Quick answer
Solar Battery A solar battery is a rechargeable battery, usually lithium-ion, that stores electricity your solar panels make but your home does not use straight away, so you can use it after dark, during a power cut, or when grid power costs most.
On its own it generates nothing. Its value comes from moving solar output to a better hour.
Quick facts
The key facts about solar battery, with sources:
- Also called
- Home battery, battery storage, home energy storage
- Size measured in
- Kilowatt-hours (kWh) of usable energy
- Output measured in
- Kilowatts (kW) of continuous power
- Two published examples
- 5.0 kWh / 3.84 kVA (Enphase IQ Battery 5P); 13.5 kWh / 11.5 kW (Tesla Powerwall 3) 12
- Safety listing to look for
- UL 9540 (system), with UL 9540A fire-test data 8
- Size limit per unit in a home
- 20 kWh, unless UL 9540A test data supports more (IRC R328 / NFPA 855) 8
Key takeaways
- A solar battery stores surplus solar power so you can use it later. It does not make power.
- Two numbers matter most: kWh (how much it holds) and kW (how much it can run at once).
- A normal grid-tied solar system shuts off in a blackout. A battery with the right wiring keeps power on.
- It pays most where the utility credits exports far below the retail price, or where outages are common.
- Look for a UL 9540 listing, read the warranty for a capacity floor, and let a licensed installer pick the spot.
What a solar battery is, in plain terms
Solar panels only make power while the sun is up. Most homes use the most power in the early evening. A solar battery fills that gap. It soaks up power the house does not need at noon and gives it back later 5.
The battery is one part of a larger kit. That kit is a battery energy storage system: the cells, a controller, an inverter and the safety parts in one listed product. When people say "solar battery", they usually mean that whole kit on a garage wall or beside the house.
The EIA splits storage specs into two numbers. Power capacity is how fast it can deliver energy, in kW. Energy capacity is how much it can hold, in kWh 6. A home battery has both, and you need both to judge it.
Where the battery sits in a solar system
- Solar panels → DC power → inverter → your home's loads first
- Surplus → battery (instead of exporting to the grid)
- Evening, outage or expensive hour → battery discharges → inverter → home
How a solar battery works
Inside the cabinet are lithium-ion cells. Charging pushes lithium ions from the cathode to the anode; discharging sends them back. The DOE describes this as a "rocking chair" design, and the reaction is reversible, which is what makes the cells rechargeable 4.
A controller decides when that happens. In self-consumption mode the battery soaks up midday surplus and runs the house in the evening. In backup mode it holds a reserve for outages. In time-of-use mode it waits for the expensive hours. Most current units do all three, with the reserve set in an app.
The battery also needs an inverter, because cells store direct current and the house runs on alternating current.
An AC-coupled battery has its own inverter and sits beside an existing solar inverter; a DC-coupled one shares a bidirectional hybrid inverter with the panels 5.
AC coupling is the usual route for adding a battery to an existing system.
A battery management system (BMS) watches every cell. It tracks voltage, current and heat, and it stops charging or discharging before a cell goes outside safe limits.
Types of solar battery setups
| Setup | How it connects | Best fit |
|---|---|---|
| AC-coupled | Battery has its own inverter and ties in on the AC side 5 | Adding storage to solar you already own |
| DC-coupled | Panels and battery share one hybrid inverter 5 | New solar and battery bought together |
| All-in-one unit | Battery, inverter and solar inputs in one box (Powerwall 3 takes up to 20 kW DC of solar) 2 | New installs that want fewer boxes |
| Modular stack | Small units added side by side (one 5.0 kWh IQ Battery 5P per 20 A branch circuit) 1 | Homes that want to start small and add later |
| Off-grid bank | Battery is the only source after dark; no utility link | Cabins and sites with no grid line; see off-grid solar |
The four numbers on a battery data sheet
| Spec | What it decides | Enphase IQ Battery 5P | Tesla Powerwall 3 |
|---|---|---|---|
| Capacity (kWh) | How long it lasts | 5.0 kWh usable 1 | 13.5 kWh nominal 2 |
| Power rating (kW) | How much it can run at once | 3.84 kVA continuous, 7.68 kVA peak 1 | 11.5 kW continuous discharge 2 |
| Round-trip efficiency | How much stored energy comes back | 90% AC 1 | 89% solar to battery to home 2 |
| Warranty | How long the maker stands behind it | >60% capacity, 15 years or 6,000 cycles 1 | 70% of 13.5 kWh at 10 years 3 |
Example: what one stored kWh is worth on a Duke Energy Carolinas (SC) bill
An example, not a forecast. It compares exporting 10 kWh of midday surplus with storing it for the evening, using two published Duke Energy Carolinas SC rates.
| Choice | Math | Value |
|---|---|---|
| Export the 10 kWh | 10 kWh × $0.0419 net-excess credit, Rider RSC 18 | $0.42 |
| Store it, use it tonight | 9 kWh back at 90% efficiency × $0.138125, Schedule RS first-1,000-kWh energy charge 1 19 | $1.24 |
The battery triples the value of that surplus because the export credit is about a third of the retail energy charge. That gap, multiplied over a year, is the economic case for storage; it ignores the battery's price and wear, which HyreSolar does not publish without dated quotes.
