About the Home Battery Payback Calculator
This home battery payback calculator estimates how much a battery such as a Tesla Powerwall, Enphase IQ or Franklin aPower can save on your electric bill, and how many years it takes to recover its cost. Each day the battery is charged with cheap energy — off-peak grid power or surplus solar that would otherwise be exported for a low credit — and discharged in the expensive peak window instead of buying grid power.
It is built for homeowners on time-of-use rates, solar owners under net-billing rules where exports earn far less than imports, and anyone weighing a quote from an installer. The savings per kWh are the peak price minus the cost of the charging energy grossed up for round-trip losses. The model then ages the battery (capacity fade) and escalates electricity prices year by year to find the payback year and lifetime net benefit.
Backup power during outages has real value that this calculator does not price, and some utilities pay extra for batteries enrolled in demand-response or virtual power plant programs; add those as an annual bonus if you have one. Enter rebates or tax credits you are sure you qualify for as an incentive, since eligibility rules change and vary by location.
With the default inputs, the payback period is 11.4 years. Change any value above to recalculate instantly.
How to use the home battery payback calculator
- 1Enter the installed price and any rebates or credits you will receive.
- 2Enter the battery’s usable capacity and how much of it you will cycle each day.
- 3Enter the peak price the battery offsets and what charging energy costs you.
- 4Adjust degradation, price escalation and battery life if your installer quotes different figures.
- 5Read the payback year and check the chart for when savings overtake the cost.
Formula and method
Usable capacity C times the daily depth of cycling d and the number of cycling days D gives the kWh shifted per year. Each shifted kWh avoids buying energy at the peak price but costs the charging price divided by round-trip efficiency η, because some energy is lost going in and out. Capacity fades by g each year and both prices rise by e each year; any fixed yearly program income B is added.
Payback is the point (interpolated within the year) when cumulative savings equal the net cost after incentives. Lifetime net benefit is total savings over the battery’s life minus net cost, without discounting future savings. Backup value, financing costs and changes to your rate plan are not included.
- C
- Usable battery capacity (kWh)
- d, D
- Share of capacity cycled daily, and cycling days per year
- η
- Round-trip efficiency
- g, e
- Yearly capacity fade and electricity price escalation
- B
- Other yearly income such as VPP payments
Worked examples
13.5 kWh battery on a time-of-use plan
Cycling 80% of 13.5 kWh every day shifts 3,942 kWh a year. Each kWh saves $0.45 − $0.12 ÷ 0.90 = $0.317, so year-one savings are about $1,248. With 2% fade and 3% price rises the $15,000 cost is recovered in about 11.4 years, leaving roughly $5,000 net benefit over 15 years.
Solar owner under net billing with a rebate
Storing surplus solar that would earn only $0.05 per kWh exported and using it at a $0.52 peak price makes each kWh worth about $0.464. Year-one savings are about $1,831, so the $8,400 net cost pays back in about 4.5 years.
Weekday-only peak with a small price gap
With only a $0.30 vs $0.15 price gap, each kWh nets $0.133 after losses, and 2,000 kWh a year saves about $267. Over 12 years that totals about $3,193 — far below the $11,000 cost, so this battery only makes sense for backup power.
Frequently asked questions
Is a home battery worth it financially?+
It depends mostly on the gap between your peak electricity price and the cost of charging. With a spread of $0.30 or more per kWh and daily cycling, payback in 7–12 years is common; with a small spread, a battery rarely pays for itself on bill savings alone and is bought mainly for backup.
How long do home batteries last?+
Most lithium-ion home batteries carry a 10-year warranty that guarantees around 70% of original capacity at the end, often with a throughput limit. Lithium iron phosphate (LFP) batteries typically handle more cycles. Expect usable capacity to fade gradually, which this calculator models with a yearly loss.
Does a battery make sense with solar panels?+
It makes the most sense where exported solar earns much less than the price of grid power in the evening, as under many newer net-billing tariffs. Storing midday surplus and using it after sunset captures the difference. Under full retail net metering, the grid already acts like a free battery, so savings are small.
What is round-trip efficiency?+
It is the share of energy you get back out of a battery compared with what you put in. Home batteries are typically 85–95% efficient, so charging 10 kWh returns about 9 kWh. The losses raise the effective cost of the stored energy, which is why the calculator divides the charging price by the efficiency.
Should I count backup power in the payback?+
Backup has real value if outages are frequent or costly, for example for medical equipment, a home office or a sump pump, but it is hard to price. Many owners compare a battery with a standby generator, or add the yearly value they place on backup as extra income in this calculator.
Results are estimates for educational purposes and are not financial advice. Rates, fees and terms vary — confirm with your lender or a licensed advisor before making decisions.