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Attribution: http://www.flickr.com/photos/ukinitaly/ / CC BY-ND 2.0
[podcast]http://www.green-talk.com/podcasts/sundasolarhotwater.mp3[/podcast]
Solar Hot water Evacuated tube collectors seem to be the rage at the International Builder’s Show last winter. I don’t know why, but those gleaming dark tubes just caught my eye. The more I learned about them, the more I liked the whole concept. Putting a solar hot water flat panel collector on my roof just did not appeal to me. I had my share of roof leaking/ water issues and just did want to go there again. (Whether this actually happens with panels does not matter. Fear is a powerful motivator.) Evacuated tubes on the other hand can be installed vertical or horizontal like a fence as well at an angle similar to the solar hot water panels. I like flexibility.
In addition, every vendor I spoke to touted that these tube were so much more efficient than its cousin, the flat panel collector. Are they more expensive than the panels? Yes. But, I was assured I would make up the difference in no time. My eyes grew wider and wider every time a different vendor spoken about these tubes. At the end of the show, I penciled in my Anna’s green wish list, “I want an evacuated tube collector.” Promise me efficiency, good payback, and you have won my heart.
Until…
Martin Holladay of GreenBuildingAdvisor.com thumped me on the head and told me to wake up. In his article, “Solar Hot Water Heating Water with the Sun Isn’t Cheap,” he discusses the argument that evacuated tubes are better than flat panels. He states,
“Evacuated-tube fans like to point out that flat-plate collectors experience more heat loss at cold ambient temperatures than evacuated-tube collectors. (True enough — if the snow ever slides off the evacuated tubes). Moreover, evacuated-tube collectors perform better during cloudy weather, and begin collecting heat earlier in the day, than flat-plate collectors.
Remember, though, that you’re not going to be collecting much useful energy on cloudy days or very cold days anyway. As explained by the author of a technical bulletin from EnerWorks, a Canadian manufacturer of solar equipment, ‘On overcast days the evacuated-tube collector will perform better than a flat-plate collector. Of course, if there’s not much sun to begin with, doubling your efficiency is not a big advantage. The question is, do you want a collector that will perform better when there is plenty of sun to be captured, or one that will perform better when there is not much sun to start with?'”
I could just hear him say, “Anna, you have to stop falling for all those marketing claims.” The tubes were pretty and why wouldn’t a green girl want to add a little green bling to her house? I put solar hot panels on the back burner since Holladay explained the payback was bleak for a cold area like mine even with the federal tax credit. But, despite the article, the evacuated tube versus panel argument still danced in my head.
As many of my loyal readers know, I attend many green exhibits and meet a variety of green vendors. At a recent Go Green Building Expo in New Jersey, I met Frank Proske, president of Sun Solar Spot, a distributor of both evacuated tubes and flat panel collectors. At the beginning of our conversation, I explained that I had heard different arguments of which system was better. He quickly pointed to both systems he had on displayed and said that he sold both and could give me an objective point of view. He explained that for colder climates, evacuated tubes were the best; whereas in warmer climates, flat panel collectors are better. Okay, this explanation was a nice and tidy for me to comprehend. To listen to the entire short podcast, click the link above. His company distributes SUNDA evacuated tube collectors as well as flat panel collectors.
After eying several different solar hot water collectors at the Builder Show, I kept scratching my head and thinking how do you know which one is right for you? I posed this question to Proske and he advised me to begin my research at the Solar Rating Certification Corporation (SRCC) website, which provides independent certification of Solar Water and Swimming Pool Heating Collectors and Systems. The website contains a list of those companies who are participating, rating summary of SRCC Certified Collectors, and SRCC Certified Systems. In both the rating summaries, you can compare each of the different collectors or systems. For an explanation about the performance data obtained, see here.
If you want to obtain a list of system and annual energy savings for your area, click here. In the location box, scroll down and find your area, and then click, “Show Selections.” I naturally clicked on the higher numbers, and noticed some were for residences that have existing gas or electric water heaters. Some mentioned positive leak protection, while others did not. Other are open loop systems, other are not. My eyes started to blur over with each of the different descriptions of the various systems. Thank goodness for Home and Power’s excellent article in which the author explained the various components of the solar hot water systems.
As I was reviewing the numbers, I kept in the back of my mind the following stated by the SRCC :
“The collector with the higher number in the box which reflects your climate and category produces more energy than those with lower numbers. While such a comparison should not be the only basis for your choice of a solar energy system, you may find it helpful. Remember, too, that the energy output of these collectors in the directory has been measured under test conditions, which are almost certainly not the same as the collector will be subjected to in your home. The remainder of the system and the quality of the installation are also critically important factors in how well your solar system works, and how much energy and money you save.”
