Author Topic: Making decent solar panels part 3 (Read 101753 times)

oztules · « **Reply #198 on:** September 08, 2011, 06:06:15 PM »

Nothing sounds quite right.

80% is no good if your pump can go 100% vacuum. 80% of whatever the pump can do means leaks.
If your pump can only get to 80% vacuum without leaks, then that is diffferent, but your pump looks like mine, and should be good for very near absolute vacuum.... so you can have no leaks..... and your bag pressure should be at the end of the gauge. If your wicking material is very good, you can stand some tiny leakage, as the pressure can still be distributed very quickly.... but no leaks is the best by far.

Your oven is very patchy from the sounds of it. You need gentle heating (why I used a fan heater... lots of warm air, not small amounts of very hot air to achieve the same temperature.), without localised hot spots, or the hot spots will melt your bag. Thickness is not a problem, temperature is, and there will be very few bags that can't stand boiling water temperatures and a bit above.... so I think localised heating from your elements being too hot, and radiating heat to the nearest plastic...... melts.

You have mentioned your aggi pipe...... good idea, but you must have wicking material for the vacuum to move the air through. What are you using for the wicking material?... do you understand it's use and reason for this material to be there? and why it won't work without it.

................oztules

dave ames · « **Reply #199 on:** September 09, 2011, 01:10:42 AM »

Quote from: Algie on September 08, 2011, 02:44:30 PM

I trid another experiment with no success again

any ideas are mostly welcome cause getting on the fringe of breaking everything

Theres good news here Algie..that is, things can only get better from where we are now!

One observation we found when using a metal oven is that the plastic bag wants to be kept away from the hot metal parts of the oven..we found that a towel or some cardboard is usefull to keep the vacuum bag away from the hot rack.

This all seems odd that metallic parts would melt a hole in the bag and the air (at the same temperature?) would not. But that's how it seems

Keep at it and things will improve

It would have been very easy to miss some important points during the first read through these tutorials..can't hurt to review all three parts of this series by our friend oztules to compare your methods?

Kind regards, dave

Algie · « **Reply #200 on:** September 09, 2011, 09:40:10 AM »

Hey guys ................. thanks for your feedback and attention at this desperate stage $:-\$

let try and make a detail report with pics

Well i think the plastic is too near to the elements so i opted to add the height of the oven, the distance from the elements to the pastic is less than 3 inches overall height of the oven is just 4 inches.

i shall increase the height by another 4 inches and see what happens..................

Algie · « **Reply #201 on:** September 09, 2011, 09:50:51 AM »

i thought so cause the bag inflatted after 30 - 45 mins so the problem there has to be solved..................

as regardings to the vacuuming of bag i still have to get it at 100%

what do you think oztules as to wicking material do i still need it

?

attachment 2 is after the cook i still think where the pipe enters has to be improved and i have no ideas for there

attachment 3 is the maximum vacuum i got ( 0 is full air in )

oztules · « **Reply #202 on:** September 09, 2011, 08:52:29 PM »

A picture is worth a thousand words.

Yes your elements are too close, perhaps a diffuser between them and the panel may help even out the temperature..... but....

Your biggest single problem is NO wicking material. Your aggie hose will do a good job.... right up until the plastic gets a little vacuum.... then it will stick together by the atmospheric pressure, and you can't transfer the vacuum any more.

Place a beach towel or some other thick porous material inside the bag on the cell side. Make sure the aggie pipe is embedded in this... This way, the air can move between the cell backing and the plastic bag... and it will work.

Even if you didn't get the elements far enough away, if it didn't rupture until 35 mins or so, and if you had of had the wicking sheet/blanket/towels in place, you would have gotten a half decent result..... even with not getting the sealing right, it would have yielded a much better result..... bottom line is

you must have wicking material in there to spread the vacuum evenly. It is the single most important thing to getting the vacuum process to begin to work.

You'll know if it is working, as the beach towel will feel almost like a rocky material when the vacuum is pulling it fully on. The pressure is enormous.. more than 13lbs/sq inch (or more than 450lbs per cell) It cannot work without the wick material to spread this about. It needs to be reasonably thick so when it gets crushed, it can still have air sneak through it if need be.

