how to convert radiation on horizontal plane to an inclined one

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Good afternoon everybody!
I have data for the hourly radiation on a horizontal plane and weather conditions for a location for a few years. I need to convert the radiation on the horizontal plane to the radiation on an inclined plane.
Do you know any page that explains well how to do that? Pveducation didn't do it good enough for me to understand.
Even better, does anyone have a matlab script that does it or an excel sheet?

Thank you!

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