Will that be paper or pastic (or glass)

[Psycogeek]

There was the question about using plastic or glass on the top of a solar assembley.

and of course I had to decide which to use.

i REALLY wanted plastic, because its light weight, and less breakable.

so i got to the point where i could test that aspect of it,on ACE, the test pannel and came up with these results, using whatever i happen to have available.

plastic sheet dirty 12%

Plastic sheet with psudo light rain still on it 10%

plastic sheet after cleaned as best as i could 8%

doubble pane argon filled thermal window 20%

cheap plastic diffusion for florescent lights, pyramid style 33%

(this is used to diffuse florescents but not milkey)

because the 2 pane glass was so poor, i would wonder if parts of it were because of its reflectivity. and that a primadonna COATED optical glass, that is more "clear" and less reflective of the light hitting it would help.

anyways, unless somone would like to say "boy that was a dumb test, glass beats the snot out of plastic"  then i am choosing plastic.

[scottsAI]

You need to test single pane glass.

Must have NO iron. (most window glass has iron). (look at the edge, look green)

Is this for solar electric?

Heat may be a problem with plastic. What temperature does it melt?

The two pane argon filled thermal window is designed to block the heat/sun from passing through. Gives a higher R value this way. People like me pay good money for the windows to work that way!

Have fun.

[Tom in NH]

I have been meaning to do similar testing. What exactly are you measuring with your percentages? Your results confirm my hunch that the plexiglas sheets on my panels yields more electricity than I would get if I were using window glass.

Thickness may be a factor. ScottsAI is right that single pane glass needs to be tested. It would be interesting to compare the low iron glass (very expensive) and regular window glass.

Over time, the plastic coverings may degrade while the glass will not. When you decide which covering is best for you, you will likely consider all the different trade-offs, price, age degredation, resistance to breakage, light transmission, availability and what else?

Tom

[Psycogeek]

indeed it was duel pane, and DESIGNED for insulative value, not light transmission.

but that was all i could find. :-(

tests were done dead shorting, and testing for total amperage of 6x.5vx3A pannels.

calculations were done and values are the loss from the topping, VS the cells being totally exposed.

Light levels (sun) were enough to get 87-92% of total stated short ratings.

i can get a pane of glass but it will end up kinda wasting that money if its RELATIVE to the plastic.

IF the glass will lose say 5% and the plastic 8% then i am ok with that loss.

but IF glass that i can purchace locally for fair prices would have only 1-2% loss then i might think about using glass instead.

i know that the plastic will yellow, become brittle (as glass) , and scarred, and wasted, but the design is such that it can be removed , tossed out, and replaced.

the IDEA is if the glass breaks then i am going to be getting 0%, because these cells will be another 500 piece puzzel.

i forgot to add one. A very THIN piece of heat shrink clear plastic had Major loss at 25-30%, designed for Packaging, it probably has UV protection in it??

i didnt get to test automotive waxes, the darn wind was making solar Kites.

[scottsAI]

Some stuff I found on the web:

The glass cover sheet should be “low iron”. Iron is a contaminant of glass that absorbs solar energy and gives the glass a greenish tint. Low iron glass will be vodka white when viewed on edge.

The cover sheet should be “tempered glass”. Tempering greatly strengthens glass and if it does break, it will break into small pieces instead of large dangerous shards. It is just too dangerous to work with untempered glass and usually not responsible to those underneath.

Redwood Plastics distributes and /or fabricates acrylic or plexiglass sheets. Acrylic or plexiglass sheet in its natural form is an optically clear plastic, transparent, lightweight material having outstanding weatherability, high impact resistance, good chemical resistance, and excellent thermoformability and machinability. Acylic or plexiglass sheet has a light transmittance of 92% and is 8 to 10 times stronger than glass of the same thickness.

G3241 Solite Low-Iron Tempered Glass

34 inch x 96 inch x 3.3mm, for glazing or panel glass replacement

This type of glass has proven to increase solar gain and heat production over plastic glazing.  $143.

Iron-oxide content: 0.01%

Transmittance: 91.0%

Based on the transmittance, they look the same.

Your test showed different clear materials gave drastically different results.

Solar cells do NOT use UV, nor IR. They use a narrow frequency in the visible spectrum.

Iron in the glass cuts down by 10% the light the solar cells needs. Still looks clear.

FYI; Most solar panels are made with glass...

Have fun.

[pyrocasto]

You dont have to use no iron glass, it would just help. Building your own panels it would be better usually to use regular, since the tempered is so expensive.

I would suggest using glass though, since it will last longer without fading like plastic has a tendencey to do.

[Psycogeek]

well then doesnt that solve my problem

i will use some good plastic for now, especially when moving it all about, and testing.

one last question for ALL

can this "tempered" glass be cut locally by my local glass dealer?

[DanG]

Tempered means one chip and the whole thing shatters. Standard glass is cut to size, heated & then tempered by massive cool air flow.

Since glass is denser then polycarbonate count on 2% more losses installed, but a few years the polycarbonate will be scratched, pitted, warped and fogging while the glass will be the same as the day you put it in.

Unless you're burning yak fat for light and heat take the time to get tempered glass -

If you're thinking temporary just use old storm window glass and make odd cell count panels, like three 24-cell panels each in 4x6 array for 25"x20" for 24V, or two 18-cell panels in two cell rows of 5 and two rows of 4 for 16"x25" - since its temporary you can go as low as 32 cells and up to 40 cells for each 12V section but remember if you start running them serial to get 36V or greater your charge controller may see overvoltage and shut down charging, but most 24V chargers will accept up to 60V input.

I say old window glass because the IR / UV coatings have only become popular as they've tightened up the energy savings in the 80's and 90's.

A temporary polycarbonate panel will have enough bounce to it the cells inside could get smashed from vibration while glass has just teeny give to it...

[ghurd]

I know some shops can cut it.

But most can't.

Plexi or acrylic has 1% better transmission anyway.

Probably cheaper too.

And some new solar (thin film) uses other spectrums.

but I still like crystal more.

[Psycogeek]

yup the stuff flexes a LOT. but then it dont break either.

a little trick sombody showed me HERE, is going to reduce the flex.

i have left a CROSS shaped gap in the cell sets, and will put a rubber buggy baby bumper in the center, and then make sure it doesnt make shadows, mabey taper it a bit. that will keep the plastic from getting anywhere neer the cells, in the case of baseball injury, or low flying dodo birds