The Department of Energy and Environmental Protection (DEEP) this month denied proposals from Eversource and Avangrid to test out energy-storage technology because anticipated costs outweighed ratepayer benefits.
The utilities were required to submit the energy storage demonstration projects, along with several other proposals aimed at better managing and balancing the electric grid, under a state law passed in 2015.
Eversource had proposed an energy storage system at a substation in Stafford that suffers from unstable voltage and has a transformer that approaches capacity during times of peak summer demand.
While DEEP said it was a good location to test storage, the 8-megawatt-hour system would cost Eversource up to $13 million plus an annual operations and maintenance cost of $350,000, totaling nearly $33 million over the 22-year life of the project -- a cost that would ultimately be borne by ratepayers.
Meanwhile, Avangrid had proposed a grid-connected battery storage system for a substation in Milford, which would cost $5.6 million plus annual costs of $300,000. That's more than the estimated $1.3 million benefit the project would provide to ratepayers.
DEEP said it has encouraged both companies to revise their proposals and resubmit them to the Public Utilities Regulatory Authority.
Though the storage projects were denied, DEEP approved five other projects proposed by the utilities, which in total could cost more than $5 million, including the development of tools to help developers site distributed energy resources and improve the improve the interconnection application process.
Correction: The original version of this story gave incorrect information about the size of Eversource's proposed storage system. It had proposed an 8-megawatt-hour system.