Tuesday, April 27, 2010

Solar Heating is Flexible

Up until just a few years ago, solar swimming pool heating was far and away the largest use of "solar energy". The reason is simple and straightforward. It makes economic sense. It competes head on against very inexpensive natural gas for heating swimming pools. The unglazed (no glass over the collector) plastic collector is low cost per area exposed to the sun and when heating low temperature water like a swimming pool (or even pre-heating domestic hot water) the efficiency is high. In other words a large portion of the solar energy exposed to the collector is collected and delivered as energy to the load. This simple and obvious combination makes for the most cost effective and therefore most viable solar energy solution. Over the last 37 years this solar energy market has thrived but there have been ups and downs.

The first low cost unglazed solar collectors for swimming pool heating were introduced around 1969 under the trade name "Solaroll". The product was made of a synthetic rubber called EPDM. It was a flexible collector. It thrived. In 1972 "Fafco" introduced the first rigid collector. This collector, still in production today, was made of a type of polypropylene. The header pipes are permanently attached to the absorber sections in the factory resulting in fixed size collectors. 4x12 has become the most common size. The advantages to this design are that they are low cost to manufacture and low cost to install. Solaroll by comparison, required the installer, dealer, or homeowner to attach all the headers to the flexible fin-tubing after cutting the fin-tubing to length. This extra work traded off with the extra capability in terms of being able to fit the collector to the space. In addition these original flexible collectors could be used in areas where freezing was an issue. If water is trapped inside a rigid collector and it freezes the tubes break and the remedies require sealing off entire flow cores. The flexible Solaroll on the other hand could be mounted flat on a roof where water will not drain out. It could freeze solid with water in it. This was the state of the art in the industry 30 years ago? What happened since? Solaroll no longer exists and Fafco was mimicked over and over again and today 75% of all solar pool heating is done with rigid polypropylene boards floating around under straps. Most in the industry can tell you flexible EPDM synthetic rubber collectors like Solaroll had a fatal flaw. Chlorine in the swimming pools caused the flexible material to break down. One of the big chemical companies proposed a solution. It was a polypropylene based flexible extrusion called Santoprene. As the story goes, it broke down faster than EPDM and the result was an industry calamity. From this point forward the rigid polypropylene collector industry thrived.

But the rigid 4x12 panels were limiting. They couldn't be applied to flat roofs without fear of freeze damage. Available space could not be fully utilized and what could be less esthetically appealing than big black rectangles on a rooftop? Where there is demand there is supply. The epdm rubber tubing collectors came back, slowly and gradually. Its been 30 years since the major fallout. Hot Sun installed a 2000 sq ft system in North Carolina using EPDM and it took only 3 years in the field for the system to start churning black crud into the pool.

Luckily Hot Sun had decided this was risky and had already switched to a plastic based alternative. The experience in North Carolina was the final straw and we went 100% non EPDM after that point... because we could! There is an undeniable appeal to using EPDM. Its tough. It usually lasts long enough that these issues occur well into the lifespan when most people don't even remember who they bought their systems from. Hot Sun's solution is not without its downsides too. There is no perfect answer. We have to use a mechanical or an adhesive connection to join the tubing and the headers. It takes more time to assemble. Theoretically flexible plastic is not as strong as flexible epdm so we have to be more careful with system pressure but what we've found are better and better thermoplastics such that today our flexible plastic is as strong as most competing epdm products with one major distinction. Powerstrip is guaranteed not to break down for 25 years. Some manufacturers of some EPDM products can't have water left in them over winter due to "freezing issues". That mindbender really means that if you leave water in the epdm tubing and it heats up the black crud will come off the solar panel and go into the pool. Freezing seems to trigger the release, we think just due to the physical stretching. We don't believe anyone else has even tried to resolve the issues with epdm in the solar business. My point is we can guarantee it won't happen for 25 years. EPDM solar manufacturers can't guarantee it won't happen in 10. The seal manufacturers have certainly acknowledged this problem. Here we're talking about chlorine in drinking water (much lower concentrations) and city water temperatures. The effect is thought to double with every 10 degree increase in temperature. The solutions are special compounds that are very expensive and even then the effect is just reduced.


  1. Hi

    solar hot water heaters are cost effective and eco- friendally These days peolple started switching towards the solar systems Not just because these systems are cost effective but these systems can increase the real estate value of a home.

    With the help of polysun solar simulator software we can make accurate cost analysis of these system.Polysun’s modularity and flexibility enable you to design and modify your system.

