Compound parabolic concentrating (CPC) collectors paired with evacuated tube receivers have great potential to supply solar thermal energy for numerous applications operating in the medium temperature range. Optical losses resulting from the gap between inner absorber tube and cusp of reflectors badly affect the performance of such collectors. In this paper, a modified design and optical performance of a CPC collector with evacuated tube receiver is presented. Effect of reflectors truncation on the collector's parameters including aperture width, concentration ratio and energy collection is also evaluated. Ray tracing simulation is performed to assess the instantaneous and daily energy collection. Optical performance of a cusp type CPC is compared with that of a modified CPC with w-shaped cavity at the bottom of reflectors to evaluate gap losses. Optical power density and daily average energy collection by cusp type CPC was 26 higher than CPC with w-shaped cavity due to relatively larger aperture size. CPC with w-shaped cavity was 11 more efficient than CPC with cusp type reflectors. © 2020 Published under licence by IOP Publishing Ltd.