Solar radiation heat transfer to surface

Solar radiation heat transfer to surface of PAC/GIL by sun. It is assumed that the sun shines directly from above onto an area of the length (1 m) multiplied with the diameter $D_o$ of the cylindrical object (and not half its circumference $\pi{D_o}/2$).

Symbol
$W_{sun}$
Unit
W/m
Formulae
$\sigma_{sun} D_o H_{sun}$