NOVELTY - The photovoltaic module comprises a first outer protective layer comprising a glass sheet, a second outer protective layer comprising a glass sheet, a crystalline silicon solar cell wafer between the first and second outer protective layers, a seal (18) provided along an edge and between the first and second outer protective layers to form a sealed cavity comprising the crystalline silicon solar cell wafer, and a sodium-containing structural glass sheet having a thickness of greater than 1.5 mm. The glass sheets have a composition including 35-45 wt.% of silicon dioxide.    USE - Used as a photovoltaic module.    ADVANTAGE - The photovoltaic module exhibits increased resistance to water ingress, reduced potential-induced sodium ion drift and potential-induced degradation rate, excellent light conversion efficiency, long lifetime, high reliability and stability, improved performance and lightweight.    DETAILED DESCRIPTION - The photovoltaic module comprises a first outer protective layer comprising a glass sheet, a second outer protective layer comprising a glass sheet, a crystalline silicon solar cell wafer between the first and second outer protective layers, a seal (18) provided along an edge and between the first and second outer protective layers to form a sealed cavity comprising the crystalline silicon solar cell wafer, and a sodium-containing structural glass sheet having a thickness of greater than 1.5 mm. The glass sheets have a composition including 35-45 wt.% of silicon dioxide, 5-15 wt.% of aluminum oxide, 10-30 wt.% of boron oxide, 0-5 wt.% of magnesium oxide, 0-25 wt.% of calcium oxide, 0-15 wt.% of strontium oxide, 20-30 wt.% of barium oxide, 20-40 wt.% of rhodium oxide, 0-1 wt.% sodium oxide, 0-5 wt.% of potassium oxide, and 0-5 wt.% of manganese oxide. The glass sheets are processed under roll-to-roll conditions, and have: a B-OH value of 0.2-0.9 mm-1; an average surface roughness (Ra) of less than or equal to 10 Angstrom ; a thickness of less than or equal to 0.5 mm; and a curvature deformation (W) of less than 0.5 mu m/cm2 as described by the equation of W = D/L2, where D is a maximum curvature of glass sheet in mu m and L is a diagonal length of glass substrate in cm.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic cross-sectional view of a photovoltaic module.    Glass sheets (11)    Metal frame (14)    Silicon wafer (16)    Seal (18)    Encapsulant layer (20)    Electrical contacts. (22)