1.6 suns at 58°20′N - the solar resource in Southern Norway

We measured an extreme overirradiance event of 1.6 suns at latitude 58°20'N during a solar resource assessment in southern Norway. The burst occurred when the sun showed in a narrow gap between broken, optically thin altocumulus clouds. The enhancement was most intense within 3° around the solar disk. The annual solar irradiation in the plane of an optimally tilted PV array peaked at 1.30 MWh/m2 in the year 2013, and measured 1.20 MWh/m2 in the previous two years. These values exclude irradiance below 0.05 suns but include reflections from the sea surface and terrain which have not been quantified. The long-term average predicted by the Photovoltaic Geographical Information System (PVGIS) is only 1.04 MWh/m2. 15 years of global horizontal irradiation data reveal that the PVGIS underestimates the local solar resource by at least 10%.