The development of innovative technologies for direct solar energy conversion is one of the main trends of modernity. The use of solar semiconductor panels is well-known in solar photovoltaics. As an alternative to this, the use of gas photoplasma can be promising. However, research in this direction is still very fragmentary so far. This paper shows the results of a systematic study of photoplasma in mixtures of sodium and inert gases to obtain photoEMF in a gas cell. A fluid modeling considering detailed plasma chemistry, radiation transfer, and charge diffusion processes and 2D simulation were fulfilled and main plasma parameters were obtained and analyzed. In particular, non-trivial dependence of EMF in a two-chamber gas cell containing sodium and argon on the pressure of the inert gas was obtained, reaching up to 1.3 eV by absolute value at 100 Torr of Ar and changing its sign near 5 Torr at the decrease of the pressure.