Equation based model for calculating hourly solar radiation values
Is there a simple but accurate model to calculate hourly solar radiation for a particular location by using other weather parameters and/or some constants? I would like to compare its accuracy with a developed model.
EDIT
I had a look at ASHREA model which states that the hourly global radiation (I), hourly beam radiation in the direction of rays (IN) and hourly diffuse radiation (Id) on the horizontal surface on a clear day are calculated as; I=INcosθz+Id IN=Aexp[−B/cosθz] Id=CIN where, A,B,C are constants and θz is the zenith angle.
There is another model by Zhang Qingyuan et al; (@Joe Huang), which is of the form; I=[Io.sin(h).(c0+c1(CC)+c2(CC)2+c3(Tn−Tn−3)+c4ϕ+c5Vw)+d]/k where; I = estimated hourly solar radiation, Io = solar constant, h = solar altitude angle, CC = Cloud cover, ϕ= relative humidity, Tn = temperature at n hours, Vw= wind speed. and other are constants.
@Joe Huang: maybe you could please throw some light and how/where to find all these constants and data source for cloud cover for a particular place. Thanks!