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HoriSol

How yield is calculated

HoriSol uses the NOAA solar position formula to compute, for every hour of the year, the exact sun position (azimuth + elevation) for your location.

How does the calculation work step by step?

  1. For each hour, check whether the sun is above the measured horizon profile — if not, the panel is shaded.
  2. From solar irradiance (direct + diffuse) the theoretical energy is computed.
  3. Shaded hours partially contribute via the diffuse component — even a shaded panel yields diffuse-light energy.
  4. The yearly sum is the expected yield in kilowatt-hours, reported with a ±10% confidence band.

Where does the solar data come from?

HoriSol pulls irradiance data from the best available source for your location:

  • PVGIS (EU Joint Research Centre) for Europe and Africa
  • NREL PVWatts for the USA
  • NASA POWER as a global fallback when the primary source is unavailable

What assumptions does HoriSol make?

  • System losses: a flat 18% (inverter, wiring, soiling, temperature)
  • Electricity price, feed-in tariff, and CO₂ factor: configurable, with per-country defaults
  • Deliberately conservative: the payback calculation ignores future electricity price increases, for example

All assumptions in detail — with formulas, sources, and limits: Methodology & Assumptions.