  2. Thanks for the self serving comments everyone. Solar domestic water heating has been around since long before conventional hot water tanks. Once we started digging oil out of the ground and burning at a cost that not only didn't and doesn't reflect environmental cost but is subsidized!!! we eliminated any chance solar heating could compete with fuel. Once you admit to your customer that it'll take 15 or 20 years to pay for itself you've talked them out of it.
    With free money from the government there is again a market just like there was in the 70's when there was a big tax credit. Anyone in the industry all that time including me can tell you the market completely died after the tax credits. It was worth it to fix them but not to put new ones in. Once again we're subsidizing these things and the market is flourishing but in many places the subsidies are disappearing. Guess what is happening to the markets and the companies set up to take advantage of the free money? Of course its a great thing and people want it. I want it even with a 10 year return after rebates but I just can't justify it economically at my own particular stage of financial life. I love solar dhw. I just think it should be done cost effectively with technology like mine and it would be if the free market allowed it. The subsidies only subsidize the technology of the past because that's the technology of the lobbying groups. Subsidies prevent change for the better. Thanks for the dialogue.

  3. Can anyone tell me if a filter is a proper solution to the "black pool disease" or is there going to be a lot of disintegration from the Solarprene panels which will then affect the efficiency of the solar panels? My solar panels had only four summers before I got the "black pool disease".

  4. Yes the cartridge filter on the return line will take the black crud out of the system if you run it thru that filter when you first start the system after its been off for a while or after a freeze. The problem is the cartridge gets plugged up fast and you have to change it at least once a season. Each epdm collector breaks down differently. Sometimes its hard particles and sometimes its more gooey. Look at your warranty and harass the manufacturer because every warranty is for at least 5 years before its pro-rated but of course the warranty is only as good as the company behind it. Its hard for a contractor to make good when the manufacturer won't budge. Thank you for commenting. If you'd like to e-mail me at ken@h2otsun.com I'd love to add you to my list of witnesses because I'm afraid I'll be sued over making this all public and the more cases I can identify, the more I can defend myself. Unfortunately the only proper remedy is replacement with Powerstrip Geon. That was the only remedy Enersol had in the above case.

  5. Ken, read your blog about black pool. My company distributed and installed tons and tons of EPDM solar pool heating collector in Florida during the 80’s. The claim to fame then was that we supplied the collector for heating the 1,000,000 gallon tank used for heating water for the divers to film the movie “Jaws” starring Lou Gossett, Jr. We, too, had massive black pooling after 8 years of installations, immediately after a severe freeze.. I will never forget the first black pool I saw. The lady showed me the pool, I immediately got severely ill, excused myself, walked around the side of the house where she could not see me and promptly “puked” because I knew that this was the first of many.I placed my hand in the pool water and could not see my finger one inch below, this pool was solid black. We learned how to treat it by flocking with alum but if any pressure was put on the pool surface, as in rubbing the surface, the pool normally had to be resurfaced. If my memory serves me correctly, Bio paid me about $100,000 for cleaning pools and that did not include resurfacing, just black pool removal.The manufacturer, Bio Energy, received our sample of black pool material and promptly reported that the problem was iron content in the pool water. Ken, I may have been born, but it was not yesterday, so I promptly sent a sample off to an independent lab, which reported that the content was carbon black. Then the war started which resulted in our company trying to alleviate customer complaints as indicated above. Well, Monsanto came to Florida, did their “dog and pony” show with Bio, we all bit on the encapsulated EPDM with PP (Santoprene) and less than two years it failed worse than the original stuff. I have a question for you since we have not kept abreast of flexible pool materials over the last 15 or so years. Are you aware of failures since the 90’s? I understand that several companies have continued to sell so called “new and improved” EPDM’s all the way thru to present and have never heard of any failures. I did supply a commercial job with Harter EPDM about 10 years ago and have not heard reports of failure. Ken, as you know, there are niche uses for flexible materials that are freeze tolerant, especially on flat roofs. I would appreciate any and all updates? Thanks in advance for your input, Ben.

  6. Thanks to the black rubber collectors on the roof, I now have a jet black pool. Not happy at all as the system is only 5.5 years old and to replace it is not a cheap process. Anyone thinking of using it should sit down and have a big think before going ahead. I believe it should not be on the market and when I replace the collectors I can assure you it will not be with the same thing,,,, even if it were free. One annoyed Aussie...

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