The incorporation of Na into Cu(InGa)Se2 (CIGS) based absorber layers is critical for fabricating high efficiency photovoltaic devices. In the present study we show that Na transport through Mo and CIGS from soda-lime glass substrates takes place through the grain boundaries with oxygen playing a critical role. Device performance drops as the Na level in CIGS is reduced but recovers by mild air heat treatment implying that Na plays a major role at the junction and at CIGS grain boundaries within the depletion region. Finally, we present results on the use of NaF as a post-deposition Na source.