Particle Size Variation...Less Is Better

I was thinking about how particle size variation will affect the "distribution" property of particles in the panel.  If you look at the video right at the end you will see that some of the particles become bunched up at the top of the panel.  From the bottom to the top there is a distribution in the density of the particles in the channel.  At the bottom the density is very high and this drops off near the top.  Why is this?

To answer this, let me first explain why the particles spread out in the first place and don't all bunch up at the top.  When water enters the bottom of the panel it can take a multitude of paths corresponding to the vertical channels.  Lets assume that one channel has particles blocking the top filter, while another channel does not.  In this case, the resistance to flow for the blocked channel will be higher, and consequently more flow will go to the unblocked channel.  This will cause the particles to rise in the unblocked channel (the flow is strong) and fall in the blocked channel (the flow is weak).  After some time the flow will slow to a point where it exactly matches the sink rate of the particles.  Why?  Because if the flow was strong the particles would block the filter, causing the flow to decrease and the particles would fall.  If the particles sank they would unblock the filter causing the flow to increase and the particles to rise.  As you can see, the only stable flow rate is one that matches the sink rate of the particles, and the particles will find this flow rate if there is a sufficient number of them.

This is the story for a mixture of particles with no variance in size.  However, it is not practical nor possible to obtain a collection of particles with zero variance in size.  The result is that the distribution of particles will be higher in the bottom of the panel and lower at the top, as you can see in the video.

The small particles feel a greater flow-force (relative to gravity) and are pushed to the top of the panel, where they stop against the panel and restrict the flow of the channel.  The larger particles feel less of a flow (again, relative to gravity), and remain closer the bottom.

To achieve a perfectly uniform mixture of particles throughout the panel we would then need all the particles to be exactly the same size.  This is obviously not going to happen.  However, it does point to an area of optimization: the smaller the variance in the particle sizes the better. 

The interested reader is encouraged to read about drag force on Wikipedia.

Wikipedia: no innovation please

Although I knew it would be met with resistance, I have attempted to get some mention of the particle panel concept into the Wikipedia article on solar thermal collectors.  This process has been interesting and is worth discussion, because it gets to the heart of innovation, self-interest and public interest.

Wikipedia is here to serve us all, and its massive daily use by million of people has changed the world for the better.  I am a proud supporter of Wikipedia (both financially and vocally).  The problem of self-interests is a huge problem for Wikipedia, and I have no doubt that wiki editors are constantly zeroing in on self-interest edits and deleting them (like they did with my addition), much to the benefit to all.  However, this leads to an interesting problem when it comes to documenting ongoing innovation of technology.

The problem is that when I read about Solar Thermal Collectors (or any other technology), I want to see two things.

First, I want to understand what it is, how it works, and why it is useful.  I do not want to be exposed to a bunch of commercial spam mascaraing as fact, pointing me to all the companies out there vying for control of one market niche or another.   Wikipedia is doing a good job with this.

Second, I want to know what is currently being done and the new paths being explored.  This is intimately tied to commercial interests.  In many ways, this is what is most exciting to people (or at least me).  I want to see the cutting edge of the field, because this is where the goldmine of information is.  If you understand what new ideas are being explored you will have a better appreciation of the problems being faced by current approaches, and you will have a chance to discover a solution for yourself.  Since Wikipedia is all about its ability to build itself and is increasingly finding itself as the first place people go to learn about a topic, it would be a fantastic place to showcase innovation as it is happening.  These new ideas need to be clearly labeled as such, the problems they are trying to address needs to be clear, and the way they work needs to be fully disclosed.  Beyond that, they deserve a space along side the status-quo.

I would really like to be able to see all the self-interests working on any particular field documented in Wikipedia.  It would help everybody and encourage innovation.  Consider the comment of the wiki editor Jojalozzo:

"My interpretation of WP:OR policy is that a technology needs to be developed and become accepted in the industry or in the DIY community before it is suited for reference here. It's the originality, novelty and fringe nature of your work that is problematic."

In other words, if its original and novel, it has no place in Wikipedia.  You can read my little discussion with the offended Wikipedia editor here.  I (reluctantly) agree with his choice to remove my addition.  However, this experience has made me realize how much we need a public forum for innovation...A place where people can come together around ideas and move ideas forward quickly and with public involvement.

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.

Reaching Out

This is going to be interesting.  To jump-start this blog I thought it would be a good idea to go out and find some forums...people who are into this sort of thing...and post some comments and get some feedback.  It seems to be working. 

