Solar battery cost dataset

How long it actually lasts

Duration is usable kilowatt-hours divided by the average draw of the circuits chosen, and the draw figures are declared model values rather than published ones. ⚠️ The shape of the table is the point: the price barely moves and the duration collapses. Central air conditioning alone can outdraw everything else on the list combined, which is why backing up “the house” on one battery gives hours rather than days. What extra circuits buy is not capability, it is a much shorter outage — and the honest fix for wanting more is a second battery or a generator rather than a bigger single unit.

Usable, nameplate and scale

The model works at 90% usable and derives nameplate from it, which is the correct direction: usable is what you get. ⚠️ Cost per usable kilowatt-hour falls steeply with size because the gateway, the subpanel and most of the labour are the same whatever the battery — so a second battery bought later is far worse value than the same capacity bought at once. Two more that no headline figure includes: adding storage to an array that already exists costs $1,750 more than including it from the start, because a retrofit needs its own conversion stage; and a lithium battery loses usable capacity below freezing, so an unheated garage in a cold state gives the smallest battery exactly when the outage is most likely.

Against a standby generator

Both figures come from models on this site at the same national wage data: $18,532 for this battery against $12,174 on our whole house generator dataset. ⚠️ They are not the same product and the money is the least interesting difference. A generator runs indefinitely on fuel, is loud, needs servicing and takes seconds to start; a battery is silent, needs nothing, transfers instantly, and then runs out. Which is right depends on whether your outages last four hours or four days, and that is a question about your utility rather than about hardware. And a thing almost nobody expects: solar panels alone do not keep the lights on in a power cut — the inverter shuts down so it cannot energise a line somebody is working on.

Line items

90% of the reference total comes from estimated rather than official figures. The reference job is 13.5 usable kilowatt-hours — 15 of nameplate — on a garage wall, retrofitted to an existing solar array, backing up essential circuits: 31 trade hours and 38.6 hours of backup. ⚠️ This dataset prices work, not tax positions: the IRS says the residential clean energy credit, which covered storage as well as panels, applies to property installed through December 31, 2025 and is not available afterwards — IRS, Residential Clean Energy Credit, retrieved 2026-08-24.

The reasoning behind each figure

Permit, and the utility notificationestimated, ±59%

• An electrical permit and an inspection, plus telling the utility that there is now something on your side of the meter that can island itself from their grid.
• ⚠️ The islanding is the part that has to be right: when the grid goes down the system must disconnect from it, so that it cannot energise a line that a lineworker believes is dead. That is what the gateway below does, and it is why a battery is not a thing you wire in yourself.

The battery itselfestimated, ±28%

• Priced per kilowatt-hour of USABLE capacity rather than of nameplate, because usable is what you get and nameplate is what is on the box.
• ⚠️ A battery cannot be run flat: a reserve is held back to protect the cells, so a unit sold as 15 kWh might give you 13.5. Comparing two batteries on their nameplate figures compares the wrong number, and the model derives nameplate from usable rather than the other way round.
• The band is a mainstream lithium iron phosphate unit at the bottom and a premium integrated system at the top. Chemistry matters for life and for how it behaves in heat: iron phosphate is the one that has become standard in home storage for good reasons.

Backup gateway and automatic transferestimated, ±42%

• The device that sits between the utility and the house, detects an outage, disconnects from the grid and lets the battery take over — and does the reverse when the power comes back.
• It is a substantial part of the cost and it is not optional for backup. A battery without one can store solar and shave a peak tariff; it cannot keep your lights on in a power cut, because it is not allowed to.
• The band is a compact gateway on a simple service at the bottom and one that has to be coordinated with a large or awkward service at the top.

Protected-loads subpanel, and moving circuits into itestimated, ±51%

• ⚠️ This line exists because a home battery does not back up a house — it backs up a subpanel. The circuits you want alive in an outage are physically moved into a second panel that the battery feeds, and everything else stays on the main one and goes dark.
• Which circuits go in is the real design decision of the whole project, and it is worth doing deliberately rather than leaving to the installer: fridge, some lighting, the internet, heating controls, and one or two outlets is the configuration that keeps a battery useful for days.
• The band covers the subpanel and moving six to sixteen circuits into it, which is more work than it sounds because each one has to reach.

