Home Battery Payback Calculator

The honest battery question

Whether a home battery ‘pays’ depends on one number most people never compute: the value of each kilowatt-hour it shifts. A battery is a machine for moving energy from a time when it is cheap (midday solar, off-peak grid) to a time when it is expensive (evening peak, an outage, load-shedding). If that spread is large and you cycle the battery daily, the sums can work; if you have full 1:1 net metering, the grid already acts as a free battery and a physical one rarely pays.

Where batteries genuinely earn

California-style net billing (NEM 3.0) is the textbook case: exports earn a few cents while evening retail power costs 40¢+, so every solar kWh stored instead of exported is worth the difference — often 25–35¢. Load-shedding and outage-prone grids (South Africa, Pakistan, parts of India) are the other: the shifted kWh is worth whatever diesel, an inverter-UPS, or lost work would have cost. In both, a 10 kWh battery cycling 0.8× daily shifts roughly 2,600 kWh a year — multiply by your spread and compare with the price.

Where they usually do not

Under full retail net metering, or on flat tariffs with a reliable grid, the shifted kWh is worth little — often only the few cents between rates. The battery then rests on backup convenience, which is real but should be bought knowingly as insurance, not savings. Our generator vs battery tool compares that insurance against a genset; the runtime calculator shows what an outage actually demands.

Reading the verdict

The comparison that matters is payback vs lifespan. A 7-year payback on a 10-year battery is a modest win; a 14-year payback on the same battery never breaks even. The cost-per-stored-kWh figure makes it intuitive: if storing costs 12¢/kWh and each stored kWh is worth 30¢, the battery earns its keep. Size the battery itself with the battery bank calculator, and model the whole system in the savings calculator.

Frequently asked questions

It depends on your per-kWh spread. Under NEM 3.0-style net billing or load-shedding, storing a kWh is often worth 25–35¢ (or the diesel cost it avoids) and a battery can pay back within its warranty. Under full retail net metering or flat cheap tariffs, it usually cannot — the grid is already your free battery.

Take what the evening/outage kWh would cost you (peak retail rate, or diesel cost per kWh, or the value of not losing power) and subtract what the stored energy would otherwise have earned (the export credit) plus roughly 10% charging losses.

Typically 0.7–1 full equivalent cycle daily for solar self-consumption, more under heavy load-shedding. At 0.8 cycles, a 10 kWh battery shifts about 2,600 kWh a year after losses.

Not directly — an outage-proof evening has real value but no market price, so this tool keeps it separate. If backup is your main goal, compare a battery honestly against a generator rather than forcing a savings story.