Adding more renewable energy sources while fossil-fuel plants are getting retired is creating wider worries over having sufficient fuel available to keep the lights on, according to the operator of the regional power grid.

“Some generators will have limited inventories of oil or LNG (liquefied natural gas), some will depend on ‘just-in time’ natural gas delivered by pipeline, and wind and solar will not have control of their ‘fuel,’” Gordon van Welie, president and CEO of ISO New England, said during an online briefing with reporters Wednesday.

“As this contingent of energy-limited resources grows, the region’s energy-security risks could become a year-round concern,” he said, noting that solar and wind have weather limitations.

He said ISO officials are developing a “multi-day-ahead energy market that will incentivize resources to have fuel when needed, whether it’s tomorrow or next week.”

New Hampshire’s consumer advocate, Don Kreis, offered another solution.

“Energy efficiency is the cheapest way to meet the next kilowatt-hour of demand and, yet, New Hampshire is well behind every other state in the Northeast when it comes to investing in such resources,” Kreis said in an email.

He said van Welie’s “persistent lament about fuel security deserves skeptical scrutiny.”

ISO New England spokesman Marcia Blomberg responded, “The ISO’s concerns about the risk that there won’t be enough energy to meet power demand during extended cold period is based on its extensive experience — stretching back more than a decade — in operating the six-state power grid through very cold winters, as well as on the ISO’s comprehensive studies of fuel security risks in New England.”

The region is seeing more nuclear and fossil-fuel plants retiring in recent years, including oil and coal plants relied upon during winter cold snaps.

“Between 2013 and 2022, more than 5,200 megawatts of oil, coal, and nuclear power plants will have retired,” van Welie said.

The region’s remaining few nuclear stations, including one in Seabrook, and another 5,000 megawatts of coal- and oil-fired generation are at risk of retirement in the coming years, he said.

“That’s a significant concern, because the region depends on these resources with onsite fuel supplies during cold weather,” he said. “The foundation is strong, but the region’s resource mix is shifting toward a fleet with less onsite fuel and more resources subject to natural gas availability or changes in wind and sun.”

Van Welie was asked whether there needs to be any policy changes when it came to approving transmission line projects.

“That’s always going to remain a state-by-state issue and I don’t see that changing” he said.

New Hampshire regulators last year rejected an application for the $1.6 billion Northern Pass project, a proposed 192-mile transmission line that would have brought 1,090 megawatts of hydroelectric power from Quebec into New England. The project is tied up in the courts.

Eversource officials there “share the concerns of our regional grid manager that fuel security remains the greatest challenge to the reliability of our energy grid in New England — particularly during the winter months when natural gas supplies are needed for home heating,” said spokesman Kaitlyn Woods.

“Burning coal and oil to meet the high demand for electricity during cold snaps drives up carbon emissions and the cost of energy for our customers, who are already paying some of the highest energy costs in the country,” said Woods, who said that’s why Eversource is “deeply committed to moving the Northern Pass project forward.”