There are a number of types of solar heat collecting systems, but for water heating we are concerned with a tried and proven system called flat plate collectors. Firstly though, let’s distinguish between solar electric (photovoltaic) modules which convert sunlight into electricity; solar pool heating panels, which are designed to raise a large mass of water a few degrees; and flat plate collector panels, which are designed to raise a smaller amount of water (say 300 to 600 litres) to useable hot water temperatures (of about 70 degrees Celsius).
The typical flat plate collector consists of a glass covered box containing vertical copper pipes (called risers) embedded into a flat sheet of metal. At the top and bottom of the sheet are thicker horizontal pipes (called headers). The water from the hot water tank typically enters the bottom left hand corner of the collector casing, travels along the header pipes, up the riser pipes as it becomes hotter and exits out of the top right hand corner, where it returns back to the insulated storage tank for use when required.
The best solar panels are made from quality components which include: copper pipes and flat copper plate; an “AMCRO” selective surface (which absorbs 95% of the available solar energy); and low iron glass (which improves solar acceptance by about 10%).
A suitable north facing mounting spot must be found for the solar panels. Generally this will be on the roof, but they may be located on a wall over a north-facing window, on a deck or even on the ground. Ideally the solar panels need to be as close as possible to, but below the storage tank.
Any angle between 15 degrees and 30 degrees is OK. On flat roofs we install a galvanised angle frame to raise the panel angle to around 25 degrees