The short version
- A battery's storage (kWh) decides how long it lasts; its power (kW) decides what it can run at once.
- Backing up essentials like the fridge, lights, Wi-Fi and outlets can last days. Backing up the whole house, including heating and cooling, drains it much faster.
- With solar, a battery can recharge during a multi-day outage when the sun is out.
- The same battery can also lower your bill every day by covering the 4–9 p.m. peak.
Storage vs power: kWh vs kW
kWh: how long
Storage, like the size of a gas tank. A 13.5 kWh battery holds 13.5 kWh of energy.
kW: how much at once
Power, like the width of the hose. It limits how many things can run at the same time.
Large motors, such as well pumps and central air conditioners, also need a burst of starting power. That can be the real limit, not storage.
Whole-home vs essential backup
Essential backup puts key circuits, like the refrigerator, lights, Wi-Fi, some outlets and the garage door, on a backup panel. Those use relatively little energy, so a battery can often carry them for days.
Whole-home backup keeps everything available, but large loads like heating, cooling, ovens and EV charging can drain a battery in hours. Many people choose whole-home backup but use the big loads sparingly during an outage. The Battery Backup Planner shows how long different choices last.
Recharging with solar
A battery paired with solar can recharge during a daytime outage, which is what makes multi-day outages manageable. Production is much stronger on long summer days than in winter storms, so plan for the worst case, not the best.
Outages in the North Bay
Winter storms and Public Safety Power Shutoffs (PSPS), when PG&E turns off power in high fire-risk weather, can mean outages lasting hours or days. If you depend on medical equipment, a well pump or refrigerated medication, backup planning deserves extra care.
Everyday savings, too
A battery isn't only for outages. Under PG&E's current solar rules, it earns its keep every day by storing midday solar and using it during the expensive 4–9 p.m. peak. Most systems keep a reserve for outages while using the rest for savings. See Solar and battery storage.
Batteries vs generators
Generators can run large loads for as long as there's fuel, but they're noisy, need maintenance and fuel storage, and don't save money day to day. Batteries are quiet, switch over automatically and lower your bill, but have limited storage. Some homes use both.
Questions to ask your contractor
- What exactly will be backed up?Ask for a list of circuits.
- How long would my essentials last with no sun?
- Can it start my well pump or air conditioner?Starting power may need to be checked.
- How much will be reserved for outages vs daily savings?
- Will it recharge from solar during an outage?
Common mistakes to avoid
- Backing up everything, then running it all. Big loads drain a battery fast.
- Planning for summer sun only. Winter storms mean weak solar.
- Ignoring starting power. Motors can need more than the battery provides.
- Forgetting the everyday value. Savings can help pay for the battery.
Run the numbers for your home
This guide is general education, not advice for your specific home. Equipment, rebates and PG&E rates change; confirm details with a qualified professional. Unfamiliar term? See the glossary. Have a question it didn't answer? Ask Robert.