It is a hard subject for skills and equipment. By photo shooting sun we could damage our precious cameras, so what left to do? Illustrations and photos manipulated in some graphic program. Subject of sun closeup was not difficult to find some examples but almost all of them have EXIF: n/a usually means that have been corrected.
Found some photo with EXIF: filled taken by Canon EOS 20D on ISO 200, city modern building on blue sky background with some sun ray, lots of photos of sunrises and sunsets also very beautiful, but no 'center sun' photo
only illustration more or less showing what I have on mind.