Until recently, you’ve had no choice but to be a passive participant in the electrical grid, paying exorbitantly for the juice that flows into your home. But you’re about to play a much more active role — if you’re not already — and get paid to send power from your home battery or electric vehicle to the energy system. Even if you’re a renter, you may be able to buy solar panels that plug into a wall outlet, turning your balcony into your own tiny power plant.

Earlier this month, a punishing California heat wave showed just how this more flexible grid can help absorb spikes in demand. According to the energy-focused nonprofit Common Charge, as the mercury climbed on October 6, home batteries from Tesla and Sunrun provided enough to power every home in San Francisco and San Jose, whose combined population is about 1.8 million, during peak hours.

This sort of adaptability doesn’t just help stabilize the grid, and it doesn’t just compensate the people who supply power — it saves all ratepayers money in the long run. “It also helps the neighbor who doesn’t have solar and batteries,” said Mary Rafferty, executive director of Common Charge. That’s because drawing on energy that’s stored locally is cheaper than building new gas plants or importing electricity from other states when demand outstrips local supply.

That’s the old, rigid way of operating a grid. Historically, a utility has met demand by forecasting when energy use is going to spike, like late afternoons during the summer, when everyone returns home and turns on their AC. By burning fossil fuels like natural gas, a utility could generate more electricity to keep the grid humming without crashing.

Then came solar panels.

Early residential adopters produced electricity during the day to power their own homes and sent whatever they didn’t need to the grid. They got paid for this, but only until the sun set.

Then came home batteries. They allow a home to store plentiful solar energy throughout a hot summer day, then send any extra to the grid for others to use. Sunrun says that last year it fulfilled 1,300 of these so-called dispatch events, and has so far done more than 800 this year, often with homeowners none the wiser. “It actually is a very seamless experience,” said Wyatt Semanek, senior director of communications at Sunrun. “They don’t even know when we’re actually dispatching the battery. We always are retaining a certain reserve of charge.”

The goal is to see this system get ever more powerful as ever more home batteries plug into the grid: The greater their number, the less a utility would need to draw from each of them. What’s more, a home with batteries can become an energy “island,” keeping its lights on during an outage.

Batteries are also helping overcome the “intermittancy” of renewables. If utilities relied on solar panels and wind turbines alone, they’d only have juice when the sun shines and the wind blows. Now, though, they’re using battery facilities to store that power and discharge it as needed. “We are able to capture that power through home batteries, through community-scale batteries, and then put clean electrons onto the grid when it’s needed most,” Rafferty said.

At the same time, utilities are experimenting with tapping EVs, which are basically giant batteries on wheels. This is known as vehicle-to-grid technology, or V2G: Instead of just drawing from the grid, the battery in some models can send power in the other direction. (Sunrun is among several companies that have launched V2G pilot projects.) Consider, for example, an EV owner who drives to work, charges there, then drives back home and plugs in again in the late afternoon. The car has plenty of juice left, so the owner can opt to let the utility take some as demand rises. Then in the middle of the night, once the spike has eased, the car will charge its battery, so it is ready to go in the morning.

All of which is to say: The goal isn’t just getting more backup batteries onto the grid, but smoothing out demand. V2G promises to be especially powerful when used with vehicles like school buses, which have enormous batteries and operate on predictable schedules, giving the utility a good idea of when that power would be available.

Whether it’s with home or EV batteries, these resources are turning owners into critical participants on the grid, relinquishing energy when they don’t need it and the grid desperately does. Sunrun says that between it and Tesla, 1.2 million batteries are installed across the U.S., capable of dispatching 8 gigawatts back to the grid, almost 11 times what was provided during the California heat wave. Then consider that there are 86 million single-family homes in the country.

“If we unleash this technology, both in California and across the country, we can see that we can power our neighborhoods, our communities, our towns, our schools with local power,” Rafferty said. “And if we do that, we are going to be able to keep costs contained, and we are going to be able to provide reliable energy for everybody.”