Battery storage and small-scale solar played a critical role in keeping New England’s electric grid reliable and may have saved customers tens of millions of dollars during late June’s major heat wave, according to a new analysis.
As temperatures soared above 100 degrees Fahrenheit and the region saw thick humidity, people cranked their air conditioners, drawing more power from the grid.
ISO New England, the region’s grid operator, said demand for electricity on June 24 peaked at 26,000 megawatts (MW) at about 6:45 p.m. — the highest level since 2013.
Small-scale solar, largely owned by private businesses and homeowners, helped meet that demand during the middle of the day, likely saving all electric customers money. And grid operators say batteries played a critical role in helping to shrink the duration of time in the evening when electricity prices were at their highest.
In addition to making it trickier to keep the lights on, extra humid heat waves like the one in June are expensive because people can’t keep sufficiently cool with fans and need to turn on more energy-intensive air conditioning into the night, which drives up demand for electricity. Many aspects of electricity prices are set based on when demand peaks for the year, which is when power tends to be most costly.
At dinner time on June 24, wholesale electricity prices soared to $1,000 per megawatt-hour (MWh) — some 23 times the average annual cost of power last year.
“It’s often 6, 7 o’clock at night, you know, when folks are heading home, they’re maybe cooking dinner, they’re doing a load of laundry or running the dishwasher, and so we’ll see electricity demand go up at that time,” said Mary Cate Colapietro, with ISO New England.
Several years ago, she said that peak would have happened during mid-to-late afternoon.
But small-scale, behind-the-meter or rooftop solar helped push it back to dinnertime, lowered the overall peak and shortened its duration, Colapietro said — part of a long-term trend the grid operator has observed. That’s because when these small systems produce power and send it onto the grid at midday, it adds to the electric load, decreasing what the grid operator and market see as demand while the sun is overhead. As solar energy begins to wane, that demand creeps back up.
That shift could have saved consumers more than $19 million, according to an analysis by the Acadia Center, a regional environmental nonprofit and thinktank.
Absent all that rooftop solar, Acadia Center estimates New England would have broken its 19-year record for peak demand.
Power banking
The Acadia Center and ISO New England say power storage also played a critical role in keeping the lights on during this heat wave.
“I think people are really starting to understand that the value of renewables increases substantially when you pair them with batteries,” said Noah Berman, with the Acadia Group.
Batteries — whether smaller ones in people’s homes, or bigger “utility scale” ones plugged into the regional transmission grid — store power when it’s cheap and plentiful, like solar energy in the middle of the day.
Then, grid operators can draw down that power at times when demand for electricity is higher and new power generation costs more, ultimately saving electric customers money. They can also leverage that power when other resources are scarce or unavailable.
New England’s grid now has about 270 MW of industrial battery storage that ISO-NE can draw on during heat events the same way it does a natural gas power plant.
That’s in addition to residential and utility-owned battery storage, like Green Mountain Power’s 72 MW virtual power plant in Vermont, which lowers demand for power at times when it’s most expensive.
The network of residential battery packs, utility-scale battery storage, electric school buses and charging infrastructure has been in use since 2015. At 72 MW, it’s now the state’s biggest source of in-state power generation and includes some 5,000 electric customers.
“The really interesting and important part about batteries is they’re dispatchable and flexible,” said Kristin Carlson, a spokesperson for Green Mountain Power. “And so you can, at any time, have it available.”
A future with more batteries?
Regionwide, batteries now make up about 45% percent of bids for new power plants in New England, and Colapietro with ISO-NE said that figure is growing. Large batteries are regulated as power plants because they put electricity onto the grid.
Green Mountain Power has a bid before Vermont’s Public Utility Commission now to expand its program, despite the fact that Vermont’s current regulations on electric utilities don’t incentivize them to invest in battery storage. Carlson said the cost savings from batteries make sense even without market incentives.
If June 24 remains the peak for the year, Carlson says battery storage and behind-the-meter solar will have saved GMP customers an estimated $3 million.
Colapietro said if battery storage continues to grow in New England, it could allow grid operators to use more electricity generated by lower-carbon resources like solar during peak periods, so the region relies less on natural gas during those times.
She said during the evening hours on very hot days like the one in June, New England electric customers are still relying largely on power derived from burning climate-warming fossil fuels.
“We did have some contribution from solar, but fossil fuels really did carry the bulk of the load during that peak hour,” Colapietro said, noting that carbon-emitting resources at that time accounted for about 74% of the energy used.
Colapietro said grid forecasters expect electricity demand in New England to peak in the winter by the next decade, as more people install cold climate heat pumps and switch to electric cars, and the region’s demand for power increases.
Analysts with the Acadia Center hope batteries and a little extra coordination on the part of grid operators and utilities could help make that future winter peak lower, saving money and carbon emissions.
