What Size Solar Battery Do I Need for My Home?
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What size solar battery do I need? Most homes need a battery sized by two numbers: the kilowatt-hours (kWh) you want to store, and the kilowatts (kW) it must deliver at once. For backing up essentials for a day, that often lands around 5 kWh; covering a whole average U.S. day takes roughly 30 kWh or more.
Short answer: add up the daily kWh of the loads you want the battery to run, multiply by the number of days you want covered, and divide by about 0.9 to allow for losses and reserve. Then check that the battery's continuous power (kW) covers everything that may run at the same time, including motor start-up.
What size solar battery do I need? Start with your goal
A home battery does one of two jobs, and the job sets the size:
Backup during outages. You size for the circuits you will keep on (fridge, lights, Wi-Fi, furnace fan, well or sump pump) and how many hours you want to ride through.
Self-consumption or time-of-use savings. You size for the evening energy you want to shift from your solar panels to after sunset, usually a few hours of household use.
Many owners want both, so they size for the larger of the two.
Step 1: Find your daily kWh
Your utility bill shows monthly kWh. For reference, the U.S. Energy Information Administration reports that in 2022 the average residential customer bought 10,791 kWh a year, about 899 kWh a month [1]. That works out to roughly 29.6 kWh a day. Your home may use far more or less, so use your own bills or a meter rather than the average. EIA also notes that homes with net-metered solar may buy less than they use [1].
A whole-home energy monitor shows which circuits use what, by the hour, which is the most useful data you can have before buying a battery.
Step 2: Add up the loads you want to back up
The table below is illustrative. The wattages and run-times are assumptions for the example, not measurements; check your own appliance labels or monitor.
Load (illustrative) | Assumption | kWh per day |
Refrigerator | Typical modern unit | 1.5 |
Wi-Fi router, phones, laptop | Small electronics | 0.4 |
LED lights | 5 bulbs × 10 W × 8 h | 0.4 |
Furnace blower | 400 W × 4 h | 1.6 |
Well or sump pump | 800 W × 1 h | 0.8 |
Total | 4.7 |
Step 3: Multiply by days of backup and add a margin
Batteries lose some energy in the inverter, and most keep a reserve so they are not drained to zero. Dividing by 0.9 is a simple, conservative allowance for this example; your installer will use the figures for your specific system.
Illustrative scenario | Daily need | Calculation | Battery to plan for |
Essentials, 24 hours | 4.7 kWh | 4.7 × 1 ÷ 0.9 | about 5.2 kWh |
Essentials, 3 days with no sun | 4.7 kWh | 4.7 × 3 ÷ 0.9 | about 15.7 kWh |
Evening self-use (10 kWh after sunset) | 10 kWh | 10 ÷ 0.9 | about 11.1 kWh |
Whole average U.S. day | 29.6 kWh | 29.6 ÷ 0.9 | about 32.8 kWh |
Solar panels recharge the battery on sunny days, so a multi-day outage needs less storage if your array can refill the battery each day. Cloudy winter days are the case to plan for.
Step 4: Check power (kW), not just capacity (kWh)
Capacity is how long the battery lasts; power is how much it can run at once. In the example, the fridge, furnace blower, pump and small loads could draw about 1.5 kW together, but motors and compressors draw more for a moment when they start. Check that the battery's continuous and surge ratings cover your largest loads starting together.
As a reference point, Tesla's Powerwall 3 datasheet lists 13.5 kWh of nominal battery energy and 11.5 kW of continuous discharge power per unit, with a 10-year warranty [2]. One such unit would cover about 46% of an average U.S. day's purchases at 29.6 kWh, so whole-home backup usually means either several units or a smaller set of backed-up circuits.
How to choose a home battery or backup power station
Usable capacity (kWh) that matches your Step 3 number, with room to expand later.
Continuous and surge output (W or kW) for the loads that run together.
Chemistry: lithium iron phosphate (LFP) is common in home units and is chosen for long cycle life.
Connection: a permanently installed battery works with your solar inverter; a large portable power station can connect to selected circuits through a transfer switch or home panel installed by an electrician.
Certifications and warranty: look for safety listings such as UL 9540 for energy storage systems, and compare warranty years.
Products that fit these specs
These picks are based on published specifications, not hands-on testing by ReneEnergy. Check current availability and specs before buying.
Emporia Vue 3 Home Energy Monitor: a whole-home electricity monitor that tracks real-time usage and supports solar and net-metering monitoring. It gives you the measured kWh numbers for Steps 1 and 2.
Anker SOLIX F3800 Plus: 3,840 Wh LFP battery rated for 3,000+ cycles, 6,000 W maximum AC output including a 120/240 V outlet, expandable with up to six 3.84 kWh expansion batteries, 5-year warranty [3]. One unit covers the 24-hour essentials example above.
EcoFlow DELTA Pro 3: 4,096 Wh LFP battery, 4,000 W 120/240 V output, listed as UL 9540 certified, expandable from 4 to 48 kWh with extra batteries and units, 5-year warranty with app registration [4].
FAQ
How long will a 10 kWh battery run my house?
Divide usable kWh by your hourly use. At the U.S. average of about 29.6 kWh a day (roughly 1.2 kWh an hour), 10 kWh lasts about 8 hours; running only essentials like the 4.7 kWh example, it lasts about two days. Real results depend on your loads and the battery's usable capacity.
Do I need a battery with solar panels?
No. Grid-tied solar works without one. A battery adds outage backup and lets you use more of your own solar after dark, which matters most where export credits are low or time-of-use rates are high.
Is there a federal tax credit for home batteries in 2026?
For U.S. homeowners, the IRS says the Residential Clean Energy Credit is not available for property placed in service after December 31, 2025 [5]. Batteries installed by that date had to have at least 3 kWh of capacity to qualify [5]. Check state and utility programs for current incentives.
How many batteries do I need to go off-grid?
Off-grid homes usually size for several days of full use plus enough solar to recharge in winter, which is much larger than a backup system. Using the average-day figure above, three days would be about 98.7 kWh before any solar recharge. An off-grid design should be done by a qualified installer.
This guide is general information, not financial, legal or electrical advice. Home batteries connect to your electrical panel; use a licensed electrician or installer for any wiring.
Related reading
Thinking about going solar?
If you are weighing solar with or without a battery, a personalized quote will show the system size and storage options that fit your home and usage.
Sources
Fact-checked November 10, 2026.
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