The air pipe input..... if that is where you losing seal, then use a heat gun to soften the plastic bag, and anothe wire tie (different orientation for each one as there is a small gap where the feed through is.

As a test, pull your vacuum on and spray some water around the seams.... and the wire tie area, and see if in fact it is there or somewhere else... the water should seep into the cracks in this case.... showing the flaw in the seal..... place you finger over the hose end to see of there is a leak in the vacuum line. It should take the gauge all the way.

Look at your cells in your top pic, there are air gaps all over the cells even. It cannot work without a medium to move the air. Where the creases are in the plastic, I'll bet there is some movement if you tug at them... with wicking they will be rock hard with no movement, and much thinner in profile.

Your so close now....

................oztules

Algie · « **Reply #203 on:** September 10, 2011, 02:51:51 PM »

To Oztules and dave

what thickness of bag did you use...

?

Im still choco bloc i have increased the height of the heating elements by 3 " and the bag is still bursting after 30 mins cooking i dont thickness of the bag is good for this job its 250 microns.............

i only found 500 miroons plastic which is black and cant see through which i dont think its ideal for the job ...........................

oztules · « **Reply #204 on:** September 10, 2011, 06:58:47 PM »

Melted plastic is melted plastic... thickness just delays the inevitable..... perhaps series the hotplates so they can't get red.... just hot.

You need to solve the wicking , then the temperature.

Let me make this clear. ............this will not work if you dont get the wicking to solve your woeful vacuum technique. Without it your aggie hose is a waste of space..... and with it the aggie hose is next to useless to... but a nice touch anyway.

If your melting the plastic, then 30 mins is probably enough anyway.

wicking wicking wicking......... thats why your failing....... and you are so close to getting it...... solve the wicking.....and get some good results.

Re-read part 2.... and understand why you need that rag in there.

...............oztules

Algie · « **Reply #205 on:** September 11, 2011, 06:37:49 AM »

Yes mate you were right i embedded the glass with a beach towel and increased the vacumm to 95 % still not 100% due to closure of the bag with the pipe the reason is that the plastic is abit tight to close with the pipe i heated also the edge but still not 100 % closed will have to treat theis problem in another way

THe wicking made a whole difference ........................................

dave ames · « **Reply #206 on:** September 12, 2011, 11:48:21 AM »

Hi Algie,

Great to hear you have some progress! Any chance you can find some large contractors garbage bags? ...the bags I've used are only 2 or 3 mils thick..your 250 micron bag is is three times that thickness... and may be giving you more of a challenge to seal?

seems you are sealing part of the bag opening with a heat gun? can you bring the entire opening around the vacuum hose and seal the whole bunched up end of the bag?

I suspect your heating elements are running as full on or off with the thermostat control? the intense radiant heat may be too much and would try to limit their heat output somehow...maybe we can series them in twos or all four in series to tame them a bit.

getting close now!

cheers, dave

Algie · « **Reply #207 on:** September 13, 2011, 10:33:10 AM »

heheheh im testing the .5mm plastic ( 500 microns ) as a bag works well does not stick after and does not melt found it far better still working on it and testing it

modified the heaters i made them up by 3 inches more will post pics soon

2011solarking · « **Reply #208 on:** September 14, 2011, 12:02:45 PM »

Oz
Could you publish the data of the vacuum device?
Where do you find it? what kind of workshop?

VERY NICE DIY!!!

dave ames · « **Reply #209 on:** September 14, 2011, 12:33:23 PM »

Hi 2011solarking,

Welcome to the group!

I agree this is a very nice DIY, Did you see that there are three parts to the oztules panel series?

http://fieldlines.com/board/index.php/topic,145005.0.html

I think he covered all the bases even about his two stage vacuum pump. I've had some luck with a cheap Harbor Freight single stage job we had around.

Hope you find the forum archives as valuable as I have.

