Solar Irradiance Measurements for PV Profiling

Hey Guys,

I'm re-opening my search for a good Solar Irradiance data source. I'll use this issue to document my findings and ask for some feedback.

Since September 2015, KMI includes irradiance in their monthly overview. I designed a small experiment to determine if there is a significant improvement in the correlation of PV-production and Irradiance versus the correlation of PV-production and Sunshine Duration on a monthly resolution. While the duration correlated on average with R² = 0.90, the irradiance had R² = 0.96. Most notably in months with lots of clouds and rain (eg. June 2016), irradiance resulted in a much better model. (Some people may have noted that EnergyID has underestimated PV-production for June because of the low number of solar hours).
I have sent a mail to SoDa to request a quotation for access to their solar irradiance database. They use MeteoSat data to estimate the irradiance components, and also calculate the values for tilted solar arrays etc. @kdebrab you once talked about a good online database... did you mean this one, or do you know a (preferably free) alternative?
@saroele in #69 you talked about some ex-colleagues from KULeuven who'd given permission to use their code to estimate irradiance based on cloud-cover measurements. Any follow-up on that?

opengridcc / opengrid-dev