by Jeff St. John
February 14, 2020

Vermont utility Green Mountain Power has lots of experience tapping distributed batteries and solar for their grid benefits.

Through a combination of early pilot projects and ongoing programs, it’s built up a fleet of nearly 4,000 households with solar-battery systems, capable of shaving peak loads and cutting capacity costs, as well as keeping the lights on during storms. It’s also building its own megawatt-scale solar-storage systems to balance its increasing share of utility-scale solar.

GMP views solar-battery resources like these as a critical part of its clean energy plans. The utility anticipates it will need 50 to 100 megawatts of “additional storage and flexible load resources” to reach its goal of 100 percent renewable energy by 2030, one of the country’s most ambitious targets. 

But increasingly, GMP sees the distributed solar-battery combination as a critical part of its climate change grid resiliency efforts as well. In fact, it’s prepared to build them first, and then ask state regulators if they’re satisfied that they’ve met their promised capabilities — before they earn a rate of return on them. 

“From what I’ve seen, that is kind of unique” in terms of utility approaches to grid resiliency, Josh Castonguay, GMP’s chief innovation officer, said in an interview this week.

“We believe in the work so much [that] if the commission agrees this plan makes sense, we’ll move forward with the work at our own risk. Once we’re complete, we’ll come in and show [them]: These are the completed projects; these are the benefits they’ll provide."

Climate change bites in New England

That’s the vision laid out in GMP’s Climate Plan, filed this month with the Vermont Public Utility Commission. The 13-page document outlines its approach to making its grid more resilient to the climate-change-influenced ice storms and floods that have hit the Northeast with increasing ferocity over the past decade, while also keeping to its clean energy promises. 

GMP’s plan includes traditional resiliency options such as grid-hardening and controls, enhanced communications systems and a stakeholder process to improve community support during emergencies. But it also includes an “innovation” section, offering several different approaches to tapping distributed energy resources for grid resiliency.

No matter what types of projects are identified, GMP is proposing that it complete each project before it asks the PUC to allow it to recover the costs from ratepayers.

The Climate Plan is an outgrowth of the utility’s Regulation Plan, the multiyear rate case that was approved, with modifications, by the Vermont PUC last year. It’s aimed specifically at improving grid reliability and resiliency, which have traditionally been strong suits for the utility.

But the kinds of extreme weather and outages it’s facing today are a “whole new world,” Castonguay said. Four of the five worst storms in GMP’s history, from a recovery effort perspective, have occurred in the past five years, he noted. Global warming is leading to heavier precipitation in the region, increasing flooding risks and intensifying the damage caused by New England ice storms. 

Last Halloween’s massive storm, which knocked out power to an estimated 115,000 customers across the state, was a potent example of the kind of challenge utilities face as a result of these intensifying effects. It was also a proving point for the backup capabilities of GMP’s behind-the-meter battery fleet, with about 1,100 customers riding through outages lasting nine hours on average. 

Lots of batteries, but installers not thrilled 

GMP’s Grid Transformation Pilot was one of the first large-scale, behind-the-meter solar-battery deployments in the country, with 2,000 residential Tesla Powerwall-solar systems eventually installed. Since then, the utility has installed another 500 batteries under pilot programs, and it hopes to move them beyond pilots through the creation of tariffs this year. 

GMP’s push to equip customers with batteries has been helped along by an unusual state regulatory compact that allows it to rate-base the capital cost of the batteries and recover the costs from customers via monthly lease and on-bill payments. The utility has applied similar approaches to providing grid-responsive water heaters, Nest thermostats and no-cost electricity for charging EVs during off-peak hours. 

Independent solar and energy storage providers in Vermont haven’t necessarily been pleased with this form of utility-funded competition and have demanded a share of the opportunities being unlocked. Last year GMP reached an agreement with Renewable Energy Vermont, an industry trade group, to launch a “bring your own device” program that offers utility incentives to third-party installed systems, as long as GMP can access them for grid services. 

That’s critical, because GMP needs to control these batteries to reduce peak loads at specific hours of the day, as well as for the rare hours every year when system peak loads are calculated. After all, it’s those revenue streams and cost reductions that have allowed GMP’s existing fleet to reduce customer costs overall, Castonguay said.  

At the same time, GMP has always promised that its batteries will be available to back up customers during blackouts. Managing both sets of priorities requires taking lots of conflicting factors and data sources into account to decide which services to prioritize when and how to adapt to changing conditions on the fly. 

GMP already uses software from Virtual Peaker to manage and optimize its behind-the-meter DERs for grid services. But as part of its Climate Plan, the utility has proposed enhancing its DER management software to better optimize its growing fleet, Castonguay said.

GMP is also looking at opportunities to improve the reliability of utility communications and grid controls, or possibly extending cellular or broadband communications to remote communities that now lack it, he said. 

Resiliency Zones

Beyond building grid resiliency from the individual customer on up, GMP’s Climate Plan focuses attention on solar-backed batteries as a community resource. One of its proposals to the Vermont PUC is to examine building one or more “Resiliency Zones,” which it defines as battery-backed grid circuits to power critical facilities. 

The proposal doesn’t come with too many details at present, which is deliberate, Castonguay said. “In terms of DERs and storage, we didn’t want to immediately [get] specific. We want this to be a stakeholder process.”

GMP will be holding meetings across its territory to seek community input and has proposed a series of criteria to prioritize communities and circuits most vulnerable to extended weather-related outages. 

But while GMP hasn’t strictly defined what its Resiliency Zones might look like, “we think it could become a pretty significant part of the technology mix, because we’re proving it works," Castonguay said, referring to GMP’s Panton project, which combines 4.5 megawatts of solar backed by 8 megawatt-hours of lithium-ion batteries. 

While the Panton system has primarily been used to reduce peak loads during heatwaves, GMP has been testing its ability to serve local grid needs such as reactive power support, conservation voltage reduction, and potentially,  islanding the entirety of the distribution circuit the system is connected to. 

In January testimony to the Vermont PUC, Castonguay detailed how GMP is using the Panton system as a prototype site for this kind of circuit-level islanding. This requires adjustments to standard grid operations to allow the solar and batteries to maintain safe and reliable electricity. GMP expects the Panton project to demonstrate these capabilities sometime this summer. 

Once the technology is proven in Panton, it could be applied to other sites. Last year, GMP built three such projects, with a total of 24 megawatt-hours of storage to accompany 14.4 megawatts of solar generation capacity. The first, a 4.5-megawatt solar array with an 8-megawatt-hour battery system in Essex, Vermont, is being targeted as the next islanding test site. 

“Something like that will open up a whole new world of capabilities, when you can offer up a whole chunk of circuit,” Castonguay said.

At the same time, GMP is also looking at potential cost-sharing arrangements with communities that want to provide backup power to individual buildings or facilities. In either case, the goal is to provide “long-duration outage resistance” to facilities needed to recover from disasters.

Beyond this framework, GMP is keeping its options open on how its proposed Resiliency Zones may develop — if, in fact, they end up being among the long list of potential projects it could pursue. If the PUC approves GMP's Climate Plan, the utility would expect the first set of projects to be identified in 2021.

“Who rises to the top of the list? We need to define a really good set of criteria,” Castonguay said.