Solar Water Heating Basics

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Solar Water Heating Systems are the most popular solar technology around; I can safely say that the majority of people have seen, heard of, or have a solar geyser or pool heating system. This is a basic introduction into how solar water heating works.

Types of Solar Water Heating Systems

There are two different categories under solar water heating; solar geysers and solar pool heating. The actual basic principle is exactly the same, no matter what type of solar water heating system you use.
Let’s begin with solar geysers. There are two types of solar geyser technologies found. The first is the Flat Panel technology which people often mistake for solar electric panels. This type of geyser is usually used when the tank is being placed on the roof. Water runs through copper pipes which are attached to a metal plate found inside a glass covered collector, which is connected to a water storage tank in or on the roof. The water is either pumped through a pipe into the tank, or the thermo-syphon principle is used.
The second, more modern type is the evacuated tube system. They use copper pipes running through the centre of glass tubes which contain a vacuum. There are two types of evacuated tube technologies; direct and indirect. Direct systems allow the water to run through the copper pipes to heat up, and then into the storage tank. The water that runs through the pipes is the same water that runs out of the tap on the other end. An indirect system, which is slightly more expensive, is basically the same, except it uses heat transfer instead of direct heating. Water runs through the pipes and heats a manifold in the tank which in turn heats water inside it. The water inside the tank is used instead of the water in the pipes. Indirect systems are used in colder areas because an anti-frost solution can be added to the water inside the pipes.
Evacuated tube systems are more efficient than flat panel systems because of the vacuum inside the glass tubes. It allows them to extract heat from the air without direct sunlight, which means that they will significantly heat the water even on winter days without much sun. It’s widely believed that evacuated tubes are too efficient for South Africa as they make the water boil, and this can damage the pipes.
Solar geysers can either be gravity fed, or pressurized. With gravity fed systems, the tank needs to be relatively high up, whereas pressurized don’t need to be. All solar geyser storage tanks are insulated, allowing the water to stay hot overnight, and for an extra day or so, in case of bad weather.
Solar Pool Heating Systems are very straight forward. They work in much the same way as the direct evacuated tube systems. The water is pumped out of the pool, up through copper tubes inside the panels on the roof, and back down into the pool. Temperatures can be regulated by altering the speed of the pump. In many cases, pool heating systems can be retro-fitted using the existing pool pump to pump the water up to the panels.
Solar Panels
Invited to exhibit at GREENEX2010
For an introduction from SAAEA or further info: