Performance of solar collector is often presented as a graph, or set of three performance variables. Values may be provided based on gross area, aperture area or absorber area. It doesn't really matter which values is used, as long as you use the correct value. ie. Don't use absorber area when using performance values based on gross area.

The three performance variables for the Century Sun collector are provided by the test lab INETI.They are as follows:

(n0=0.880 a1=0.505 a2=0.019)
Above DATA is given to absorber area