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Clean energy journalism for a cooler tomorrow

Vermont’s biggest utility dramatically expands home battery subsidies

Since 2015, Vermont’s Green Mountain Power has helped a limited number of customers install home batteries each year. Now the program cap is gone.
By Julian Spector

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A white Tesla powerwall hangs in a utility room under stacked rolls of paper towels on a shelf and next to a framed cat photo
(Steve Russell/Toronto Star/Getty Images)

One of the nation’s first and most prolific home battery programs is gearing up for unprecedented growth.

Vermont utility Green Mountain Power got in early on using small-scale solar and storage in customers’ homes to improve the overall functioning of the grid. Since 2015, the company has subsidized customers who want battery backup power, in exchange for using those batteries to lower grid costs for all customers during hours of peak electricity demand. Now that fleet has grown to 4,800 batteries totaling 27 megawatts of capacity.

After a string of extreme weather disasters in Vermont this year, more customers asked for batteries to power their homes through winter storms, floods and heat waves. But state regulators had enforced a cap on how many people could join the program each year, and the waitlist to get Tesla Powerwalls through this program had stretched past 2026.

We were filling up the customers at the beginning of the year pretty quickly and then creating a waiting list,” said Josh Castonguay, the top innovation executive at the investor-owned utility, which serves 270,000 customers in Vermont. Clearly the program is successful, it’s performing as we expect, and customers are looking for this.”

Now that cap is gone. On August 18, the Vermont Public Utility Commission decided to remove the annual limit of about 500 customers receiving Tesla Powerwalls and 500 receiving credit for acquiring their own batteries (technically the cap was 5 megawatts per program). In just a few years, Green Mountain Power scaled from a small pilot test to an annual battery program, and now it has secured free rein to meet organic demand from customers, at least until the program goes up for renewal in three years.

Customers who opt for the Powerwall pay the utility $55 per month for use of the battery, with no money down. The payments stop after 10 years, at which point the household can use the system for free until it stops working; then the utility will pick it up for safe disposal via recycling. The bring your own device” offering pays households that buy and install their own battery system up to $10,500, a substantial chunk of the cost for popular models.

These individuals benefit from cheaper access to energy storage, but the reason regulators sign off on the program is that Green Mountain Power uses these devices to lower its total demand on monthly and annual peak-consumption hours. Those savings pass on to the whole customer population, and they aren’t tiny — in recent years, the fleet has shaved off $3 million in annual peak costs.

When the home battery program started, the utility touted the ability of battery backup to help homes get through winter storms that regularly knock out power lines in remote parts of the state. Now climate change is helping fuel disastrous weather throughout the year, further raising the appeal of backup power. Three of the worst winter storms the utility has ever dealt with happened this past winter, Castonguay said, and July brought the worst flooding in the state since 1927 (an event which, the National Weather Service points out, preceded modern flood control in the area).

But beyond helping customers weather outages, the battery fleet also serves as a forward-looking investment in a more electrified future for the utility itself. Green Mountain Power already sources carbon-free power for its customers, but it anticipates electrifying vehicles and buildings to achieve economywide decarbonization. Those new loads will change demand patterns, and having a flexible fleet of batteries that can respond to utility signals will help Green Mountain Power manage those broader shifts, Castonguay said.

This large-scale integration of small, distributed resources remains rare among regulated utilities — most struggle to move beyond the pilot scale with such programs, much less enlist thousands of households to participate in a cleaner, nimbler grid.

Utilities often seem uninterested in proving the potential of small customer-centric devices to take on roles previously served by large utility-owned projects. They might view the decentralization trend as threatening to their business models and their primacy in the power system. Green Mountain Power has managed to give its customers preferential access to new clean energy technologies, while keeping the utility in the central role of orchestrating it all.

Julian Spector is a senior reporter at Canary Media. He reports on batteries, long-duration energy storage, low-carbon hydrogen and clean energy breakthroughs around the world.