NOVELTY - The back sheet (1) is a laminate having a front face side resin film (2), a barrier film (3) and a back face side resin film (4) in this order that are laminated through an adhesive layer (5). The front face side resin film contains polyolefin as a principal component. The barrier film comprised by an aluminum foil has a substrate film (6), and an inorganic oxide layer (7) that is laminated on the back face of the substrate film. A voltage endurable film is provided between the front face side resin film and the barrier film.    USE - Back sheet for the photovoltaic modules of fixed-roof stationary solar batteries. It is also for the solar batteries of small electric equipments such as electronic calculators.    ADVANTAGE - Since the front face side resin film includes polyolefin as a principal component, it is excellent in adhesiveness with the ethylene-vinyl acetate copolymer generally used in the filler layer and has favorable resistance to hydrolysis. The back sheet improves durability of the photovoltaic modules and promotes extension of usable time period of the photovoltaic modules socially demanded. By providing a barrier film with an inorganic oxide layer laminated on the back of the substrate film, high gas barrier properties are achieved, and the mechanical strength, cost reduction capability, productivity and voltage endurance are enhanced. By using the aluminum foil as the barrier film, gas barrier properties of the back sheet are also enhanced. By placing the voltage endurable film between the front face side resin film and the barrier film, the voltage endurance of the back sheet is improved and regulation of the thickness of the voltage endurable film is effectively met with an increase the voltages of the photovoltaic system. By laminating each film through an adhesive layer, improvement of the strength, durability and toughness of the back sheet is achieved, and sealing and protecting functions compensate the defects of the inorganic oxide layer. By using a polyurethane-based adhesive, decrease in adhesive strength of the barrier sheet and delamination resulting from long-term use of the back sheet are prevented, and yellowing of the adhesive layer is diminished. Since polyethylene terephthalate is inexpensive and has various functions such as excellent heat resistance and voltage endurance, formation of the back face side resin film enhances the cost reduction capability, heat resistance and thermal dimensional stability of the back sheet. Since the polyethylene naphthalate is excellent in resistance to hydrolysis and heat resistance, the back face side resin film improves the durability of the photovoltaic modules and extends the usable time period of the photovoltaic modules.    DESCRIPTION OF DRAWING(S) - The drawing shows the schematic cross-sectional view of the back sheet.    Back sheet (1)    Front face side resin film (2)    Barrier film (3)    Back face side resin film (4)    Adhesive layer (5)    Substrate film (6)    Inorganic oxide layer (7)