Solar Panel Payback Calculator
See how long a solar system takes to pay for itself, with your own tariffs and panel degradation.
Results
The dashed line marks the value you entered.
What this tool does
A solar system saves two different amounts of money for every kilowatt-hour it makes. The part you use in the house saves you the price you would have paid to buy it; the part that goes to the grid earns whatever your supplier pays for exports, which is usually much less. That split is why the self-consumption share matters more than the size of the array. Panels also fade, typically around half a percent a year, so each year's saving is slightly smaller than the last and the total is a geometric series rather than a simple multiplication. Every price here is yours to enter: the tool carries no tariff table for any country.
Formula
first-year saving = output × (self-use share × import price + exported share × export price)
Variables
| Symbol | Meaning | Unit |
|---|---|---|
cost | Installed cost of the system | — |
prod | Output in the first year | kWh |
shr | Share you use yourself | % |
pimp | Price you pay per kWh | — |
pexp | Price you are paid per exported kWh | — |
deg | Output lost each year | % |
yr | Years to look ahead | yr |
PB | Years to break even | yr |
S1 | Saving in the first year | — |
TS | Saving added up over those years | — |
NP | Position after paying for the system | — |
Worked example
- Installed cost of the system7000
- Output in the first year5200 kWh
- Share you use yourself45 %
- Price you pay per kWh0.22
- Price you are paid per exported kWh0.06
- Output lost each year0.5 %
- Years to look ahead20 yr
- Years to break even10.4 yr
- Saving in the first year686.40
- Saving added up over those years13,095.07
- Position after paying for the system6095.07
Limitations
- Prices and emission factors are yours to enter. The tool ships with no tariff table and assumes nothing about your country or supplier, so change the defaults to match your own bill.
- The result is an estimate based only on the values you type. Real situations often include factors this calculator does not know about.
- This is an informational calculator, not personalised financial advice. Rates, fees, taxes and contract conditions vary between institutions and countries.
- The calculation runs at full precision and only the display is rounded. If you copy an intermediate value and retype it, small differences can appear.