How the battery ROI estimate works
The financial value of a battery comes mainly from replacing expensive imported electricity with solar energy that would otherwise have been exported at a lower rate.
1. Compare import and export rates
A larger gap between what you pay to import and what you earn to export improves the potential battery benefit.
2. Apply surplus and efficiency
Only surplus solar that can actually be stored is counted, after round-trip losses.
3. Divide cost by annual benefit
The upfront battery cost is divided by the estimated yearly value retained in the home.