Evacuated Tube Solar Panels - what's the deal?!?!

[Bart]

On a travel forum I frequent, one of the posters mentioned he was using " evacuated tube solar panels" to supplement the natural gas heat he uses in his pool. I asked him about that type vs. the "normal" black plastic tube type and the advantages, etc. He didn't have much knowledge of the pros and cons, but said this:

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To be honest I am not sure about the relative pros and cons of the two types. I think the ones that you have may be a bit cheaper and less fragile. With mine I can't direct the water flow to the panels during the day as if water is sitting still in the panels get super hot and if you push cooler water through them it can cause the glass tubes to shatter. So given these drawbacks I am guessing that the glass tubes must be a little more efficient at heating otherwise no one would use them.

Last year was the first year that we had them and the installer said that six panels said that six panels should be enough to keep the pool at 84 without using gas. It was a very cool summer so that didn't quite work - we still did use our gas heater to keep the temp in the mid 80s.

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I asked him if he used a floating bubble cover and night and he said he didn't (!!!!), so maybe that's why he wasn't able to maintain the temp he wanted (although it might have been the cool weather).

Now here's the kicker - - - - He lives in TORONTO!!!

So my questions are:

1) Does anyone know anything about this type of solar heating? (it seems like it must pump out a lot more heat than the traditional ones)

2) What's the deal with the "can't direct the water flow to the panels during the day as if water is sitting still in the panels get super hot and if you push cooler water through them it can cause the glass tubes to shatter" statement? Does that just mean you have to run it all day instead of turning it on for the first time at noon when the tubes are super hot compared to the water temp?

3) Is it worth looking into replacing my current system with one of these?


My system works fine, but it doesn't do so great on the ends of the season when we need it most (especially for my wife who likes the pool WARM!). I'm just wondering if a guy in Toronto is getting good results (without a cover) then could I do much better being much further south with these evacuated tubes?

 

[JasonLion]

Evacuated glass tubes are better when the air temperature is very cold, since the vacuum helps prevent heat loss to the air. Regular panels are better when the air temperature is at all warm. The glass tubes are optimized for domestic hot water heating in the winter, which means large temperature gains at low flow rates in very cold air. That isn't what you want for a typical pool install, though it can make sense in far northern areas. For a pool you typically want very high flow rates and very low temperature gains.

Evacuated glass tubes need fancier control systems that can prevent sudden temperature shifts. Typically this is dealt with by having multiple destinations for the heat, home heating, domestic hot water, pool, etc. so the tubes can be run continuously, preventing sudden temperature changes. You can get the same effect manually with a simpler controller, but I don't recommend that as the tubes are fairly expensive and thus not so good to break.

In Virginia there is no way that evacuated glass tubes are going to be a good solution. Regular pool panels are always going to be more efficient (well indoor pool heat in January might be an exception).

 

[Bart]

Thanks Jason! I was sort of hoping that the evacuated tubes would get my pool to 90 degrees in April and October, but wasn't really looking forward to coming up with a big wad of cash to rip out the current system and install a new one!

 

[chem geek]

As noted in the thread Solar Panel Technology Comparisons, there are also glazed panels which are metal (usually copper painted black) tubes in a glass enclosure. They are less expensive than evacuated tubes and are generally more efficient unless the temperature difference becomes very large, so in very cold climates with domestic hot water heating temperatures (i.e. 120ºF). For pools, if you want more heating from the sun when there is wind or colder temperatures, then glazed panels work better. They are more expensive than black flat plastic unglazed panels.