Passive Solar Hot Water
One of the cheapest and most effective ways to use solar energy is for heating water — replacing electric geysers with solar heaters can reduce your bills quite dramatically. These panels are quite different from the solar photo-voltaic (PV) panels which produce electricity in that they contain no electronic parts and are fairly easy to maintain.
There are two types of panels and their usage depends on budget and climatic factors.
In most tropical climates, the ordinary collectors work well. These collectors consist of copper fins that heat up rapidly and transfer this heat to copper pipes attached directly behind them. The pipes supply hot water to a storage tank by thermo-siphon and the whole assembly is put behind a glass pane for protection.
The other type of panel becomes necessary in places with extreme climates. Called Evacuated Vacuum Tube Collectors these are much more efficient but also more expensive. Here an outer tube of borosilicate glass has an absorptive layer and an inner tube to which the heat is transferred. Here too, the water rises by convection into a storage tank.
You will definitely need to have an insulated collection tank to store the hot water generated, especially if you want to use it before the sun comes up the next morning. Also make sure that the piping from the panel to the tank is properly insulated – this is something the installers often “forget”.
There are times of the year when heating won’t be very effective – due to cloud cover, for instance. For the monsoon and for early winter mornings, it might be useful to pipe the water though instant-type heaters in individual bathrooms to boost the temperature.
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