What is a solar battery and how does it work?
A solar battery is a rechargeable bank that stores your panels' surplus DC electricity so you can use it later instead of selling it to the grid. During the day, when your panels make more than the house is using, the extra charges the battery. In the evening, overnight, or during a blackout, the battery discharges through an inverter to power your home. It turns solar from a daytime-only source into something you can tap around the clock.
Adding a battery makes a hybrid system: panels, a battery, and an inverter that can pull from either the array or the storage. This is different from a plain grid-tied system, which has no battery and leans on the grid as its storage through net metering. If you are still deciding whether you need one at all, start with can you use solar panels without a battery, then come back here for the hardware details. For how the inverter side converts and routes the power, see how a solar inverter works.
How is a solar battery rated? kWh, usable capacity, and power
A solar battery is rated by two numbers that do different jobs: capacity in kWh (how much total energy it stores) and power in kW (how much it can deliver at once). A Tesla Powerwall 3, for example, holds 13.5 kWh of usable energy and can put out 11.5 kW of continuous power. Capacity decides how long your battery lasts; power decides how many appliances it can run at the same moment. You need enough of both.
Watch the difference between total and usable capacity, set by depth of discharge (DoD). A lithium LFP battery is typically 90 to 100% usable, so nearly all of its rated kWh is available. An old-style lead-acid battery is only about 50% usable without shortening its life, so a 10 kWh lead-acid bank really gives you about 5 kWh. That gap is a big reason lithium dominates home storage today. For the same watt-hour math applied to a small portable battery, see what a 100Ah battery can run.
How big does a solar battery need to be to power a house?
For essentials backup, most homes want 5 to 10 kWh of usable storage, which covers a fridge, lights, internet, phone charging, and a few outlets through an evening or a short outage. To run a whole house overnight, including heating or cooling, you need far more, usually 20 to 30 kWh, because the average US home uses around 30 kWh a day. That is often two or three battery units stacked together, which is where the cost climbs fast.
Size the battery to your backup goal, not your whole power bill. Decide which circuits you need to keep alive and for how long, add up their daily watt-hours, and buy enough usable kWh to cover that window with some margin. Most owners land on a single 10 to 13.5 kWh battery for essentials rather than trying to power everything. The panel side is a separate calculation: size your array to your usage with the solar panel calculator, and remember the battery only needs to be big enough for the loads you want to protect.
What kind of battery is best for solar?
For home solar, a lithium iron phosphate (LiFePO4, or LFP) battery is the default choice, and it is what most home systems ship with today. LFP lasts longer, gives you more usable capacity per kWh, and runs cooler and safer than older lithium chemistries or lead-acid. It costs more up front than lead-acid but wins on cost per usable kWh over its life because it survives thousands more cycles. Compare the two chemistries in LiFePO4 vs lithium-ion.
Lead-acid batteries still make sense in one narrow case: a tight-budget off-grid or backup build where the low sticker price matters more than lifespan and you can accept the 50% usable limit and shorter life. For almost everyone else, lithium is the better long-run value. See the full breakdown in lithium vs lead-acid solar batteries, and for ready-to-buy home units, the best solar battery backup for home.
How much does a solar battery cost in 2026?
A whole-home solar battery runs roughly $10,000 to $20,000 installed, or about $1,000 or more per usable kWh including the inverter, wiring, and labor. The battery unit itself is often $8,000 to $12,000; the rest is installation. A single 10 to 13.5 kWh battery for essentials backup lands near the low end, while stacking multiple units for whole-home coverage pushes toward the top. These are estimates that swing with your installer, region, and how much electrical work your panel needs, so treat any quote as specific to your home and see our disclaimer.
One thing has changed for 2026: a battery you buy and own no longer qualifies for the 30% federal residential tax credit. The Section 25D credit that used to cover home storage of 3 kWh or more expired for anything placed in service after December 31, 2025. Do not budget around a federal credit that is gone. Some states and utilities still offer storage rebates or incentives, and those vary widely, so check your current local programs before you assume any discount. For the wider cost picture on solar itself, see how much solar costs.
Is a solar battery worth it?
A solar battery is worth it in three situations. First, if you get frequent or long outages and want to keep the fridge, lights, and internet running, a battery is the only way grid-tied solar stays on during a blackout, since a standard system shuts off in an outage for safety. Second, if your utility has weak net metering or net billing that pays little for exported power, storing your surplus instead of selling it cheap recovers much of that lost value. Third, on steep time-of-use rates, a battery lets you charge on cheap daytime solar and discharge during the expensive evening peak.
If none of those fit, and you are on full-retail net metering with a reliable grid, a battery is usually a comfort purchase, not a money-saver. The grid already stores your surplus for free and pays it back at full value, so the roughly $10,000-plus you would spend on storage buys backup power and independence rather than a faster payback. That is a fine reason to buy one; just go in knowing which you are paying for. Weigh it against your export credits in how net metering works.
Frequently asked questions
How long will a solar battery last on a charge?
It depends on the load. A 10 to 13.5 kWh battery running essentials only (a fridge, lights, internet, and a few outlets, roughly 500 to 800 watts on average) lasts about 12 to 24 hours. Powering a whole house, including heating or air conditioning at 1.5 to 2 kW, drops that to more like 6 to 9 hours. On a sunny day the panels recharge it, so the battery mainly has to cover nights and cloudy stretches.
What is the life expectancy of a solar battery?
Most home lithium batteries last about 10 to 15 years and carry a 10-year warranty that guarantees roughly 70% of the original capacity at the end of it. LiFePO4 cells are typically rated for 4,000 to 6,000 or more charge cycles, which is one cycle a day for well over a decade. Capacity fades slowly with age and use rather than failing all at once, so an old battery still works, just with less storage.
How much does a lithium solar battery cost?
A home lithium battery unit usually costs $8,000 to $12,000, and a fully installed whole-home battery runs about $10,000 to $20,000 once you add the inverter, wiring, and labor, or roughly $1,000 or more per usable kWh. Prices vary a lot by installer and region. Note that owned batteries no longer qualify for the federal residential tax credit as of 2026, so check current state or utility incentives instead.
Can you add a battery to an existing solar system?
Yes. If your system already has a hybrid or battery-ready inverter, adding a battery is straightforward. If you have a plain string inverter or microinverters with no storage support, an installer can AC-couple a battery, which adds a second battery inverter to bolt storage onto your existing panels. It costs more than including a battery from day one, but retrofitting is common and does not require replacing your panels.
Are lithium batteries good for solar?
Yes, lithium is the standard for home solar storage, and LiFePO4 (LFP) is the most common type. Compared with lead-acid, lithium gives you far more usable capacity per kWh (about 90 to 100% versus 50%), lasts several times as many cycles, charges faster, needs no maintenance, and runs cooler. It costs more up front but wins on cost per usable kWh over its life, which is why nearly all new home batteries are lithium.