How Much Solar Battery Storage Do I Need?
Most homes need between one battery and a few, and the right size depends on what you want to power and for how long.
Most homeowners who want backup for key items need about 10 to 15 kilowatt-hours (kWh) of storage. Running a whole home through a long outage typically takes 20 to 40 kWh or more.
A kWh is the energy a 1,000-watt device uses in one hour. Battery size is listed in kWh. Your goal decides the number, so start there.
Why do I need a battery with solar panels?
You do not always need one. Panels make power in the day, and a battery saves some of it for night or for an outage.
Without a battery, your system usually shuts off when the grid goes down. This is a safety rule so line workers are not shocked by power from your roof. A battery with the right inverter lets you keep power on during an outage.
A battery can also help if your utility pays little for extra power you send to the grid. See what net metering is first. If your utility credits you fairly for exported power, a battery may add cost without saving much money.
How do I work out my battery size?
Add up the watts of what you want to run, multiply by the hours you want it on, and divide by 1,000. The answer is kWh.
Here is a simple way to do it:
- List the items you must keep on: fridge, lights, internet, phone chargers, a well pump, medical devices.
- Find the watts on each label, or in the manual.
- Multiply watts by hours of use per day, then add the items up.
- Divide by 1,000 to get kWh per day.
- Multiply by the number of days you want to cover.
Two cautions apply. First, a battery cannot be drained fully, so usable capacity is what counts. Check the usable kWh on the spec sheet. Second, motors such as a well pump or air conditioner pull a big burst of power when they start. The battery and inverter must handle that peak, not just the daily total.
For comparison, the U.S. Energy Information Administration reports that an average U.S. home uses roughly 10,000 to 11,000 kWh per year, or about 30 kWh per day. Your own bill shows your real number. See average electric bills by state to see how your area compares.
How much does a solar battery cost?
A home battery installed typically costs several thousand dollars up to around $20,000 or more, depending on size, brand, and the work needed at your home.
These are typical ranges only. Quotes vary by region, installer, and equipment.
| Goal | Typical usable storage | What it usually covers | Typical installed cost |
|---|---|---|---|
| Basic backup | 5 to 10 kWh | Fridge, lights, internet, chargers for about a day | Typically several thousand to around $12,000 |
| Partial home backup | 10 to 20 kWh | Essentials plus some outlets, a well pump, or one small cooling load | Typically about $10,000 to $20,000 |
| Whole-home backup | 20 to 40+ kWh | Most of the house for a day or more, depending on use | Typically $20,000 and up |
| Shift power to evening | Match your evening use | Use stored daytime power after sunset | Varies with the size you pick |
Ask for a written quote that lists the battery, inverter, wiring, permit fees, and any panel upgrade. Rebates and tax credits change often. Confirm what applies to you with your installer and a tax professional.
Why is my solar battery draining so fast?
Your battery may be too small for your loads, or a large appliance may be running on it. Check which items are on the backup circuit.
Common causes:
- Heavy loads such as electric heat, a dryer, or an air conditioner are on the backed-up panel.
- The system is set to use the battery at night, so it drains by design.
- The battery is old and holds less than when new.
- Cold weather lowers how much a battery can deliver.
Look at your app's usage graph to find what draws power and when. If nothing makes sense, ask your installer to check the settings.
Why is my solar battery not charging?
The most common reasons are low sun, a setting that limits charging, or a fault in the system. Check the app for alerts first.
Look at these items:
- Panels may be shaded, dirty, or covered with snow.
- The battery may be set to charge only at certain times, or to hold a reserve.
- A breaker may have tripped.
- Internet or app problems can hide the true status.
Do not open the battery case. Do not reset high-voltage parts yourself. If the app shows a fault code, write it down and call your installer or the maker.
Can I do it myself or should I call a pro?
You can do the math and the checking yourself. Installing, wiring, and connecting a battery to your home should go to a licensed pro.
Use this checklist:
- Do it yourself: read your last 12 months of bills for kWh use.
- Do it yourself: list the items you must keep on in an outage, with their watts.
- Do it yourself: decide if you want backup, evening savings, or both.
- Do it yourself: check the app for alerts, shade, and settings if the battery acts strange.
- Call a pro: installing a battery or wiring it to your main panel.
- Call a pro: adding a battery to existing panels, because the inverter may not work with it.
- Call a pro: permits and utility sign-off, which most places require.
- Call a pro: any smell, swelling, heat, or smoke from the battery. Stay away and call emergency services if there is smoke or fire.
Get at least three quotes. Give each installer the same list of loads and the same goal, so you can compare them fairly.
Next step
Ready to size a battery for your roof? Compare local solar installers and ask each one for a battery quote.
Find solar installersElectric bills by stateQuestions people ask
How many kWh of battery does an average home need?
For essential backup, about 10 to 15 kWh usually works. Whole-home backup for a day or more typically needs 20 to 40 kWh or more, depending on your use.
Can one solar battery run my whole house?
Sometimes, but not always. It depends on the battery size, the inverter's power limit, and big loads such as air conditioning or electric heat.
Do I need a battery if I have net metering?
Not always. If your utility credits exported power at a fair rate, a battery mainly adds backup power. Ask your utility about its current rules.
Can I add a battery to solar panels I already have?
Often yes, but your inverter may need a change. A licensed installer should check your system first.
Why does my battery not last as long as the label says?
Labels often show total capacity, not usable capacity. Heavy loads, cold weather, and age also cut how long it lasts.
Sources: U.S. Energy Information Administration.