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Solar · Flagship calculator

Solar Payback Calculator

Project year-1 savings, simple payback, 25-year lifetime return and CO₂ avoided from a rooftop PV system. Editable location yield, self-consumption share, panel degradation and electricity price inflation — the same variables an installer uses in their business case.

Your system & tariff

Presets are annual averages for an unshaded, south-facing, ~30° tilt array. Pick "Custom" to enter exact values from PVGIS or NREL PVWatts.

Typical home: 4–8 kWp · large home w/ EV: 10–15 kWp.

Nordics 800 · UK 950 · Central EU 1100 · South EU 1450 · US SW 1700.

Turn-key price minus every subsidy, grant or tax credit.

EU avg 0.23 · UK 0.19 · Norway 0.02 · US 0.37.

35%

No battery: 25–35% · With battery: 60–80% · With battery + heat pump + EV on daylight hours: 80%+.

Year-1 savings

€1,036

2,310 kWh self-consumed at retail + 4,290 kWh exported.

Simple payback

8.7 years

Installed cost €9,000 ÷ year-1 savings. With inflation & degradation: year 8.

25-year net profit

€26,326

ROI 293% · lifetime savings €35,326 minus installed cost.

CO₂ avoided

46.6 tonnes

1,980 kg/year in year 1 · 155,469 kWh generated over 25 years.

Year-1 generation

6,600 kWh

LCOE

€0.06/kWh

Compare LCOE to your retail price

Solar is 81% cheaper per kWh than grid electricity.

How the math works

The calculator is a year-by-year cash-flow model — the same structure a project developer uses. Four inputs drive everything else: system size, specific yield, self-consumption share and electricity price:

Year-n generation = kWp × yield × (1 − degradation)^(n−1)

Year-n savings = self × retail + export × FIT, both grown by inflation

Simple payback = installed cost ÷ year-1 savings

LCOE = installed cost ÷ lifetime kWh generated

Specific yield is the multiplier that turns a nameplate kWp into an annual kWh number. It bundles irradiance, tilt, azimuth, temperature losses and inverter efficiency into one figure. If you have exact site coordinates, pull the number from PVGIS (Europe) or NREL PVWatts (US) and enter it as a Custom location.

Self-consumption is the second-largest driver of payback after yield. A retail-priced kWh you avoid is worth 2–4× an exported one at typical tariffs. Shifting laundry, dishwashing, hot-water heating and EV charging into daylight hours has zero capital cost and can push self-consumption from 30% to 50%+ before you even consider a battery.

LCOE (levelised cost of energy) divides the installed cost by lifetime kWh produced — the "true" cost per kWh of your solar electricity. Well-sited residential PV in 2025 lands at €0.05–0.10/kWh, cheaper than any grid tariff in Europe. That is why the technology is now compelling even without generous export tariffs.

Frequently asked questions

How is solar payback actually calculated?
Payback is installed cost (net of grants) divided by annual savings. Annual savings are your self-consumed generation valued at the retail electricity price plus your exported generation valued at the feed-in / export tariff. This calculator uses year-1 savings for simple payback and a full year-by-year model — with panel degradation and electricity price inflation — for lifetime return.
What yield should I use for my location?
Annual specific yield (kWh per kWp installed per year) is the single most important number. Rough regional averages for an unshaded, south-facing, 30° tilt array: Nordics 800–900, UK 900–1,000, Central Europe 1,050–1,200, Southern Europe 1,350–1,600, US Southwest 1,600–1,800. For a precise number use the free PVGIS (Europe) or NREL PVWatts (US) tools with your exact coordinates and roof geometry.
What is self-consumption and why does it matter?
Self-consumption is the share of your solar generation you use directly at home rather than exporting to the grid. It matters because retail electricity prices are typically 2–4× higher than export tariffs, so every kWh you self-consume is worth much more than one exported. Without a battery, homes typically self-consume 25–35% of PV output. Add a home battery and this rises to 60–80%; add a heat pump or EV that runs on daylight hours and self-consumption climbs further.
What panel degradation should I assume?
Tier-1 panels lose 0.4–0.6% of rated output per year. Manufacturers typically warrant 80–85% of original output at year 25, but field data shows most quality modules still exceed 90% at year 25. This calculator uses 0.5% per year by default — override it if your manufacturer publishes a specific curve.
Should I include electricity price inflation?
Yes — it materially changes the lifetime return. Over the last 20 years European retail electricity has risen 3–5% per year on average, US around 2%. The calculator lets you set an annual inflation rate that is applied both to the retail price you avoid and the export tariff you receive. Set it to 0% for a conservative "prices stay flat" scenario.
How do grants and tax credits change the answer?
Enter the installed cost net of all grants, subsidies and tax credits. In the US the federal ITC covers 30%. In many EU countries VAT is reduced or removed on domestic PV. Local schemes may add cash rebates. The calculator does not model any tax on export income because rules vary by country — check local guidance for that separately.
Does this calculator include a battery?
No — batteries are modelled indirectly via the self-consumption slider. Increase self-consumption to 60–80% to reflect a battery, but remember to add the battery cost to the installed price. A dedicated battery payback calculator will follow in a later release.

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