Where a solar battery earns its keep: three jobs
- Backup. Keeps chosen circuits running when the grid goes down. A grid-tied solar system without storage shuts off in an outage. See battery backup.
- Self-consumption. Stores midday surplus instead of exporting it, which matters where the utility credits exports below the retail rate.
- Rate shifting. Discharges during peak-price hours on a time-of-use rate, known as energy arbitrage, or trims demand spikes on a rate with a demand charge.
Where solar batteries show up today
Home batteries are the small end of a fast-growing field. The EIA reports that utilities in 42 states listed 1,094 MW of small-scale battery capacity in 2021. About 71% of it was tied to net-metered systems, which are mostly rooftop solar 6.
In a house, the unit is most often on a garage wall or an outside wall. Some homes put it in a basement or utility room. The building code limits where it can go, which the rules section below covers.
Sources: [6]
What a solar battery does well, and where it falls short
What it does well
- Keeps power on through an outage, which panels alone cannot do.
- Raises the value of surplus solar where export credits are low.
- Silent, with no fuel to store and no exhaust.
- Can be charged by the sun again the next day, so a long outage is not a fuel problem.
Where it falls short
- Loses roughly a tenth of what it stores (89%–90% AC round trip on the two data sheets above).
- Capacity fades with years and cycles; warranties guarantee a floor, not the original size.
- Covers part of a house unless sized and wired for whole-home backup.
- Adds a permit, an inspection and, in some homes, an electrical panel change.
Limits you will notice at home
Power, not just size, caps what runs. A battery can hold plenty of kWh and still trip if too many big loads start at once.
The Powerwall 3 lists 11.5 kW continuous and a 185 LRA motor start rating 2. LRA (locked-rotor amps) is the surge a motor, like an AC compressor, pulls in its first second.
Heat and cold slow it down. Tesla says output may be de-rated above 40°C (104°F) 2. Enphase lists a best range of 0°C to 30°C (32°F to 86°F) 1. A hot west wall in summer can cost you some output.
It wears out. NLR (formerly NREL) models a home battery over a 15-year life at about one cycle a day, and notes it may need replacing within that time as it fades 7.
Some of the box is held back. Enphase keeps a 2% safety limit plus 3% for its own electronics at night inside the stated usable capacity 1. Read "usable" on every quote.
What drives the cost of a solar battery
HyreSolar does not print battery prices without dated, sourced quotes. What we can show is what makes one quote higher than another.
NLR's cost model for home batteries breaks the price into these parts: the battery pack, the battery inverter, the other hardware, install labor, supply chain costs, permits and interconnection, sales and overhead, and profit 7.
At home, the big swing factors are how many kWh you buy, whether you need a new main panel or a backup switch, how far the battery sits from the panel, and whether you add it to old solar or buy both at once. The solar cost guide covers system pricing.
Lifespan and warranty. Tesla warrants Powerwall 3 to hold 70% of 13.5 kWh at 10 years, with unlimited cycles for solar self-use, time-of-use and backup. Other uses are capped at 37.8 MWh of total output 3. Enphase warrants more than 60% capacity for 15 years or 6,000 cycles, whichever comes first 1.
Tax credit. The federal 25D homeowner credit ended for property placed in service after 31 December 2025 11. Do not trust a quote that still counts 30% off.
How a solar battery gets installed
A licensed electrician or solar installer does every step that touches wiring. This is the usual order.
- Site visit: the installer checks your main panel, your loads and where the battery can legally go.
- Design: they pick the battery size, the circuits to back up and AC or DC coupling.
- Permit: they file plans with your city or county building department. Many also file with the fire marshal.
- Utility paperwork: if the system ties to the grid, the utility reviews it. See solar interconnection.
- Install: mount the unit, wire the backup switch or gateway, and connect it to the panel and solar.
- Inspection: a building inspector checks the work against the code your area uses.
- Turn on: once the utility gives permission to operate, the installer sets the reserve and modes in the app.
Looking after a solar battery
There is little to do by hand. The IQ Battery 5P uses passive cooling with no fans 1. Keep the space around the unit clear so air can move, and keep stored items away from it.
Keep it online. Tesla expects the owner to supply internet for Powerwall 3, with cellular only as a backup 2. Without a link, you lose alerts and remote updates.