When I looked at the calculations of the different systems for my area , I couldn’t help myself from jumping to the highest annual savings. However, this may not be the best practice when comparing it to cost. According to the SRCC,
“One method is to compare the energy output for each dollar spent on different collectors. Or, in other words, how many Btu (or MJ) does a dollar buy if spent on Collector #1 versus Collector #2? This question can be answered by dividing the energy output by the cost of the collector. For example, you are considering a solar water heating application. Collector #1 has a rating in Category C (for water heating) under the correct climate column of 29 MJ (per collector per day) or 21,000 Btu (per collector panel per day). Collector #1 sells for $387. Collector #2 is rated at 35 MJ or 33,000 Btu; it sells for $675. Thus:
Collector #1 29 MJ/$387=0.07 MJ/$ or 27,500 BTU/$387=71BTU/$
or
Collector #2 35 MJ/$675=0.05MJ/$ or 33,000 BTU/$675=49/BTU/$
or
Collector #1 is the better buy, based on performance under the test conditions alone. The higher the number of MJs or Btu per dollar, the more cost-effective the collector is…all other things being equal. Remember, though, that the design and quality of the rest of the system and the installation are also critical to a good solar energy system.”
When I asked Proske how much a typical solar hot water system would cost installed, he replied it would cost between $8000 and $9000 to install a system for a family of 4 with an 80 gallon water tank. He did not specify if that price was for flat panel or evacuated tube collectors although during the conversation, he told me that tubes cost about 20-30% more. To inquire if your state provides solar hot water rebates, see here.
For the DIYer, see the following site for information on how to build your own solar hot water system:
Build it Solar Solar Water Heating
Build your own solar thermal panel
Readers, if you have installed a solar hot water system,
- which system did you use? (Companies who install, please do not comment. See your questions below.)
- what kind of rebates did you receive?
- what did you determine was your payback?
For solar hot water companies
- evacuated tubes versus flat panels?
- geothermal systems that also heat hot water versus solar hot water?
- why your system is better than the other ones out there? (Differentiate cold versus warm weather climates.)
knutty knitter says
October 29, 2009 at 9:52 pmWe have evacuated tubes now into their 3rd year. Being careful we only need to heat water two or three times a month for about an hour or so. Cost was large but we had to renew anyhow. We have had trouble with the cylinder so will replace with something better under original warranty. All good otherwise. I think it will take us another three years to pay it off in savings which is really good.
viv in nz
Luc J says
October 30, 2009 at 11:51 amGreat article – and long. I never looked at the difference between flat panel and tubes from that angle. Indeed, it makes little sense to double the output when there’s little output anyhow. And pay more for the system, even.
You made the point that everyone should make a decision based on specific data for the specific situation.
.-= Luc J´s last blog ..Solar Charger For All Your Gear: Freeloader Pro =-.
Martin Holladay says
October 30, 2009 at 2:26 pmAnna,
Thanks for mentioning my article. Another article that mentions solar hot water collectors is “Martin’s Useless Products List.”
Green Talk says
October 30, 2009 at 11:36 pmMartin, I really enjoyed your article. What would your recommend for heating radiant rather than solar hot water? Your choice of energy efficient heating of hot water? Anna
chris says
October 30, 2009 at 4:50 pmIt was always my understanding that flat panels were going to trump tubes in cold climates that experienced alot of snow. While a couple of inches of snow will block tubes, several inches will quickly slide off a flat plate collector.
Green Talk says
October 30, 2009 at 11:34 pmChris, just repeating what Frank said. Interesting point though. Do you know anyone who installed flat panels for this reason or any information or reports about snow with either flat vs tubes?
Anna
Swimming Workout says
April 11, 2011 at 1:19 amA solar hot water system is a perfect tool for every swimmers. Usually, swimmers do their workouts at night where water are very cold. By using this system, it will really help swimmers for their practice.
Washington says
January 12, 2017 at 7:55 amA solar hot water system is a perfect tool for every swimmers. Usually, swimmers do their workouts at night where water are very cold. By using this system, it will really help swimmers for their practice.
Aiden says
November 22, 2017 at 2:33 amYour idea of building a solar hot water system is marvelous. I would include that your idea of using evacuated tube collectors rather than the flat-plate collectors is perfect because it’s way more energey efficient. It saves heat energy and we get more light.