Abstract
The main types of solar water heating systems include thermosiphon systems. This article develops a thermal calculation model for a solar system with thermosiphon circulation to evaluate its efficiency. The model considers heat losses, heat exchange in the collector and tank, and the effect of ambient temperature. The system performance was tested in April and May using a microcontroller-based device that simulated hot water consumption. The evaluation was based on solar energy share and thermal efficiency. During four days of continuous operation, the forced circulation system showed better performance. For the thermosiphon system, the solar energy share was 0.56, and the thermal efficiency was 59.7%. For further analysis, it is possible to consider the influence of various factors on the efficiency of thermosiphon systems and systems with forced circulation. It is important to note that the efficiency of a thermosiphon system largely depends on solar radiation and ambient temperature. Under conditions of high temperatures and intense solar radiation, such a system can perform well; however, its performance may decrease during cold or cloudy days. The obtained results showed that the thermosiphon solar system achieved a solar fraction of 0.62 and a thermal efficiency of 68.2% under two-month spring testing conditions. During continuous operation, the efficiency decreased to 50.0%, indicating the influence of prolonged loading and the need for further optimization. The temperature difference in the system reached 16 K, confirming active heat transfer between the collector and the storage tank. A detailed techno-economic and environmental assessment was not the main focus of this study and is planned for future research.