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

[Stormwind]

And for good reason. Surely the members at the backpacking forum are aware of phony participation with the sole intent of providing marketing links to attract web-search rating hits, and not to truly participate or promote the forum they are spamming in any intelligent manner.

No one is trying to give anyone free advertising - I posted here because (1) there is much more solar PV knowledge here that could help iterate the design, (2) RyanH isn't even subscribed to the BPL forum anymore so he can't post there but could post here (and the second link was a Facebook post), and (3) I prefer open forums and non-paid ones myself so I was hoping the discussion would occur here instead.

I also did not want to "copy and paste" RyanH's posts (I saw a previous post on this forum where someone was criticized for it), which is why I put in a link to the post rather than copying the contents - as links are meant to be used. And it would be wrong to copy-and-paste rather than link without RyanH's permission.

At the very least, if and when you do this, extend the courtesy in the other direction by posting a link directly back to SolarPanelTalk *publicly*, and not to this thread, but to the site in general at least. Some of us may be watching to see if that link is removed.

There was no intent here other than starting the discussion here with knowledgeable, interested solar PV folks and iterate on the design.

I added a top-level link to SPT on the BPL post (of which I have no affiliation other than a poster), but I'm not going to remove the link to the post and force people to try and find the post themselves (very user unfriendly and discouraging of participation) rather than just click a link to it.

I hope other new users get a warmer welcome on this forum. This was posted merely in the spirit of cooperation and people working together on making things - not competition between forums/web sites.

[PNjunction]

P.P.S. This is DIY/MYOG (Make Your Own Gear) - it used to have more links to actual and possible components used in making the panel but admins considered them advertisement links and removed them.

And for good reason. Surely the members at the backpacking forum are aware of phony participation with the sole intent of providing marketing links to attract web-search rating hits, and not to truly participate or promote the forum they are spamming in any intelligent manner.

I also note the backpacking forum doesn't even allow posting unless you subscribe! It is READ-ONLY, until you pay up for a subscription.

Generally, on most forums, one can refer to another forum/blog etc, but it is usually frowned upon so you aren't seen as a promoter from the other site - ESPECIALLY if it involves a subscription or other form of monetary compensation to make a post. In other words, don't do it unless you absolutely have to in order to keep some semblence of professionalism for all involved.

Would RyanH be upset if I paid for a subscription, and posted nonsensical questions about whether square pockets are better than circular pockets on my diy backpacks made from discarded ladies' handbags along with a link to where you can get them?

See what I'm saying? Maybe ask the moderators of that forum how they feel about getting free advertising from a solar site that is not based on a subscription model to even make a post.

I'm not trying to be a self-appointed forum cop here, but this is just basic general forum courtesy that has been in effect for many many years on most forums...

At the very least, if and when you do this, extend the courtesy in the other direction by posting a link directly back to SolarPanelTalk *publicly*, and not to this thread, but to the site in general at least. Some of us may be watching to see if that link is removed.

[Stormwind]

A related question: does anyone know what backing material and cover material/encapsulant is used on the flexible solar panels (using SunPower Maxeon cells) that are commercially available?

Example - ApolloFLEX Mono-TL 300W Flexible panel (there seem to be at least several brands):

ApolloFlexMono300Panel.jpg

From the limited pics I have found, it appears to be a semi-rigid flexible plastic backing panel with clear plastic over the cells.

I'm hoping that information can help us with ideas for the lightweight backpacking USB charging panel.

I found a description of materials for one manufactuer's flexible panel: they use aluminum backing, EVA, and ETFE film and claim others use PET for backing and film:


LensumFlexiblePanel.jpg

Which leads to the question: for a needed strength/rigidity, would carbon fiber, aluminum, or PET be lightest (and at what thickness would be needed)?

[Stormwind]

Hi all,

RyanH has made great progress creating ultralight solar PV USB charging devices for lightweight backpacking, greatly beating the power-to-weight ratio of commercially available systems (like the Bushnell PowerSync SolarWrap Mini using Powerfilm cells).

Anyone have any suggestions on improvements? (Please post here, not at forum links below)

A high level summary of components (if you prefer not to follow the links below):

1. SunPower Maxeon cells due to their light weight and solid copper backing, increasing their strength and decreasing need for additional stronger backing. Cells are half or quarter cut to get to V and A needed for DC-DC converter
2. Depron foam backing due to combination of light weight and stiffness (but may not be durable enough)
3. A specific DC-DC buck down converter due to light weight, efficiency, and Apple charging support
4. A lightweight covering/"encapsulant" (spray-on) to reduce weight vs plastic films or glass

RyanH detailed an earlier device (2.75oz, 21W max theoretical, about 10W-12W in real usage) here: Backpacking Light forum


He detailed a newer device (1.7oz, 9.4W max theoretical, about 6W in real usage) here: Facebook group post


ULSolarPVUSBCharger2.jpg


Some thoughts:

1. DC-DC USB converter: If we could find a converter like the Adafruit VERTER 5V USB Buck-Boost converter that could boost lower voltage and operate in a V and A range produced by the cells, the device might also produce power in lower power conditions. (The design avoids a battery to reduce weight since the devices being charged already have their own batteries.)

2. Series wiring of half and quarter cells: The cells are half or quarter cells wired in series to get the V and A into a range supported by the DC-DC converter. Of course, this means any shade cuts off power production, but the high power-to-weight ratio and strong solid copper backing of the SunPower Maxeon cells makes this trade-off worthwhile currently.

3. Carbon fiber vs Depron foam: RyahH reports the foam might not be durable enough after a long hike with a device on his pack. Carbon fiber panels or a combo of carbon fiber and Depron foam (which is disappearing from market due to manufacturer) might be worth the heavier weight trade-off. (Many of the structural ideas are from the lightweight RC airplane community.)

4. RyanH has tried many different lightweight encapsulants/protective coverings for the panels - Freeze-Tite and Krylon Clear Gloss spray paint for example - but reports some scratching on his panels during his last long hike with the panels hanging off his pack. Someone else reported success with Flex Seal Clear. I don't know the light transmission, haze, or chemical interactivity stats of any of these.

Thanks!
-Jason

P.S. I emailed RyanH a link to this post - he's provided lots of great info to me via email. The photo is also from RyanH.

P.P.S. This is DIY/MYOG (Make Your Own Gear) - it used to have more links to actual and possible components used in making the panel but admins considered them advertisement links and removed them.