NOVELTY - UV-curable adhesive organopolysiloxane composition comprises e.g.: (A-1) comprising (a) linear organopolysiloxane having at least two silicon-bonded alkenyl groups per molecule and (a1) three-dimensional network organopolysiloxane resin units; (B-1) comprising (b) an organohydrogenpolysiloxane containing at least two silicon-bonded hydrogen atoms per molecule, but not alkoxy group, and (b1) an organohydrogenpolysiloxane containing one trialkoxysilyl group bonded to silicon via an alkylene group and one silicon-bonded hydrogen atom per molecule; and (C) a photoactive platinum complex catalyst.    USE - The composition is useful for forming Fresnel lenses for concentrator solar power systems (claimed).    ADVANTAGE - The composition has a sufficient pot life at room temperature and upon brief UV exposure, the composition is cured to glass which exhibits desired hardness and other physical properties.    DETAILED DESCRIPTION - UV-curable, adhesive organopolysiloxane composition comprises: (A-1) comprising (a) 50-90 wt.% of a linear organopolysiloxane having at least two silicon-bonded alkenyl groups per molecule and (a1) 10-50 wt.% of a three-dimensional network organopolysiloxane resin units of formulae (I) R12R2SiO1/2 and (II) R13SiO1/2 and silicon dioxide units, where the molar ratio of ((I)+ (II))/silicon dioxide is 0.5/1-1.5/1, and contains 5x 10-3-1x 10-4 mol/g of alkenyl groups, and the sum of components (a) and (a1) is 100 wt.%; (B-1) comprising (b) an organohydrogeripolysiloxane containing at least two silicon-bonded hydrogen atoms per molecule, but not alkoxy group, in an amount to give a molar ratio of silicon-bonded hydrogen in component (b) to the total of alkenyl in components (A-1) and (D) of 0.1/1-5.0/1, and (b1) an organohydrogenpolysiloxane containing at least one trialkoxysilyl group bonded to silicon via an alkylene group and at least one silicon- bonded hydrogen atom per molecule, in an amount to give a molar ratio of silicon-bonded hydrogen in component (B1) to the total of alkenyl groups in components (A-1) and (D) of 0.05/1-2/1, with the proviso that a molar ratio of silicon-bonded hydrogen in component (B-1) to the total of alkenyl in components (A-1) and (D) is 0.5/1-7.0/1; (C) a photoactive platinum complex catalyst; and (D) a branched organopolysiloxane oligomer units of formulae (I) and/or (II) and (III) R1SiO3/2 , and contain at least two alkenyl groups per molecule, in an amount to give a molar ratio of alkenyl in component (D) to the total of alkenyl in components (A-1) and (D) of 0.1/1-0.6/1.    R1 = unsubstituted or halo-substituted monovalent hydrocarbyl exclusive of alkenyl; and    R2 = alkenyl.    An INDEPENDENT CLAIM is also included for Fresnel lens for concentrator solar power systems comprising a glass substrate and UV-curable adhesive organopolysiloxane composition cured and bonded to the substrate.