The simple payback period is calculated by dividing the net initial cost by the estimated annual net financial benefit. The benefit includes the electricity purchases you avoid and any revenue from surplus energy, less the related operating expenses.
Illustrative example: if an installation costs 8.000 euros and provides a net benefit of 1.000 euros per year, the simple payback period is approximately 8 years. The amounts are hypothetical and do not constitute an offer or forecast for your property.
In practice, the result varies with self-consumption, production, electricity purchase and compensation prices, maintenance, and possible equipment replacements. Financing and the gradual decline in performance also affect cash flows.
Ask for more than one scenario and a separate assessment of the additional cost of the battery. Include subsidies or tax benefits only when it has been confirmed that they apply to your specific situation. Simple payback is a comparison tool, not a guarantee of future performance.