In this paper a results of an experimental research on passive solar air collectors are presented. An impact of application of two designs of absorber surface with wavelike baffles on thermal efficiency was investigated. Absorber surface designs consist of three panels of waveshaped sheet of aluminum, coated in black paint. One design differs from another by placing middle sheet in reverse and creating an alternating pattern. The experiment was conducted under steady state artificial radiation conditions in a laboratory environment. Flow through each collector was buoyancy driven. Irradiance was changed in a range of I = 0-990 W/m(2). Measured values were: air temperature at inlet and outlet, mean air velocity at the inlet duct of the collector, irradiance at multiple points. The impact of irradiance on temperature increase, volumetric flow rate and thermal efficiency is shown. It was established that best performing design in terms of thermal efficiency is that with wavelike baffles without sheet reversing. For irradiance I = 756 W/m(2) it's thermal efficiency equals eta = 73.8%, while for the same irradiance efficiency of colector with reversing is eta = 58% and flat plate collector's is eta = 46%. Performance coefficients FOUL and F-O(tau alpha) are found by linear regression method on collected data and compared with available research worldwide. This comparison shows an overall good performance of proposed designs.