Green Mountain Power’s virtual power plant (VPP) – the state’s largest energy source – cut an estimated $6 million from all customers’ peak electricity costs during Vermont’s early July heat wave.
As temperatures climbed into the high 80s and low 90s and air conditioners pushed electricity demand higher, Green Mountain Power (GMP) dispatched 90 megawatts (MW) from its VPP. The network combines residential batteries, utility-scale storage, and other clean energy sources.
GMP says the 90 MW dispatch was roughly equivalent to taking 50,000 homes off the grid during the peak. Avoiding electricity purchases when wholesale prices are at their highest reduces the costs that ultimately get passed on to all GMP customers – not just those with residential battery storage.
The estimated $6 million saving follows the $11 million that GMP says its VPP saved customers last year.
Vermont’s biggest power resource isn’t a power plant
GMP’s virtual power plant now has 110 MW of capacity, making it Vermont’s largest single power resource by capacity, according to the utility.
More than half of that capacity – 53 MW – comes from residential battery systems. The rest includes utility-scale batteries, EV chargers, hydroelectric plants, and commercial buildings that can temporarily adjust their electricity use.
More than 5,000 GMP customers now have over 10,000 batteries enrolled in the VPP. During a grid peak, GMP can draw on some of that stored electricity as one coordinated power source while leaving participating homes with backup power for outages.
The batteries can now supply nearly 10% of Vermont’s summer peak electricity demand. GMP says that’s the highest storage-to-state-peak ratio in New England.
Home batteries do two jobs at once
GMP was the first US utility to offer a state-approved, tariffed home battery lease program. Customers can currently lease two Powerwall batteries for $55 per month or pay $5,500 upfront for a 10-year lease. In return, GMP gets access to some of the stored electricity during peak demand. (I participated in this program when I was a Vermont resident, and it was fantastic. Having two Tesla Powerwalls in our cellar kept our electric bill reasonable, and the lights on and water running when the power went out.)
Customers can also buy their own compatible battery through GMP’s Bring Your Own Device program in exchange for an upfront incentive.
That gives participating households quiet backup power while also turning thousands of individual batteries into a grid resource.
“It is reassuring and keeps us comfortable at home, and we also love how the program is reducing power costs for all GMP customers, too,” said GMP customer Pollyanna Bladyka, whose batteries have kept her home powered through damaging storms.
The growing VPP has already allowed GMP to permanently close peaker plants in the towns of Vergennes and Rutland following an ISO-New England retirement process. Peaker plants operate when electricity demand surges, but they’re often expensive and carbon-intensive. GMP says it plans to retire more peaker plants as its battery network grows.
Read more: The US’s largest virtual power plant now runs on 75,000 home batteries
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