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Solar · Calculator

Solar Payback Calculator

Estimate year-1 savings and simple payback for rooftop solar from your own generation estimate, self-consumption share and electricity prices. Optional year-by-year and CO₂e views.

Your system & prices

Pre-filled prices, cost and self-consumption are example values — replace them with your own. Generation must come from an estimate for your roof.

Currency
Generation estimate

Get it for your address from PVGIS or PVWatts.

Share of generation used at home.

Optional lifetime scenario

Both rates default to 0%. They are your assumptions, not forecasts supplied by this site.

E.g. from your panel warranty.

Enter a generation estimate for your roof to see savings and payback.

How the math works

Annual kWh = kWp × specific yield (or your annual estimate)

Year-1 saving = kWh × self% × import price + kWh × (1 − self%) × export rate

Simple payback = installed cost ÷ year-1 saving

Year-n saving = year-1 saving × (1 − decline)^(n−1) × (1 + price change)^(n−1)

Worked example: 4,000 kWh/year at 30% self-consumption, 0.25 import and 0.05 export gives 1,200 × 0.25 + 2,800 × 0.05 = 440 per year. A 6,000 system then pays back in 6,000 ÷ 440 = 13.6 years. See the solar output guide for getting a location-specific generation estimate, and the solar payback guide for what simple payback leaves out. Every assumption is listed under sources and methodology.

Frequently asked questions

How is simple payback calculated?
Year-1 saving = self-consumed kWh × the price you pay for grid electricity + exported kWh × your export rate. Simple payback = installed cost (after any grants) ÷ year-1 saving. It assumes output and prices stay as entered.
Where do I get my expected generation?
From a location-specific estimate: your installer's quote, or a free location-based tool such as the European Commission's PVGIS or NREL's PVWatts. Enter the annual kWh directly, or the specific yield in kWh per kWp per year together with system size. The calculator does not supply regional yields because they depend on location, orientation, tilt, shading and system losses.
What is self-consumption?
The share of your solar generation you use at home instead of exporting. Each self-consumed kWh is valued at your import price; each exported kWh at your export rate. It depends on when you use electricity, so estimate it from your own usage pattern or a monitoring app.
Should I include degradation or price changes?
They are optional and set to 0% by default, so the base result contains no forecast. If you want a scenario, enter your panel warranty's degradation rate and an energy-price change you consider plausible. The year-by-year result then shows when cumulative savings first cover the cost. Sums are nominal and not discounted.
How is the CO₂e figure calculated?
Optional. Generation × the electricity factor you choose. This is an estimate of grid emissions the generation could displace on average; the real effect depends on what the grid would otherwise have produced at that time. Panel manufacturing emissions are not included.
Does this include a battery?
Not directly. A battery changes your self-consumption share and adds cost — enter both if you want to model one.

Keep exploring

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Solar hub

Solar guides on output, payback and batteries.

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Panel output guide

Where the specific yield input comes from.

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Solar payback guide

System size → energy → savings → payback, with a worked example.

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Home battery guide

How a battery changes self-consumption.

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