The region’s last coal-fired power plants, located in Bow and Portsmouth, are expected to switch to large-scale solar power and battery-storage under plans put forward by their owner, Granite Shore Power, marking New Hampshire’s first big transition into 21st-century electricity production.

“We’ve been planning this for the last six years,” Jim Andrews, president and CEO of Granite Shore, said Wednesday. “From our earliest days as owners and operators … we were firmly committed to transitioning our facilities away from coal and into a newer, cleaner energy future.”

Andrews credited tax incentives and loan programs through the federal Inflation Reduction Act with making the project tenable by removing some of the financial risks for investors. The project will sell power into the grid, and won’t be directly supported by ratepayers.

The agreement was executed Wednesday among Granite Sore, the Environmental Protection Agency, and two environmental groups that have pressured the coal plants to shut, Sierra Club and the Conservation Law Foundation. It still requires state regulatory approval and permission to export electricity into the grid.

“The end of coal in New Hampshire, and for the New England region as a whole, is now certain and in sight,” Tom Irwin, Vice President Conservation Law Foundation in New Hampshire, said in a statement.

 Under the proposal Schiller Station, a dormant power plant in Portsmouth, would host New England’s biggest battery-storage facility, with a capacity of generating 150 megawatts for two hours. It would not have solar arrays, but rather charge the batteries from the power grid to store the electricity. It would operate as a way to time-shift electricity generation, which is increasingly important as intermittent solar and wind power replace fossil fuel plants. 

Merrimack Station, the coal-fired power plant in Bow that still operates intermittently, would have a solar farm of around 100 megawatts on fields adjacent to the power plant and a large-scale battery facility on a small island created by the plant’s cooling canal. The coal-fired boilers in Bow would continue operating to meet production obligations and collect capacity payments, through 2026. The site has a permit to operate through June 2028 but under the agreement will definitively close by then. 

Schiller Station has guaranteed it will not operate its coal-fired boilers after December 31, 2025.

Work at Schiller will proceed first, Andrews said, with construction starting as early as 2025. Work at Merrimack Station would follow.

These solar and battery projects are unusual in size for New Hampshire, which might raise concerns about approval. However, their placement on industrial sites with connections to the power grid, meaning new towers or lines don’t need to be built, should ease their path through the state’s Site Evaluation Committee, which must approve all large energy projects. A bill making its way through the legislature could make things even easier: SB 451 would allow much faster approval when a project “repowers” an existing facility with different or improved technology and doesn’t increase the maximum output of the site.

Around the country, a number of closed power plants, usually those that burned coal, have become solar farms to take advantage of existing grid connections. Batteries are increasingly being added to those sites.

A potential obstacle is the interconnection queue, a backed-up list of power plants that want permission to send electricity into the grid. Hundreds of solar and wind projects throughout the country already fill the queue.

Granite Shore Power is an investor group that owns both plants as well as the gas-fired power plant in Newington, purchased in 2018 from Eversource. The Newington plant will not change.

Andrews said that long-term, Granite Shore wants to use the port facilities at Schiller Station to support energy systems, including offshore wind facilities. The Schiller project will be called Jacona 2, Andrews said, in honor of the S.S. Jacona, the nation’s first floating electric generation ship. It was moored at Portsmouth in the early 1930s and provided electricity and steam for the city up until the end of World War II, when it moved to the Pacific and provided power in Hawaii, South Korea and finally Okinawa. 

Merrimack Station has two large coal-fired units. The older generates 114 megawatts of electricity and was built in 1960 while the second, which can produce 346 megawatts, came online in 1968. A megawatt is enough electricity to power between 700 and 900 new Hampshire homes. Sitting on 343 acres alongside the Merrimack River, it is served by a rail line operated by CSX, which has brought trainloads of coal to the plant for more than half a century.

Merrimack Station was built to generate electricity almost continuously, operating as what is known as a baseload plant, but electricity from natural gas and renewables is now cheaper than electricity from coal plants so for years it has been a “peaker plant,” producing power only during periods of peak demand. In the previous year, for example, the two units operated slightly over 500 hours, or about 21 days.

The station also makes money from capacity payments, in which it guarantees to be able to produce a certain amount of power on demand.

Two smaller, kerosene-fired turbines also exist in Bow. They total just 35 megawatts in output but are valuable because they can be turned on and off very quickly to help stabilize the grid. They will remain in operation.

Schiller Generation Station is located on 81 acres along the western banks of the Piscataqua River in Portsmouth. It has two, units capable of firing coal or fuel oil, a fuel oil-fired combustion turbine and a biomass boiler that burns wood chips. They have a combined total output of 155 megawatts, although they have not operated for several years.