Can Solar and Batteries Outlast an Extended Power Outage?

Even by the standards of the generally well-informed clean-energy customers in California's Bay Area, Todd Karin is a savvy one.

Karin works as a postdoctoral researcher in the energy storage and distributed resources division at Lawrence Berkeley National Laboratory. Last year, he chose to add solar and storage to his home, first buying an array of Panasonic panels and then adding a Tesla Powerwall a few months later. 

Karin said the decision to go solar was an environmental and economic one, but the energy storage he had installed was in preparation for an uptick in power outages. He lives in a part of rural Solano County situated between San Francisco and the Central Valley. Though power outages roiled the Bay Area last week — with Pacific Gas & Electric reporting a peak of 738,000 impacted customers — Karin and many of his neighbors were prepared.

“Almost all of our neighbors have generators. You can hear it when you go outside,” Karin said. “One of our neighbors got a generator from a hospital that they were throwing away. They could light up the whole town if PG&E would let them.”    

The outage was the first extended test for Karin’s backup system. PG&E cut electricity to his house for a little over two days. Without power, the well and pump system supplying water to his home can’t function. But the Powerwall largely worked, allowing the house to use water, the fridge and even a table saw for a bit of woodworking.    

California's outages come at a time when many residential solar sellers are rushing battery products to market or working to expand attachment rates for new sales. Sunnova, Sunrun, SunPower and Tesla all offer in-house storage products for home solar customers. Those products join a growing crowd of storage vendors including Simpliphi, LG Chem and the latest entrant, Generac, a company formerly focused solely on backup generators.

Not quite full resilience

PG&E’s public safety power shutoffs could mean a windfall of business for residential storage providers. Outage areas ringing the Bay Area align with the home base of some of the most likely clean-energy buyers. And though fire is a natural part of California’s landscape, extreme weather worsened by climate change is making wildfires more severe, compelling more customers to look for resilient energy solutions. On Monday, the California Department of Forestry and Fire Protection was managing several fires burning throughout the state.

California also remains the top state for residential solar installations. In January a state mandate goes into effect requiring all new homes to include solar. California’s storage market is also the biggest in the U.S. and grew 70 percent from Q2 to Q3, according to Wood Mackenzie Power & Renewables.

In a market flush with options, though, it can be unclear how they all stack up — especially in the event of an extended power outage.

No solar-plus-storage system currently on the market can completely support average U.S. electricity usage during a days-long blackout. But customers can rely on them for some of the basics, analysts say. 

"Depending on the size of the battery, these home solar-plus-storage systems can add a certain level of resilience: keeping the lights on, the internet running, food from spoiling, etc. It’s definitely valuable,” said Michelle Davis, a senior solar analyst at WoodMac.

“But the average solar and battery sizes being installed today couldn't support an HVAC system, standard hot water heater and other loads in a typical home for more than a few hours. So is it full resilience during a blackout? No, definitely not.” 

Karin said he used an electric burner for most cooking to try to conserve power. Mild temperatures meant no need for climate control, but that would have sucked up too much electricity anyway. However, lack of access to HVAC can be dangerous for many people during an outage.

Karin's system also didn’t perform seamlessly. For reasons unknown to him, his SMA string inverter repeatedly tripped off. Though it didn’t interrupt his power, it did likely put added wear on the system. Tesla did not respond to request for comment about whether other customers had reported issues. 

How long will my battery system last?

Some batteries will also provide longer backup than others. The 13.5-kilowatt-hour capacity of Tesla’s Powerwall, for instance, outranks Sunrun’s Brightbox at 10 kilowatt-hours. But those systems have the same power rating, at 5 kilowatts, which means they offer the same “maximum load coverage,” according to WoodMac’s director of solar, Ravi Manghani.

“Typically, during a power outage, one wouldn't aim to draw at the maximum 5 kilowatts," a load roughly equivalent to running a clothes dryer, microwave and hair dryer all at once, Manghani said.

“An average homeowner typically will draw 2 kilowatts maximum during an outage, and an average of 750 to 1,000 watts during the course of the outage," he said. "This means a Brightbox will last for 10 to 12 hours, while a Powerwall will last for 12 to 15 hours.” 

Certain applications and programs already on the market, such as Sense and Powerley, can also give homeowners an idea of their usage. But in a Catch-22, the apps might require power to function, though data on past power usage could help homeowners identify which appliances to prioritize. 

Recent data suggests that many homeowners installing energy storage systems are opting for two batteries instead of one for greater backup capacity. 

John Berger, CEO at residential solar and storage company Sunnova, told Greentech Media that the company has seen an influx in demand for storage from existing customers looking to update their systems, as well as new customers asking for batteries from the start. In terms of how long the system can last, however, Berger offers what he called “a rather unsatisfying answer.” 

“It depends on how much power your home uses, how big it is, what the weather is in your particular area,” he said. “Some of our customers may be able to have a whole home backup with one or two batteries, and then in other cases that may still not be enough.” 

Coming soon: Your personal nanogrid

Sunnova is working on integrating traditional generators and demand-side management alongside its storage-plus-solar system to create a “nanogrid” that the company will then manage as a service provider. 

Because conventional generators use fossil fuels, that solution isn’t as clean as solar-and-storage alone, but it could offer higher reliability during extended outages. 

Whatever solution customers choose, Berger said most recognize that climate change is worsening the impact of natural disasters, whether or not they live in California.

“We see it all around the country and around the world,” said Berger. “This seems permanent; this is not going to go away. It’s not a one-time event, or two times. It’s not just the wildfires; it’s the hurricanes as well.” 

“There's no reason to sit in your house and wonder when the utility is going to shut off the power or when the power lines are going to go down. Frankly, that’s a bit archaic,” he added.

“We should, as a society — and not just in the United States, but globally — be demanding better service. […] Right now, an increasing number of folks are able to go out there and get that better service.”