MMWEC and participating municipal light plants (MLPs) have been ahead of the curve when it comes to integrating energy storage into MLP power portfolios, in alignment with the Commonwealth’s decarbonization goals. MMWEC Member utilities began integrating innovative resources such as energy storage into their portfolios as early as 2016, when the Sterling Municipal Light Department installed the first utility-scale energy storage system in the region.
MMWEC and its Members have been serving as leaders in innovative technology through the use of Distributed Energy Resources (DERs), including lithium ion batteries and flywheels. Three MMWEC Members participated in the state’s Advancing Commonwealth Energy Storage (ACES) grant program through its Energy Storage Initiative, and were awarded grant funding in 2017.
More recently, MMWEC partnered with leading energy storage developer, Lightshift Energy, as part of a larger energy storage initiative. Through the partnership, more than 50 megawatts of energy storage are planned within Massachusetts MLP communities.
Additionally, MMWEC’s innovative Peak Forecasting and Remote Dispatching programs help the MLPs to optimize the flexibility and benefits of their energy storage systems. From 2017 through 2024, MMWEC’s Peak Forecasting and Remote Dispatching programs have saved Members and participating light departments $33.8 million in avoided energy, transmission, and capacity costs.
Read on to learn more about the many energy storage projects MMWEC Members have installed so far.
Paxton Municipal Light Department (PMLD) installed a 3 megawatt/9 megawatt hour energy storage project through the Lightshift Energy/MMWEC partnership in 2024. The system, located at PMLD’s substation, charges during low-cost periods of low energy demand, and discharges during higher-cost peak demand periods. This peak shaving approach results in a projected savings of at least $6.5 million throughout the lifecycle of the energy storage system.
Holden Municipal Light Department (HMLD) installed a 5 megawatt/22 megawatt hour energy storage project through the Lightshift Energy/MMWEC partnership in 2024. The system, located at HMLD’s Chaffins Substation, charges during low-cost periods of low energy demand, and discharges during higher-cost peak demand periods. This peak shaving approach results in a projected savings of at least $10 million throughout the lifecycle of the energy storage system.
West Boylston Municipal Light Plant (WBMLP) has installed a flywheel energy storage system (FESS), the first long-duration flywheel in the Northeast. The flywheel began operating on January 1, 2019.
The 128 kilowatt (kW) behind-the-meter FESS is interconnected through the plant’s existing 370 kW solar project. WBMLP’s flywheel system stores solar energy generated midday and discharges that energy during periods of peak usage in the afternoon and evening. WBMLP’s system contains 16 flywheels with a capacity of 8 kW each.
The FESS uses electricity generated from the adjacent solar field as well as from the WBMLP distribution system to drive a motor that spins the steel flywheel, storing kinetic energy. When the flywheels are called upon to discharge energy, the motor then functions as a generator powered by the momentum of the flywheel, converting kinetic energy back to electricity.
Groton Electric Light Department (GELD) has installed two, 3 MW energy storage systems in cooperation with Lightshift Energy. Both systems came online in 2024. In addition to reducing grid load during peak events, Groton II, located at Florence Roche Elementary School, is equipped to provide direct backup power to the school. The project is a testament to the MLPs’ innovative approach to clean energy, with the pairing of a peak shaving project and microgrid that brings multiple benefits to the local community.
Wakefield Municipal Gas & Light Department (WMGLD) has installed a 5 MW energy storage system through the Lightshift/MMWEC partnership, as part of the larger Wakefield Energy Park project. The battery came online in 2025. It will power two new Wakefield high schools and operate as a resilient, grid-connected microgrid. Designed primarily to reduce peak demand on the grid, the energy storage system is expected to save local customers $20 million over the life of the project. The Wakefield Energy Park is expected to be completed in 2026.
Sterling Municipal Light Department (SMLD) made history when the department installed its 2 megawatt (MW), 3.9 megawatt hour (MWh) utility-scale battery project in 2016, the first of its kind in Massachusetts. SMLD was also the first light department to develop a community solar-plus-storage project in the state. Online since 2018, the 1 MW, 2 MWh battery is exclusively powered by its 1 MW community solar project.
The SMLD projects have been visited and studied by utility professionals around the world and are frequently referenced as examples in energy storage webinars, meetings, and conferences.
Holyoke Gas & Electric’s Mt. Tom Energy Storage System pairs a lithium ion, utility-scale battery with the department’s Mt. Tom Solar Farm for a total capacity of 3 MW/6 MWh-AC.
Installed in 2018 and operated by Engie Storage, the system boasts both the largest utility-scale energy storage system and the largest community solar project in Massachusetts.
In 2023, HG&E installed a 5 MW energy storage system through a partnership with Convergent Energy.
Ashburnham Municipal Light Plant’s 3 MW, 5 MWh lithium ion battery went online in January 2019.
The project was made possible through an ACES grant, which covered 25 percent of the cost of the battery. The ACES program, a partnership between the Massachusetts Clean Energy Center (MassCEC) and the state Department of Energy Resources (DOER), is a competitive grant initiative aimed at piloting innovative, broadly-replicable energy storage projects to advance energy storage technologies in Massachusetts. The remaining cost of the project was funded through the pooled loan program operated by MMWEC.
Wakefield Municipal Gas & Light Department’s (WMGLD’s) 3 MW, 5 MWh lithium ion battery became fully operational in March 2019. The system is directly connected to WMGLD’s Beebe Substation.
This project was also funded through an ACES grant, which covered approximately 30 percent of the cost of the battery. The remaining project costs were financed via the pooled loan program operated by MMWEC.
Templeton Municipal Light & Water Plant’s (TMLWP’s) 1.6 MW, 3.2 MWh utility-scale battery went online in May 2019. It is tied into TMLWP’s circuit supporting senior housing, elder care, and an inpatient treatment center. The project’s design allows for future switching upgrades to the system that will allow the light department to island the circuit and supply the facilities solely with battery power, if needed.
TMLWP was the first member of MMWEC to install a standalone battery system without grant funding. Half of the project costs were funded through TMLWP and half were funded through MMWEC’s pooled loan program.
