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Flexible Solar Cells

7K views 34 replies 13 participants last post by  aeroscott 
#1 ·
Has anyone tried those new "flexible" solar cells?

I've been installing regular silicon cells (polycrystaline) on my cars for while now, and I have never had a problem with them, until these last three snow storms we had. One of my hoods actually collapsed from having almost three feet of heavy, wet snow on it (and of course all the cells cracked and broke) but my other car, which hardly had a foot of snow on it came out looking like this.

I'm not sure if they cracked due to the weight of the snow bending the hood, or it was temperature related.... but I'm willing to bet it's the hood bending from the weight. I used 2-part epoxy to hold them onto the hood, then two coats of non-UV clear on top of them to protect and seal them.

Does anyone who tried this have any ideas, or should I just go with the flexible panels that they are now selling??? And how do they make the panels flexible? If they are crystaline cells, then won't they crack as well?

- Paul
 

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#2 ·
Has anyone tried those new "flexible" solar cells?

And how do they make the panels flexible? If they are crystaline cells, then won't they crack as well?
There are some variations in the 'how' question .. but in short , some are not crystalline ... these can be very durable ... some will not crack ... they can still be damaged and stop working ... but some of them can take allot of flexing and allot of punishment.

Don't forget the roll the adhesive will play as well ... the adhesive will also have to allow for flexing ... if the adhesive cures ridged, it will impair the ability of the flexible cells to flex.

Now for the bad ...
The flexible cells are significantly more expensive $ per watt of power.

The flexible cells are significantly less efficient and will produce less electrical energy under the same conditions and coverage.

Many of the flexible cells degrade much faster over time than the crystalline variations do... so 20 or so years from now don't expect the same kind of 80% initial power output many of the crystalline style cells offer.

So there will be a trade off.

Are there specific flexible cells you are looking at?
 
#3 ·
Here's what I don't understand...

I know that thin film cells can easily be made into flexible materials, because they are essentially sprayed on (there's more to it than that, but...)

The problem is that thin film isn't worth using on cars because the efficiency is extremely low (maybe 7% ???) and would not even make a difference for your batteries. Now take a look at these:

http://cgi.ebay.com/NEW-80W-Flexible-Mono-Solar-Panel-12V-Battery-Charge-/130486935588

These are monocrystaline cells, but they are flexible. Now, from what I see, they are basically the same type of crystaline cells that I have on my car. How come those give a little, and mine wont? I tested the epoxy, and it gave a lot more than the cells did. It didn't snap until well after the cell did.
 
#5 ·
The problem is that thin film isn't worth using on cars because the efficiency is extremely low (maybe 7% ???) and would not even make a difference for your batteries. Now take a look at these:

http://cgi.ebay.com/NEW-80W-Flexible-Mono-Solar-Panel-12V-Battery-Charge-/130486935588
From the pictures ... it looks to me like the cells are ridged , and the panel flexes at the joints between cells... so the panel is flexible but not the cells themselves... But some of the usual details are missing ... like power warranty information ... craftsmanship warranty information ... amount of flex tolerance , etc ... You can always write them and ask for more details... but without additional details I would not risk the ~$433 for 80 Watts ... ~$5.41 / watt is not particularly good.

I agree the true flexible cells are low efficiency , high cost , high degradation.... but high flexibility and high durability... it is a trade off.
 
#4 ·
How well were they sealed. Is it possible water seeped in under the cell and froze breaking out the cell area? Also wonder if the issue could be the uneven application of a hard epoxy and thermal expansion of the under laying metal that caused the cells to crack.

I would be skeptical of the flexibility implied in the picture if the cells used are Monocrystalline. The majority of flex would be between the cells not the actual cells. I think they mean they are encapsulated in a flexible medium.
 
#9 ·
I know, I though of that but it's a shame that you have to stiffen a stock hood.... you think they would have built it to withstand the elements from the factory :mad:

Although you can't really tell in the pictures, the hood itself DID get permanently warped from the weight of the snow. Dang shame.

On the flip side, the cells are pretty cheap... about $2 each. I've broken them before (by accident), but never that many at the same time! I think a really, really, really heavy coat of clear may help.
 
#10 ·
PZigouras

I like the idea of incorporating solar cells to my project and interested in how this turns out as far as the best way to install and seal the cells on top of a car.

I was thinking of just running them to the 12v aux battery to reduce the power through dc to dc conversion and in affect draw less power from my main pack. I would be interested in the results you have seen in real world application and where you purchase your cells.
 
#11 ·
PZigouras

I like the idea of incorporating solar cells to my project and interested in how this turns out as far as the best way to install and seal the cells on top of a car.

I was thinking of just running them to the 12v aux battery to reduce the power through dc to dc conversion and in affect draw less power from my main pack. I would be interested in the results you have seen in real world application and where you purchase your cells.
Are your solar cells powering your 12 volt battery or traction pack?
 
