solar radiation
 

while i was tring solve solar radiation by using star CD,i have three problems,which are coordinate system,solar intensity and the emisivity of out surface.

Is coordinate system determining the direction solar radiation or the position of solar ?

How can i determine solar intensity which incident to solution domain? i want incidenting solar intensity which is 800w/m2

when i impose out surface emisivity,the temperature down to minus.why is it happen. If impose the emisivity 0,the result was reasonable.