A solar array in Guilford, Vermont. Credit: Beyond My Ken / Wikimedia Commons

Green Mountain Power is developing three projects to add 14.4 MW of solar and 6 MW of storage to its system.

A Vermont utility is adding solar panels and battery storage in hopes of lowering costs and improving reliability on hot summer days when electricity demand — and prices — tend to spike.

State regulators approved the first of three projects by Green Mountain Power on Jan. 16, when they granted a certificate of public good for a project in Essex that combines a 4.5-megawatt solar array with a 2-megawatt battery.

The Essex project, first proposed in August, is located on about 25 acres of a former sand pit. GMP has similar projects planned in Milton and Ferrisburgh. Together, the proposed nameplate capacity would provide 6 megawatts of battery storage, including 24 megawatt-hours of energy over a four-hour period, along with about 14.4 megawatts of solar energy.

Construction on all three projects is expected to start in the spring and take about four months, though a start date has not been announced. The goal is to have them available to provide system benefits during the summer.

“Battery storage complements the project’s solar array by providing a source of dispatchable energy on the circuit — capturing energy produced by the solar array during peak solar hours and injecting it back into the grid during peak load hours when it is most valuable for customers to drive down costs,” Kirk Shields, director of development and risk management for Green Mountain Power said in testimony before the Vermont Public Utility Commission.

The Essex solar array is projected to produce about 8,000 megawatt-hours of electricity annually under a 25-year power purchase agreement. The Tesla Powerpack system can provide electrical output for up to four hours, at a levelized cost of about 8 cents per kilowatt-hour. The complete project will cost about $14.3 million, including the solar array, battery storage and interconnection.

GMP and solar company Green Lantern Development are building the project. In filings related to GMP’s most recent rate case, the company said the three joint-venture solar-battery storage projects are intended to drive down grid costs. The commission approved the overall rate case on Dec. 24, 2018. The Milton and Ferrisburgh projects were first proposed in December 2017.

The utility said there are multiple benefits. Energy storage and discharge during targeted peak load can save customers money on transmission and capacity. Other benefits include frequency regulation services to earn revenue for customers when the batteries are not dispatching energy to the grid, providing opportunities for energy arbitrage in times of high prices, and possible “islanding” capability.

The battery storage system, combined with other generation and storage resources in the area, would allow GMP to island a subset of Essex customers from the interconnected power grid during emergency and planned outages.

“Serious climatic events and changing weather patterns make improvements to system reliability and resiliency for customers even more important,” the company wrote.

Microgrid storage projects were highlighted as a component of GMP’s strategy to incorporate intermittent renewable energy sources in the company’s 2014 Integrated Resource Plan.

Bill is a freelance journalist based outside Albany, New York. As a former New England correspondent for RTO Insider, he has written about energy for newspapers, magazines and other publications for more than 20 years. He has an extensive career in trade publications and newspapers, mostly focused on the utility sector, covering such issues as restructuring, renewable energy and consumer affairs. Bill covers Maine, Vermont and New Hampshire and also compiles the Northeast Energy News daily email digest.