Posted by: Yes Solar Cape (Cape Town, South Africa) – 31 August 2010
When going solar it is best to ensure that you are getting a quality product and system.
Solar systems are subjected to extreme conditions of heat and cold, rain, hail, etc. Unless they are carefully designed, they may have only a short life and will then not be economical in the long run.
A solar hot water system should last 15 to 20 years. Warranties vary, so look for a product that offers a 10-year warranty on the tank and panels.
A simple measure of a system’s efficiency would be the value of the Eskom rebate attributed to that system, providing that you ensure a like-for-like analysis, e.g. comparing a 150 litre against a 300 litre would not be a fair comparison.
Thermosyphon systems are normally complete on-roof hot water systems. The bottom of the tank has to be above the top of the collector (solar panels), for the thermosyphon action to work. These systems are low on maintenance since there are no moving parts.
In indirect (closed) systems, due to the solar radiation and differences in the specific weight of cold and hot fluids, the heat exchange fluid rises to the top of the collector. From here it flows into the heat exchanger of the storage tank and heats the water in the tank.
Flowing out of the heat exchanger the cold heat exchange fluid in turn flows back into the collector and is heated there. The heated water then flows into the hot water lines and can be used directly for cooking, washing or showering.
Look for the heat exchanger process. Some systems offer only a partial jacket heat exchanger or use an element along the axes of the tank. Make sure that you opt for a full jacket heat exchanger. This will provide greatly increased heating efficiencies.
Check the tank insulation. Polyurethane of 60mm maximises heat retention. This will ensure that heat loss is slowed down, especially during the night when its cold.
Only SABS approved systems qualify for the Eskom rebate. A SABS test report does not imply SABS approval. Look for the SABS stamp of approval.