Polypropylene, Power Panels and NPR

I'm back from my business trip, rested up, with snow falling outside.  I managed to move the panels forward a bit while I was stuck in the hotel room.

• Following up on a comment from the instructable article I wrote, I looked into Coroplast as a material instead of Polycarbonate.  It turns out that Coroplast is actually polyproylene plastic, so I got educated on the Wikipedia article.  This is definitely what I should have used.  
• No degradation from water exposure.
• Resistance to corrosion and chmical leaching
• Resistance to imapact and freezing
• Can be joined with heat fusion rather then gluing
• Heat resistant
• Used to make filters in the .5 to 30 micron range, so I could possibly use plastic rather then steel mesh for the particle filters.
• Is commonly recycled (number '5')
• Inexpensive.  $26.99 for a 6mm 4'X8' panel. 
• Compare this to the $120 for the Polycarbonate
• Half the cost for the 3mm panel.  For the cost of one Polycarbonate panel I could get 10 Coroplast panels without any of the problems of the Polycarbonate.
• I looked into plastic welding, which I am going to try rather then gluing.  They are not super cheap, but not prohibitively expensive either.  I have a new design idea that will eliminate, hopefully, all or most of the headaches with the manifold.
• Sent an email to the "Living on Earth" radio program on NPR, which has a segment called "Cool Fix for a Hot Planet".  The were asking for user ideas, so I told them about mine.  My email:
• Living on Earth,
  
  my girlfriend just told me about your show and the "Cool Fix for a Hot Planet" segment.  I have what I think is are two good ideas and wanted to share. 
  
  I think I have found a way to create very inexpensive solar thermal panel out of recycled plastic. This is a hard problem, because solar thermal panels get hot if not used, and plastic melts if it gets too hot.  I have found an inexpensive way to build an efficient solar thermal panel that can turn itself off (not get hot) when not in use.  The mechanism could be a fundamental innovation to solar thermal energy capture.  (see my blog url below)
  
  Since thermal energy can be used for both heating and cooling (heat can drive an absorption cooler for AC), and since heating and cooling account for the majority (65%) of the energy we consume and it is overwhelming driven by fossil fuels, finding a really cheap way for people to access solar thermal energy to heat and cool their home is fundamentally important.
  
  The problem at hand is that we, as a world, need to find solutions to our energy problems, and these solutions are the same solutions that will solve the climate and sustainability problems.  This is a serious time crunch!  We have serious problems that need to be solved quickly.  The only way this is going to happen is to find ways to get everybody working together on the same problems.  This is how I intend to do this:
  
  I have decided to make my whole process of trying to develop these panels public, from inception to production.  Thus far my idea is only a spark of inspiration, a leaky prototype, and a partnership with two patent attorneys and my mother.  My hope is to both get the help of the public and to inspire others to solve problems openly and using public participation.  I think there are people out there with good ideas and little time, and people who may not be as creative (or have the time to be) but have expertise in all manners of areas.  If an idea is good we need it fast.  If an idea is bad, its flaws need to be found quickly.  Egos, fear and greed need to get out of the way.  If thousands of ordinary people across the world work together around ideas put forth by people not afraid to do so, the result will be extraordinary.  innovation would happen so quickly!  As an example, my idea requires that I be an expert on plastics, which I am not.  However, I am willing to bet that there is a plastic engineer out there who wants to solve our climate/energy crises and who could offer advise that would take me years to acquire on my own.  Likewise, it is possible that my idea just will not work for some reason that I cant see, but somebody else with expertise in a particular area could.  We need solutions, not hype or fear of being wrong. I want to start this sort of open public innovation by putting forth my particle panel concept, which so far I believe to be (but it may not be!) a good solution.
  
  Please check out my blog at:
  
  http://www.particlepanels.com/
  
  Like I said, I have only just begun.
  
