What storage actually costs on a plug-in array

A plug-in array is panels plus a grid-tied microinverter, and the microinverter's job is to push alternating current into the house circuit at the grid's frequency and phase. It contains no charger, no battery terminal and no controller. Adding a battery to it is not a cable purchase.

What a battery needs is a charger, a discharge inverter and a controller that decides moment by moment whether to charge, discharge, serve the house or export. Those three functions live inside a battery inverter, which is a different device in a different box.

So the cost question becomes a choice between three architectures. Each has a different price, a different amount of electrical work, and a different answer to "what happens in an outage".

Before comparing cost, compare contents. A quote that omits one item on this list is not cheaper, it is incomplete.

The third column is where budgets break. Two routes with similar hardware cost can differ by the price of an electrician and a permit, which is often more than the battery itself at this scale.

For the architecture detail behind each row, the guide on adding a battery to plug-in solar covers why the certified pair is brand-locked and why a third-party battery cannot join it.

The figures below are planning ranges for a small residential system, expressed in US dollars. They are not quotes, they exclude incentives, and they move with capacity, brand and labor market. Use them to decide which route is in your budget, not to negotiate a price.

Read the middle column as a ratio, not as a price list. The certified route costs roughly two to three times the portable route for the same kWh, and the fixed route costs three to four times the certified one, because at that point you are buying an installation rather than a product.

The comparison gets sharper when the price is divided by the energy it buys. A 1 kWh station and a 5 kWh rack battery are not comparable at the sticker level, but they are at the per-kWh level, once the installation is included.

At the small end, one kWh of portable storage plus the panel to charge it lands in the mid hundreds to low thousands of US dollars. At the fixed end, the same kWh can cost less in hardware and more in labor, which is why the per-unit figure flattens out as systems get larger.

That is the argument for a bigger system if you are already paying for an electrician. It is also the argument against buying the largest portable station, because the labor you are avoiding is exactly what makes the larger systems cheaper per kWh.

Four items regularly fall outside the shopping list, and each one is large enough to change the answer.

Electrician time. Anything that connects to house wiring needs one, and the price depends far more on the house than on the battery.

Permits and inspection. Most jurisdictions require both for a fixed battery, and the fee is independent of system size.

Interconnection with the utility. A system that can export needs an application, and some utilities charge for the review.

Changeover equipment. Running house circuits during an outage requires a transfer switch or an interlock, which is a separate device with its own installation cost.

A portable station avoids all four, because nothing is connected to the building. That is a real advantage and it is also a real limitation, since the station can only serve what is plugged into it.

Take a household with an 800 W plug-in array, already installed and paid for, and a 300 W evening kit to protect. Two budgets, two honest outcomes.

Around 1,000 USD. That buys a station in the one to two kWh class with a solar input, plus a folding panel. It runs the kit for about five hours, and it can be recharged from the existing array if the station's input accepts it. No electrician, no permit, no interconnection. The limitation: the array no longer exports, because it now feeds a box instead of the wall.

Around 5,000 USD. That buys a certified pair with installation, which keeps export capability and adds a backed-up circuit. It runs the same kit for longer, and it can be configured to charge from the array and discharge in the evening without anyone moving a cable. The limitation: it is brand-locked, and the utility now has to know about it.

The 4,000 USD difference buys automation, export and a circuit. Whether that is worth it depends on one question: will anyone be home to move a cable? If the answer is no, the certified route is the only one that behaves the way people expect storage to behave.

This is the part most cost pages leave out. Storage is a poor purchase in four situations, and recognizing them saves more money than any optimization.

No time-of-use tariff and no outage concern. Without a price difference to arbitrage or an outage to survive, storage has nothing to sell you. More panels return more kWh per dollar and do not degrade.

An array too small to refill it. A battery that never refills from the sun is being recharged from the wall, which is a round trip that loses energy. Size the array first.

A battery larger than the evening load. Paying for cells that never discharge is the most common overspend in this category, and it is invisible because the product page only shows capacity.

An outage plan that includes 240 V loads. No portable station runs a well pump or a dryer, so if those are in the plan, storage at this scale does not deliver the backup being bought.

These are the units whose capacity, output and solar input are recorded in our data. None of them carries a printed price here, because a printed price is wrong within weeks; the retailer's page is the only current source.

For sizing rather than costing, the battery sizing calculator turns a daily need into a bank size, and the unit converter handles the amp-hour arithmetic that small systems invite.

Pricing a battery retrofit. There is nothing to buy; the architecture changes or nothing happens.

Comparing hardware only. The route that looks cheaper on the product page often loses once an electrician and a permit are added, or wins once they are not needed.

Buying storage before sizing the array. A battery cannot refill itself, and an undersized array makes storage a wall-charged round trip.

Assuming incentives. Any figure here excludes them, and eligibility varies by state, by utility and by year. Check before relying on a number.

Paying for capacity you never use. The right size is set by the evening load and the array's daily output, not by what is on sale.

If a figure here disagrees with a calculator on this site, the calculator is the source of truth and the changelog records each correction.

Two quotes for the same storage often differ because they are not describing the same scope. Before comparing the bottom line, check that both include the same four items: the storage itself, the equipment that charges and discharges it, the electrical work, and the paperwork.

A quote that lists only the battery is a hardware price, not an installed price. Ask what happens to the array that already exists: is it rewired to the new inverter, does it keep exporting, and does the small grid-tied unit come off the wall or stay in parallel. Each answer changes both the cost and the behavior afterward.

Then check the backup scope. "Backed up" can mean one dedicated circuit, a sub-panel, or the whole house, and the price difference between those three is larger than the difference between battery brands. A quote that says backed-up without saying how much is not a comparable number.

Finally, ask what is excluded. Permits, inspection fees, utility application charges and any panel or racking changes are commonly left out, and they land on the invoice regardless. A quote that names its exclusions is more useful than one that is simply lower.

None of this is a reason to distrust installers. It is a reason to compare scopes before comparing prices, because at this scale the electrical work is often a third of the total and it is the part most easily left out of a headline figure.

On the cell chemistry itself, the comparison of LiFePO4 and NMC explains why it is a smaller factor than depth of discharge.