solar tubes vs flat panels

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homer3-7

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Which system would be better performance wise. I have been told that three flat panels would equal two panels of tubes, is this true?


Also I was thinking of getting a triple colied tank with separate coils on the solar panels, oil burner and back boiler of solid fuel. Does this sound like a good plan to anyone out there or could someone recommend a better system?
 
homer3-7 said:
Which system would be better performance wise.
1. I have been told that three flat panels would equal two panels of tubes, is this true?

Also I was thinking of getting a triple colied tank with separate coils on the solar panels, oil burner and back boiler of solid fuel.
2. Does this sound like a good plan to anyone out there or could someone recommend a better system?
Click to expand...

1. no thats not true.... its specifically depends on the product. They all have different efficiencies..... tubes "tend" to be more efficient because they have more glazed area that recieves light at right angles... look up the HARP database if you want to compare specific product efficiencies...

2. thats a fairly standard system these days.... the only awkward part may be keeping the back boiler on its own open system, whereas the boiler and panels should be on a pressurised system
 
The Harp Database has fundamental flaws which I have raised with SEI years ago, but to no avail. In relation to the flask type of tube, they only account for the noon efficiency, and don't take into account Incidence angle modifier - the fact that the tubes optimum output is not at noon.

The essential difference between tubes and flatplates is insulation. Vacuum systems have no air molecules to convect the heat from the absorber back out to the exposed glass. Thus they are more efficient at higher water temperatures, lower air temperatures, and when the level of sunshine is lower. At all other times, flatplates are slightly more efficient, but if you think about it, either system will work well on hot sunny days, whereas vacuum systems work better in spring and autumn and have the effect of stretching the season.

So why doesn't everyone have 'em? Because after about 20 years the vacuum will be lost and the tube will need to be replaced, whereas flatplates last about twice that long. On the other hand, the tubes are very easy to replace. Here there is a distinction between flasks (usually Chinese) and tubes (where there is a single layer of glass with the heat pipe welded in). Flasks are very cheap - about €5 each, whereas tubes are extremely expensive.

The last consideration is aesthetics. Flatplates are quite inconspicuous. Q
 
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