Home batteries proved their resilience value during Vermont’s Halloween blackout.

Vermont – A major rain and wind storm struck the state at the close of October, knocking out power to some 115,000 customers. Among those affected, 1,100 homes managed to keep the lights on thanks to pilot programs specifically designed to promote resilient backup power with energy storage. The battery backup service lasted nine hours on average, but the longest instance stretched to 82 hours.

The event offers a timely data point for other jurisdictions mulling the use of home batteries for resilience. Northern California community power purchasers yesterday requested proposals for home batteries to keep customers powered during the region’s fire-season safety shutoffs. Such a model remains cutting-edge, but Vermont utility Green Mountain Power has shown it can be done effectively.

A couple of years ago, Green Mountain Power launched a Grid Transformation Pilot that allowed homeowners to pay a monthly fee to host a utility-owned and controlled Tesla Powerwall battery. The residents could use it for backup in an outage, and the utility could dispatch the capacity to manage peak demand at other times.

The program previously generated more headlines by saving hundreds of thousands of dollars during annual system peak events than for fulfilling the backup function. In 2018, GMP’s network of batteries reduced consumption during the ISO New England peak hour, saving about $600,000 on capacity fees. This year, a larger number of batteries, totaling 10 megawatts of capacity, responded to a late July peak, saving nearly $900,000 from a single hour of operation.

“We think about our need to deliver reliability constantly,” said Josh Castonguay, the utility’s chief innovation officer. “This has provided us with an amazing tool that can deliver reliability and also pay for itself.”

Those successes made for favorable economics for the utility system as a whole. But the Powerwalls hadn’t had a major opportunity to chance to demonstrate the backup benefit that was promised.

That changed on Halloween.

“We had near-100 mph gusts on top of some of the ridge lines,” Castonguay said. “We had damage across the entire state.”

The 1,100 homes that islanded from the grid accounted for the largest home-battery backup event in the utility’s territory so far, he added.

One reason for that: The utility keeps adding more batteries.

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