Energy Storage

Sterling Municipal Light Department signs solar-plus-storage PPA

Sterling Municipal Light Department in Massachusetts has signed a power purchase agreement for a community solar project paired with energy storage.

The project developer, Origis Energy USA, says it is the first solar-plus-storage project in Massachusetts.

Origis Energy is developing the 1 MW rooftop solar array that will be combined with a 1 MW, 2 MWh energy storage system and will sell the output to public power utility Sterling Municipal under a power purchase agreement. Origis says the solar-plus-storage facility will be able to deliver 1.7 MWh annually.

The storage component of the project will allow Sterling to stretch the power from the solar panels into the evening. Peak load in New England, like the rest of the country, is shifting into the evening, Sean Hamilton, Sterling Municipal’s general manager, said. “We want to avoid duck curve issues” that come with that shift, he added, referring to the name that has been given to a graph displaying the steep ramp up of evening load as solar output fades.

“After our first energy storage project, we realized the value that storage brings to ratepayers through things like peak shaving,” Hamilton said.

Sterling Municipal installed battery system in 2016

Sterling Municipal installed a 2-MW, 3.9 MWh battery storage system at its Chocksett Road substation in 2016. The storage facility is designed to provide backup power for the town’s police department for up to 12 days. The $2.5 million project was built with a $1.46 million grant from the Massachusetts Department of Energy Resources and a $250,000 grant from the U.S. Department of Energy.

In addition to its backup function, Sterling Municipal uses the batteries to shave peak load and reduce the amount of power it has to buy from the ISO New England. The project saved the utility $400,000 last year, says Hamilton.

The town of Sterling, Mass., and Sterling Municipal Light Department in late 2017 received the leading by example award from the Commonwealth of Massachusetts related to the utility’s installation of this project, the first utility-scale battery storage project in New England, and energy efficiency work performed in Sterling.

Sterling Municipal also already has about 3.5 MW of solar power in the form of three ground mounted arrays and about 500 kW of rooftop solar panels scattered throughout the town.

“The project with Origis gives the community the opportunity to have solar power, not just those who have the means or live in houses that are not well positioned for solar panels," said Hamilton.

In all, about 35% of Sterling Municipal’s power is generated from renewable resources that the utility buys under contract, says Hamilton. That includes three solar contracts (including the new one with Origis), three wind contracts, and six contracts with small hydropower plants.

In addition, about 35% of Sterling Municipal’s mix of power resources comes from the Seabrook nuclear plant in New Hampshire, bringing the utility’s overall mix of carbon dioxide free generation to about 71%.

Construction on the Origis solar-plus-storage project started in January and is expected to be completed by the end of March. The solar panels will be located on commercial property owned by RockBreakers LLC and managed by Vincent CampoBasso, a resident of Sterling.

CampoBasso will lease rooftop space to Origis, which will take possession of the tax benefits and environmental attributes of the project. That arrangement works out well, Hamilton said, because Sterling Municipal is tax exempt and cannot use the tax credits but it benefits from a lower contract price from Origis.

Sterling Municipal will operate the project. Dispatch for the municipal utility is handled by Massachusetts Municipal Wholesale Electric Company.

Cost savings was another driver of the project, Hamilton said. Solar costs have come down, making solar power competitive with wholesale power from ISO New England. But the solar project, being locally sited, also avoids transmission charges, he said.