Annual solar output calculator
Calculates the annual yield hour by hour with the full PVGIS power chain (module temperature, low light, reflection, mounting type) — and the lifetime total including degradation. 0.5% per year sounds like nothing; over 25 years you lose about 6% of the naive total, one and a half years of output for a 10 kWp system. Plus the warranty checker: at what measured shortfall does a warranty claim begin? Coverage today: the DACH grid at 0.25° — a US grid built on NREL NSRDB data is in preparation.
The formulas behind the calculator
Every number above can be recomputed: the full calculation path, all assumptions and the data source with retrieval date — plus cross-validation against independent references. Disclosed, not claimed.
An estimate based on the stated assumptions. The final design must be checked by a qualified professional against the rules that apply where you are.
Data as of: 2026-07-30
| Step | Formula | Value | Provenance |
|---|---|---|---|
| Hourly energy simulation (IAM, Faiman, Huld) | Σ_8760h P_STC · G_eff/1000 · η_rel(Huld) · η_sys, T_m Faiman(roof) | 9,948.3 kWh | measured |
| P50/P90 from individual years | P50/P90(n = 19, ref 35°) | 9,166.1 kWh | measured |
| Degradation sum factor | Σ (1-0.005)^(t-1), t = 1..25 = 23.556 | 234,340 kWh | assumed |
| Manufacturer warranty floor | min(t): 99.0 % → 87 % @ 25 a | 8,655 kWh | measured |
- Formula
E_1 = Σ_h P_STC · G_eff/1000 · η_rel(Huld) · η_sys · E(t) = E_1 · (1−d)^(t−1) · E_tot(n) = E_1 · (1−(1−d)^n)/d- Valid for
- DACH grid at 0.25° resolution (1,155 points, PVGIS-SARAH3 2005–2023), all orientations, terrain horizon, level calibrated to the multi-year mean. Year one is provably identical to the monthly calculator's annual total and inherits its PVcalc cross-validation (±1.7%). Degradation as a geometric series, median 0.5%/a per Jordan & Kurtz 2013 — reference: 20 years deliver 19.08 times year one, not 20 times.
- Not covered
- Near shading, snow cover, spectral correction (see calculator 27), inverter failures and replacement, tariff and price paths — that is what calculators 41, 48 and 50 are for. The manufacturer warranty covers module power, not kWh directly; the warranty checker translates it into energy via the weather year.
- Data sources
- JRC Photovoltaic Geographical Information System (PVGIS), European Commission — endpoints tmy, MRcalc, printhorizon · PVGIS API v5_3, solar radiation database PVGIS-SARAH3 · retrieved 2026-07-30
The same array at nearby locations
35° tilt, south-facing, identical array — the closest cities around your location, each with its own weather grid point. Every row is computed with the same formulas as your result above.
| Location | Distance | PSH/day | P90 kWh/m² | Optimum |
|---|---|---|---|---|
| Berlin | 1 km | 3.58 | 1,208 | 40° |
| Oranienburg | 19 km | 3.50 | 1,194 | 40° |
| Blankenfelde-Mahlow | 20 km | 3.58 | 1,198 | 35° |
| Potsdam | 22 km | 3.59 | 1,215 | 40° |
| Bernau | 22 km | 3.52 | 1,209 | 35° |
| Ludwigsfelde | 26 km | 3.64 | 1,219 | 40° |
| Königs Wusterhausen | 29 km | 3.57 | 1,203 | 40° |
| Strausberg | 33 km | 3.63 | 1,232 | 40° |
| Eberswalde | 45 km | 3.57 | 1,227 | 40° |
The sunniest and the dullest nearby place are 4 % apart — location beats tilt optimisation. Clicking a place opens its location page in a new tab.
Frequently asked questions
How many kWh does a 10 kWp system deliver per year?
In Berlin at 35° tilt, facing south, roof-mounted: around 10,000 kWh in year one — about 1,000 kWh per kWp. The number comes from the hourly simulation with module temperature, low-light and reflection losses for your grid point, not from a rule of thumb. Sunnier sites in the south of the DACH region reach 1,100–1,150 kWh per kWp.
Why does the calculator build degradation into the lifetime total?
Because a system does not deliver its as-new value for 25 years. At the median rate of 0.5% power loss per year (Jordan & Kurtz 2013), about 6% of the naive total "25 × year one" is missing over 25 years — one and a half years of output for a 10 kWp system. The reference: 20 operating years deliver 19.08 times year one, not 20 times.
What does the warranty checker do?
It translates the power warranty from the module datasheet (e.g. "87% after 25 years, 1% in the first year, then linear") into a minimum-yield curve for your site. You see the annual yield you may expect at minimum under warranty — around 8,700 kWh in year 25 for 10 kWp in Berlin — and the measured shortfall that justifies a claim. If even the expected path falls below the warranty, the calculator warns you: the assumed degradation is then higher than the manufacturer guarantees.
What does the P90 value in year one mean?
Your system reaches that yield in 9 out of 10 weather years — computed from the 19 real years (2005–2023) in the dataset. For financing, P90 is the dependable number: in Berlin it sits about 8% below the expected value. A single dull year is not a system fault — it is priced in.
Does sizing follow the first or the last operating year?
Both, depending on the question: inverter and grid connection are sized for year one (highest output), economics and self-sufficiency for the average — and anyone who still needs to cover a load at the end of the term (say an EV) works with the final year: at 0.5%/a that is still about 89% of the initial value. The calculator reports all three.
Where do the numbers come from, and how accurate are they?
Year one runs through the same calculation chain as the monthly output calculator — cross-validated against PVGIS PVcalc at four reference sites (annual total within 1.7%, deliberately slightly conservative because the PVGIS spectral correction is not freely available). The degradation maths is a closed-form geometric series, tested against the specification's reference calculation.
What degradation rate should I enter?
The default of 0.5% per year is the field-study median (Jordan & Kurtz, NREL) and fits classic PERC glass-foil modules. Modern datasheets guarantee better: TOPCon typically 0.40% per year (often stated as "87.4% after 30 years"), heterojunction down to 0.25%, glass-glass builds at the low end. Fraunhofer ISE field measurements often find only ~0.15% in practice. Honest advice: for planning, enter the warranty rate of your chosen module — for the economics, keep the conservative 0.5%.
Does this calculator work outside Germany, Austria and Switzerland?
Not yet. The hourly grid currently covers the DACH region (1,155 grid points at 0.25°). For other regions the official tools are the best choice: NREL PVWatts for the United States, or PVGIS by the European Commission — this calculator is cross-validated against PVGIS. A US grid built on NSRDB hourly data is in preparation, with the same degradation and warranty analysis.