In this photo from October 2016, Rhonda "Honey" Phillips poses next to a Tesla Powerwall battery and inverter connected to a solar panel array in her yard in Middletown Springs, Vermont. Phillips is one of the growing number of Green Mountain Power customers using the Tesla battery to store solar energy when her panels aren't collecting it. Credit: Dave Gram / Associated Press

The “bring your own device” programs “are maybe Vermont’s greatest export,” one supporter says. 

Green Mountain Power wants to turn its pioneering home battery storage pilot programs into permanent offerings for customers. 

Vermont’s largest electric utility earlier this year filed proposals for two new tariffs — one for utility-owned batteries and one for customer-owned batteries — with the Public Utility Commission. On Oct. 16, the commission held a public hearing on both proposed tariffs in Montpelier. 

The energy storage tariff would allow customers to lease Tesla Powerwall batteries from Green Mountain Power and pay either a one-time, upfront fee or a monthly payment. The “bring your own device” (BYOD) tariff is for customers who would rather buy or lease a battery from a range of approved providers.

The proposed tariffs are extensions of two successful pilot programs. Under the BYOD pilot launched earlier this year, customers could enroll their battery for 10 years and receive an $850-per-kilowatt upfront incentive payment or an equal amount in ongoing bill credits. Electric vehicle chargers were also eligible devices; enrolling them earned participants an extra $10 credit each month.

Whereas many investor-owned utilities have resisted the rise of customer-owned distributed energy resources, seeing them as a threat to their business model, solar and storage advocates say Green Mountain Power, or GMP, has taken a lead in embracing their potential.

“I think that BYOD programs are maybe Vermont’s greatest export,” said Chris Rauscher, director of policy and storage market strategy at Sunrun, a residential solar and storage company. Sunrun recently started participating in the BYOD program, offering GMP customers the chance to purchase or lease its Brightbox home battery system. “It has changed the way that utilities in the region, and, frankly, around the country, look at behind-the-meter customer-sited resources, and kicked off this new dynamic where utilities are the ones going to the commission and touting the benefits these bring to the grid and all ratepayers. It’s a really remarkable paradigm shift from just five years ago.”

Read more: With utility’s support, solar-plus-storage takes off in Vermont

According to Green Mountain Power and Renewable Energy Vermont, the trade group that worked with the utility to design and launch the “bring your own device” pilot, the program offers a range of benefits. Having access to thousands of customers’ batteries enables GMP to draw power when it’s needed most, shaving peak demand and reducing its peak system usage charges from the New England Independent System Operator, which manages the region’s electric grid. The result is increased reliability and lower overall costs for ratepayers, because running oil- and gas-burning peaker plants to meet short periods of peak demand for electricity is expensive.

For customers, having battery storage means they can keep the lights on during a power outage. And sharing that stored energy with the grid means they help lower system-wide costs. 

But it also means they cede some control over their batteries to Green Mountain Power. Peak events can happen several times a month, for hours at a time. The utility notifies customers in advance through a smartphone app or text message.

If approved by the Public Utility Commission, each program will be open to a maximum of 500 customers per year, and available on a first-come, first-served basis. The incentive payments that enrollees receive are calibrated to reflect the value of the services that their batteries and other devices provide to the grid. 

“In a place like Vermont, a BYOD program that provides value to the customer will definitely drive battery deployment in a way that Vermont would not have seen otherwise,” Rauscher said. 

The program fits into Green Mountain Power’s broader plans for integrating more distributed solar into its supply portfolio and further decarbonizing its fuel mix. 

“The ultimate goal is getting to a place where every single [solar] PV installation that goes in has some kind of storage with it,” said Josh Castonguay, the utility’s vice president and chief innovation officer. “You can turn that into a much more predictable, manageable, flexible resource that you can do a lot of things with, in terms of reliability. This new flexible grid is going to be more and more critical as we get more and more distributed.” 

He noted that GMP’s most recent modeling projects penetration of 60,000 electric vehicles in its service area by 2028. Having more storage available — including behind-the-meter home batteries — will be critical to managing the charging of all those vehicles, and meeting that demand.

The utility is targeting areas where the need for storage is greatest — substations in Vermont where remaining circuit capacity is limited — with a bonus incentive payment of $150 per kW. Of the two proposed tariffs, Rauscher sees BYOD-type programs as the future. He notes that the majority of batteries being enrolled in similar programs in New Hampshire, Massachusetts and New York are owned by customers or third-party aggregators like Sunrun. “This is done without risking ratepayer capital,” he said. “This is all pay for performance. And GMP really pioneered that.”

Jonathan Mingle is a freelance journalist focused on science, climate, energy and the environment. He is a former Middlebury Fellow in Environmental Journalism, and the author of "Fire and Ice: Soot, Solidarity, and Survival on the Roof of the World," a nonfiction narrative book about the health and climate impacts of black carbon pollution. He lives in Vermont.