ABSTRACl High-efficiency Ill-V solar cells can he used costeffectively in high-concentration modules. The Fraunhofer ISE - in co-operation with the loffe Institute St. Petersburg - has developed the FLATCONTM-modules: Fresnel Lens All-glass Tandem-cell CONcentrator modules. A 500x concentration is obtained by using Fresnel lenses which are fabricated dircctly on a glass sheet. The module housing is made totally out of glass. High-efficient dualjunction cells of Gao.dslno,sP/Ca,n,Ino.liAs are applied. Outdoor measurements showed module efficiencies of > 22 %. Furthermore, a new tracking system as well as a monitoring measurement set UP has been installed. The latter allows a continuous monitoring of up to 20 modules. First results are presented.