Will my solar and battery keep my home running during a PG&E outage?

Grid-tied solar is required to switch off when the grid goes down. This is a safety rule that protects utility crews working on the lines, and it applies to almost every home solar system. The result surprises many homeowners: a roof full of panels will not run the house during a daytime outage on its own.

For the panels to keep producing when the grid is gone, the system needs two things working together, a battery and an inverter configured to run independently of the grid. With those in place, the system can detect the loss of grid power and switch to a backup mode that keeps the home powered.

The system includes an automatic transfer switch. When the grid signal falls outside the normal voltage and frequency range, the system disconnects from the grid in a fraction of a second and begins supplying the home from the battery and solar. This is often called islanding, because the house becomes its own small grid.

The switch is automatic. You do not need to flip a breaker, start a generator, or be home for it to work. When the grid comes back and stays stable, the system reconnects and returns to normal operation.

There is an important design choice here: whole-home backup versus partial backup. Some installers back up only a few essential circuits behind a small subpanel. Potrero designs for whole-home backup, so the goal is to keep the whole house running rather than asking you to choose a handful of outlets in advance.

Runtime depends on three things: how much energy the battery stores, how much power your home draws, and how much the sun recharges the battery during daylight. A home running heavy loads through a dark, smoky storm draws down the battery faster than a home covering only the refrigerator, lights, internet, and a heat pump.

As a rough guide, with about 30 to 60 kWh of storage most homes get one to three days of full-home backup during a Public Safety Power Shutoff or storm. A standard Potrero design uses two EG4 batteries at about 28.6 kWh, and the number of batteries can be raised when multi-day resilience is a priority.

The recharge point matters more than people expect. During a multi-day outage, the solar array refills the battery every sunny day, so a backup event with good sun can last far longer than the raw battery size suggests. An outage with little sun leans almost entirely on stored energy, which is the case worth planning around.

Many Bay Area outages come with warning. PG&E aims to notify customers one to two days before a Public Safety Power Shutoff, which gives you time to prepare the system rather than react to it.

Two settings help. Battery Last Mode tells the system to run the home from solar first, then the grid, and only then the battery, so you enter the outage with the battery as full as possible. AC charge mode lets the battery top up from the grid to a target level, which is useful before a forecast storm or on a cloudy day when solar will not reach a full charge on its own.

Used together, these let you walk into a planned outage at or near 100% state of charge, which directly extends how long the home stays powered.

Backup is only useful if it can run the loads you actually care about. The hardest common load is a central air conditioner, because the compressor needs a large burst of current to start. The inverter Potrero uses can cold-start a 5-ton air conditioner, briefly supplying up to roughly 190A or 45kW to get the compressor moving.

For continuous loads, the system can deliver about 16 kW during the day while solar is producing and about 12 kW at night on battery alone. That covers typical household demand and even Level 2 EV charging, though during an outage it is wise to manage large optional loads so the stored energy lasts longer.

If backup matters to you, make the installer be specific. A quote that promises battery backup without defining what stays on, and for how long, is not really answering the question.

Potrero treats whole-home backup as a default design goal, sized from your PG&E interval usage and your backup priorities rather than a generic battery count. The smart panel adds a layer of control, so during a long outage you can prioritize and shed loads to stretch critical circuits like the refrigerator, medical equipment, heat, well pump, and internet.

The right backup target depends on your area. Homes in parts of the Bay Area that see frequent or multi-day Public Safety Power Shutoffs may want more storage, while homes with rare, short outages may not. The point of the design conversation is to match the system to how often the power actually goes out where you live, and what must stay on when it does.