Solar payback calculator
Project 25 years of generation, self-consumption and export value. Every assumption is editable — including degradation and inverter replacement.
Your situation
Defaults are starting points from typical published ranges — never facts. Change any value that does not match your situation.
Estimate only. Based on the assumptions you entered. Get a site-specific survey before spending money.
Simple payback
Year 11
First year cumulative cash ≥ 0
25-year net gain
€12,848
After cost and inverter replacement
Avg. annual saving
€922
Gross bill/export savings ÷ 25
Year-1 generation
6,000 kWh
Year-1 saving
€840
Cumulative cash position
Formula with your numbers
generation[y] = 6 kWp × 1000 × (1 − 0.5/100)^(y−1)
selfUsed = generation × 30%
exported = generation − selfUsed
price[y] = 0.28 × (1 + 2/100)^(y−1)
saving[y] = selfUsed × price[y] + exported × 0.08
cumulative = −9000 + Σ saving − inverter(1200 @ yr 12)
year-1 gen = 6,000 kWh; year-1 saving ≈ €840
Frequently asked questions
Why do installer quotes often show a faster payback?+
Many quotes assume high self-consumption, optimistic specific yield, rising electricity prices, and ignore inverter replacement. This calculator makes every assumption visible so you can match your own bill and roof.
What is specific yield?+
Specific yield is annual AC generation per kilowatt-peak of panels (kWh/kWp/yr). It depends on location, orientation, tilt, shading and system losses. Region defaults here are mid-range starting points only.
Does self-consumption matter more than generation?+
Often yes. Electricity you use yourself displaces the full retail rate; exported energy usually earns much less. Raising self-consumption (or adding a battery) can improve payback more than a slightly larger array.