Equation based model for calculating hourly solar radiation values

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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.

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I had a look at ASHREA model which states that the hourly global radiation (I), hourly beam radiation in the direction of rays $(I_N)$ and hourly diffuse radiation $(I_d)$ on the horizontal surface on a clear day are calculated as; $$I = I_N cos\theta_z + I_d$$ $$I_N = Aexp[-B/cos\theta_z]$$ $$I_d=CI_N$$ where, $A, B, C$ are constants and $\theta_z$ is the zenith angle.

There is another model by Zhang Qingyuan et al; (@Joe Huang), which is of the form; $$I = [I_o.sin(h).(c_0+c_1(CC)+c_2(CC)^2+c_3(T_n-T_{n-3})+c_4\phi+c_5V_w)+d]/k$$ where; $I$ = estimated hourly solar radiation, $I_o$ = solar constant, $h$ = solar altitude angle, $CC$ = Cloud cover, $\phi$= relative humidity, $T_n$ = temperature at n hours, $V_w$= wind speed. and other are constants.