Bulging Solar Pannel Its gonna Blow!

[Psycogeek]

Ok so i capped ACE the solar pannel today.

put it in the "clean room" overnight, which has only 30% relative humidity

then i put the top on , sealed every nut bolt , every possible orafice.

BUT

i didnt think it was THAT sealed.

it bulging up in the sun (OH NO!)

its bulged up 1/2" , the picture only partly shows how high it is.

http://home.comcast.net/~tvv0/DSC00765.jpg

it is starting to look like i put a dome on it.

and i still got moisture from somewhere (#&$^#*@!)

http://home.comcast.net/~tvv0/DSC00766.jpg

boy have i still got a lot to learn :-)

Shesa going to explode , or worse yet what happens when it cools down and it starts going convex on me.

[Psycogeek]

ok i put a tiny hole in, and it isnt air, or steam that is bulging it.

it must be the very tight fit on the plastic top. the top fit into the metal corners very tight. i thought that would be perfect.

but , the plastic once it was heated enough (being pushed from the sides) just flexed up.

the plastic is almost 1/4" thick stuff, it really firmed up the pannel, after it was on. i was not expecting it to go liquid (flexable) on me, it was nessisary for the ridgedness of the whole frame, keeping the glass of the cells from being bent under any conditions.

[Volvo farmer]

Just wondering. Have you checked your output with and without the top sheet of plastic on? 1/4" sounds pretty thick and might reduce the useable light that gets to the cells. I took a piece of "low-E" glass and put it in front of one of my panels and the output dropped about 25%. When I put a piece of regular old clear tempered in front, it dropped about 5%. I've heard plexiglass is worse than glass for light transferance so you might want to check this out.

[Psycogeek]

did that test in the other thread.

its about 8% .

right now i can get 3A at 18V or 9A at 6V.  which is close enough to the "rated" specs of the cells to be just fine by me.

i got it charging batteries now, and FINALLY got the:

Motion sensing, Solar charging, Li-Ion storage, LED lights,

Lighting up the kitchen when you go in there.

WOW , after 2 months i got one project done :-(

i think if i every really want to "go solar" i will buy things completed with long warrenties.

[ghurd]

The more air in the PV, the more matter there is to expand with heat.

That is so thick front to back, it could be acting like a solar water heater almost?

Could the pressure be condensing the water vapor?

With the homebrew, I think I am leaning toward a small vent at the bottom.

I am sure I'll stay with factory PVs.

But I am pretty lazy...

OK, Really lazy, but honest!  

Just thoughts.

G-

[Tom in NH]

My panels were designed with ventilation and the plexiglas covers sometimes bulge quite a bit, too. I think its because of uneven expansion and contraction and the plexiglas is screwed down to the plywood around the edges. My feeling is, so what if it moves a little. The condensation is your primary concern, I think. If your backing is plywood, and if it's not hermetically sealed, you won't be able to prevent humidity from eventually working its way through the plywood. If your panel is hermetically sealed, you might have luck putting it in a walk in freezer and letting it cool down before you plug the hole you drilled. Cold air holds substantially less moisture than warm air does. If you can seal it with cold dry air inside, it will be very dry and way less prone to condensation when you take it out of the freezer and let it warm up to normal.

I'm always telling myself to buy panels ready made. They're cheaper that way and probably just as good as homemade. Then I go out and buy more plexiglas and solar cells and plywood. Is there a name for that mental illness? I guess I just like the smell of solder fumes.

--Tom

[Psycogeek]

yes it is too thick, even though the base is on the inside of the metal frame.

that means more air of all types inside it to have 'issues' with.

i didnt really know how high to make it, or if i should slide the plastic in under the frame instead of on top.  but this way at least i can disasemble it in mere minutes.

if i was ever stupid enough to do this again, i would use a nice aluminum backing, instead of the thin wood, with engioneered bracing, specially when i aint no engioneer , nor can i even spell it.

