OverKill Solar
May 13, 2010
Evacuated Tube Collectors
- Flat Plate Solar Collectors
Over the past 12 months I have taken the time to diligently re-educate myself about the practical use of Solar applications. I began in earnest with Solar 2009 held in Buffalo, New York. I went there specifically to get a handle on what is new or practical in the industry and what is hype or spin. I was specifically interested in the evolvement of Solar Thermal applications. I had installed Solar Hot Water and Radiant Floor Heat in the late 70′s and early 80′s and believed them to be cost effective and practical. After a year of studying their applications and being a technical adviser to projects where solar thermal was installed–I still do with caveats. I believe you have to differentiate and define the parameters of how much water you need to heat and to what temperature. Hence the word “OverKill Solar.”
I had visited the Henry Gifford’s Web Site, www.energysavingsscience.com, during the early winter of 2009 and was turned on to a book called Solar Hot Water Systems, Lessons Learned 1977 to Today by Tom Lane. Henry Gifford is a former heating systems contractor and an energy efficiency expert who believes that results tell the story, after occupancy, not the awarding of a designation. He is especially harsh on LEED accreditation. In defense of the LEED program, it hasn’t even reached its teenage years, so it has a lot to learn. You have to start somewhere and USGBC had the guts to develop LEED and it is still evolving–not part of this blog.
On Henry’s site he referenced Tom Lane’s book as the only book you will need on Solar System Design. What he should have said was Solar Thermal Design-meaning the use of solar to heat water for various applications. I ordered the book and then went to Solar 2009 to take a course from Tom. It was worth the time, travel and expense. Tom Lane was my kind of teacher, practical with common sense. I respected what he had to say to the point of taking his recommendation to attend a Solar Instruction Seminar in Florida being put on by a manufacturer of Solar Thermal Panels.
First a quick explanation of Solar differences. Solar Photovoltaics, the glamor child of the alternative energy field, is about generating electricity. Solar Thermal is about heating water. Solar Thermal has been around the United States since first commercially introduced in the 1890′s in California. It is a system that has gotten the bugs out. It is economically justified for commercial and multi-family(apartment, condo’s, townhouses)applications without subsidies. Depending on what state you are in, and other contributing factors, Solar Thermal can be cost justified, when applied with common sense to single family residential applications.
When I say common sense I mean defining what it is you want to accomplish and then proceeding to plan accordingly. Too many times in the United States we jump on the glamor product without doing research. In the Solar Thermal Industry one of those is evacuated tube collectors. To heat water for applications that require temperatures of 150 degrees or lower, Flat Plate Collectors have it all over vacuum tubes in cost, durability and effectiveness. If you need water hotter than 150 degrees in winter and 180 degrees in summer, vacuum tubes may be a good fit. But the majority of applications in this country can be economically accomplished with Flat Plate Collectors, besides being safer and many produced in the United States.
This Over-Kill was demonstrated to me first hand a couple of months ago. I saw an over-designed commercial system that couldn’t be installed as designed because there was no room for the specified 550 gallon storage tank. The system uses vacuum tubes(evacuated tubes) when flat plate collectors would have done the job just as efficiently and would have been a better economic approach. Plus the system could have been designed to utilize the area allocated for storage or pre_heating while taken full of advantage or REC’s and other credits. As it turned out, two 120 gallon hot water solar storage tanks were substituted as pre-heaters to the main unit. A serious problem developed after installation, as the evacuated tubes heated the water so hot(over 190 degrees), that the glue used on the CPVC (wrong) pipe used to take the heated water from the storage tank to the primary water heating unit loosened and the system piping exploded and super heated water went everywhere. Luckily no one was hurt! There were no heat dissipators on the vacuum tube system and copper piping should have been used, but that is a story for another day.
I had observed during this same time period, three single family residential systems utilizing vacuum tubes and had seen excessive heat generation for domestic water provisions, even with heat dissipators. I opened the storage closet where the solar thermal hot water tank was located. I was blown over by the heat. I then looked outside and saw this ugly black box sitting on the siding___it was a heat dissipator__to get rid of excess heat. Why would anyone pay additional costs to heat up something that you have to discharge the heat from. To me that is like paying for 10 gallons of fuel and running 2 gallons of it on the ground because the tank won’t hold it. I am reminded of using a hammer to drive a thumb tack–over kill solar.
We will discuss this evolution of solar thermal more, but seeing first hand the overkill of a vacuum tube system, when applied to common residential water heating, convinced me again of the need for common sense, practical designs when using solar applications. I am a great believer in Solar applications. I applaud the efforts, but I am more a believer in applying it using (CECSEE) Cost Effective, Common Common Sense, Energy Efficient___Green standards.
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