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Finished the charging circuit!!!

A project log for Ultra-Portable Sustainable Electric Generator

Combines 3 projects I just started: foldable 50W solar panel, campfire-based thermoelectric generator, & RasPi2 lapdock. Fits in a backpack.

dylan-bleierDylan Bleier 05/26/2015 at 23:520 Comments

I finished the charging circuit / enclosure, sealing everything in with excessive amounts of hot glue and re-used dirty plexiglass. There's even space left over to add the Boarduino when I get around to that. I also cut a tarp to size for the solar panel and have something almost perfect in mind for a rigid box for the solar panel – a large contractor's clipboard. The last crucial item I need now is the encapsulant for the solar panel. Since I don't have a lot of time before I need to move and start a full time summer job until August, in a place where I might not have access to a full shop and all the things I need, I'm going to try to overnight some encapsulant and finish the panel before I have to leave. Then I can use the device over the summer and see if it holds up or if I should change anything. I'll probably be able to do a bit of work on the other parts (the lapdock and the thermoelectric generator) before August, but I'll be really busy with other things. Anyway, the reason I was waiting to do the encapsulant was that the ideal material to use (according to NREL research presentations I saw online) was about a millimeter thick of TPO (thermoplastic olefin) or TPU (thermoplastic urethane). You can't just go to the hardware store to find suitable materials for this, as you probably want something you can melt on in sheet / film form with all the right additives to slow down solar degradation from heat as well as UV and visible light exposure. The only thing I've seen so far is $300 rolls of TPU or TPO on ebay, the quality of which is not guaranteed in the least. There's probably something better that could be found, but since I'm running out of time, I'll just get some EVA (ethylene vinyl acetate), the standard that's been used successfully for decades in the solar industry but probably isn't actually that great because the degradation modes over years can include yellowing and browning due to production of acetic acid which corrodes solar cells. With this project, if I use it for an hour or two a day, it could still potentially last decades.

Unfortunately, I can't find my camera right now, so I can't take decent pics to share. I'll try to borrow someone else's camera soon.

solar panel to do list:

- order EVA (and TEDLAR?) with fast shipping

- rewire cells using the good quality flexible wire, adding a diode in series before the plug, clip sharp corners (?), test

- gently swab/wipe cells with methanol to remove corrosive rosin flux and any dirt/dust; allow to dry fully (6+ hrs at room temp with air flow?? or use a heat gun on low)

- immediately seal in a cool, low humidity room, using a shop vac to pull a vacuum between the EVA and the panel + TPE backing in order to prevent bubbles; seal each cell individually using a heat gun to melt the polymer film. seal the TPE/solar cell/EVA/FEP. trim so EVA is not exposed and the edge is TPE/FEP sealed together. add butyl flashing tape to seal even better.

- glue or sew (*if there is a suitably large margin of plastic) the solar cells in place on the tarp. sew the flexible wires into place on the tarp to secure them.

- add foam weather stripping to the sides and if necessary, the middle of each cell to protect them while in the box. Fold it up and put it in the case, stick it in a backpack, and go test it out!

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