The subject of the work is an analysis of two types of solar collectors: flat-plate and evacuated tube collectors in the same, natural working conditions during the period from 1st May 2017 to 30th September 2017. The scope of work includes a descriptive presentation of a measuring setup, located on the roof of the building of the Construction University of Warmia and Mazury in Olsztyn, and also the research methodology, as well as an analysis of the results and conclusions obtained. The measurements allow a comparison of the efficiency of the flat-plate and evacuated tube collectors by calculating heat yields, based on the following variants: average hourly irradiation, outdoor air temperature, temperature of the medium supplying the collectors and temperature of the returning medium. An analysis of the heat yield was made in relations to the individual absorber surface, to determine which of the tested collectors showed higher efficiency under real operating conditions during the spring-summer period.