Do not park it at 100% for months. The DOE notes that holding lithium-ion cells at a high charge for long periods is one of the main causes of capacity fade 4. A backup reserve below full, set by your installer, is a common middle ground.
Check the app each month. Look for error codes, a dropping usable capacity, or a battery that never charges fully on sunny days.
Warning signs and when to call a pro
- The app shows a fault, an offline status for more than a day, or a sudden drop in usable kWh.
- The unit is hot to the touch, swollen, hissing, or smells sharp or sweet.
- Backup did not switch on in the last outage.
- Water, rodent damage or a car bump near the unit.
- Any of these: call your installer. If you see smoke or fire, leave the house and call 911.
Safety rule
A battery stays live even when the grid is off. Never open the cabinet or touch its wiring. Only a licensed electrician or installer should work on it.
Rules that apply to a home solar battery
Product listing. UL 9540 is the safety standard for energy storage systems. Its third edition was published on 28 June 2023 by UL Standards & Engagement 9. UL 9540A is a separate fire test; its results can allow closer spacing or larger sizes.
Where it can go. The 2021 International Residential Code, section R328, and NFPA 855 Chapter 15 set the home rules. Each unit can be up to 20 kWh.
Units must sit at least 3 feet apart unless UL 9540A data shows less is safe.
The total is capped at 40 kWh in utility closets, basements and storage rooms, and 80 kWh in garages, on outside walls or outdoors 8.
Not in bedrooms. R328 bars batteries from sleeping rooms and closets that open into them. A garage install may need a heat alarm and, in a driving path, a barrier against car impact. One California city's handout shows how a building department applies these rules 10.
Your local edition rules. States and cities adopt codes on their own schedule. South Carolina enforces the 2021 codes 13. Ask your installer which edition your permit uses.
Solar battery vs related terms
| Term | What it means | How it differs |
|---|---|---|
| Solar battery | A home battery charged mainly by your panels | The homeowner word for the whole product |
| BESS | Battery plus controls, inverter and safety parts | Wider term; also covers grid-scale sites |
| Lithium-ion battery | The cell family inside most home units | A chemistry, not a full product |
| LFP battery | Lithium iron phosphate, one lithium-ion type | The chemistry on both data sheets above |
| Whole-home backup | A battery setup that powers the full panel | A design choice, not a battery type |
| Generator | Burns fuel to make power | Runs as long as fuel lasts; see battery or generator |
Misconceptions
- Myth Solar panels keep my lights on in a blackout.
- Reality A grid-tied system without storage shuts off when the grid fails. Backup needs a battery and the right switch gear.
- Myth The kWh on the box is what I can use.
- Reality Some sheets list nominal capacity and some list usable. Enphase holds 5% inside its usable figure for safety and electronics 1.
- Myth A battery lasts as long as my panels.
- Reality Battery warranties run 10 to 15 years on the two sheets above, with a capacity floor of 60% to 70% 1 3.
- Myth Any battery will run my central AC.
- Reality Only if its power rating and motor-start rating can handle the surge. Check LRA on the data sheet 2.
Solar batteries in SC, GA and VA
South Carolina had the longest outages of any state in 2024, nearly 53 hours per customer, mostly from Hurricane Helene 12.
SC utilities also credit exports very differently, from net-excess credits near 4 cents per kWh to legacy net metering for customers who applied before 1 June 2021 18 14.
On Dominion Energy SC's Solar Choice rider, storage counts only if it charges solely from onsite renewables 15. Georgia Power limits residential renewable systems to 10 kW 16.
Virginia allows residential net metering up to 25 kW on investor-owned utilities 17.
Is a solar battery worth it for you?
A battery tends to make sense when one or more of these is true. Then run the checks before you sign.
- Your utility pays far less for exports than it charges for power, or uses a time-of-use rate.
- You lose power often, or someone at home needs power for medical gear.
- Ask whether the capacity on the quote is usable or nominal, and which efficiency figure the savings estimate assumed.
- Check the battery is listed to UL 9540 and ask where it will be mounted; residential codes limit kWh per unit and per location 8.
- Ask which circuits stay on in an outage. A licensed electrician sets that, not the app.
- Read the warranty for a cycle or throughput cap, not only the years.
Next steps
- Battery sizing toolMatch kWh and kW to the loads you want to keep on
- Home battery storage optionsWhat installers offer and how to compare quotes
- LFP vs NMC: what data sheets actually say
- Solar battery statistics
- How often new solar systems include a battery, by state
Questions about solar battery
Do I need a battery to have solar panels?
No. A grid-tied system works without one and uses the grid as its backstop.
The catch is that it shuts down during an outage for line-worker safety, and surplus goes to the utility at whatever export rate applies. A battery addresses both.
If your utility pays close to retail for exports and outages are rare, solar alone may be enough.
Can a solar battery power my whole house?
It can if it has enough power rating to start and run your largest loads at the same time and the wiring backs up the main panel.
