A 13.6 m(2) east-west aligned CPC-collector (compound parabolic concentrator) with flat absorbers, proposed for use in large-area applications, has been built and tested and compared with a flat plate collector. The performance of the CPC at a working temperature of 50 degrees C over ambient can be described by F＇eta(0) = 0.75 and F＇U-L = 2.5 W m(-2) K-1 while the flat plate collector is described by F＇eta(0) = 0.80, and F＇U-L = 3.3 W m(-2) K-1. The large difference in heat loss coefficient is to a large degree explained by absorption of solar radiation in the reflectors in the CPC-collector. The incidence angle dependence of the optical performance of the two collectors showed a similar appearance. Both collector constructions are based on the LGB (long ground based) technology, which allows them to be built in large modules up to 170 m(2).