Solar Water Heating

Passive Systems
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Almost everyone has had experience with passive solar water heating...

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How many times have you turned on the hose in the yard and nearly burnt yourself with hot water? While you weren't looking, old Sol was quietly working to give you hot water, even if you didn't want it. Well if it's that easy, imagine what you can do if you're actually trying to make hot water. 

Passive solar hot water systems are probably the oldest commercially available solar systems. At the turn of the century there were large numbers of solar water heating systems on roof tops, especially in Los Angeles and Florida. Very little has changed from the original concept. Put a water holding tank in a box, with glass on the side facing south and fill it with water. No moving parts, nothing to break down, free fuel and no pollution.

The passive solar water heater is known today by many names; PSWH, Batch Heater and Bread Box are the most common and then there is the very technical; Integrated Collector and Storage System (ICS).

The PSWH of today usually starts with a 40 gallon, glass lined tank. These tanks come disguised as ordinary electric water heaters, which are stripped of their appliance shell and insulation. Painted flat black, with high temperature engine or barbecue paint and they're ready for solar.

In integral collector storage systems, the solar water storage system is built into the collector. The potable water in the collector unit is heated by the sun and delivered by city or well water pressure to an auxiliary tank (which contains non-solar back-up heating) or directly to the point of use.

A thermosiphon solar water heating system has a tank mounted above the collector (normally on the roof) to provide a natural gravity flow of water. Hot water rises through piping in the collector, which is mounted below the tank; heavier cold water sinks to the lowest point in the system (the collector), displacing the lighter hot water which rises to the tank.

The ICS and thermosiphon systems are simple since they use no pumps or controllers and water always flows through the collector.

Material from: Florida Solar Energy Center
Credits: John Harrison & Tom Tiedeman FSEC-EN-9 Revised May 1997
Further text and diagrams by Andrew Sorter