Solar Production Calculator

How We Calculate Solar Production (Full Methodology)

This calculator applies a transparent, step-by-step approach based on physical parameters and documented assumptions. Results are indicative and can vary depending on site, weather, and installation quality.

1) Main inputs & units

• System power (kWp): (number of panels × panel power in Wp) ÷ 1000.
• Peak Sun Hours (PSH): annual equivalent full sun hours, expressed in kWh/kWp/year (regional value, editable).
• Simple Mode: uses annual PSH and a global Performance Ratio (PR).
• Expert Mode: adds geometry (tilt/azimuth) and a detailed PR reconstructed from losses.

2) Geometry: tilt & azimuth

Production varies with panel tilt and orientation. The calculator applies a simplified geometric correction:

• Tilt: moderate penalty if far from ~30°. Internal cap avoids extreme corrections (≈ up to ~15%).
• Azimuth: 0° = South, −90° = East, +90° = West. Penalty increases with deviation, capped (≈ up to ~20%).
• The geometric factor is bounded for realism (≈ 0.70 to 1.05).

3) Performance Ratio (PR) & detailed losses

The PR groups together the main system losses. In Expert Mode it is recalculated from the fields below; in Simple Mode you adjust a single PR slider.

• Inverter efficiency: fraction (e.g., 0.9–1.0) representing DC→AC conversion efficiency.
• Cabling & mismatch: loss % (e.g., 3–5%). Includes wiring resistance, connector losses, module tolerance mismatches.
• Soiling (dust): loss % (e.g., 2–8%, higher in dusty areas). Reduced with regular cleaning.
• Shading: loss % (e.g., 0–10% depending on obstacles). Significant if nearby trees, chimneys, walls.
• Temperature effects: integrated into the global PR. Reference values: gammaT (loss slope, ~−0.35%/°C) and NOCT (Nominal Operating Cell Temperature, ~45°C).

Not explicitly modeled: annual module degradation (~0.3–0.7%/year), downtime, inverter clipping, seasonal soiling (sand, pollen), snow, albedo. For conservative estimates, reduce PR slightly (−1 to −3 points).

4) Annual, daily & monthly production

• Annual production: kWh/year = kWp × PSH × PR × geometric factor (in Simple Mode: without explicit geometric factor).
• Daily average: kWh/year ÷ 365.
• Monthly breakdown: chart uses a normalized distribution (12 values summing to 1) to reflect seasonality. It redistributes annual production but does not simulate real monthly weather.

5) Economics & ROI

• Electricity price (€/kWh): net or gross depending on context; default is realistic for 2025.
• Self-consumption rate (%) : fraction of produced kWh consumed instantly (e.g., 60–100%).
• Annual savings (€) = annual kWh × electricity price × self-consumption rate.
• Payback time (years) = installation cost ÷ annual savings. Excludes inflation, maintenance, financing.

6) CO₂ avoided

• CO₂ avoided/year = annual kWh × CO₂ factor of local grid (kg/kWh). Displayed in tonnes if needed (÷1000).
• The default factor depends on country; editable for local grid mix.

7) Default values & boundaries (editable)

• Default PR: 0.9 (Simple Mode). In Expert Mode recalculated from losses.
• Electricity price: 0.2 €/kWh (editable).
• Self-consumption: 90% (editable).
• Indicative PSH France: region-based (e.g., South-West ≈ 1500, South-East ≈ 1650 kWh/kWp/year).
• UI ranges: tilt 0–60°, azimuth −180° to +180°, losses 0–50% (shading, soiling), etc.

8) Limitations & best practices

• Results are indicative (typical deviation ±10–20%). For contractual sizing, request a full study.
• Avoid shading, use correct cable sizing, keep modules clean.
• Compare scenarios (realistic vs. optimistic) by adjusting PSH, PR and self-consumption rate.