1. I left some comments for Rob over at iwilltry.org.  This dude is obviously sharp as a tack and is doing some some great things.  He wrote an article over at instructables on how to build a solar thermal panel with plastic, but ran into the problem of overheating.  This is exactly what I was trying to solve with the particle panel idea.
2. I joined the forum over at solarpaneltalk and started a thread. These guys are great and very helpful.
3. I left some comments over at The Sietch Blog.  Scroll down to comment 194 to see the discussion. Turns out there is an expert who calls himself CaptBilly behind the blog, who is very outspoken and full of great info.  He is pretty concerned about the panel not having low enough emissivity.  I understand what he is saying, and he has a good point.  Many thanks CaptBilly for the lesson.  I also think I am on the right track.  Nothing he has said so far is making too nervous. (but perhaps it due to ignorance?)  Its exactly these sort of details I need to know if I am going to succeed at this.  My main goal is to drastically increase the Watts/Dollar of solar thermal energy.  If the efficiency of the panel drops a little over current systems but the cost goes down by 80%, the net gain is still very big.  Actually, I am going to be blunt.  If the cost of solar thermal panels were reduced by 80% it would cause floodgate to open.  I, by the standard of my peers, make a lot of money.  And even I could barely afford to use solar thermal to heat my house (or geothermal...I was quoted 40k).  To be honest, when I went to my local distributor and they quoted me $3,000 for one 4'X8' solar thermal panel it pissed me off.  This is not a technology that should be expensive, and the fact that it is not dirt cheap tells me there is a gotcha somewhere (and you know what I think that gotcha is...right?).
4. I started a thread over at Tree Hugger.  Maybe its just too mainstream, because as of now 12 people have viewed it and no comments.  I have a feeling its going to really take work to make people see the advantages of cheap solar thermal.
5. I created an instructable.  This site is really great.  Many great great people. What a fantastic way to use the internet!

Interestingly, I received an email from a guy in Portugal who is interested in exploring a business arrangement.  I think its a good sign, considering that the site was up for all of maybe 24 hours.  I referred him to Luis Ortiz, who is a partner in this idea (and a patent attorney), and will be handling any legal/contractual matters.  The fact that Luis and Kermit have partnered with me on this and waived their fees is the only way I could have filed a patent on this idea.  Its people who make things happen, not money or technology.  Remember that everyone.

Well, I am now packing for a business trip.  (I consult for a couple of government programs that are trying to build chips like brains, partly inspired by my work) I will be gone all week.  I'll try to check in and answer comments and keep up with the activity if I can.

So after my discussion with CaptBilly, I thought I would look around a bit.  He doesnt understand how this concept could result in a less expensive panel.  Thats sort of unnerving, particularly since he seems to be so knolwedgble.  I found references to "all polymer" absorption plates in the wikipedea article on solar thermal panels.  I googled that and found this paper.  I hesitate to order the article, as the abstract seems to say it all:


"Venting and evaporative cooling are modeled as possible techniques for protecting polymer absorbers in single-glazed, flat-plate solar collectors from exceeding the material temperature limit during dry stagnation. Four venting options are considered: (I) venting above the absorber plate, (II) venting below, (III) dual venting, and (IV) venting with evaporative cooling. Results indicate that in hot, sunny conditions, venting may not provide adequate cooling to lower the absorber temperature to the relative thermal index of the polymeric materials currently in use or under consideration for this application. Venting combined with evaporalive cooling from a wetted pad directly beneath the absorber plate is identified as a potential method of overheat protection in hot, dry climates."

So it appears other are struggling with this problem.  Could the particle panels be the solution?  Stay tuned...








Blue Skies,

Alex

Launch

Well, this is it.  I wish I could do more but time does not allow.  This is where I must start.

Welcome everybody to the first post of my new blog dedicated to what I hope will become a new and important technology in solar energy capture.  Read about how I came up with the idea, read about the idea itself, read a little more about why I made this blog,  download and print a little white paper I wrote, check out the instructable I set up, and contact me if you have any questions or think you know how you can be a part of this project.  I will be using feedback I get on this site to help guide my posts. 

Check out the video I made of my first plastic particle panel below.

I have received some comments that indicate some confusion as to why these panels are a good idea, or what the innovation is.  That means I am not doing a good job in explaining things.  Let me try:

The temperature inside a modern solar thermal panel can exceed 150C if the panel is "stagnant", or not in use.  This is why they are built out of metal and glass.  This is also why they are expensive, heavy(metal & glass) and fragile (glass). The design I show here eliminates the danger of overheating (it can "turn off"), which means it can be made out of plastic instead of metal and glass.  If the panel could not turn off (like all current solar thermal panels), a plastic panel would deform if it got hotter then 115C.  

This design reduces the cost and weight by 80% and is many times more durable (because there is no glass).  The result is a solar thermal panel that is much cheaper, much lighter, many time more durable and equally (or perhaps more?) efficient as what is on the market today.  

That why I think this is a good idea.  Please call me on this if I am wrong or you see any problems with my logic.




note about the video: I think the stuff I say about the turbulent flow being less resistive to flow is not correct. I think its actually opposite. Anyway, something to look into.  If anybody out there can explain to me how/why those convection current are set up, please leave a comment!