Build A Solar Hot Water System
The provision of hot water consumes from 25% - 35% of the average household’s energy needs and therefore contributes significantly to greenhouse gas production. Obviously if you’re going to be “clean and green” hot water is a great place to start a campaign of energy reduction. In warm climates there are many simple do-it-yourself hot water system ideas you can use to cut your energy needs.
In Australia (and many other countries) there are vast areas of “warm climate” zone where the production of hot water is literally a piece of cake. Areas that receive a lot of sunshine, few heavy frosts or freezing temperatures are ideal for year round production of hot water to supplement or even replace current hot water requirements - using very simple home-built low tech hot water systems.
Amazingly, very few of the ideas are employed because people seem to live a “mainstream” existence and opt for commercially available solar hot water systems, that’s if any consideration is given at all, to cheaper “greener” alternatives. Often the initial cost of installing commercially available solar hot water outweighs the immediate benefits so the consumer is left in a circle that’s quite vicious to the environment!
Cheap Home Built Solar Hot Water System Passive Thermosyphon Type
The following is an outline of a simple rooftop solar hot water system used in a warm climate zone where freezing temperatures will not occur. It’s an extremely low-tech system that could easily be built by a competent handyman.
A view of the roof and hot water system:
The roughly rectangular patch on the roof is the "solar collector" which is simply 37 lengths of 1/2" diameter soft garden grade poly pipe joining top and bottom manifolds. In this case the total amount of poly pipe is around 240 metres and more than enough for a family of 6.
A closer view of the hot water tank. The tank is a low pressure fabricated copper sheet cylinder with insulation and sheet skin. The unit is fitted with a 3.6 kW electric backup wired into off-peak power.
Finding appropriate hot water storage tanks for home built solar hot water systems is a difficulty. Commercially available hot water tanks designed for mains pressure do not have extra porting for the passive solar thermosyphon. This unit comes from Jem products of Brisbane.
Close-up of the bottom manifold and 1/2" poly pipe tubes which are pushed onto 1/2" copper pipe stubs sweat soldered into the 1" copper pipe. Note the 10mm thick rubber strips to anchor and provide clearance from the zincalume sheet roofing. To eliminate galvanic action and corrosion the copper manifolds must be kept clear of the roof sheeting.
Below detail a short section of manifold:
As you can see the solar collector is very low tech. The overall low efficiency is adequately compensated for by the sheer size of the solar collector area of around 24 sq metres.
I've seen the soft garden grade poly pipe last seven years with no sign of deterioration or decreased flexibility in quite extreme conditions.
This system uses passive thermo-siphon to circulate hot water. Cold (denser) water falls and makes its way to the bottom manifold. The line feeding cold water to the bottom manifold should be insulated to prevent it heating which would upset the natural thermo-syphon. Water gaining heat rises up the roof slope (a minimum inclination of 8 degrees is suggested - most roofs will have adequate pitch) and is delivered to the top manifold and then to the uppermost part of the tank.