How this calculator works
- The calculator estimates the energy the battery can usefully deliver over a year from usable capacity, daily cycles and round-trip efficiency.
- It then values each delivered kWh using the difference between the cost of charging or forgone solar export and the grid electricity that the battery helps you avoid.
- Recurring maintenance or subscription costs are deducted before the simple payback period is calculated.
What can change the result
- How often the battery genuinely cycles
- The gap between cheap and peak electricity prices
- Round-trip losses and usable capacity
- Whether stored solar would otherwise earn an export payment
How to read the result
Treat the payback period as a planning estimate, not a guaranteed return. Compare it with the product warranty, expected battery life and a more conservative scenario with fewer cycles or a smaller tariff spread.
A useful way to stress-test the answer is to change the most uncertain input by 10 to 20% and see whether your decision still looks sensible.
Worked example
A 10 kWh battery used for around three-quarters of a full cycle per day can shift a meaningful amount of energy, but payback depends heavily on the price gap and how often the battery is genuinely useful.
Frequently asked questions
Why use opportunity cost for solar?
If exported solar would otherwise earn money, storing it is not free. Use the export value you give up as the stored energy cost.
Does this include degradation?
No. Reduce average usable capacity or useful cycles for a more conservative long-term estimate.