Comparison between SolaRes estimates of the tilted solar irradiance and measurements by the PVlive network

The aim of SolaRes is to provide precise and accurate estimates of solar resource for any location on the globe, in any meteorological and ground surface conditions, and for any solar plant technology. To suit most applications, not only the Global Horizontal Irradiance (GHI) is computed at 1-minute time resolution, but also the direct normal irradiance (DNI), the Diffuse Horizontal Irradiance (DifHI) and the components in tilted planes with any orientation (GTI, DifTI). To make comparisons with ground-based measurements, the circumsolar contribution in measured DNI is also computed.

SolaRes was validated in clear-sky conditions encountered in northern France, affected by local and transported anthropogenic pollution and irregular incursions of Saharan desert dust to Europe. For the validation, AERONET provided the input spectral AOT data. Tests were also done with CAMS-NRT as input data source, and comparisons with measurements made on the ATmospheric Observations in LiLLe (ATOLL, France, 50.61167°N, 3.141670°E) platform provided RMSD in GHI smaller than 3% at 1-minute resolution, and RMSD in DNI of 8% [Elias et al., submitted to AMT].

In this work, the performances of SolaRes are evaluated in all-sky conditions encountered in northern France and in Germany. The Copernicus Atmosphere Monitoring Service in the near real time mode (CAMS-NRT) provides the input spectral aerosol optical thickness (AOT) data, and the Nowcasting Satellite Application Facilities (NWCSAF) provide the cloud optical thickness. The SolaRes estimates of the three solar resource components GHI, DNI, and DifHI are compared with measurements acquired at ATOLL. The SolaRes estimates of GHI and GTI are compared with measurements made by the PVlive network [Lorenz et al., 2022; and Dittmann et al., 2024 for the data]. Each PVlive station is equipped of a horizontal thermopile pyranometer, and 3 tilted silicon sensors, orientated eastwards, southwards and westwards.

RMSD in GHI is found to be 18% at the PVlive station of Freiburg for one year of data (2021) at 1-hour resolution. RMSD in GTI slightly increases to reach 20% at a tilt angle of 25° orientated southwards, and 21% at the same tilt angle but orientated westwards.

The satisfying comparison scores in GTI are obtained by considering a solar spectrum restricted between 300 and 1100 nm to simulate the Silicon detector. Improvement will be performed by considering the detailed spectral response as well as the angular loss.

SolaRes in its standard mode considers horizontal homogeneous cloud field. Performances could be improved by selecting such observed situations. Moreover, DifTI could be individually tested by selecting measurements in shadows occurring for example for the eastwards instrument when the sun sets down.