The units for the solar radiation sensor are W/m2. That sounds simple enough on the face of it. However, exactly what area does it relate to? Is it in the horizontal plane ie parallel to the ground? Is is a plane normal to the sun? Is it something else?!
Wy do I want to know? Well, I have an array of PV solar panels that are partially shaded, especially in winter, and I'd like to compare the solar radiation from the weather station with the apparent radiation on the PV panels. I have all the specs for the panels including the maximum power generated in W/m2 and efficiencies etc and want to estimare the percetgae losses due to shading. Knowing exsctly what the weather station is measuring is key.