By Chris Blackburn [email protected]
Chris Blackburn is director of penguinaircon.com, specialists in air conditioning, solar, pool and underfloor heating, based in Almancil.
As a company with an energy-saving ethos, we sometimes receive enquiries from DIY enthusiasts seeking to maximise their return-on-investment by making their own solar system.
My initial response is: “Have you worked out the working hours you’ll need to put into such a project plus the cost of materials?”
Buying a commercially-available system usually works out cheaper – not to mention safer! – as they have mass production standards on their side.
Commercial systems are more efficient, more reliable, are guaranteed and, if regularly maintained, will last 15 years or more.
“Could a home-made system offer the same?” However, my next – even if commercially irrational – answer is: “Excellent! Let me tell you how to do it or at least point you in the right direction!”
For me, the best way to understand a technology is to break it down into component parts, to see how it all fits together. And there’s no better example of harnessing the sun’s energy than a simple thermosyphon solar hot water system.
Nowadays these are so common on Algarve rooftops – a water tank fixed horizontally over one or two solar panels – as to be unremarkable.
And whatever the brand, they all rely on a concept that is genius in its simplicity.
When a liquid is heated it expands, becoming less dense and therefore more buoyant than cooler liquid, so it rises to the top.
This is of course ‘convection’ – a principle that is utilised most effectively in a thermosyphon solar system.
As the liquid at the bottom of the solar panels is heated by the sun, it rises through a system of copper pipes, gaining heat all the time, and then flows into a jacket surrounding the water tank. The two liquids therefore never mix – the solar system is in fact a closed circuit, so the solar-heated liquid simply radiates (or ‘exchanges’) its heat to the domestic-use water inside the tank.
The solar-circuit liquid cools as it gives its heat, to be replaced by further warm water rising up from the panels below.
Through this continuous cycle, the water in the tank gradually gains heat until it’s hot enough for a bath or shower.
So, although ingenious, there’s nothing particularly sophisticated about a solar panel. It’s basically a continuous circuit of copper tubing, looped inside a box to maximise its length.
The box itself is painted black to absorb the sun’s heat and has a thermal lining to reduce heat loss. To maximise heat absorption, aluminium strips are usually fitted around the length of tubing.
The box is glazed, which not only protects the tubes inside but has the property of ‘trapping’ heat – as in a greenhouse, where the glass allows visible light and short wavelength infra-red radiation to pass through, but preventing the longer wavelengths of heat from escaping.
For DIY buffs, the internet has plenty of solutions available – just Google “thermosyphon DIY” and start building.
But if you prefer your home systems to come ready-made, supplied and installed – and guaranteed to work well – then it’s recommended that you seek the services of a professional solar company.