#12 ·
I use 48 cells (24 x 2 in parallel) in this car to charge my 12V accessory battery. I actually never have to plug in the 12V charger, because it gets almost 100 watts continuously when I park it outside.

My Explorer has 150 cells (about 80 volts total) that charge my 144V primary battery pack. I push the 80V into a low frequency 2;1 transformer then rectify it to get about 160V worth of charge. There's no charge controller so, in theory, it could someday overcharge the pack, but that'll take weeks.... so I'm not worried about it. Plus they are flooded batteries, so I don't think they really care too much about a few extra volts.

- Paul
 
#14 · (Edited)
These flexible rollups are very low efficiency. And actually using any solar cell is not really worth it for a car. EXCEPT the bragging rights as you can very easily convince passersby that the solar cell contributes A LOT to running the EV and they also will assume you are running for free.

Francis
 
#17 ·
Don't get me wrong, I am a solar guy and off the grid and have 109 x 195Watt panels, 9 charge controllers, 3 inverters, running my welding/fabricating shop and plan to charge my EV Yaris with solar.

But for me my 144v pack charges up the Aux Battery through the Dc/Dc converter and I will have a small solar panel on the dash to keep the Aux battery feeding electrons to the clock and misc stuff when parked. I figured it was such a trade-off sacrificing the Aerodynamics of the EV by mounting large panels and so little to gain.

Francis
 
#18 ·
Here is something that seemed to work for short trips:

http://evalbum.austinev.org/838

According to their website:

"From June to November 2000, 2001 and 2002 the SBB traveled an average of 50-80 miles per week using only energy gained directly from the sun (about 10-15 miles of free driving per day). It cost literally nothing to drive and produced virtually no air pollution for a period of six months each year."
 
#19 ·
flexible solar cells are a great new technology. Im loving how the solar energy generation technology just keeps advancing, and not only getting better but getting cheaper too. For starters it was the regular solar panel, then its the solar concentrators, then also the portable solar panels, for camping and such, and now thin film panels that can be moulded to fit all sorts of interesting new applications. Whats next?
 
#20 ·
I was thinking of a 1kw array on my ranger . at 5.9 hours/day yearly average sun at full power . 10 days would be a full charge (50kwh). better in summer and much less in the dead of winter . thinking of glued on clear coated monocrystalline cells with a fold-out set to augment output . cell weight is not much with out glass .
 
#22 ·
fold out might not work in a crowded parking lot , unless going vertical . I was heating the glass on a broken solar panel comes loose at about 250f. and noticed how incredible the cells look . The color shifting iridescence are so cool .Just need a way to protect them as in clear coat that lasts or is easily replaced .
 
#26 ·
Many epoxy resins break down in sunlight without another protective coating over them. There may be better alternatives.

I don't think the epoxy in the back was an issue, because the cell itself blocks almost all the sunlight from hitting the epoxy. I think the encapsulation (top coat) was a bigger issue.

I only sprayed the equivillant of ONE layer of clear coat over the cells, so they were not encapsulated really well. I have a feeling that if I had sprayed a very thick layer... maybe 3 to 4 coats, they may have flexed with the hood and not broken.

I tested this out today by putting several layers of clear tape on both sides of a cell, then bending it. Although it did eventually crack, it flexed MUCH more than a regular cell, which crumbled almost immediately. I am going to re-coat the rest of my cells after I replace the broken ones.

One more thing... if anyone is going to try this, be aware that MOST automotive clear-coat has UV protection built-in, and I think that you should NOT use those. They do make non-UV clear coat, but it's hard to find... make sure you ask. I'm sure the UV-protection blocks out a good chunk of the spectrum, not just UV.


- Paul
 
#27 ·
Yes I was talking about the top coat. As to auto clear coat, the clear coat without UV inhibitors may also yellow and break down. Look into that before you apply it. I would not expect a thin layer of resin of any type to add much strength to the cells, thicker coats tend to be less flexible, not more. Bottom line is if the cells don't respond well to flexing the answer is to reinforce the substrate to reduce the amount of flexing. Stiffen up that hood.
 
#30 ·
Since the snow actually collapsed part of the hood itself, strengthening the hood goes without saying.

Funny thing is, when I stood on my old 1984 Firebird's steel hood, I caved it in. When I replaced it with a fiberglass hood, believe it or not, I could actually stand on it just fine. I think I may wind up going with a glass hood and then stiffening it up a bit... it will still weigh less than the stock hood, with less flex.

I believe it was a GlassTek hood... very well-made
 
#35 ·
I hooked up 700watts of 32v panels to my charge controller ( trace C40 DVM) on the 12v system . The panels just pull down to the battery voltage . In this case you loose the amperage of splitting the voltage and doubling the amps . Back to the point all you need is a low voltage and high voltage cutout .
 
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