This is more of a general EPW question, but I’m hoping someone here can give me some clarity anyway.
Intuitively, I would think that Direct Normal Radiation (DNR) tends to peak during widday when the sun is over head, just like Global Horizontal Radiation (GHR) and Diffuse Horizontal Radiation (DHR). This seems to be the case for most cities, e.g. Melbourne, Australia:
However, Moorabbin’s EPW file, which is very close to Melbourne, looks like this (note the local minima in DNR):
I’ve noticed the same behaviour for Sydney’s weather file:
Could there be a fault in the way that some weather stations measure DNR, or is there an explanation that I am missing?