I must have shot the sun 30 times but it was always to ashy where exactly did you do this.
If the sun is up, you can draw the arrow and point it at where you think the sun may be at that time of day, and if your cursor passes over the sun, it will darken your screen briefly (or lighten, if using the blessed arrows). The trouble with the southern part of Solstheim is it's damn hard to tell what time of day it is, especially since the nighttime looks like the day time. The sky during the day never gets bright, and the aurora above the ash and clouds at night light up the ground and sky so much at night that there really is no difference from AM to PM. Of course, if you're a vampire, you can always tell if it's day time.
Another issue is that with Solstheim being so mountainous and hilly, during the early and later parts of the day, the sun may be obscured by parts of the island itself. If it's early or late in the day, try getting to high ground: Highpoint Tower, on top of one of the shorter mushroom towers in Tel Mithryn, or somewhere up on Moesring Pass. It could also help to go the the eastern part of the island in the morning; if you're in Raven Rock, you probably won't have line-of-sight with the sun until midday.