Dimensional analysis methodology was applied to I-V data of PV modules and analyzed to relate the parameters defining conversion of photovoltaic power. A single equation model was developed, relating normalized efficiency to normalized cell temperature and irradiance. The developed model was validated on reported data of different module makes of mono-crystalline cells. The error average was around 1%. The study revealed that the effect of normalized temperature change on normalized maximum efficiency is identical for all mono-crystalline cell makes. The influence of irradiance on efficiency was shown to depend on the module's specific technology.