  Blue Skies,
  Alex Nugent
•  I got a response that they may air it, but I don't know if that is their canned response or if they mean it:
• Dear LOE Listener,
  
  Thank you for your comments.  Living on Earth may use excerpts from your response in an upcoming listener letters segment.  If you do not want us to use your name or letter, please respond to this email within 3 days.  You may also call our listener line 800-218-9988 and leave a voice message, or call 617-629-3638 to speak with a member of our staff.
• I came across a new company making polymer (plastic) solar thermal panels!  Obviously very interested in how they solve the stagnation problem, I emailed them and got a good deal of information, although it was not totally straight forward.  Here is what I found out
• On the question of stagnation, in PVT applications we circulate our cooling fluid through the collector winter and summer and our control system will simply dump the thermal load during the summer at night back through the collectors to always maintain a safe storage temperature with plenty of capacity to accomodate the next day of sun.  Our thermal storage tanks are sized so that each panel has 40 liters (11 gallons of thermal storage per tank) .  This is curious to me, because it means that if the power goes out, a circuit breaker flips, a pump failed, etc, then the system fails and the panels overheat.  I called them on this and they explained:
• "We protect the enclosure by the open to atmosphere flow channels in the enclosure that mate via adhesive with collector plate. In our case our absorber is an aluminum sheet that is black anodized for corrosion protection on front and rear sides. Since we gravity feed the collector fluid from the top and the plumbing is not pressurized and open to atmosphere the following happens when the downward fluid flow stops.  If there is sun incident on the collector air that is now in the collector is driven upward due to heating and out the vents that are part of the plumbing arrangement. The air to supply this thermosiphon effect comes from the storage tank or on the larger systems our pulse/recircualtion tank. The flow is sufficient enough to maintain a much lower stagnation temp. In order to gravity feed water unpressurized we developed as part of the flow pattern an effective air venting system that works well in moving air through the collectors. This is much different than the standard collector where the plumbing (small copper tubes) are closed to atmosphere in a presuurized arrangement thus have no potential to provide passive cooling. Typically the insulated box is well sealed which drives temperatures."
• So what they have done, I think, is simply cut air vents at the top of the panel to insure the panels stays cool.  This is problematic, because it this effectively breaks the insulation and opens up a path for convective loss, which is very serious for bigger temperature differentials.  As I understand it, convection heat loss is the reason vacuum tube panels are so much more efficient at higher temperature differentials (i.e when its really cold outside and you are trying to heat the water to to 120F.  Consider that that the temperature outside is 0C, which it is here in Santa Fe in the winter.  Now, if we want to heat our hot water to 50C (120F), that's a temperature differential of 50C.  The power efficiency of a flat-panel collector drops by almost 50% between 20 and 50C differential.  Check it out on Wikipedia.  This is for standard panels without holes in the top to let air out.  I can only image the heat loss of a panel at 50C temperature differentials with an open-atmosphere hole.
• It appears PowerPanel has "solved" the overheating problem by limiting the use of their panels to moderate climates.  If its really hot there panels must be both vented and the pumps run 24/7 to cool them at night.  In colder climates, the efficiency seems like it must drop off really quickly.  The reason why this is not really such a bad thing is that they also integrate photovoltaic in the panels.   I have asked for an efficiency plot, which will show the efficiency of thermal absorption at various temperature differentials. We will see if they will send it to me.  
• Since they are also meshing photovoltaic with thermal, I think the above limitations may work in niche areas considering it also provides some electricity.  However, I am only further encourage that the particle panel concept is something that is really needed right now.
• They also told me their panels were made from polypropylene, so I am on the right track:
• Plastic Portion of our panel is constructed from TPO (Thermoplastic Olephin) It is basically Polyproplylene mixed with EPDM (synthetic rubber)  Part of enclosure is  EPP (expanded polyproylene) foam that backs the TPO providing structure and insulation all in one package. All components are rated for the temperatures anticipated with a stagnant collector and we have the TPO formulated with significant UV stabilizers so that the sun does not break it down over time.