This is your site for solutions. Please contribute your knowledge, leave a note, support Appropedia or let the world know about this resource.

From Appropedia

The principle of the thermosyphon system is that cold water has a higher specific density than warm water, and so being heavier will sink down. Therefore, the collector is always mounted below the water storage tank, so that cold water from the tank reaches the collector via a descending water pipe. If the collector heats up the water, the water rises again and reaches the tank through an ascending water pipe at the upper end of the collector. The cycle of tank -> water pipe -> collector ensures the water is heated up until it achieves an equilibrium temperature. The consumer can then make use of the hot water from the top of the tank, with any water used is replaced by cold water at the bottom. The collector then heats up the cold water again. Due to higher temperature differences at higher solar irradiances, warm water rises faster than it does at lower irradiances. Therefore, the circulation of water adapts itself almost perfectly to the level of solar irradiance. A thermosyphon system's storage tank must be positioned well above the collector, otherwise the cycle can run backwards during the night and all the water will cool down. Furthermore, the cycle does not work properly at very small height differences. In regions with high solar irradiation and flatroof architecture, storage tanks are usually installed on the roof. Thermosyphon systems operate very economically as domestic water heating systems, and the principle is simple, needing neither a pump nor a control. However, thermosyphon systems are usually not suitable for large systems, that is, those with more than 10 m² of collector surface. Furthermore, it is difficult to place the tank above the collector in buildings with sloping roofs, and single-circuit thermosyphon systems are only suitable for frost-free regions.