Home battery payback calculator
A battery earns money by storing solar power you would otherwise export cheaply, and giving it back in the evening instead of buying from the grid. So its value depends on one thing above all: the gap between the price you pay and the price you get. Enter your own numbers below. The defaults come from a real 5 kWh system in central Portugal, measured from July to October 2026.
Value of one stored kWh: –
Estimated yearly saving: –
Simple payback: –
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How it works
Yearly saving = energy shifted × (import price − export price ÷ efficiency). Payback = battery price ÷ yearly saving. With the defaults: 1,370 kWh × about €0.14 ≈ €190 a year, so a €3,000 battery needs almost 16 years.
Assumptions
- Energy shifted is what actually goes into the house from the battery in a year. A 5 kWh battery that fills every sunny day shifts roughly 1,200–1,600 kWh a year in Portugal; less if it often stays half-empty.
- Prices are held flat. Higher grid prices shorten the payback, lower export prices shorten it too.
- No battery degradation, no subsidies and no extra income from dynamic tariffs or grid services.
- Backup power during an outage is not counted. Many batteries need extra hardware to power the house when the grid is down.
This calculator gives an estimate, not financial advice. See the measured data behind the defaults in the Energy Home Lab video on YouTube.