The Coroplast was not a total loss, as I was able to test out my new plastic welder, and I have a back-up project planed for the material should they not work out for particle panels. The plastic welder is a $200 tool which is nothing more then a glorified heat gun with some nozzle attachments and the ability to set the temperature in 10F increments. It takes a little getting use to, but the principle is similar to metal welding: you raise the temperature of two surfaces you want to weld and melt a rod of like material into the joint. The result is a solid joint. Of course, its not as easy as it sounds. If you go too fast or too slow, if the heat gun is too hot or too cold, or if the materials being joined differ in thickness, things may not work out just right. This last condition is going to be the challenging one when welding the manifold onto the end of the panel. Since the panel is thin (~1/64-1/32), it will not take much heat to melt and deform it. If the manifold material it thick, or the welding rod, by the time those components start to melt the panel will have collapsed. This will indeed be challenging. Of course, that's assuming I can find the right plastic.
It appears I must now take a closer look at polypropylene. The wikipedia article indicated that it can be made "crystal clear" when it is biaxially oriented. I have no idea what that entails, so i'll have to look into it. Another option would be acrylic, since that could hold up to the water exposure. However, I cannot find it in corrugated double-wall sheets and I suppose this is because it would be rather brittle. My troubles with finding the proper plastic in a corrugated double-wall form has led me to think up some other designs that I would prototype with solid sheets or tubes.
On a non-technical note I met with a gentlemen representing an early seed capital firm. It was a good meeting, but mostly entailed me getting him up to speed on solar thermal and the potential market for very cheap solar thermal. This subject is deserving of its own post, so I'll hold off on that for a later time.
Don't give up on the translucent white coroplast yet. My wife and I finally got one of these built and tested. We built it as a drainback system and used plain water dyed black using pond dye. We got tempered glass panes from Craigslist to build this and the next ones. We used an old hot water circulator pump also from Craigslist.
ReplyDeleteWhen you see the difference between empty and full coroplast it does look fairly dark. I have pics of a half full panel while it was draining back which show the difference.
We did a 4 hour test on a clear day, readjusting the panel angle a few times during the test. The full spreadsheet is available but I was not sure if it could be posted here. It is a 1.814 square meter panel with 37.85 liters (10 gal) of water in the system. We used a 55 gallon plastic drum for the tank. The tank and hoses were not insulated.
Starting temp was 53.8 F. At the 1 hour mark the temp was 92.7 F, average power was 952 watts, 52% efficient. At 2 hours, 117 F, 768 watts, 42%. At 3 hours, 127 F, 593 watts, 33%. At 4 hours, 130 F, 464 watts, 26%. We also did a stagnation test with no water in it, and it got up to 152 degrees F inside the box on a 45 degree day. We are looking forward to mounting it permanently and testing reliability/longevity. One thing we still need to do is get UV clear paint to help protect the panel from UV breakdown, and see if that affects the efficiency much.
John,
ReplyDeleteThis is very cool! If you have a link to your pictures I would love to see it. Otherwise, if you contact me through this blog we can exchange emails.
The bottom line for me is cost. If we can cut the cost of the solar thermal panel by 80% and the efficiency drops by 20% then its still a good improvement. Something tells me that a perfect plastic is out there, and it may even be that a properly formulated polypropylene will work. My hope is that we can find an off-the shelf material so that people can construct them for themselves.
Are you planning on running the system with the dye long-term? If so I would definitely like to keep informed on how it works. My searches on the topic indicated that dyes were problematic over time: they bleached, precipitated from solution, or stained the inside of the panel.
I would love any more details on your work! If you don't yet have a blog on it, I'm sure I am not the only one who would love to follow it.
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