Payback period
The time needed for the cumulative savings or revenues of an investment to equal its initial cost.
The payback period is the simplest investment metric: how many years until an asset has repaid its upfront cost from net cash flows.
Example: a 6 kWp rooftop PV system costing 9,000 EUR and producing 6,000 kWh per year, with 35% self-consumption valued at 0.32 EUR/kWh and exports paid 0.08 EUR/kWh, saves about 672 + 312 = 984 EUR per year. Simple payback is roughly 9 years.
The discounted payback period applies the discount rate to each year's cash flow before summing, giving a longer and more realistic figure, especially at high interest rates.
Typical simple paybacks (European and US data, 2024 to 2025): residential PV 6 to 12 years, shorter in sunny regions with high tariffs; home batteries 10 to 15 years or more where export credits are generous, faster under net billing; heat pumps 5 to 15 years depending on gas and electricity prices; LED retrofits under 2 years; industrial efficiency measures often 1 to 4 years.
Payback ignores cash flows after the break-even year and the time value of money, so it understates the value of long-lived assets such as PV modules lasting 25 to 30 years. For investment decisions, NPV and IRR are more robust. Not to be confused with energy payback time.
Related terms
All terms →- NPV (Net Present Value)
The sum of all future cash flows of a project discounted to today, minus the initial investment; a positive NPV indicates value creation.
- IRR (Internal Rate of Return)
The discount rate at which a project’s net present value equals zero, representing its effective annual return.
- Discount rate
The annual rate used to convert future costs and revenues into present value, reflecting the time value of money and investment risk.
- Self-consumption
The share of on-site generation, typically rooftop solar, that is used directly by the producer rather than exported to the grid.
- Energy payback time
The time an energy system must operate to generate as much energy as was used to manufacture, install and decommission it.
- CAPEX
Capital expenditure: the upfront investment to build an energy asset, usually quoted per kW of capacity for power plants or per kWh for storage.