The data from three solar thermal collector systems installed in dormitories of the University of Latvia in Riga are analysed in detail to obtain parameters that characterise the operation of such systems in real operation conditions in Riga, Latvia. All the systems were installed in 2019�2020 and the data for one full year is available for the study. The area and the power output for the observed solar thermal collectors are similar�63 m2 with 51 kW for each. The differences exist only in the orientation of the collectors depending on the building�s roof, tilt angle and the mounting combination (one or two rows). Each system is equipped with hot water accumulator tanks with a total volume of 3000 l to ensure hot water supply during peak demands (typically in the mornings).
Analysis of the recorded data from the systems shows the actual energy produced with the help of solar thermal collector systems in real operation conditions. Calculations determine the actual energy production, which is estimated in the range of 320�380 kWh/m2 annually, or 395�470 kWh/kW per installed power output depending on the system�s spatial orientation. The most efficient is a south-east-oriented collector at a 25� tilt angle, reaching 50% efficiency (from available energy) during the summer days. The difference from the planned 500 kWh/m2 is explained due to higher cloudiness and the fact that the system is not even activated on cold days.