Home batteries generally come as an option alongside rooftop solar panels. Batteries have prevented widespread blackouts in Puerto Rico this year. Photo / 123RF
Blackouts are routine in Puerto Rico, where an ageing and storm-battered fleet of oil, gas and coal plants teeter constantly on the edge of collapse.
By the time the northern summer ends, the power will go out 93 times, according to a forecast from the island’s grid operator, LUMA.
But a solution is rising to alleviate the sticky, summer misery. Roughly one in 10 Puerto Rican homes now have a battery and solar array for back-up power.
The batteries don’t just protect the homeowners who purchased and installed them: they’ve also become a crucial source of back-up power for the entire island grid.
A network of 69,000 home batteries can generate as much electricity as a small natural gas turbine during an emergency, temporarily covering about 2% of the island’s energy needs when things go wrong.
For a system that’s always in crisis mode, that buffer can make a big difference. LUMA, which through agreements with homeowners can use stored power in emergencies, has already called in the back-up batteries 30 times this year to ease shortages.
“It has very, very certainly prevented more widespread outages,” said Daniel Haughton, LUMA’s transmission and distribution planning director.
“In the instances that we had to [cut power], it was for a much shorter duration: a four-hour outage became a one- or two-hour outage.”
Puerto Rico’s experience offers a glimpse into the future for the rest of the United States, where batteries are starting to play a big role in keeping the lights on.
Authorities in Texas, California, and New England have credited home batteries with preventing blackouts during summer energy crunches.
As power grids across the country groan under the increasing strain of new data centres, factories, and EVs, batteries offer a way for homeowners to protect themselves – and all of their neighbours – from the threat of outages.
Batteries have been booming in the US since 2022, when Congress created generous installation tax credits for homeowners and power companies.
Home batteries generally come as an option alongside rooftop solar panels, according to Christopher Rauscher, head of grid services and electrification for Sunrun, a company that installs both. More than 70% of the people who hire Sunrun to put up solar panels also get a battery.
With the tax credits – and the money saved on rising electricity costs – solar panels and batteries make financial sense for most American homes, according to a study Stanford University scientists published on August 1.
About 60% of homes would save money in the long run with solar panels and batteries.
In a blackout, most US homes would be able to cover about half of their typical energy needs, protecting key appliances like the fridge or the air conditioner.
The benefits are especially strong in sunny, disaster-prone states such as California, Florida, and Texas.
Those batteries can have broader benefits, too.
Utilities pay customers hundreds of dollars a year to sign their batteries up to form “virtual power plants”, which send electricity to the grid whenever power plants can’t keep up with demand.
California’s network of home batteries can now add 535 megawatts of electricity in an emergency – about half as much energy as a nuclear power plant.
Battery installations are set to break another record this year. But analysts expect the red-hot growth will cool at the end of this year, when tax credits for home batteries expire under the new Republican tax and spending law.
“We’re expecting a rush of installations at the end of 2025 as people try to take advantage of this, followed by a contraction in 2026,” said Max Issokson, a distributed solar and storage analyst at the energy research firm Wood Mackenzie.
When the tax credits go away, the share of US homes that would save money installing solar panels and batteries will drop from 60% to just under a third, the Stanford scientists say.
Even though growth may slow, there will still be tens of thousands of new home batteries installed next year, Issokson said.
Some wealthy homeowners can simply afford to pay higher prices for back-up power.
Others will accept “third-party ownership” offers. In that sort of set-up, companies install solar panels or batteries on customers’ homes for free; the company owns and maintains all the hardware and sells the cheap electricity it generates to the homeowner.
In the long run, battery costs are expected to keep falling, putting them back within financial reach for most American homeowners in the early 2030s, according to Tao Sun, a Stanford environmental engineer and lead author of the study.
Homeowners looking for back-up power have a choice between batteries and generators fuelled by natural gas, propane, petrol or diesel.
A generator can generally cover your entire home’s energy needs as long as you have fuel to keep it running. Solar panels and batteries may only cover your most essential appliances, such as the fridge, the lights or the air conditioner.
While both options are pricey, generators have an edge on upfront cost. Buying and installing a typical standby generator could cost somewhere between US$7000 and US$15,000, while a home battery system might cost between US$10,000 and US$20,000, according to a guide from the tech news and review site CNET.
For home batteries to last through days-long outages, they need to be paired with rooftop solar panels, which could add another US$20,000 to the price, according to listing data from EnergySage, an online marketplace for solar panels and batteries.
Once you’ve paid the high start-up costs, solar panels and batteries are cheaper to run and maintain. You have to buy fuel to refill a generator, but solar panels refill batteries for free.
Plus, homeowners can make thousands of dollars a year lowering their energy bills, selling solar power back to the grid or enrolling their batteries in a virtual power plant, depending on their power company’s policies and state regulations.
“Over time, you would get the full payback for your system and basically get your back-up for free,” said Ram Rajagopal, an associate professor of civil and environmental engineering who co-authored the Stanford study.
Generators have been around longer than home batteries, so it may be easier to find a contractor to install a generator.
Batteries take up less space, run silently and carry zero risk of carbon monoxide poisoning.