Ultralight Solar PV USB charger for backpacking - suggestions to improve design?

[inetdog]

A find that has increased my hope for success - last year someone on EEVblog created a similar lightweight flexible panel (but they did have access to professional panel laminating equipment):

http://imgur.com/dQe8nuE found on EEVblog via http://www.eevblog.com/forum/chat/su...278/#msg530278

I am betting that they also had access to professional materials without having to search the internet. It is much easier to get a small quantity (even free for "evaluation") if you have a presence with the suppliers to start with.

[Stormwind]

A find that has increased my hope for success - last year someone on EEVblog created a similar lightweight flexible panel (but they did have access to professional panel laminating equipment):

http://imgur.com/dQe8nuE found on EEVblog via http://www.eevblog.com/forum/chat/su...278/#msg530278

[Stormwind]

One road bump - I'm having difficulty sourcing clear frontsheet material (clear Tedlar, Teflon FEP or ETFE, etc), especially in the relatively small quantities I need.

If anyone knows a source of clear frontsheet material, I'd greatly appreciate the info.

I also asked over in the DIY Solar Panel Tools and Materials forum:

https://www.solarpaneltalk.com/forum/diy-solar-panels/tools-and-materials/335914-small-order-source-of-flexible-frontsheets

Thanks!

[PNjunction]

Quite frankly, I think for this application (ultra lightweight cellphone charger), the use of the typical p-n junction cell should be replaced with an entirely different solar cell:

The DSSC, or Dye Sensitized Solar Cell. Already in things like solar keyboards, etc:

http://gcell.com/

Use these and you may not have to play with so many tricks to get the efficiency to where you want it with pnjunction panels. There are quite a few videos explaining how DSSC cells work. Put simply, "artificial photosynthesis" should ring a bell amongst the nature crowd. These are real things, and didn't just come about yesterday.

In fact, perhaps one of their backpacks might even be an off-the-shelf solution, unless you want to diy it with their own cells. THIS is the direction I'd head for this ultra-light application.

[PNjunction]

Um, ok I guess we're going in this direction now -

I suppose we need a background on testing the claims of various solar power usb charging panels, battery banks, AND wiring considerations. By far the best to weed out exaggerated claims is by this guy, MJlorton:

STC, PTC and spectra

https://www.youtube.com/watch?v=UBUwcTrJRf0

Part 2:

https://www.youtube.com/watch?v=Fij5Iw6F7SQ

General notes about some commercial solar 5v chargers

https://www.youtube.com/watch?v=MgRloFSeWoE

We'll note that he set up extensive testing rigs to find out if manufacturers are exaggerating from either infrared or ultraviolet sensitivity. Many of these panels do "ok" with visible sunlight, but may have much more sensitivity to utraviolet or infrared spectra. You can follow his testing with multiple series of these videos, and actual meet and greets with the panel manufacturers.

He's about the only guy that gets down to real testing, and not just the usual run of the mill backyard camping marketer type which exist by the hundreds. (yawn.

[Mike90250]

1. Encapsulant: I wonder if there is an encapsulant lighter than EVA film. (Any suggestions?)

EVA is pretty magical "glue" It is UV resistant I believe, but not water vapor resistant (that's the job of glass and tedlar)

2. Back sheet: Starting with Tedlar to see if it is lightweight yet strong enough without a PET or other backing material. (Any suggestions for anything lighter?)

EVA film glues tedlar to the back of the cells, and via the gaps in cells, to the front side EVA, when you have a vacuum laminater.

3. Front sheet: Going to try clear Tedlar, and also try to get some ETFE film, 3M Ultra Barrier Solar Film 510-F, and other flexible front sheet material to compare. Unfortunately weight per square meter is not commonly included on the data sheets - I might have to buy and weight them myself to compare. (Anyone does so already, have suggestions?)

"Film" is about as light as you will get, Thicker/heaver = sheet. No idea about actual weight

[Stormwind]

Another quick thought. SunElec.com is giving away de-installed solar roof tiles, U pay shipping.
Freebies not likely to last long, a couple ought to do for camping, if you hurry.
contact John directly per his site:

Thanks @Mike90250!

