GMP Grid Resilience Plan Will Overhaul T&D

October 23, 2023 by Shannon Cuthrell

Vermont’s leading utility introduced a plan to overhaul its transmission and distribution infrastructure to eliminate outages by 2030. The program will focus on undergrounding and storm-hardening activities while scaling energy storage installations. 

Green Mountain Power (GMP), Vermont’s largest utility with more than 260,000 customers, filed what it calls a “first-in-the-nation” plan with state regulators to accelerate its grid resilience upgrades and, ultimately, eliminate outages by 2030. 


Green Mountain Power clears snow from a power line in March 2023.

Green Mountain Power clears snow from a power line in March 2023. Image used courtesy of GMP


The “Zero Outages Initiative” will oversee storm-hardening for GMP’s distribution lines, including undergrounding, installing protective devices, and adding tree wire or spacer cables. GMP also aims to increase its microgrid and energy storage capacity, including vehicle-to-home (V2H) and vehicle-to-grid (V2G) opportunities. 

GMP estimates that the first phase will require a $250 million investment for undergrounding and storm-hardening lines and an additional $30 million for energy storage. The company will use circuit-level data and community population information to determine the best approach for its 300 circuits. 

According to the petition filed with the Vermont Public Utility Commission (PUC), GMP will organize the work by zones within each circuit of its service area, ranging from protecting three-phase distribution lines near substations to installing storage solutions in rural areas where single-phase lines are more difficult to storm-harden or place underground. In areas where microgrids are the ideal community-level resilience option, GMP will install systems that pair renewable generation with battery storage to power an isolated portion of a circuit in emergencies. 


Green Mountain Power recently announced a major power resilience plan.

Green Mountain Power recently announced a major power resilience plan. Image used courtesy of GMP


Storm-Hardening Solutions

GMP has been upgrading its infrastructure for years, installing 50 miles of underground lines in rural areas or where lines remained undamaged through storms. Part of that effort involved adding spacer cables, which prevent outages even when trees fall on lines. Since 2020, GMP has deployed storm-hardening improvements on over 330 miles of distribution lines. 

Recent storm severity in Vermont prompted GMP’s petition to scale up its prevention efforts amid the rising cost and frequency of repairs. In the past 12 months, three major storms caused the most outages in GMP’s history, totaling over $45 million in repairs. GMP has racked up $115.7 million in damage repairs since 2013, not including prevention investments. 


A visualization of the distribution circuit zones targeted in GMP’s Zero Outages Initiative.

A visualization of the distribution circuit zones targeted in GMP’s Zero Outages Initiative. Image used courtesy of GMP


Michael Burke, who leads GMP’s field operations, presented the details in a testimony to regulators. First, the company will rapidly underground its primary distribution lines, which is more cost-effective than overhead construction or storm-hardening overhead single-phase distribution lines. Burke also mentioned that undergrounding can be used on three-phase mainlines when conditions allow. Where above-ground solutions are more feasible, undergrounding can be combined with storm-hardening measures, such as installing a spacer cable in a mainline feed wire. 

The Zero Outages Initiative also focuses on spacer cable and tree wire additions for overhead lines. The plan calls for storm-hardening all three-phase or primary overhead lines with insulated wires capable of handling tree damage. That includes installing spacer cable on mainline feeders, which leave substations and feed power into Vermont’s towns. 

Spacer cable provides full insulation using a 0.5-inch-thick steel messenger positioned above the insulated aerial cable, shielding it from fallen trees and other hazards. Burke mentioned that spacer cables have no cross arms outside of the end of the cable runs. The three-phase configuration is only 18 inches across, minimizing tree contact with less surface area than the typical 8-foot cross-arm setup. 


Examples of lines equipped with Marmon Utility’s Hendrix Spacer Cable Systems.

