Solar Payback Calculator — Portugal
Estimate your rooftop UPAC system's yearly production, electricity-bill savings, payback time and 20-year net profit. Defaults reflect a typical Portuguese rooftop: €1,200/kWp installed, 1,550 kWh/kWp yield, €0.25/kWh grid electricity and €0.05/kWh surplus value.
1 · Your system
2 · Live results
yearly = self × price + exported × surplus value20-year net ignores panel degradation, inverter replacement and electricity price changes — see the explainer below.
How solar payback works in Portugal
A rooftop UPAC (Unidade de Produção para Autoconsumo) earns money two ways: every kilowatt-hour you use yourself avoids buying grid electricity at roughly €0.20–0.30/kWh, and surplus you export can be sold at a low market-linked rate — though for most households self-consumption is where the money is.
The formula
| Step | Calculation | Example (defaults) |
|---|---|---|
| Yearly production | kWp × yield | 8 × 1,550 = 12,400 kWh |
| Self-consumed | production × self-use % | 12,400 × 40% = 4,960 kWh |
| Exported | production − self-consumed | 7,440 kWh |
| Yearly value | self × price + exported × surplus value | 4,960 × 0.25 + 7,440 × 0.05 = €1,612 |
| Payback | install cost ÷ yearly value | 9,600 ÷ 1,612 ≈ 6.0 years |
| 20-year net | yearly value × 20 − install cost | €22,640 |
Portugal specifics
- UPAC registration: a self-consumption unit must be registered with the DGEG. Small systems face light requirements, but surplus sale requires registering and metering — your installer normally handles this.
- Yield advantage: Portugal's sun gives 1,400–1,700 kWh per kWp per year — southern regions do best — and install prices around €1,200/kWp keep payback at 5–7 years.
- Self-consumption first: export compensation is low, so size the system to your daytime consumption and use self-use share honestly in the calculator.
- Battery: raises self-consumption to 60–80% but adds several thousand euros; re-run the numbers with a higher self-use share and the battery cost included.
Frequently asked questions
What is a UPAC?
UPAC (Unidade de Produção para Autoconsumo) is Portugal's legal framework for self-consumption solar. It covers the rooftop system that produces electricity mainly for your own use. The unit must be registered with the DGEG (Direção-Geral de Energia e Geologia); very small systems have simplified requirements, while selling surplus needs proper metering and registration. Installers typically handle the process.
How is exported surplus paid in Portugal?
Surplus can be sold to the grid or to a retailer, typically at a low market-linked rate — often around €0.04–0.08/kWh. Because this is far below the retail price you pay (~€0.25/kWh), self-consumption drives almost all of the return. The calculator lets you set the surplus value you actually get.
What self-consumption rate is realistic?
Without a battery, a typical household uses 30–50% of its own production; the rest is exported. With a home battery this rises to 60–80%. Higher daytime usage (home office, pool pump, air conditioning, EV charging at home) pushes the rate up for free.
How does orientation affect yield in Portugal?
A south-facing roof in Portugal yields roughly 1,500–1,700 kWh per kWp per year; east/west roofs yield about 15–20% less but produce more morning and evening power — which can raise self-consumption. Heavy shading hurts disproportionately; a shaded section can drag down a whole string unless optimizers or microinverters are used.
Is a battery worth it in Portugal?
It depends on your numbers. A battery shifts evening consumption to stored solar power, raising self-use from ~40% to ~65%+, but adds €4,000–8,000 to the install cost. Model it: add the battery cost to the installation price and raise the self-consumption share — if the payback time drops, it pays for itself. Low surplus prices make batteries more attractive.
Last updated: September 2026.
Disclaimer: True EV Cost tools are for information only and are not professional financial advice. Surplus rates, registration rules and electricity prices change — confirm current figures with your installer and the DGEG before investing.