Attaching ebay cells to glass

[Volvo farmer]

So I went to the local glass shop to see what they could do for me on this panel I'm making. They said they can seal the whole thing up like they do with double pane windows, so I might try that. Anyway, he gave me a tube of this auto glass urethane adhesive and said it would be better than silicone to stick stuff to glass. Only one thing, It has carbon black in it and it's conductive. I could not think of why this would be a problem since the glass is not conductive and each cell will only have one blob in it's center attaching it to glass. Is my thinking correct or am I making a big capacitor or something here that will screw up my solar panel?

[Chiron]

A capacitor (non electrolytic) needs to have 2 condutive materials or plates seperated by an insulator, since there's no condutor on the other side of the glass the capacitance, if any, would be very small and in a DC application insignifigant.

HTH

[Tom in NH]

You should be ok. Just be careful there is no unintended connection between the top side and bottom side of the cells. A few blobs of the stuff in the wrong place could mess things up.

I wonder if the electrical properties are such that you could just glue the cells together in series instead of soldering them.  --Tom

[Chiron]

There are glues and epoxies that are conductive enough for electric/electronics circuits, used mostly in microelectronics but I'd guess that windshield RTV is conductive enough to cause problems but not conductive enough to be useful in the connections between cells.

.

[John II]

I have another thought that is not electrically related. And that is... The "blob" will block the light on the PV cell where ever it is applied. This will weaken the output of the cell. Your PV cells will only produce power up to the -weakest link- in the chain. This may not be a significant issue, but then again it might turn out to be an issue? Just a thought anyhow.

Other than that I really like the idea because you are giving each cell a micro shock absorber mount, which is fantastic. I think I'd stick to tempered glass if I could though.

John II

[John II]

And yet another thought (smile)

If I understand correctly most "sealed" windows are filled with Nitrogen gas. When the sealed window finally leaks out the gas and allows air to inter... there is some kind of chemical reaction that takes place and leaves your glass white and chemically etched. This would not be good for a PV panel. In fact I think it would ruin it. I have yet to see a nitrogen sealed window panel last more than 10 to 15 years before it starts leaking (not to say that they don't last longer) I just haven't seen one personally that did. While your glass and PV's should last an easy 40 to 60 years perhaps much longer, a Nitrogen sealed glass enclosure probably won't.

Another problem with a nitrogen enclosure is that the cells may not be able to dissipate the heat they generate. A hot PV cell needs to be able to dissipate the heat, or it will produce much less power.

In my last purchase of commercial Panels manufactured in France, they sandwiched the cells between two tempered glass plates. The back of the panel consist of a white glass plate. It is said that the glass plate quickly sinks the heat off of the PV cells lowering their temperature which drastically increases the panels output on extemely hot days.

Many clear silicon sealants have corrosive abilities that will damage metal and PV's but ideally, if one laid the glass panel face down, placed your strings of cells on top of that face down, then poured a thick layer of UV protected clear resin or clear silicone over it would probably be the best long term protection, but getting something that's guaranteed not to react with your PV cells or the wiring and not yellow after 20+ years might be the tough part.

John II

[Joel]

Your comment about the glass disipating the heat got me to wonder.  I've been using silicone on the backs of my cells which has terrible thermal transfer properties for disipating heat.  What if something like JB weld which seems to have very good thermal transfer properties was used instead.  Anyone have any ideas on how to test this?  I have a tube and a lot of time on my hands...

Joel

[pyrocasto]

If it has good transfer properties as you said, it should work fine. A heat sink adheasive might be a little better though.

[Psycogeek]

using JB-weld here to heat epoxy the 3 watt LEDs, its just a thin layer , because i can actually press the led into the mix.

but its working just about as good as the overpriced arctic silver stuff, but its on very thin, the other parts are aluminum, not copper.

Some of my thoughts on heatsyncs.

Copper is 2X better heat TRANSFER than aluminum

and the other stuff like silver, and the alloys that are designed for thermal transfer are not MUCH better, not worth it anyways.

when you look at a thermal transfer chart the big jump from steal, to aluminum, but to silver the jump is not so big.

so the most practical thermal metal is copper, not the overpriced ones.

then copper Transfers heat, well sometimes you want to get RID of the heat.

so good combinations of pulling it away then getting it OUT into the air, would be copper base, but aluminum fins.  which make up some of the better cheap processor syncs, and the weight is considerably reduced.

i have some cheap taisols, that blew away my total copper syncs that weiged to darn much anyways.

[Psycogeek]

oops , correction

in thermal transfer rates for metals there is a

 big jump from steel to aluminum,

 big jump from aluminum to copper

but very small jumps from copper to the other overpriced metals and alloys.

[Joel]

When you are refering to 3 watt LEDs I'm assuming you are talking about Luxeons.  That is good too, because I will be building a custom LED tail light for a Harley and wanted to use the casing as the heat-sink for the LEDs.  Now I don't need to experiment and waste a $6 LED.

Joel

[Psycogeek]

yes, the OTHER super bright leds are not as good, they are much cheaper but not as bright, or everdrivable.

the star thing under the leds emitter, is sufficient to keep it operational in air (at spec), but for longevity, and to overdrive them and stuff, i usually have them mounted on anything that will pull the heat away.

so in that situation heat transfer is not Critical, like with power regulaters, and processors and stuff.

[Psycogeek]

Jb weld doesnt seem like it would flex one bit, no give for expansion and contraction.

it looks like its just full of ground metals, of some non magnetic variety, i wonder if its aluminum?

[pyrocasto]

I thought it was magnetic because as someone said they glued their magnets down with it, and it seeped up and around the entire magnet!

[Psycogeek]

oops, my misteak, i could READ the package :-)

its a STEEL epoxy, , i dont understand why my fridge magnet didnt like to attract to it, but it does say steel.