Search all WA Government Sites Print this page	Close-couple thermosyphon (mains pressure) This is the most common system on the market. It consists of roof mounted solar collectors combined with a horizontally mounted storage tank located immediately above these collectors. In most solar hot water systems, a pump is not required. This is because hot water is lighter than cold water and rises through the solar collectors to enter the storage tank. When this happens, cooler water at the base of the storage tank is forced out and flows down to the bottom of the collectors. This cycle is continuously repeated while the sun is shining. Most commercially available solar hot water systems employ this natural cycle, commonly referred to as 'thermosyphon flow'. Systems are also available where the storage tank is located within the roof space instead of close-coupled to the collector. The base of the tank must be situated at least 300 mm above the collectors. Some systems supply hot water by gravity-feed rather than mains pressure. Forced circulated system (mains pressure pumped) With a pumped system, the tank is located below the level of the collectors, usually at ground level. Water must therefore be pumped from the tank to the collectors and back. Pumps are not expensive to run, typically costing less than $10 per year. This system can be used when the roof structure isn't strong enough to support a close-coupled system.
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