National Grid will install a 48 megawatt-hour battery energy storage system, or BESS, on Nantucket, 30 miles off the coast of Massachusetts, to help delay expected grid modernization investments.

Nantucket has experienced significant growth and demand for electricity, both of which are expected to continue for the foreseeable future, the utility says.

At present, the island’s electricity is supplied via two submarine cables. These connect with the mainland transmission system on Cape Cod. In the event of a cable failure, two 6 MW diesel generators provide partial back-up power.

National Grid says the diesel generators are reaching the end of their useful life and need to be replaced. And, given the growth forecast, the island’s emergency electricity back-up system needs to be expanded. A third submarine cable likely will be needed in about 12 years.

National Grid explored several options and settled on the battery energy storage system and a new diesel generator. Together, they are expected to supply the island with power in the event of a cable failure.

National Grid says that it expects that with the BESS, the need for a third cable can be delayed for 15 to 20 years beyond the current 12-year forecast. The BESS will be 6 megawatts with an eight-hour duration, resulting in the 48 MWh system. It is being provided by Tesla.

The BESS is the latest of several National Grid battery systems. The company also has roughly 30 energy innovation pilots underway across the three states it serves, including microgrids, smart grids, community solar projects, geothermal heating and cooling, and distributed energy installations.

National Grid is an electricity, natural gas and clean energy delivery company that supplies more than 20 million people through its networks in New York, Massachusetts and Rhode Island. National Grid also delivers gas and electricity across Great Britain.