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Solar Battery Payback Calculator

Payback and horizon net value from peak and off-peak rates, round-trip efficiency, cycling rate, and capacity fade.

Inputs

Cost and rates

Installed price after any incentive you have already confirmed.

Usable kWh cycled, not nameplate.

Equivalent full cycles per year. One cycle a day is 365; backup-only use is far fewer.

The rate you avoid by discharging: your peak time-of-use rate, or the retail rate for self-consumption.

What you pay to recharge, including solar you would otherwise export. Enter 0 if solar charges the battery for free.

Energy returned per unit put in. 85-95% typical; this is why charging losses reduce arbitrage value.

Ongoing costs and life

Maintenance, monitoring, and a replacement reserve.

Annual capacity loss. Lithium commonly loses 1-3% a year under normal cycling.

Warranty term or the period you are evaluating.

Result

Net value over the horizon
$-1,889
Net savings in year 1
$778
Simple payback (0 = does not pay back)
11.6 yrs
Energy cycled in year 1
4,050 kWh
Battery cost per kWh cycled
$0.243
Energy cycled over the horizon
37,043 kWh

What to check

  • Peak and off-peak rates from your own tariff sheet, including seasonal and weekend windows.
  • What charges the battery: cheap grid energy (you pay for it) or surplus solar (you give up the export credit).
  • Round-trip efficiency, because charging losses mean you buy more kWh than you deliver.
  • Cycles per year: near 365 for daily arbitrage, far fewer for backup-only use.
  • Warranted throughput as well as cycles; whichever limit arrives first ends the savings stream.
  • Capacity fade, and incentive law as it stands today rather than as advertised at signing.

Keep going

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Screening model at constant rates. It assumes your tariff windows, rates, and cycling pattern stay fixed, ignores demand charges and sell-back clauses, and does not account for tax treatment of any incentive. A payback of zero means the battery does not pay back at the entered rates within the horizon, not that it has no value: backup and outage avoidance are not monetized here.

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