Data sources for solar production forecast (Belgium)

Recommendations for reliable, regularly updated data for temperature, solar hours, sun up/down, and seasonality.

Primary: Open-Meteo (forecast + current)

Best fit for live and forecast data. No API key for non-commercial use.

Aspect	Details
URL	https://open-meteo.com/
Docs	https://open-meteo.com/en/docs
Updates	Forecast models refresh every 1–6 hours (e.g. ECMWF 6h, HARMONIE 1h). Current conditions from 15‑minute data.
Uptime	~99.9%, redundant EU/NA servers
Coverage	Global; Belgium well covered (European models).

What you get

Temperature: temperature_2m (hourly, daily min/max, current).
Solar radiation (hourly):
shortwave_radiation (GHI), direct_radiation, direct_normal_irradiance, diffuse_radiation,
optional global_tilted_irradiance (with tilt/azimuth for panels).
Sun up/down: daily sunrise, sunset, daylight_duration, sunshine_duration (WMO: direct > 120 W/m²).
Daily totals: shortwave_radiation_sum (MJ/m²) for “solar hours” style metrics.

Limits (free, non-commercial)

10,000 requests/day, 5,000/hour, 600/minute; 300,000/month.
One request can return 7–16 days forecast + many variables; design to batch variables in a single call per location.

Example (Belgium, e.g. Brussels)

GET https://api.open-meteo.com/v1/forecast?latitude=50.8503&longitude=4.3517&timezone=Europe/Brussels
  &hourly=temperature_2m,shortwave_radiation,direct_radiation,diffuse_radiation
  &daily=sunrise,sunset,sunshine_duration,daylight_duration,shortwave_radiation_sum,temperature_2m_max,temperature_2m_min
  &forecast_days=16

Secondary: PVGIS (seasonality and long-term baseline)

Use for climatology and seasonality, not for real-time or forecast.

Aspect	Details
URL	https://ec.europa.eu/jrc/en/pvgis
API	https://joint-research-centre.ec.europa.eu/.../api-non-interactive-service_en
Updates	Datasets (e.g. SARAH) are updated periodically (every few years); use for long-term averages, not “regular” live updates.

Good for:

Monthly/yearly average irradiance and PV yield.
Seasonality (e.g. monthly factors for Belgium).
Optimal tilt/azimuth and system design.

Not for:

Hourly/daily forecast or “today’s” production.

Summary

Need	Source	Update frequency
Temperature (current + forecast)	Open-Meteo	Hourly model runs, 15‑min current
Solar irradiance / “solar hours” (forecast)	Open-Meteo	Same as above
Sun up/down, sunshine duration	Open-Meteo	Daily in forecast
Seasonality (monthly factors, Belgium)	PVGIS (or Open-Meteo historical)	PVGIS: infrequent; Open-Meteo Historical: on request

Practical choice for a reliable, regularly updated pipeline:
Use Open-Meteo as the main datasource for temperature, solar hours, and sun up/down; add PVGIS (or Open-Meteo Historical) when you implement seasonality and long-term baselines.

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