NOVELTY - Use of coating agent for coating back sheet of photovoltaic module, is claimed. The coating agent comprises coating composition containing resin component and crosslinking component. The resin component comprises polyester, poly(meth)acrylate copolymer, pigment and/or filler, lacquer additive, light stabilizer, phosphoric acid ester (PO(OR)n (OH)m) and organic solvent. The crosslinking component comprises polyisocyanate and organic solvent.    USE - The coating agent is useful for coating back sheet of photovoltaic module (claimed).    ADVANTAGE - The coating agent is environmentally friendly, replaces fluorine-containing resin, and has excellent weathering stability and adhesion to the film substrate.    DETAILED DESCRIPTION - Use of coating agent for coating back sheet of photovoltaic module, is claimed. The coating agent comprises coating composition containing resin component and crosslinking component. The resin component comprises 3-20 wt.% polyester based on nonvolatile content of resin component having hydroxy number of 60-300 mg potassium hydroxide/g and glass transition temperature of -65 to 50 degrees C, 10-40 wt.% poly(meth)acrylate copolymer based on nonvolatile content of resin component having hydroxy number of 50-250 mg potassium hydroxide/g and glass transition temperature of -65 to 50 degrees C, 40-86 wt.% pigment and/or filler based on nonvolatile content of resin component, 0.1-10 wt.% lacquer additive based on nonvolatile content of resin component, 0-6 wt.% light stabilizer based on nonvolatile content of resin component, 0.01-1 wt.% phosphoric acid ester of formula (PO(OR)n (OH)m) based on nonvolatile content of resin component, and 20-50 wt.% organic solvent based on total weight of resin component. The sum amount of the of polyester, poly(meth)acrylate copolymer, pigment and/or filler, lacquer additive, light stabilizer and phosphoric acid ester is 100 wt.%. The crosslinking component comprises 30-100 wt.% polyisocyanate and 0-70 wt.% organic solvent. The sum amount of resin component and crosslinking component is 100 wt.%.    n = 1-3;    m = 0-2;    n + m = 3; and    R = 1-16C alkyl substituted with aromatic group and/or optionally contains ether oxygen atom, or aromatic group.    An INDEPENDENT CLAIM is also included for photovoltaic module comprising the back sheet coated by applying and curing the coating agent.