Many systems back up a subpanel of chosen circuits instead. The Powerwall 3 lists 11.5 kW continuous per unit, and up to four can be linked. See whole-home battery backup for how installers size it.
How long does a solar battery last?
Warranties are the published guide. Enphase warrants more than 60% capacity for up to 15 years or 6,000 cycles on the IQ Battery 5P.
Tesla warrants Powerwall 3 to hold 70% of its capacity at 10 years.
DOE notes lithium-ion batteries often have a life or warrantied life of 10+ years and 1,000+ cycles, depending on use.
Does a solar battery charge from the grid?
Most can, if the settings and the utility's rules allow it. Some export-credit riders only treat storage as part of the solar system when it charges from onsite solar. Dominion Energy SC's Solar Choice rider is one example. Ask your installer before turning on grid charging, so you do not lose a credit.
Is a solar battery the same as a battery energy storage system?
A home solar battery is one kind of battery energy storage system (BESS). BESS is the wider term. It covers the cells, controls, inverter and safety parts as one listed unit, and it also covers utility-scale sites measured in megawatt-hours. On a home quote, the two words usually mean the same box.
How long will a solar battery run my house in an outage?
Divide the usable kWh by the power your backed-up loads draw. A 13.5 kWh battery running a steady 1 kW load lasts about 13 hours before losses, less with an AC or well pump. Sun the next day can recharge it. Our battery sizing tool does this math with your own loads.
Where can a solar battery be installed in a home?
Under IRC R328 and NFPA 855, common spots are garages, outside walls, outdoors on the ground, and enclosed utility rooms or basements. Batteries are not allowed in bedrooms or closets that open into them. Each unit is capped at 20 kWh, with totals of 40 or 80 kWh by location, unless fire-test data supports more.
Is a solar battery safe to have at home?
A listed, code-compliant install is designed to be. Look for a UL 9540 listing, and ask for UL 9540A fire-test results. Both data sheets above cite them. The code also limits size, spacing and location. Keep the unit clear of clutter, and call your installer if it gets hot, swells or shows a fault.
Can I add a battery to my existing solar system?
Usually, yes. An AC-coupled battery has its own inverter and connects beside the solar inverter you already have. The installer checks panel space, backup wiring and utility rules first. Adding storage may need a new permit and a fresh utility review. Your solar warranty terms are worth checking before work starts.
Sources
- Enphase Energy, IQ Battery 5P data sheet (DSH-00010-11.0-EN-2025-05-06), retrieved .
- Tesla, Powerwall 3 Datasheet (2024), retrieved .
- Tesla, Powerwall Limited Warranty (USA), effective 21 August 2023, retrieved .
- US DOE Office of Electricity, Lithium-ion Batteries Technology Strategy Assessment (DOE/OE-0031, July 2023), retrieved .
- US DOE Solar Energy Technologies Office, Solar-Plus-Storage 101, retrieved .
- US EIA, Energy storage for electricity generation, retrieved .
- National Laboratory of the Rockies (NLR, formerly NREL), Annual Technology Baseline 2024: Residential Battery Storage, retrieved .
- UL, 2021 Residential ESS Requirements (IRC R328 and NFPA 855 Chapter 15 summary, 2021), retrieved .
- UL Standards & Engagement, ULSE publishes third edition of UL 9540 (28 June 2023), retrieved .
- City of Monte Sereno (CA), Residential Energy Storage Systems building requirements (7/2024), retrieved .
- IRS, Residential Clean Energy Credit (§25D), retrieved .
- US EIA, Today in Energy: Hurricanes in 2024 led to the most hours without power in 10 years, retrieved .
- SC Building Codes Council, code adoption, retrieved .
- South Carolina Code Title 58 Ch. 40 (Act 62 of 2019, customer-generators), retrieved .
- Dominion Energy South Carolina, Residential Solar Choice rider (Rider to Rate 5), retrieved .
- Georgia Power, Behind-the-Meter Interconnection Summary for Residential Customers (rev. 15 Aug 2025), retrieved .
- Code of Virginia §56-594 (net energy metering), retrieved .
- Duke Energy Carolinas (SC), Rider RSC Residential Solar Choice (effective 1 January 2026), retrieved .
- Duke Energy Carolinas (SC), Schedule RS (Docket No. 2025-172-E), retrieved .
Expert review
Written by the HyreSolar Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: Specifications copied from the current Enphase and Tesla data sheets and the Tesla US warranty; mechanism from the DOE lithium-ion assessment and DOE Solar-Plus-Storage 101.
Lifetime and cost drivers from the NLR ATB; placement rules from the UL summary of IRC R328 and NFPA 855; tariff and SC figures from sc-local/facts.js and the EIA.
The example multiplies published numbers only.
Suggest a correction. We fix errors and say what changed.