Liu and Jordan extended their model of division, which is valid for monthly average radiation values, to the valuation of daily global radiation received on an inclined surface. If K is the daily clearness index, which is equal to H/Hex (i. e. the ratio between daily radiation and extraterrestrial radiation received on a horizontal surface on a specific day), the ratio between diffuse radiation and global radiation received on a horizontal surface on a certain day has to be cal­culated as follows:

D/H = 1.0045+ 0.04349K -3.5227K2 + 2.6313K3 se K < 0.75 (^

D/H = 0.166 seK > 0.75

The direct component is calculated by the difference:

B = H — D (44)

The daily global radiation on an arbitrary inclined surface can be calculated using the following expression:

E = Rb B + Rd D + Rr(B + D) (45)

where Rb, Rd and Rr are the inclination coefficients of direct, diffuse and reflected radiation determined, respectively, by eqns (29), (32) and (34), but for the chosen day [1].