Not sure which model Gooserider has got but if it's a 65 or 165 it would definitely interfere.
This report [EDIT] (that link was broken -- use this link instead) [END-EDIT] talks about the effect you refer to where the evacuated tubes are "too good" so don't allow for faster melting of frost, hence reducing their efficiency. However, even ignoring that, you have to be careful about the efficiency claims with evacuated tubes since the quoted efficiency numbers are often quoted relative to the collector (black absorber) area inside the tube and not to the gross area of the installation that includes the non-collecting air space between the tubes and inside the tubes to the side of the collector. It is this gross area that is relevant since that is how much space it actually will take up on your roof and is what determines how many panels you need to achieve a certain rate of temperature rise. The charts I made in my post at the start of this thread are all relative to gross area.Gooserider said:Well, some of the stuff I've seen on evac tubes vs. flat plate seemed to suggest that even though the tubes had higher efficiency in theory, the flat plates tended to come out ahead in the "real world" - it was actually a case of the tubes getting hurt by being TOO efficient! In essence a glazed flat plate does leak a certain amount of heat, but a tube doesn't. Thus if you get much snow or frost on the collectors overnight (which I suspect that we would) the plates melt it off and self clean almost as soon as the sun starts to hit them, probably before they'd even start really producing, and get to work very early in the day. The tubes take a lot longer to self clean, so they may work like gangbusters once they turn on, but often that doesn't happen until mid afternoon - not enough time for them to catch up with the flat panels that had been producing all morning.
It's interesting to note that these reports show that the evacuated tube efficiencies are not as low as my table would imply. Either these manufacturers have higher efficiency tube designs (less gaps between the tubes) or the tubes are better at capturing sunlight throughout the day, possibly due to their curved reflective backs.mas985 said:If your interested in solar panel efficiency, check out this site:
Hot Water Ratings
Pool Ratings
Glass tubes tend to have a lower efficiency than the glass panels. However, this testing was done at high temperature so it might not be as relevant to winter time performance.
For better topic coherence, I replied over here.Gooserider said:As to the solar cover, ...
chem geek said:This report talks about the effect you refer to where the evacuated tubes are "too good" so don't allow for faster melting of frost, hence reducing their efficiency. However, even ignoring that, you have to be careful about the efficiency claims with evacuated tubes since the quoted efficiency numbers are often quoted relative to the collector (black absorber) area inside the tube and not to the gross area of the installation that includes the non-collecting air space between the tubes and inside the tubes to the side of the collector. It is this gross area that is relevant since that is how much space it actually will take up on your roof and is what determines how many panels you need to achieve a certain rate of temperature rise. The charts I made in my post at the start of this thread are all relative to gross area.Gooserider said:Well, some of the stuff I've seen on evac tubes vs. flat plate seemed to suggest that even though the tubes had higher efficiency in theory, the flat plates tended to come out ahead in the "real world" <Snip>
Richard
What was interesting was that the Florida gov't ratings site that was linked to earlier in the thread seemed to show the flat plates actually did better in terms of BTUs / sq ft / day.
mas985 said:What was interesting was that the Florida gov't ratings site that was linked to earlier in the thread seemed to show the flat plates actually did better in terms of BTUs / sq ft / day.
Yes, but they were testing in what would be considered warm ambient temperatures. In colder weather, the evac tubes might actually perform better since they have some insulating qualities that are less likely to lose the heat .
chem geek said:This link seems to work (for now). Sorry about the other link -- it used to work, but links go bad as people move things around on their servers or shut down their websites completely.
launboy said:Anyone ever thought of making their own glazed panels out of flat black pool heater panels? I've been considering trying it out this fall. During the summer the normal panels do fin for our pool, and hopefully will work for the hottub too.
I'm more worried about the fall and winter. I don't think the panels will do much during our cold snowy Wis. winters, but during the spring and fall I think a home-made box around a mat would help quite a bit. What do you all think?
Thanks,
Adam