Next month, when summer heat and winter cold near their peak in each of Earth’s hemispheres, grid operators will face their highest electricity demands of the year. Space heating and cooling make up about 50 percent of all energy end uses worldwide, putting enormous strain on grids and sometimes forcing utilities to use more expensive, polluting plants.

But it doesn’t have to be that way. To take some of the load off during peak demand, manufacturers are pairing batteries with residential air conditioners and heat pumps. The batteries charge when power is plentiful, and discharge, running the heating or cooling system, when the grid is strained.

A company offering this service in New York City is the startup Every Electric. The company distributes briefcase-size, 2-kilowatt-hour portable power banks that connect to plug-in air conditioners. It then uses software to aggregate those units into a virtual power plant (VPP).

The strategy of reducing power demand at key times of the day, known as demand response, enables individual electricity customers to partake in good grid citizenship. It also turns what have been traditionally energy-guzzling machines into grid assets.

Every Electric’s program makes “watts drop off the face of the Earth” during peak grid use, says Andrew Wang, co-founder and CEO of the company. “The air conditioner plugs into the power bank, the power bank plugs into the wall, and then as a company, we essentially manage whether the electrons come from the wall or come from the power bank to keep the air conditioner powered while helping reduce strain on the grid,” Wang says.

Residents can request a power bank for each plug-in air conditioner in their home at no cost or for a refundable deposit. Every Electric further incentivizes participation in the program by giving back to residents a portion of its earnings, which it draws from partnering with New York’s electric utility, Con Edison. Wang says the total yearly rebate for a home amounts to a typical July or August electricity bill.

Over 10,000 of Every Electric’s batteries have been requested by New York City residents, but only about 1,000 have been shipped, resulting in a waitlist, says Wang. Last month, he told the Associated Press that his company planned on shipping about 2 megawatts worth of power banks this summer. But now he says the company has already exceeded that figure. Fulfilling all requests this summer would mean Every Electric would provide over 20 megawatts of flexibility to the grid—enough energy to power a few thousand homes.

“I think people really feel the air conditioning hit their bills,” Wang says of the response to the program so far.

Air conditioners become grid assets

Heating and cooling systems that respond to grid needs are just one element of VPPs—a term that describes the aggregation of small power contributions or load shedding from the grid in a decentralized way. VPPs might include residential solar panels, battery storage systems, grid-friendly EV chargers, or a combination of all of these and other elements.

Heating and air conditioning have been incorporated into VPP programs previously, but those usually involved using smart thermostats to throttle heating or cooling during peak hours. That works to curb energy use, but can mean sacrificing comfort.

“Air conditioning has been used for a couple of decades that way, in that it has been used as a demand response resource,” says Ron Domitrovic, senior program manager at the nonprofit energy research institute EPRI. “When there’s a grid need through some sort of dispatch…air conditioners were asked or told to turn off or to cycle,” he says. An air conditioning program that integrates battery storage could be more appealing, because residents wouldn’t be subject to unwanted temperature shifts.

Programs like Every Electric’s also enable demand response at a hyperlocal level. Wang says Con Edison can tell the company if a particular neighborhood needs more energy freed up, and Every Electric can then instruct the power banks in that area to switch on and temporarily cut off air conditioning units from the grid. The company’s current power banks can power a plug-in air conditioner for up to four hours, depending on how efficient the unit is.

Every Electric is actively planning pilot programs with new utilities outside of New York City, especially in New Jersey, Massachusetts and other areas of the Northeast where plug-in air conditioning units are dominant.

Carrier builds battery-enabled heat pumps

In other regions of the United States, central air conditioning is much more commonplace. In response, the global heating, ventilation and air conditioning (HVAC) provider Carrier, based in Palm Beach Gardens, Florida, last year launched a pilot program of residential heat pumps with batteries built directly into the units. Carrier’s machines, which provide both heating and cooling, can switch between grid power and stored energy, depending on demand.

The Carrier pilot began in 50 homes but has now expanded to a number of cities across the U.S. in partnership with several utility companies. Domitrovic, whose institute is collaborating with Carrier on the program, declined to disclose the locations of the trials or the preliminary results.

“What I can say is that [the test units are in] a cross section of climates, both cold and warm, in order to gauge effectiveness and usefulness,” Domitrovic says. The trials collected data this past winter and are currently in the process of collecting summer data. Carrier’s innovation in HVAC made news a couple of years ago when the company tested cold-climate heat pumps that aimed to perform at 100 percent capacity at -15 °C.

Wang says Every Electric is not in the business of creating new units with built-in hardware like Carrier’s. He says his company’s value is instead in its ability to tap into both new and legacy air conditioning units, some up to 20 years old. Portable batteries also offer flexibility for city living and renters.

On the downside, plug-in air conditioning units don’t use as much power as heat pumps, and only operate during warm months, so the positive impact of turning them into demand response machines is less than it is with heat pumps. Plus, adding a 50-pound battery to your home adds bulk to smaller spaces.

“I think what’s valuable for us is understanding, fundamentally, how do people use electricity, and how does having the ability to shift that create value, both for the grid and for them—the people who pay for their electricity,” Wang says.