Irradiance data sources
Modelling recommendations
Several PV simulation tools allow users to select the source of irradiance and meteorological data. The following data sources are recommended, as they have shown good performance when validated against measured irradiance in Norway [1,2]:
- Up to 65ºN (TMY and time series): Solargis (paid service), PVGIS Sarah-3 (free). Meteonorm is commonly used but was found to overestimate irradiance by 3.5% [1] and is therefore not recommended.
- TMY, across Norway: Climate data for buildings [3].
- If a TMY is not needed and only an irradiance time series is required, we recommend using the MET Norway Solar map [4] or local ground-based measurements.
Horizon shading can be a substantial loss factor in Norway due to the complex topography. It should be accounted for by adding a horizon mask to the irradiance data, either by measuring the local horizon or by calculating it from topography maps (e.g., as provided by PVGIS or Solargis).
Background: State of the art & knowledge gaps
The choice of solar irradiance and meteorological data sources can have a significant impact on PV yield modelling. In the Nordic region, solar irradiance data have higher uncertainties. This is mainly due to snow cover, a high frequency of overcast conditions, topography leading to substantial horizon shading for some parts of Norway, and the high latitude giving poor view from geostationary satellites. Due to viewing angle limitations of geostationary satellites, satellite-based irradiance data are currently only available up to about 65° N for most products, and up to 66° N for CAMS. Within the SUNPOINT project, IFE and MET Norway validated commonly used solar irradiance databases [1] and developed a new solar irradiance dataset for Norway based on machine learning, using ground-based measurements, weather models, and satellite imagery as inputs [4,5]. In the validation, Solargis and PVGIS Sarah-2 performed best, while Meteonorm, which is commonly used in PVsyst and PV*SOL, overestimated irradiance by 3.5%. NMBU and MET have developed TMY data based on CERRA (Climate data for buildings [3]), showing good agreement with SUNPOINT irradiance data and temperature data from SeNorge [2].
Improving irradiance data above 65° N will require the integration of polar-orbiting satellites. Additionally, further research is needed on accurate modelling of horizon shading and on incorporating climate‑change impacts on future irradiance to ensure reliable irradiance estimates in Norway. While the accuracy of irradiance data under Nordic conditions has been systematically investigated, other relevant parameters (for example, temperature and wind) have been less studied.
ReFERENCES
[1] H.N. Riise, M.M. Nygård, B.L. Aarseth, A. Dobler, E. Berge, Benchmark of estimated solar irradiance data at high latitude locations, Solar Energy, 2024.
[2] T.K. Thiis, A.J. Petersen, H.F. Fuglestvedt, H.O. Hygen, Typical meteorological years tailored for high latitudes based on high-resolution reanalysis data, Journal of Building Performance Simulation, 2025.
[3] NMBU: Klimadata for bygninger - dataset.
[4] MET Norway: SunPoint solar irradiance map - dataset.
[5] J. Rabault, M.L. Sætra, A. Dobler, S. Eastwood, E. Berge, Data fusion of complementary data sources using Machine Learning enables higher accuracy Solar Resource Maps, Solar Energy, 2025.
Last update: 27.4.2026