The Influence of Weather Conditions and Operating Parameters on the Efficiency of Solar Power Collectors Based on Empirical Evidence

The influence of solar irradiance, ambient temperature and buffer tank temperature on the efficiency of solar collectors was evaluated in the climatic conditions of north-eastern Poland (climatic zone IV) characterized by relatively low irradiance (annual average of 900 kWh/m²). Two types of solar power collectors (flat-plate and evacuated tube collectors) were compared in terms of energy gains, collector efficiency and glycol temperature between May and September 2016. The collectors were mounted on the roof of a building on the campus of the University of Warmia and Mazury in Olsztyn. The roof had a pitch of 45°, the collectors had a tilt angle of 30°, and they faced west of true south. Measurements were performed separately for the analyzed solar collector systems operating simultaneously in identical weather conditions. The combined absorber surface was 4.64 m² in flat-plate collectors and 3.23 m² in the evacuated tube collector. Both systems were connected to a water buffer tank. Empirical data were recorded with a controller and were processed and stored in a computer. The factors responsible for differences in the efficiency of the examined collectors are discussed in the paper.