[Psycogeek]

ahh so it isnt just me.  i cant figure out who would sell a plexi-glass window , if it was going to bulge out like a solar skylight :-)   but i guess its because of the high heat of the solar cells themselves.

guess that is one more 'factor' in glass or plastic discussions.

[ghurd]

I don't believe the cells will gain as much solar heat as something flat black.

The whole RE idea is a sickness.

I have well over, well lets just say 'KWs' of solar here.  (I sell them)

Here I pretty much just run my cell phone, lab batteries, etc from mini solar.

Can't afford real solar.

So why can I afford well over $1000, maybe over $2000 for wind?

I live in a bad place (city) for it.

And I think small is cool.

The smaller the better.

My biggest success so far is 'around' 3/4 amp at 12V.

That is 2 Grand for 8 watts.  $250 a watt!

What was I thinking!

Honestly, the 8 watts cost about $8 with all brand new parts.

Except the tower, tail and stuff, that is all junk from the garage.

So there must be 1992W of parts here!

And the shop is all solar, except 8W of wind.

G-

[DanG]

your 8% loss w/ the strength of 1/4" sheet cover seems a good compromise. Usually for the same application glass will add 2-3% loss over equivelent plastic just because of greater density.

I got to change alot of lexan and plexiglass from graffiti damage while working and speculate we are erring in 'fixing' polycarbonate glazing. The outdoors stuff I got to work with always had frame pockets 3/16" or more greater on all sides of length-width of plexiglass to allow for lateral expansion. Also it moves alot 1st few heat-cooling cycles and binds up in a equilibrium spot between the two extremes until the seasons change. Polycarbonate expansion per degree F between 40 and 140 can be major!

Coutesy of ceebaileys.com

Whenever screws or bolts are used through holes drilled in the Plexiglass as for the securing of an aircraft windshield or window, consideration should be given to the expansion or contraction of the Plexiglass as effected by changes in temperature. Plexiglass expands or contracts with temperature at the rate of 1/16 inch per foot per 100 degrees F. temperature change. For example a line of holes at the top of the windshield 36 inches across using a 1/8 diameter. screw would require that the holes be 5/16 inch in diameter to take care of a temperature spread of 100 degree F.. When holes are drilled with insufficient clearance excessive strain is placed on the windshield and may cause the holes to crack out at high or low temperatures.

Putting cover glass on loosely for a day or two and tightening it while the whole assembly is sun-heated might reduce the moisture while easing expansion warp;

If  plexiglass indents you're over-tightening;

Use a finishing washer (http://tinyurl.com/8tz98) even over trim plate pieces;

Make sure the plexiglass holes are at least 35% oversize of the fastener;

Use 32-TPI hardware for even low tourqes;

Silicone dielectric gel makes a great lubricant & helps weatherize seals..

For my panels I am tempted by single sheet tempered glass cover and laminating the cell strings to it w/ sign plastic then casting fiberglass resin over it and puddling it into a aluminum frame for mounting. The laminate would keep resin from infront of cells and make access easier for repairs & no back plate to retain heat...

[Psycogeek]

well sombody coulda mentioned that BEFORE i choose plastic :-)

if it expands and contracts in the heat, its really going to bow the whole thing, warping the frame along with it.

the glass cells are STUCK on the farme with 4 lines of silicoln sealer, which will give it a BIT of flex.  but these cells were rejects, and they have been crumbling like a cookie.

if that top cover KEEPS flexing 1/8" (1/16th per foot) i forsee more glass cell damage :-(

[DanG]

I've got a sheet of lucite-tuf .177" 36x72" I haven't cut yet just because I'd have to post whatever may happen with it : )

[Psycogeek]

Update.

each very hot day, with full sun, the plastic rises a bit during the hot day.

when it cools it goes down, but not FLAT, like it was when new, so the movement up and down is about 1/4" -3/8" approx.

[pyrocasto]

Well at least you know it's sealed. ;-)

I need to replace the glass on mine, but dont know for sure if it was the heat or an uneven frame that broke it...