Soren popped into my head. [name_m]Helios[/name_m] as well, since [name_m]Helios[/name_m]/Helio is the Greek personification of the sun, perhaps [name_u]Sonny[/name_u]/Sunny could be a nickname?
Other names relating to the sun:
[name_m]Cyrus[/name_m]: sun in Persian
[name_m]Apollo[/name_m]: Greek god of the sun
[name_u]Blaze[/name_u]
[name_m]Elio[/name_m]: means sunny and spirited
[name_u]Phoenix[/name_u]
[name_u]Kiran[/name_u]: means sunbeam
[name_m]Taner[/name_m]: means born at sunrise
Here are some out-of-the-box ones:
Solanus
Sonnen
[name_u]Sondre[/name_u]
[name_m]Socrates[/name_m]
[name_m]Sohan[/name_m]
[name_m]Sorell[/name_m]
Solan
Hope this helps 