Solar & battery payback calculator
Most solar calculators divide cost by a flat savings number and stop. This one models what actually drives the real answer - rising electricity prices, what your money could earn elsewhere, and for batteries specifically: self-consumption, round-trip efficiency, degradation, and realistic cycling. Including the honest case where a battery does not pay back.
What this model actually accounts for
Most public solar calculators do one division: cost ÷ a flat annual savings figure. That understates the case, because electricity prices rise - so this tool escalates savings the same way the site's general payback calculator does, then goes a step further and asks what that money could otherwise have earned, discounting the whole cash-flow stream at a rate you set.
Battery economics are a different, harder problem, and most calculators quietly oversimplify it. This one models four things separately rather than folding them into one guess: self-consumption value (storing solar surplus that would otherwise export at a low rate, using it at the retail rate instead), time-of-use arbitrage (only where a real peak/off-peak spread exists - zero on a flat-rate plan), round-trip efficiency (real batteries lose 8-15% of what goes in, not 0%), and degradation (a 10-year-old battery typically holds 75-85% of its original capacity, so year-10 savings are meaningfully lower than year-1 savings). Backup power value is kept as its own separate line rather than blended into the financial number, because it's a genuinely more subjective figure than the rest.
When a battery does not pay back
This is the part most sales-oriented calculators leave out. In a flat-rate electricity market with no time-of-use spread and no meaningful incentives, a battery's value comes almost entirely from self-consumption alone - and that is often not enough to clear the upfront cost within the battery's useful life. A battery that shows a 20+ year payback here is not a rounding error; it is the honest answer that this particular battery, at this cost, in this market, is closer to a lifestyle purchase than a financial one. That does not make it a bad decision - backup power and energy independence are real things people value - but the numbers should say so plainly rather than getting buried under an optimistic headline figure.
Why the same battery can pay back in 4 years in one market and 18 in another
The single biggest driver is the gap between your retail rate and your export rate, and whether a time-of-use spread exists at all. A market with a $0.30+/kWh peak-to-off-peak spread (parts of California, Australia) can pay a battery back in 4-6 years. A flat-rate market with a narrow retail-export gap can stretch that past 15 years for the exact same hardware. There is no universal answer - which is exactly why this calculator asks for your actual rates rather than assuming a number.
Common questions
Because they're usually very different numbers, and a battery's core value depends on the gap between them. Solar surplus you don't store gets exported at the low export/feed-in rate. A battery lets you use that same energy yourself in the evening at the much higher retail rate instead - that difference, not the sticker price of electricity, is what a battery is actually worth per kWh stored.
Real households don't fully cycle a battery every single day - cloudy days, low winter solar production, vacations, and low evening demand all reduce it. Calculators that assume 365 days of full cycling overstate annual savings, typically by 20-30%.
Every charge/discharge cycle loses some energy as heat in real battery chemistry and inverter conversion. 85-92% is the realistic range for home lithium batteries - so 10 kWh of stored solar becomes roughly 8.5-9.2 kWh of usable evening power, not 10.
In markets with peak and off-peak electricity pricing, a battery can charge during the cheap period (or from free solar) and discharge during the expensive peak period, capturing that price spread daily. Where no such spread exists - a flat-rate plan - this value is genuinely zero, and the calculator will show that honestly rather than inventing a number.
Only if you enter one - and even then it's shown as a separate contributor, not blended invisibly into the main financial figure. Unlike self-consumption and arbitrage, which are derived from real rates you enter, backup value is inherently a judgment call, and treating it with the same false precision as the rest would be dishonest.
Not necessarily - but it does mean the case for it isn't primarily financial. A long payback is the honest signal that backup power, energy independence, or other non-financial reasons are doing the real work in that decision, not the electricity bill savings.