NOVELTY - A polyester film comprises polyester layer on one or more surface layer. The polyester layer has thickness of 30-250 mu m and surface roughness of 0.10-0.50 mu m. The reduction of thickness of polyester film after endurance test is 15 mu m or more and the elongation retention after endurance test is 40% or more. The endurance test involves irradiating surface of polyester layer by radiation of 180 W/m2 for 102 minutes (t-1) using xenon lamp, and continuing irradiation of xenon lamp by applying 16 degrees C plus minus 5 degrees C water shower to polyester layer surface for 18 minutes (t-2).    USE - Polyester film is used for back sheet for solar cell (all claimed). Can also be used for component for magnetic recording media, electric insulation, condenser and packaging component.    ADVANTAGE - The polyester film has excellent film wear-proof property and durability, and provides solar cell having improved service life. In the polyester film, the reduction of film thickness is small and the decrease of wet heat resistance, weather resistance and electrical insulation is suppressed when used outdoor for long period of time.    DETAILED DESCRIPTION - A polyester film comprises polyester layer on one or more surface layer. The polyester layer has thickness of 30-250 mu m and surface roughness of 0.10-0.50 mu m. The reduction of thickness of polyester film after endurance test is 15 mu m or more and the elongation retention after endurance test is 40% or more. The endurance test involves irradiating surface of polyester layer by radiation of 180 W/m2 for 102 minutes (t-1) using xenon lamp at 65 degrees C and relative humidity of 50 %RH, and continuing irradiation of xenon lamp by applying 16 degrees C plus minus 5 degrees C water shower to polyester layer surface for 18 minutes (t-2) in the quantity of 2.1-L plus minus 0.1 mL/minute. The total time ((t-1)+(t-2)) of radiation is 120 minutes. The irradiation processes are repeated 1500 times. An INDEPENDENT CLAIM is included for manufacture of polyester film, which involves melt-kneading polyester resin composition with extruder, extruding and solidifying the mixture by cooling roll to form non-oriented polyester film. The temperature of cooling roll is more than Tg-70 degrees C and less than Tg-30 degrees C. The time (residence time) of the mixture in cooling roll is 20-120 seconds.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of solar cell. (Drawing includes non-English language text)    Back sheet (1)    Sealing material (2)    Electricity generating element (3)    Transparent substrate (4)    Surface at side of sealing material of solar cell back sheet (5)