Solar Heating

By John Heeran, Energy Advisor

Date:

Tuesday, May 12, 2009

SOLAR ENERGY is appealing to people due to the fact that after the initial investment it is relatively cheap and to its renewable nature and it's free availability.

There are two types of solar collectors, flat plate and evacuated tube.

Flat Plate Solar Collector. The Flat plate System is designed with an insulated, waterproof box containing a dark absorber plate under one or more translucent or transparent covers. Conducting fluid. Conducting fluid or water passes through pipes located below the absorber plate. The flat plate does not have the insulating benefits of the evacuated tube, but is still the most common type of collector for many people.

Evacuated Tube Solar Panel. Evacuated tube collectors are made of a series of modular tubes, mounted in parallel, whose number can be added to or reduced as hot water delivery needs change. This type of collector consists of rows of parallel transparent glass tubes, each of which contains an absorber tube. The heat tubes are copper bars inserted in each glass tubes and surrounded with a foil like material which uses the ultra violet light from the sun to transfer heat to the copper tubes, which in turn heats the water being pumped through the manifold. New advances in technology and manufacturing have brought the cost of making the evacuated tube system more affordable.

There are a lot of different opinions which is better, the evacuated tubes or the flat panel? On average, the aperture of an evacuated tube captures solar radiation more efficiently than the flat plate, in Ireland there are more days with very poor levels of solar radiation, and on these particular days the evacuated tubes may out-perform the flat plates. The sum contribution of solar radiation on these days however is only a few percent of the total annual solar radiation. The greater wind speeds experienced in Ireland are also a factor, as the flat plate collectors will lose heat faster than evacuated tubes collectors in windy conditions.

While there may be specific circumstances in which the evacuated tubes may be the better option, there is clearly a need for further research into the performance of solar collectors before any clear conclusions can be drawn. In the meantime, the claims that evacuated tubes collectors are more efficient than flat plates should certainly be treated with suspicion.

There is however considerable variation between different models. Much more significant however is the relationship between the aperture area and the gross dimensions of the panel.

Whereas the aperture of a flat plate collector may exceed 90% of the total area of the panel, on some evacuated tubes it is as low as 52%. As anyone who has looked at an evacuated tube solar collector will know, there is a lot of space between the tubes!

One 'fact' which should be treated with the proverbial pinch of salt is the repeated claim that solar panels will provide ' up to 60% of domestic hot water requirements'. But how can the supplier know that without first calculating what those annual requirements are? The short answer.... they can't. This figure is based on generously sized systems working at high levels of efficiency and should be looked upon as a best case scenario.

One rarely mentioned factor which has a huge influence of the efficiency of the system is the management of the resource by the people using it. The energy aware household will try to match demand with supply. It makes sense to synchronize maximum hot water demand with periods of high output from the solar panel.

The 'energy oblivious' household, on the other hand, will unreasonably expect their solar panels to deliver hot water 24/7 and will invariably be disappointed when there is no noticeable difference in conventional energy use

So at the end of the day I would do my home work before spending a load of your hard earned cash. Overall it's a good idea but don't rush out and buy the cheapest system you can find.

If you are interested in buying an Electric Monitor you can e-mail me at info@thermaloss.ie. This will show you how much electricity each product uses and also how much green house gas is produced.

Hopefully this helped you out.
I must sign off now but you can check in next week for more energy saving news. Don't forget if you have any questions you can e-mail me on info@thermaloss.ie and I will try to include them in my column.

Thermaloss can help locate possible heat loss problems and eliminate heat loss in your home, thus reducing your heating bills.

Find out where you need to improve before forking out big money!

Look at improving energy efficiency as an investment.

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