Editing revision 2 of 2009-018

From: "Sue Bookchin" <sueboo@ns.sympatico.ca> Date: 2009-04-14 (Tue) 14:36:28 ADT Subject: Re: Put_Me_On_The_Solar_NS_Mailing_List I gather from the newsletter, that you are all overwhelmed with questions about solar power, (and I guess that's a good thing!), but i don't know if i can expect an answer for this question... i will ask just in case. At the home show, i noticed two companies who are using evacuated tubes for solar rather than flat panels. can someone tell me the advantages/disadvantages of one over the other? we are planning to install solar for domestic hot water and i'm not sure which to pursue... thanks for any help you can provide! sue **************************************************** Answer: Hello Sue, I don't think we have a definitive answer for this question as a group, but I will tell you what I think about it from my experience. I did some very rough calculations about this, and I found that the flat plate collectors and the evacuated tube collectors perform similarly, in terms of how much energy they will produce on an annual basis for domestic hot water. It's pretty approximate, and others might disagree or have other information. As far as I know, there hasn't been a comparative test done in Nova Scotia - that's a test we would like to perform, because people often ask us this question. Some of the differences are: - In colder conditions, in winter, the evacuated tube collectors have higher output in laboratory tests. (So, for example, if you were primarily looking to heat a building in winter, the evacuated tubes are likely to give more output.) - In warmer conditions, in summer, the data I have seen shows that most flat plate collectors have higher output in laboratory tests. - It can be difficult to compare them with these tests, but it looks like the differences between summer and winter tend to even out. I did a rough approximation in a software program called RETScreen, and over the course of a whole year the estimated output from each kind was about the same. - The evacuated tube collectors can reach higher temperatures, so they can work better in situations where you need higher temperature water, such as heating for radiators in a building. On the other hand, such high temperature water is not needed for domestic hot water. - The flat plate collectors are simpler in their construction and not subject to the possibility of losing the vacuum in the tubes. You might have to occasionally replace a tube in the evacuated tube collectors if they lose vacuum. I have heard varying reports, with most people having no problems and a couple that have had to replace tubes unexpectedly. - On the other hand, I asked one manufacturer and found that it's not too expensive to buy a replacement tube if it becomes necessary. - With some evacuated tube collectors there can be an issue with snow and ice staying on the glass tubes and reducing performance at some times in winter - I read a report of a comparison test done in Germany, where accumulation of ice and snow reduced the evacuated tube collector performance to less than that of the flat plate collector. Snow and ice tend to shed from the flat plate collectors more quickly. - There is a Nova Scotia manufacturer of flat plate collectors, in Dartmouth, so if you prefer a product that is produced locally, that might also be part of your decision. - Finally, the prices vary a lot between different brands of both flat plate and evacuated tube collectors. It's hard to pin down a comparison on price because they vary so much. So there are quite a few differences between them, but personally I consider them both good. You could make the decision based on your own sense of the value and quality of the product, the supplier and the installer. I realize this may have just made the decision more complicated, but I hope it is of some help. Regards, Wayne Groszko

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