Below are key equation relevant to the computation of beam solar radiation:
Bhc(t): clear sky hourly (t=hr, MJ m-2 h-1) or daily (t=d, MJ m-2 d-1) beam irradiance on a horizontal surface
Bic(t): clear sky hourly (t=hr, MJ m-2 h-1) or daily (t=d, MJ m-2 d-1) beam irradiance on an inclined surface
Bh(t): hourly (t=hr, MJ m-2 h-1) or daily (t=d, MJ m-2 d-1) beam irradiance on a horizontal surface
Bi(t): hourly (t=hr, MJ m-2 h-1) or daily (t=d, MJ m-2 d-1) beam irradiance on an inclined surface
Gh(t): hourly (t=hr, MJ m-2 h-1) or daily (t=d, MJ m-2 d-1) global irradiance on a horizontal surface
Gi(t): hourly (t=hr, MJ m-2 h-1) or daily (t=d, MJ m-2 d-1) global irradiance on an inclined surface
Dh(t): hourly (t=hr, MJ m-2 h-1) or daily (t=d, MJ m-2 d-1) diffuse irradiance on a horizontal surface
Di(t): hourly (t=hr, MJ m-2 h-1) or daily (t=d, MJ m-2 d-1) diffuse irradiance on a inclined surface
Ri(t): hourly (t=hr, MJ m-2 h-1) or daily (t=d, MJ m-2 d-1) ground reflected diffuse radiation
S(t): hourly (t=hr, MJ m-2 h-1) or daily (t=d, MJ m-2 d-1) extra-terrestrial solar radaition
tb: clear sky transmissivity for beam solar radiation
H(t): hourly (t=hr) or daily (t=d) geometric factor