Your future air conditioner might act like a battery

As temperatures climb on hot days, many of us are quick to crank up our fans or air conditioners. These cooling systems can be a major stress on electrical grids, which has inspired some inventors to create versions that can store energy as well as use it.

Cooling represents 20% of global electricity demand in buildings, a share that's expected to rise as the planet warms and more of the world turns to cooling technology. During peak demand hours, air conditioners can account for over half the total demand on the grid in some parts of the world today.

New cooling technologies that incorporate energy storage could help by charging themselves when renewable electricity is available and demand is low, and still providing cooling services when the grid is stressed.

We say, take the problem, and turn it into a solution," says Yaron Ben Nun, founder and chief technology officer of Nostromo Energy.

One of Nostromo Energy's systems, which it calls an IceBrick, is basically a massive ice cube tray. It cools down a solution made of water and glycol that's used to freeze individual capsules filled with water. One IceBrick can be made up of thousands of these containers, which each hold about a half-gallon, or roughly two liters, of water.

Insulation keeps the capsules frozen until it's time to use them to help cool down a building. Then the ice is used to drop the temperature of the water-glycol mixture, which in turn cools down the water that circulates in the building's chilling system. The whole thing is designed to work as an add-on with existing equipment, Ben Nun says.

Nostromo installed its first system in the US in 2023, at the Beverly Hilton hotel in Los Angeles. It has a capacity of 1.4 megawatt-hours, and it also serves the neighboring Waldorf Astoria. The installation contains 40,000 capsules, amounting to about 150,000 pounds of ice. It usually charges up for 10 to 12 hours, starting at night and finishing around midday. That leaves it ready to discharge its cooling power between the late afternoon and evening, when demand on the grid is high and solar power is dropping off as the sun sets.

Using the IceBrick increases the total electricity needed for cooling, as some energy is lost to inefficiency during the cycle. But the goal is to decrease the energy demand during peak hours, which can cut costs for building owners, Ben Nun says. The company is in the process of securing roughly $300 million in funding, in part from the US Department of Energy's Loan Programs Office, to fully finance 200 of these systems in California, he adds.

Nostromo's IceBrick is made of individual capsules that freeze and thaw to store energy. NOSTROMO

While building owners can benefit immediately from these individual energy storage solutions, the real potential to help the grid comes when systems are linked together, Ben Nun says.

When the grid is extremely stressed, utility companies are sometimes forced to shut off electricity supply to some areas, leaving people there without power when they need it most. Technologies that can adjust to meet the grid's needs could help reduce reliance on these rolling blackouts.

This kind of approach isn't new-many commercial units have large tanks that hold chilled water or another cooling fluid that can drop the temperature in a building at a moment's notice. But Nostromo's technology can store more energy with much less material, because it uses the freezing and melting process rather than just cooling down a liquid, Ben Nun says.

Startup Blue Frontier has differentiated itself in this space by building cooling systems that use desiccants. These materials can suck up moisture-like the little packets of silica beads that often come with new shoes and bags. But instead of those beads, the company is using a concentrated salt solution.

Blue Frontier's cooling units pass a stream of air over a thin layer of the desiccant, which pulls moisture out of the air. That dry air is then used in an evaporative cooling process (similar to the way sweat cools your skin).

Desiccant cooling systems can be more efficient than the traditional vapor compression air conditioners on the market today, says Daniel Betts, founder and CEO of Blue Frontier. But the system also benefits from the ability to charge up during certain times and deliver cooling at other times.

The key to the energy storage aspect of desiccant cooling is the recharging: Like sponges, desiccants can only soak up a limited amount of water before they need to be wrung out. Blue Frontier does this by causing some water in the salt solution to evaporate, typically with a heat pump, to make it more concentrated. The recharging system can run constantly, or in bursts that can be timed to match periods when electricity is cheap or when more renewable power is available.

The benefit of these energy storage technologies is that they don't require people turn their cooling systems down or off to help relieve stress on the grid, Betts says.

Blue Frontier is testing several systems with customers today and hopes to manufacture larger quantities soon. And while commercial buildings are getting the first installations, Betts says he's interested in bringing the technology to homes and other buildings too.

One challenge facing the companies working on these incoming technologies is finding a way to store large amounts of energy effectively without adding too much cost, says Ankit Kalanki, a principal in the carbon-free buildings program at the Rocky Mountain Institute, a nonprofit energy think tank. Cooling technologies like air conditioners are already expensive, so future solutions will have to be priced competitively to make it in the market. But given the world's growing cooling demand, there's still a significant opportunity for new technologies to help meet those needs, he adds.

Just rethinking air conditioning won't be enough to meet the massive increase in energy demand for cooling, which could triple between now and 2050. To both do that and cut emissions, we'll still need significantly more renewable energy capacity as well as gigantic battery installations on the grid. But adding flexibility into air-conditioning systems could help cut the investment needed to get to a zero-carbon grid.

Cooling systems can help us cope with our warming climate, Ben Nun says, but there's a problem with the current options: You'll cool yourself, but you keep on warming the globe."