The reason they were so ineffective is that most panels only work when the customer is connected to the power grid. They automatically shut off during outages, unless they’re connected to a solar battery storage system, which most customers don’t own.

Why do the panels shut off? Safety, according to industry officials.

“It’s actually a requirement for our solar inverters that they do shut down,” said Audrey Lee, vice president of energy services for the national solar company Sunrun. “And that’s because in an outage, we wouldn’t want the power from the solar to flow back on the grid. If there was a utility employee working on that grid, that backflow power would be very dangerous for them.”

Lee added that powering your home during an outage “really does come down to having the right equipment, having the battery to do that.”

Here’s how battery-connected systems work during an outage: Solar energy powers the home during the day and any excess energy is used to charge the battery. The battery can then be used at night, or when the grid goes down, according to a USA Today article.

Battery storage costs several thousand dollars on top of the cost of panels. SMUD has a resource that allows customers to estimate the costs of adding battery backup to a solar system.

Starting next year, a new law requires all new homes in California to have solar panels. Homebuyers will have the option of either paying for solar panels outright, leasing them, or entering a power purchase agreement with developers.