Home Battery Payback Calculator
Whether a battery actually pays back on rate arbitrage — with round-trip losses counted honestly.
✏️ These numbers were filled in from a shared link — change anything to make it your own.
How battery arbitrage works
Each cycle you charge cheap and discharge expensive. Round-trip losses mean you must buy more than you get back:
savings per cycle = (usable kWh × peak rate) − (usable kWh ÷ efficiency × off-peak rate)
That is the whole economic case, and it collapses quickly when the spread is small. At a $0.05 spread a 13.5 kWh battery cycled daily saves only a few hundred dollars a year — nowhere near enough to justify five figures of hardware.
Be honest about the backup value
Most people buying batteries want backup power, not arbitrage returns, and that is a perfectly good reason to buy one. But it should be priced as what it is. Set the backup value to what you would actually pay per year for reliable power through outages — if you lose power twice a year for a few hours, that number is small; if you are on a well, work from home, or run medical equipment, it may be large.
Sizing solar first? Use the System Size Calculator and Solar Payback Calculator.
Assumes one full cycle per counted day and a fixed peak/off-peak spread. Real savings depend on your utility's rate schedule, seasonal changes, how much of the battery you actually cycle, and whether solar or the grid charges it. Excludes any grid-services or virtual-power-plant payments. General information, not financial advice.
Frequently asked questions
Do home batteries pay for themselves?
On electricity savings alone, often not — or only barely, over a very long horizon. Batteries earn money by charging when power is cheap and discharging when it is expensive, so they only pay back where the peak-to-off-peak spread is large. If your utility has flat rates, the arbitrage value is essentially zero and the battery is a backup-power purchase, not an investment.
What is round-trip efficiency?
Batteries lose energy on the way in and out — typically around 10%, so a 90% round-trip efficiency means storing 10 kWh gets you about 9 kWh back. That loss eats directly into arbitrage margin, because you buy more kWh than you resell to yourself. This calculator accounts for it rather than assuming a perfect battery.
How should I value backup power?
Honestly, and separately. Backup is a real benefit but it is insurance, not income — its value depends on how often your power fails and what an outage costs you in spoiled food, lost work, or medical equipment. Rather than bury it in the payback, enter what you would genuinely pay per year for that peace of mind and see how much it moves the result.
Does a battery make solar pay back faster?
Usually the opposite. Adding a battery adds significant cost, and unless your utility pays very poorly for exported solar or has steep time-of-use rates, exporting to the grid is simpler and cheaper than storing. Batteries make the most sense where net metering is weak or unavailable.