Thread: Insolation per country?

I'm doing a regression analysis on several European countries and I want one of my variables to represent average insolation (or solar radiation) per country. However, I cannot find these kind of data in any website: I can only find maps that give you the insolation for a given point.

Does someone know a website that provides this kind of data? Or could someone propose me a way to calculate this insolation per country?

Thank you in advance.

OY Not Solar Electric Products

Or perhaps create your own from city data:
Apricus - Insolation Europe