I found some interesting videos during my research - the most informative one I think was a video from Lensun (a Chinese flexible panel manufacturer) layering (on top of what look like PET backing and EVA film) strings of Sunpower cells, then EVA film, then the ETFE front sheet film. They then rack it, in preparation for heating (to melt the EVA) in a vacuum.

https://www.youtube.com/watch?v=i1eiqMoxqR4

They uploaded some other interesting videos also, including laser cutting of cells, at: https://www.youtube.com/channel/UCcy...Dt0Kl7w/videos

Now I just have to wait for all the materials to arrive for my next attempt (using vacuum cleaner and heat gun or oven). I've also been waiting on some pre-made (but heavier than desired) 5V 6.5W and 13W flexible panels with USB charger to arrive, to compare construction.

My current thoughts:
1. Encapsulant: I wonder if there is an encapsulant lighter than EVA film. (Any suggestions?)
2. Back sheet: Starting with Tedlar to see if it is lightweight yet strong enough without a PET or other backing material. (Any suggestions for anything lighter?)
3. Front sheet: Going to try clear Tedlar, and also try to get some ETFE film, 3M Ultra Barrier Solar Film 510-F, and other flexible front sheet material to compare. Unfortunately weight per square meter is not commonly included on the data sheets - I might have to buy and weight them myself to compare. (Anyone does so already, have suggestions?)

[PNjunction]

Also, in the open source software/hardware community (and similarly the lightweight backpacking community), new projects re-use libraries/components from so many other projects (by design of the other projects) that cross-posting and linking (to ask questions, get expert input for the components, and share improvements) is the norm. For example, check out projects on GitHub and other open source portals to see how it works. In this case, we need more solar PV expertise so we go where we can find it and learn.

I'm familiar with the process, trust me having run Unix boxes for decades and compiling the code from various repositories. Long before Linux became a thing.

BUT what we don't do is spray code all over the place, hoping that the various communites (gnu / linux, freebsd, Openbsd, Netbsd and all the rest) magically come together from disparate codebases. Hence your reference to github.

Thing is, Solarpaneltalk is not github, nor should it be for pet projects picked from other communities, dividing their membership. People and software are different things.

What I smell coming is a big agenda.

Let's review:

1) You want an ultralight solar panel to charge your cellphone while trekking.
2) Commercial units, which are already more efficient / longer lasting, already exist as commodity items.
3) "Development" has stopped or stagnated on your pet project from somebody else's work.
4) You want us to do all your engineering for you, having demonstrated nothing of your own in this field, but mere links to the work of others.

The most practical answer to your maker-toy, is to just eat another bite of a Snickers / energy bar, and carry a proven commercial commodity device with you to compensate for those extra ounces.

[Mike90250]

Another quick thought. SunElec.com is giving away de-installed solar roof tiles, U pay shipping.
Freebies not likely to last long, a couple ought to do for camping, if you hurry.
contact John directly per his site:

[Stormwind]

Humidity over just a couple % sends water vapor right though most paint, rubber, plastic, epoxy. It takes a mm or so of tight metal (not porous aluminum or cast iron)
Tedlar is an engineered plastic that is vapor tight. Glass is also. In commercial panels. tedlar and glass make up 99% of the barriers.

Thanks @Mike90250!

Researching Tedlar, it appears there is also transparent Tedlar film available (though I haven't yet found light transmission or haze data for it yet).

References:
1. DuPont Tedlar datasheet that describes clear Type 2, 3, 4, and 5 Tedlar forms
2. DuPont Tedlar Adhesive and Lamination Guide

I wonder if a sandwich of clear Tedlar, adhesive, solar cell, adhesive, and standard Tedlar backing film would work, be a proper water vapor moisture barrier (assuming properly sealed), and be lightweight. My current lack of access to a vacuum pump or autoclave may make the prototyping process difficult, though.

Edit: I found some light transmission stats for clear Tedlar forms and they look fine (compared to panel plate glass and the light wavelengths, 400nm-1200nm, used by Sunpower cells):

Sunpower wavelengths:
sunpower-wv.PNG

Tedlar transmission % for wavelengths:
tedlar-wv.PNG

.. and that somehow led me to 3M Ultra Barrier Solar Film which is actually sold as a flexible solar PV glass replacement, especially for flexible panels. Apparently "flexible solar front sheet" is the search term I've been looking for.

[Stormwind]

Stormwind - I meant no offense.
So I'll get to the point quickly - it is just UNCOOL to cherry-pick another forum's threads or maker projects, no matter where you go. That only weakens / disperses the original community who may not want to change forums, and will miss the involvement of their members. It results in a disjointed effort jumping back and forth, and may be especially unsettling for those who paid for posting services.

