How to make sure your solar-plus-battery system works…

As catastrophic storms and wildfires continue to ravage the power grids, more and more people are adding home batteries to rooftop solar panels to provide backup power during extended outages. As Puerto Ricans saw after Hurricane Fiona and Floridians saw after Hurricane Ian, even smaller solar-plus-battery setups can be a lifeline when power goes out.

However, setting up these systems with the goal of maintaining power during power outages requires a different approach than setting them up to, for example, reduce household electricity bills or get paid to provide excess solar power during periods of high grid demand. Projects designed to power the most important devices in a home for days, weeks, or months require more forward planning and real-time juggling between a family’s energy needs, battery charge level, and the amount of sunlight on any given day.

“It’s like running your own little nanogrid in your home,” said Javier Rúa-Jovet, chief policy officer of the Solar and Energy Storage Association of Puerto Rico, an industry group.

Rúa-Jovet, who lives in San Juan, relied on his own system for weeks after Fiona shut down Puerto Rico’s entire power grid in September 18 – almost five years to the day after Hurricane Maria devastated US territory. Many other Puerto Rican families used modest solar-plus-battery setups to cool insulin, power hospital beds at home, or charge laptops and cell phones.

“We have growing concerns about electrical reliability in the United States, and they have increased because of climate change,” said Will Gorman, a graduate student at Lawrence Berkeley National Laboratory in California — a state where utility companies occasionally shut down grid infrastructure to do this avoid the risk of starting wildfires in the warming, drying region.

With demand for solar-plus-battery systems increasing, Gorman and other researchers recently analyzed how the technology might perform during a three-day blackout in different climates and different scenarios for a new study. ​“At the highest level, we have found that solar and storage systems can provide backup power fairly reliably for the majority of the United States,” he said.

More specifically, solar panels paired with a standard-sized, 10-Kilowatt-hour battery could meet a home’s critical electricity needs for three days. This can include powering refrigerators, lighting, internet services and well water pumps for a single family home. systems with a 30-kilowatt hour capacity could also run heaters or air conditioners, though not everywhere.

“A customer may hear claims that all you need is one 10-kilowatt-hour system and you [entire] Home is going to be great,” Gorman said. ​“We wanted to communicate the capabilities and limitations of these systems in a given region.”

How a project performs ultimately depends on how well it is designed before the net goes dark and how effectively it is managed afterward. Here’s a general guide from energy experts on adding home batteries for backup power.

Plan ahead and lean big

According to Fidel Neverson, the best place to start is with a good old-fashioned spreadsheet. Neverson manages clean energy projects in the Caribbean for the think tank RMI, and he lives in St. Vincent and the Grenadines. (Canary Media is an independent subsidiary of RMI.)

Home and business owners looking to add new solar-plus-battery systems should sit down with potential installers and create a detailed bill of their electricity loads — how long they use certain devices, how often, and for how long — to better understand how much daily backup power they need during an extended outage. Then estimate how much solar energy is needed to meet those requirements in the fewest solar scenarios: during the rainy season, in the winter months, or on cloudy days that often follow hurricanes.

“I always prefer to be extremely careful and not oversize the system [just to save] the customer money,” he said, because ​“If they then have a long-term grid failure, the system cannot provide them with their energy.”

Neverson said another consideration is how well the technology will work as it ages, gradually generating and storing less electricity over time. That could mean designing a system larger than today so it can still power critical loads of five or more 10 years on the road. He also recommends designing the battery system so that it can be operated independently 24 hours without charging via the solar panels.

While a more cautious approach like this is more expensive for the homeowner, ​“It gives you a little bit more assurance in terms of reliability if you have a long-term outage,” he said.

Still, there are ways to limit the size and cost of a battery backup system. Households can proactively select which circuits receive power when the system is in backup mode by adding a secondary switchboard at the same time as installing the battery system. Only critical energy loads are connected to this panel, while circuits that power less essential equipment such as washing machines and freezers remain connected to the original panel.