The solar radiation energy incident upon a surface can be calculated according the methods in the ASHRAE manual and is dependent upon latitude, longitude, time of day and cloud cover. The maximum temperature of a surface is the temperature at which the solar radiation heat gain is equal to the sum of all heat losses from the surface (i.e. natural convection, conduction, etc). A surface like a pipe in still air will have heat losses to the fluid inside the pipe as well as natural convection losses to the ambient air, and it is the balance of these heat transfer mechanisms with solar flux that gives the maximum surface temperature.