How Rooftop Solar Cut New England's Peak Demand by 2,000 MW

On June 24, 2025, a heat wave pushed New England's electricity demand to its highest level in more than a decade. The grid held, and rooftop solar did a lot of the lifting.

Solar panels on homes and businesses shaved thousands of megawatts off the peak and pushed it hours later into the evening. One analysis estimates that saved about $19.4 million in wholesale power costs in a single day.

Here is what happened, why it matters for the "solar can't help at peak" argument, and what it means for owners of existing solar.

What Happened on New England's Grid on June 24, 2025?

On June 24, 2025, New England's grid demand peaked at 26,024 MW between 6 and 7 p.m., the highest level since 2013, according to ISO New England. With about 2,550 MW of generating capability unavailable, ISO-NE declared a Power Caution and an Energy Emergency Alert Level 1 starting at 5:22 p.m.

The grid stayed reliable through the event. But it ran with little margin during the evening hours, when solar output was fading and demand was still high.

That timing is the story. Without solar, the peak would have looked very different.

What Is a Capacity Deficiency Event?

A capacity deficiency event happens when a grid operator doesn't have enough available generation to comfortably cover demand plus required reserves, so it takes emergency steps to keep the lights on. On June 24, that meant ISO-NE declaring a Power Caution and an Energy Emergency Alert Level 1.

An EEA Level 1 is an early warning, not a blackout. It signals that all available resources are in use or committed and that the grid operator may need to take further steps if conditions worsen.

These events are costly even when they end without outages. Wholesale prices spike during tight hours, and those costs eventually reach ratepayers. That's why shaving the peak, or shifting it to a time when more supply is available, has real financial value.

How Much Did Behind-the-Meter Solar Reduce the Peak?

Behind-the-meter solar cut New England's peak by more than 2,000 MW and pushed it about three hours later, according to ISO New England. Without it, ISO-NE estimates demand would have peaked around 3:40 p.m. at 28,461 MW.

Behind-the-meter solar means systems on homes and businesses that reduce what those customers pull from the grid. The grid operator doesn't dispatch them, but it sees their effect as lower demand.

The key numbers from the day:

• ●Actual peak. 26,024 MW, between 6 and 7 p.m.
• ●Peak without behind-the-meter solar. About 28,461 MW, around 3:40 p.m.
• ●Reduction. More than 2,000 MW, and roughly 2,400 MW in Acadia Center's analysis.
• ●Timing shift. The peak moved about three hours later.

How Much Money Did Rooftop Solar Save?

Acadia Center estimates behind-the-meter solar avoided as much as roughly $19.4 million in wholesale electricity costs on June 24 alone, by suppressing wholesale prices during the hottest part of the day.

That's a single day. Peak days drive a disproportionate share of wholesale power costs, so shaving the highest hours has an outsized effect on what ratepayers ultimately pay.

The savings also came from systems that were already installed. No new permitting, supply chain, or interconnection queue was involved.

Doesn't Solar Fail When Demand Peaks?

Solar alone can't cover the evening hours, and June 24 showed exactly where that limit is: demand peaked after solar output had faded. Critics have long pointed to this as solar's weakness.

But the event also showed the fix. Acadia Center's Kyle Murray told RTO Insider that more behind-the-meter solar paired with storage could have "potentially completely avoided that absurd price spike later in the evening."

That's the case for pairing solar with batteries. Solar handles the afternoon, and storage carries the stored energy into the early evening peak. A New York study found that distributed solar paired with storage could save billions for the same reason.

Solar did its job on June 24. With storage beside it, it could have covered the evening too.

Why Does Distributed Solar Matter for Grid Reliability?

Distributed solar is already built, spread across thousands of sites, and producing at the hours of highest summer demand, which makes it one of the fastest reliability tools a grid has.

Its advantages during a heat wave:

• ●Already in place. No new permitting or construction timeline.
• ●No interconnection wait. The systems are already connected behind customers' meters.
• ●Spread out. No single failure takes all of it offline.
• ●Matches summer peaks. Output is highest on the hot, sunny days that drive demand.

Puerto Rico has shown the same thing at scale, where a virtual power plant of home solar and batteries delivers real capacity.

What Does This Mean for Existing Solar Owners?

Every system in that 2,000+ MW reduction was only counted because it was producing. Systems with failed inverters, degraded panels, or lost monitoring didn't contribute.

For commercial owners in New England, the lesson is straightforward. A working system earns more on the days that matter most, and a broken one leaves that value on the table.

It's worth checking whether your commercial solar system is still performing. Adding storage may also be worth a look when you repower.

Start With a Ballpark Estimate

Peak days like June 24 are when existing solar proves its value. Find out what your existing solar project may be worth and whether repowering or adding storage would make it worth more.

Sources: ISO Newswire, "Grid remains reliable as June heat wave brings highest peak in over a decade"; RTO Insider via Acadia Center, "Behind-the-meter Solar Shines in ISO-NE Capacity Deficiency Event"