Protected-loads subpanel, and moving circuits — labour

• Modelled at 1.1 hours per circuit moved plus a fixed 5 hours for the subpanel itself, so backing up more of the house genuinely costs more labour rather than the same labour.

AC coupling, to add storage to solar that already existsestimated, ±49%

• ⚠️ Adding a battery to an array that is already up costs more than including it at the start, and the reason is electrical rather than commercial. An existing system makes alternating current; the battery stores direct current. Retrofitting means a second conversion stage and its own inverter, where a battery designed in from the beginning could have shared one.
• It is still usually worth doing rather than replacing a working inverter, and it is a real number that a retrofit quote should show separately.
• Applies only when there is existing solar. A battery installed with no solar at all does not need it, and a battery installed at the same time as the panels does not either.

Wall mounting in a garageestimated, ±53%

• A structural wall fixing for something that weighs several hundred pounds, and short runs to the panel because the panel is usually on the other side of the same wall.
• The cheapest place to put a battery and normally the right one. ⚠️ The catch is temperature rather than money — see the conditioning line below.

Outdoor installation with a rated enclosureestimated, ±46%

• A pad or a structural mount, a rated enclosure, and weatherproof conduit back to the house.
• ⚠️ It costs several times a garage wall and it puts the battery where the weather is, which is the thing that shortens its life. It is the answer when there is no wall to spare rather than a preference.

Mounting inside conditioned spaceestimated, ±52%

• Structural mounting inside a utility room, plus making good around it and whatever separation the clearances require.
• Kindest place for the battery and the fussiest to arrange: there are rules about clearances and about what a battery may be mounted next to, and a utility room shared with living space is not automatically allowed. ⚠️ Worth asking your installer to point at the requirement rather than taking it on trust.

Conditioning the space where it sitsestimated, ±60%

• ⚠️ A lithium battery loses usable capacity in the cold and will not charge at all below freezing without heating, which is why a battery in an unheated garage in a cold state is a battery that is smallest exactly when the outage is most likely.
• The fix is insulation and a little heat where it stands, or moving it inside — and it is far cheaper than buying more capacity to make up for the loss.

Installation, connection and commissioning

• Modelled at 0.55 hours per usable kilowatt-hour plus a fixed 12 hours: mounting, the runs, the gateway, the terminations, and commissioning the whole thing including a deliberate test of the outage transfer.
• Ask to see that test. A backup system that has never been proven to transfer is a backup system nobody has checked.

Not included in this dataset

Anything about your tax position

⚠️ Residential storage was covered by the federal residential clean energy credit, and the IRS page — read on 2026-08-24 — says that credit covers property installed through 31 December 2025 and is not available for anything placed in service after that. This page prices work, not tax positions. Check the IRS and a tax professional; state and utility programmes are separate and are not modelled here.

The solar panels themselves

Priced on our solar panel installation page. A battery works with or without solar — without it, it charges from the grid when electricity is cheap and runs the house when it is expensive, which is a completely different economic case.

What your utility pays for exports, or charges at peak

Whether a battery pays for itself outside of outages depends entirely on your tariff: time-of-use spreads, demand charges and export rates vary by utility and change. There is no national figure to publish and inventing one would be the least reliable thing on this page.

A second battery

Backing up air conditioning or an electric range realistically means more than one, and the cost is close to linear in the battery and much less than linear in everything else — the gateway, the subpanel and most of the labour are already paid for.

A service upgrade if the panel is full

The subpanel has to be fed and the gateway has to fit. On an old or full panel that becomes a service upgrade, priced on our electrical panel page.

Replacing it at the end of its life

A home battery has a warranty measured in years and cycles, and it does not last as long as the panels beside it. The replacement is a real future cost and it is not in this figure.