Experimental study of stratification and the impact of insulation thickness in local solar water heater storage tanks during the rainy season in Burkina Faso

Abstract

Burkina Faso relies mainly on fossil fuels for its energy production; however, given the rapid development of renewable energy technologies in recent years, Burkina Faso has been seeking other inexhaustible and environmentally friendly sources of energy, among which solar energy is considered the most important. Domestic hot water production is one of the most promising applications of solar energy for countries such as Burkina Faso. Thermal stratification has been identified as a means of increasing the thermal efficiency of a tank and, consequently, of the entire system. Stratified storage is characterized by a separation of temperature levels within the same tank, resulting in a thermal gradient between the hot and cold zones. The thin separation layer is called the thermocline. This study consisted of analyzing the stratification of the storage tank by evaluating the temperatures of the layers of water stored at different heights. The results show that stratification occurs as soon as heat accumulation begins and that the temperature difference between the top and bottom remains virtually constant at around 3°C to 4°C. Overall, the maximum temperature reached exceeds the threshold required for domestic or service applications, with an experimental value of 53°C. In addition, the theoretical temperature of the stored water varies between 50°C and 65°C depending on the thickness of the insulation; an experimental maximum stored power of approximately 1400 W. In terms of optimization, the results show a major loss between 1 cm and 20 cm, and a marginal loss beyond 20 cm. Therefore, 20 cm to 40 cm corresponds to the optimal zone. Thus, good tank insulation requires approximately 20 cm of glass wool thickness. Storage efficiency is therefore characterized by maintaining stratification in the tank throughout the day.