The original posts are on two completely forums by original maker himself. Also, in the open source software/hardware community (and similarly the lightweight backpacking community), new projects re-use libraries/components from so many other projects (by design of the other projects) that cross-posting and linking (to ask questions, get expert input for the components, and share improvements) is the norm. For example, check out projects on GitHub and other open source portals to see how it works. In this case, we need more solar PV expertise so we go where we can find it and learn.

Anyway, good luck with your project. I can't add much more than to say read the DIY Solar Panel sub-forum here for additional clues as to why this type of project is not really practical, but can be more of an educational technical exercise, which is always a good idea.

Thanks, I'll read that forum more too.

As for practicality, there are Chinese manufacturers already selling lightweight flexible panels with USB chargers so we know it is practical: we are just trying to reduce the weight further (since every ounce matters when hiking for a week with everything carried on your back).

Examples of such devices/panels commercially available (found on AliExpress):
1. 13W 5V flexible panel with USB charger
2. 6.5W 5V flexible panel with USB charger
3. Backpack with 10W 5V folding panel with USB charger

From the above examples, it would appear the supporting structure and encapsulant are the main areas of opportunity to decrease weight.

[PNjunction]

Stormwind - I meant no offense.

This forum is renown for getting to the point very quickly, mainly due to helping others avoid a major financial setback, or outright physical danger. This can be overlooked in more social-club forums until it is too late 60 messages down the line.

So I'll get to the point quickly - it is just UNCOOL to cherry-pick another forum's threads or maker projects, no matter where you go. That only weakens / disperses the original community who may not want to change forums, and will miss the involvement of their members. It results in a disjointed effort jumping back and forth, and may be especially unsettling for those who paid for posting services.

Do you know how many of Sunking's posts in other forums would be worthy of discussing here? Plenty, but it would be uncool to the other board to cull his ideas or posts over here, splitting the communities of both.

Anyway, good luck with your project. I can't add much more than to say read the DIY Solar Panel sub-forum here for additional clues as to why this type of project is not really practical, but can be more of an educational technical exercise, which is always a good idea.

[Mike90250]

Humidity over just a couple % sends water vapor right though most paint, rubber, plastic, epoxy. It takes a mm or so of tight metal (not porous aluminum or cast iron)
Tedlar is an engineered plastic that is vapor tight. Glass is also. In commercial panels. tedlar and glass make up 99% of the barriers.

[Stormwind]

Now, having perused the other site and looked at the construction, I'm going to say those panels will have a limited lifetime. None of the techniques will prevent water vapor from getting inside the enclosure and eventually damaging the cells.

Any ideas on a lightweight method to prevent water vapor permeation? One crazy idea I saw online - use Flex Seal Clear to encapsulate the whole cell (though I don't know the light transmission and haze %'s or its chemical compatibility with all the other components).

Would keeping the device out of the rain in a water-proof enclosure (only using it when sunny/no rain) prevent water vapor damage, or does humidity by itself cause it?

The other way the cells are going to fail, is from micro cracking. When wafers are cut, there is damage done to the edge, laser cut, diamond saw, score and snap, all initiate stress cracking along the edge, that propagates across the entire wafer, damaging it. For a DIY experiment, not a problem, but if you are in backcountry, and rely on solar power, you will be disappointed sometime,

Six uncut cells in serial would be about 3.5V at 5.9A - so a less efficient DC-DC boost converter would be needed (if a component exists that can boost that to 5V can be found), instead of the buck-down converter, to avoid cutting the cells at that size of a device.

For cut cells, I wonder which method is the least damaging - I'd guess laser cut. I wonder what method all the small flexible panel manufacturers (mostly in China from my searches) use on their SunPower cells when cutting.

Another line of thought - if the device only lasts 5 years that might be okay - by that time I hope solar PV cells would have made efficiency and power-to-weight ratio improvements (maybe OPV cells) to the point we'd want to build a new device anyway.

[Mike90250]

As long at this is not a scheme to drive traffic to another site, I'm ok with it.

Now, having perused the other site and looked at the construction, I'm going to say those panels will have a limited lifetime. None of the techniques will prevent water vapor from getting inside the enclosure and eventually damaging the cells.
The other way the cells are going to fail, is from micro cracking. When wafers are cut, there is damage done to the edge, laser cut, diamond saw, score and snap, all initiate stress cracking along the edge, that propagates across the entire wafer, damaging it. For a DIY experiment, not a problem, but if you are in backcountry, and rely on solar power, you will be disappointed sometime,