat wave, from a virtual power plant it now rates at 110 megawatts, the utility said on July 28. That makes it the largest single resource on the Vermont grid, and the Concord Monitor repeated it on Sept. 29 in a piece by David Brooks.

The arithmetic behind that headline is more interesting than the headline, because it shows what a home battery is and is not doing when a utility calls it a power plant.

What the 110 megawatts is made of

A virtual power plant is a set of small devices that a utility controls remotely and treats as one generator. GMP's release puts residential batteries at 53 megawatts of the 110. The remainder is utility-scale batteries, EV chargers, hydro plants and commercial buildings that agree to cut load, according to Electrek's account.

More than 5,000 GMP customers hold more than 10,000 batteries in the program. Dividing 53 megawatts by 10,000 gives at most 5.3 kilowatts per battery, which is the discharge rate of a single home unit, not a plant. The scale comes from count, and the count depends on customers keeping their equipment plugged in and enrolled.

1. Rated capacity110 MW
2. Dispatched in early-July heat wave90 MW
3. Residential batteries53 MW

Source: Green Mountain Power release, July 28, 2026; Electrek, accessed 2026-09-29

Of the rated 110 megawatts, 90 were pulled in the heat wave, or about 82 percent. Nothing in the release says how long the 90 megawatts were held; it describes the $6 million saving as coming from a single peak hour. A battery's value is a matter of energy as well as power, so a figure in megawatts with no duration cannot be compared with a gas turbine that runs all afternoon.

What the $6 million paid for

GMP estimates the July dispatch cut $6 million from all customers' peak electricity costs, after an estimated $11 million in 2025. GMP counts the saving across all customers, including the ones without a battery, which is the utility's argument for subsidising the batteries.

The customer's side of the deal is set by a lease. Electrek lists two Powerwall batteries at $55 a month, or $5,500 upfront for a 10-year lease. Paid monthly, that comes to $6,600 over the same 10 years, so prepaying saves $1,100, or about 17 percent. The utility and Electrek do not say who owns the battery at the end of the term or what the customer gives up in dispatch rights.

Option	Price	Total over 10 years
Monthly lease, two Powerwalls	$55 a month	$6,600
Upfront lease	$5,500	$5,500

Which power plants left

The shift is not only about money saved. GMP said it permanently closed peaker plants in Vergennes and Rutland after the ISO New England retirement process, and plans to retire more as the battery network grows. A peaker is a plant built to run for the few hours a year when demand is highest, which is the same job the batteries are doing.

GMP says the storage now meets nearly 10 percent of Vermont's summer peak demand, the highest storage-to-state-peak ratio in New England. Mari McClure, GMP's president and chief executive, said in the release that the strategy "reflects what's possible when we innovate in partnership with our customers and the communities we serve." The release supplies no independent audit of the 10 percent figure.

What would change the read

Every figure here is the utility's own, repeated by Electrek and the Concord Monitor without an outside check. The measurement that would settle it is a duration: megawatt-hours delivered during the peak, from ISO New England's meter data rather than GMP's estimate. Until it exists, the 110 megawatts is a rating, and the 90 is the only number that has been tested. Related hardware reporting: Tesla's Roadster flying demo, which has slipped five times since 2025, and Amazon's Greenwood, Indiana robotics plant, due by 2028.