Examples of lines equipped with Marmon Utility’s Hendrix Spacer Cable Systems. Image used courtesy of Marmon Utility


In areas with single-phase distribution, GMP will underground lines wherever possible and use overhead storm-hardening where undergrounding is not feasible. Burke estimated that GMP’s work could cover over 3,500 miles by 2030. Recent construction innovations have reduced the installation cost of cable-in-conduit undergrounding, which is now comparable to installing overhead hardenings in many areas. Undergrounding also offers better lifetime maintenance costs than overhead repairs, as underground cable-in-conduit systems are stable and can withstand flooding and other grid impacts. 


Battery Storage Expansion

The Zero Outages Initiative aims to scale GMP’s residential battery storage capacity, complementing its broader distribution-scale storage expansion. Burke mentioned that about 3,000 GMP customers have connected storage devices via GMP’s energy storage system (ESS) tariff, bring-your-own-device (BYOD) tariff, or pilot programs. GMP’s petition noted that in last winter’s storms, customers with battery systems could maintain power for over 77,000 hours across 2,300 events. 

GMP’s ESS program, which provides Tesla Powerwall home batteries for a $55 monthly lease payment, amassed a lengthy waiting list that led Vermont’s PUC to lift the yearly ESS cap. The BYOD program allows customers to join their stored energy with hundreds of other battery- and EV-charger users. Several devices are compatible with the program, including Powerwall 2.0, SolarEdge’s StorEdge, and Generac PWRcell. 

The Zero Outage Initiative proposes supplying utility-owned batteries directly to customers in areas where batteries are better than storm-hardening or undergrounding. GMP also plans to expand its use of microgrids, a community-level storage solution enabling shared access and load management to maintain power in outages. Last year, the company began operating a fully renewable microgrid on part of a distribution circuit. The Panton microgrid pairs a 1 MW / 4 MWh battery with a 4.99 MW solar generation facility. 

Josh Castonguay, GMP’s chief innovation and engineering executive, stated in a pre-filed testimony that utility-scale, mobile, portable, and customer-sited storage support the growth of distributed renewables while providing resilience from outages. On the utility-scale side, the company has received a grant from the U.S. Department of Energy to test battery use cases that optimize the transmission system and renewable energy utilization. 

Castonguay said battery storage is a proven flexible distributed energy resource with several other benefits, including peak demand reduction, voltage regulation/reactive power, power factor correction with inverter equipment, and frequency regulation. Energy time-shifting is another benefit, taking advantage of rapidly fluctuating energy pricing by discharging when prices are high and charging after prices fall. 

GMP also plans to scale its use of portable batteries to back up entire circuits. The company recently deployed a 2 MWh mobile battery-on-wheels, Nomad Transportable Power System, on a power circuit for commercial customers. The system helped a local manufacturing facility keep the power on during routine maintenance that would have otherwise required a six-hour outage for the site’s 24/7 operations. 


GMP deployed a Nomad Transportable Power System as a mobile battery for a manufacturing operation.

GMP deployed a Nomad Transportable Power System as a mobile battery for a manufacturing operation. Image used courtesy of GMP


Vehicle-to-Everything Storage

Castonguay cited the role of customer programs supporting load management and resilience, including smart panel upgrades, V2H, V2G, and vehicle-to-everything (V2X) charging from electric vehicles, which provide backup capacity and load management functions. Solar-plus-storage systems can also offer backup power in extended outages. 

Castonguay mentioned that V2X is an ongoing focus for GMP as EV adoption grows in Vermont. GMP customers account for about 7,000 of the state’s 10,000 EVs, representing an attractive opportunity to unlock controllable loads and storage capacity. Two Powerwall batteries in a home provide about 27 kWh of energy storage backup, and the average EV can offer between 85 and 120 kWh. 

V2X products use bi-directional charging, in which EV batteries supply power to an external load. In V2H loads, the EV offers a form of demand response similar to stationary batteries. Likewise, V2G applications allow EV storage to supply power to the grid, supporting GMP’s virtual power plant and battery resource fleet. 

GMP is testing several V2X applications, including V2G with Fermata Energy and Wallbox, and teaming up with a school district to supply stored energy from buses to the grid when they aren’t in operation.