Do solar panels work in a power outage?
Not on their own. The Department of Energy notes that rooftop solar panels alone are not enough to make a home resilient, because grid-connected systems are designed to switch off when grid power goes out; keeping power on needs a properly configured inverter and a storage system.[1] A battery is what stores energy for the hours without the grid, and solar recharges it during the day if the inverter is set up to run in island mode.
How to size a solar battery backup
Size the battery for energy first and power second. Energy, in kWh, decides how long you can run; power, in kW, decides how much can run at the same moment.
- Daily energy. The average U.S. home used 863 kWh a month in 2024,[4] about 28.3 kWh a day. Backing up only essentials (refrigerator, lights, internet, a furnace fan or well pump) takes less; add up their watts × hours.
- Hours. Energy for the outage = daily kWh × hours ÷ 24.
- Losses. Divide by an efficiency allowance. The national lab's technology baseline uses 85% round-trip efficiency for home batteries;[3] using the full round-trip figure for a battery charged before the outage leaves a small margin.
- Power. Check that the batteries' combined kW covers your largest loads at once, especially anything with a motor.
| Backed-up use per day | 12 hours | 24 hours | 72 hours |
|---|---|---|---|
| 5.0 kWh | 2.9 kWh · 1 unit | 5.9 kWh · 1 unit | 17.6 kWh · 2 units |
| 10.0 kWh | 5.9 kWh · 1 unit | 11.8 kWh · 1 unit | 35.3 kWh · 3 units |
| 15.0 kWh | 8.8 kWh · 1 unit | 17.6 kWh · 2 units | 52.9 kWh · 4 units |
| 20.0 kWh | 11.8 kWh · 1 unit | 23.5 kWh · 2 units | 70.6 kWh · 6 units |
| 28.3 kWh (U.S. average home) | 16.6 kWh · 2 units | 33.3 kWh · 3 units | 99.9 kWh · 8 units |
| 40.0 kWh | 23.5 kWh · 2 units | 47.1 kWh · 4 units | 141.2 kWh · 11 units |
Solar recharging changes the multi-day column: on a sunny day the panels may refill much of the battery, on a cloudy one very little. The table assumes no recharging, which is the safe case for an outage that comes with a storm.
Battery size and power: what homes are installing
The median home battery installed in 2025 held 13.5 kWh, the same as in 2024, while median power rose from 6.0 kW to 11.4 kW.[2] At 85% efficiency one such battery delivers about 11.5 kWh, enough for about 10 hours at the average home's 28.3 kWh a day, or much longer for essentials only.
Batteries are now a common add-on: 37% of new home solar systems in 2025 came with storage, up from 25% in 2024, led by California at 74%.[2] California's switch in April 2023 to a net billing tariff, which credits exported solar at a lower rate on average, made storing midday power more valuable there.[5]
How much a solar battery costs
A home battery adds about $1.3 per watt of panels to a solar system at the 2025 medians: $4.90 per watt for systems with storage vs. $3.60 without, about $10,010 on a 7.7 kW system. For cash purchases the gap was $2.1 per watt.[2] The national lab's bottom-up model puts a 5 kW, 12.5 kWh home battery at $885 per kWh (2023 dollars, 2024 costs), about $11,063 installed.[3] About 80% of LBNL's paired-system price data come from California, so treat both figures as reference points, not quotes.
| Measure | Value | Source |
|---|---|---|
| Extra price of solar + storage over solar alone, 2025 median | $1.3/W of PV ($10,010 on 7.7 kW) | LBNL |
| Extra price for cash purchases | $2.1/W of PV | LBNL |
| Modeled cost, 5 kW / 12.5 kWh system | $885/kWh ≈ $11,063 | NLR ATB 2025 |
| Federal tax credit for a battery installed in 2026 | 0% (30% through 2025) | IRS |
The residential clean energy credit covered battery storage of at least 3 kWh through 2025, but it is not available for property placed in service after December 31, 2025.[6]
Paying for itA battery bought with a new solar system can be financed with it. Compare a HELOC, a home equity loan and a personal loan with the home improvement loan calculator, or see the draw-period payment with the HELOC payment calculator.
Worked example
- Load: the whole house at the U.S. average, 28.3 kWh a day, for 24 hours = 28.3 kWh.
- Losses: 28.3 ÷ 85% = 33.3 kWh of battery.
- Units: 33.3 ÷ 13.5 = 2.47, so 3 batteries (40.5 kWh).
- Power: 3 × 11.4 kW = 34.2 kW available, above the 5 kW example peak load.
Backing up essentials at 10 kWh a day instead needs 1 battery for the same day. To see what the panels themselves cost and save, use the solar panel cost calculator and the solar calculator.
Frequently asked questions
How big a battery do I need to run my house?
Daily kWh × hours of backup ÷ 24 ÷ efficiency. A full day for an average home (28.3 kWh) needs about 33.3 kWh, or 3 batteries of 13.5 kWh. Essentials only need much less.
How long will a 13.5 kWh battery run a house?
About 10 hours at the U.S. average of 28.3 kWh a day after 85% efficiency; roughly twice as long at half that load.
Do solar panels work during a power outage without a battery?
Usually not. Grid-tied systems are designed to switch off when the grid goes down; backup needs a suitable inverter and storage.[1]
Sources
- Solar and Resilience Basics
- U.S. Distributed Solar and Storage: 2026 Data Update (Tracking the Sun)
- Annual Technology Baseline 2025: Residential Battery Storage
- Electric Sales, Revenue, and Average Price, Table 5A: 2024 Average Monthly Bill, Residential
- California residents are increasingly pairing battery storage with solar installations (Today in Energy)
- Residential Clean Energy Credit