![]() ![]() Adding an additional panel, or a few more tubes could make up the difference. Sometimes the "taste police" trump the small performance hit with less than ideal orientation. off true south with negligible impact on performance, I believe 2.5% diminished for 30 deg.Īnd the panel tilt doesn't carry a huge performance penalty. Although our home was to be constructed facing south, to take advantage of passive solar, I hadn't realized it was off by a few degrees from mag south - away from true south! - until we got serious about solar.ĭave, don't get too hung up on orientation. "Too ugly" The vac tubes gave me the option to install a flush-mounted array while angling each of the tubes the almost 20-degrees needed to be true-south. Lois put the kibosh on having a tilted rack. Flat panels may need to be angled to get the best exposure and that became an issue here at our own home. How it looks can be a deciding factor too. We've been through the snow pack issue before :) Keep the tubes 50 degrees in snow country to assure snow shedding. I suspect many of the new un familiar imports may not be around for the long run, regardless of type of collector, flat or tube. Manufacture and their history would be another concern. Also warranty, I've seen some tubes with a mere 10 year warranty. Looks? Some like tubes, some prefer panels. Other considerations are ease of installation, a plus for tubes. Caleffi Idronics 3 has formulas to show performance difference. that calculates BTU production per $ cost. The Srcc website has a good $$ comparison calculator. This put the payback another 7- 10 years down the road with generous fuel cost increases His numbers using a well know German flat panel, compared to a well know quality evac tube showed 40 bucks per square foot for panels, $105 for the tubes. possibly 1/2 as much.Ī solar contractor in Montana sent me a large home solar design recently. You might find you could double the flat panel square footage and still be less $$ than the tubes. Ret screen is a free download, Maui Solar, T-sol, F- Chart and Poly Sun are a few others. Most all of the solar design software will let you play the money game for investment payback, etc. Now if the tubes cost 3 times as much to purchase, you need to pencil that into the formula. Where they're at, and what you're asking them to do, is the key question. They really don't generate addition BTUs magically as some ad slicks lead you to believe. With evac tubes you are mainly buying a better r value between the absorber and outdoor conditions. The energy just isn't available in a cold cloudy winter sky, regardless of the 1/2" space between the glass (R-value) with a vacuum. I'm not 100% convinced they perform a lot better in cloudy conditions. IF you require higher operating temperatures, or see frequent temperatures below 15F tubes perform better. So if your system can operate at radiant 110- 115F supply the (95F example works). ![]() At 95F return to the panels, in a 15F ambient temperature (outdoor) the performance with 200 BTU/ square foot of solar radiation, is about equal. When you run the numbers using the data from various manufactures on the SRCC website we find. Temperature requirements, climate in your area, and budget. ![]() It can be downloaded from their website : There's lots to know and I recommend you bone up on solar requirements.Ĭaleffi has written an excellent solar document that gives all piping diagrams and a no-nonsense approach to the types of systems available. These modules and controllers make solar easy to install and use. We use a closed loop with manual fill,(with special glycol) and either the Caleffi or Viessmann pump module and controller. I've seen that the Chinese are exporting evacuated tubes at significant discount to the German product, but their ability to hold vacuum may be in question. The flat panels have water in them, the evacuated tubes do not. The evacuated tubes attach to a "collector header" which contains the heat exchanger. The evacuated tubes will produce more BTU's PSF of panel, especially on cloudy days. Where do you draw the line between the two types of solar collectors? How do you decide which is more appropriate for the job at hand?įlat panels are more appropriate when you have snow loads to consider. Here's another interesting thread that appeared on the Wall. ![]()
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