As the sun and its brightness is a confirmed strategic component. How about an indicator (maybe toggleable) to show Commanders if their units are facing towards the sun or not? That way a Commander might say, "We may have an advantage if we flank through this angle".
Now that I think about it... FPS could use this as well. Eventually i think some sort of compass will be added on top? If that would be the case, a transparent "Sun" icon could indicate the player if he/she is facing the sun or not and act accordingly.