Fun stuff!
Dave

2011solarking · « **Reply #210 on:** September 14, 2011, 01:26:05 PM »

hi Dave
I know all parts.
I cannot find the vacuum device data.
Could you give me the yours?

thanks!

dave ames · « **Reply #211 on:** September 14, 2011, 02:09:24 PM »

2011solarking,

Here is the one I have:
http://www.harborfreight.com/25-cfm-vacuum-pump-98076.html

Don't think I paid more than $50 for it some time ago. I used it because I had it and if we were buying new for this solar project might go with the two stage pump to be sure..most especially if one were to be making larger panels with it. (I've only messed with making some smaller modules)
http://www.harborfreight.com/two-stage-3-cfm-air-vacuum-pump-66466.html

Some folks won't know what you are talking about unless you call it a HVAC pump.

cheers, dave

Algie · « **Reply #212 on:** September 15, 2011, 02:47:14 AM »

im using a single stage vacuum pump its suffucent to vacuum a bag.................

Old Greybeard · « **Reply #213 on:** October 16, 2011, 01:07:16 PM »

First of all, this is my first post; I joined here because I found this superb thread on EVA encapsulation - many thanks to oztules for the pioneering work and experimentation.

I already have some semi-flexible solar panels, from Sunflex in China. They are aluminium sheet, then EVA, then the cells, then another layer of EV with a layer of some kind of plastic on the front. They are ideal for my purpose (the canopy on a solar powered small boat) but I'm now looking to make some custom shaped panels to fit the deck areas. These won't get walked on (the deck is only 4mm plywood) but the panels do need to flex enough to take the deck curvature (maybe 30mm over 800mm, so not much).

I'm wondering if I could use this DIY process but using acrylic instead of glass. I know acrylic works just fine from a light transmission perspective, but I'm not at all sure whether it would tolerate being cooked without marking. My plan would be to get a big glass sheet, lay the acrylic on it, then use the method oztules has devised, but with the EVA only bonding to the acrylic (I may need to mask around the edges if the EVA flows out.

If anyone has a feel as to whether or not this adaptation might work I'd be grateful. I already have some 2mm acrylic sheet and a big pile of Evergreen 3" x 6" cells, I just need to get some EVA and build and oven.

OG

bj · « **Reply #214 on:** October 16, 2011, 01:19:18 PM »

Not sure about acrylic. Have messed about with Plexi, (perspex across the pond) and as long as you don't
get silly with the heat, it is fine. It does cloud eventually though. Suggestion would be to get a small piece
and heat it up to the optimal EVA temp and see.

Old Greybeard · « **Reply #215 on:** October 16, 2011, 01:41:53 PM »

Many thanks for that. The acrylic sheet I have is actually Perspex (polymethyl methacrylate, in chemist-speak) so from what you say it may be OK. I'm guessing that I'd be best using a modest temperature and extending the "cure" time, to minimise the risk of marking the acrylic.

Time to order some EVA and start experimenting, methinks!

OG

2011solarking · « **Reply #216 on:** October 21, 2011, 02:53:14 PM »

hi, Oz
I just made a small panel with 1x4 cells of 3x6 inches.
It generates 4 amp of short circuit current and is great.
My problem is that after measuring the Isc, some cell appear broken. (i measure Isc direct with the multimeter in + and -)
I think that running the panel delivering Isc could make over heating the cells and because they are inside the pael, they cannot expand and they were broken.
what do you believe?
how do you measure Isc?

thx
good work!

Madscientist267 · « **Reply #217 on:** October 21, 2011, 08:39:07 PM »

Isc is pretty straight forward for the most part -

My version of the measurement: A meter in current mode, directly across the panel output (just as if you were measuring voltage), high noon, clear sky, panels perpendicular to the sun's rays.

As long as your panel doesn't have enough "oomph" to blow the fuse in the meter, that's your reading.

Just remember that it's not a "real world" measurement. Only useful for comparing panel to panel.

Steve

oztules · « **Reply #218 on:** October 21, 2011, 09:30:20 PM »

"My problem is that after measuring the Isc, some cell appear broken. (i measure Isc direct with the multimeter in + and -)
I think that running the panel delivering Isc could make over heating the cells and because they are inside the pael, they cannot expand and they were broken.
what do you believe?"

The cells them selves are silicon, an an stand quite extreme heat..... more than the sun can provide. The glass is the same kind of material, and I believe the expansion rate is the same. The EVA has enough flex to allow it to expand... so I find it unlikely. The only problem with heat is the V drops with temp.

If the cells were fine before (and 4A sounds good), and they were not broken by the vacuum, I don't unerstand why they ecided to fail after the curing.

What is the Isc now. If it is still 4A, they may not be broken at all?

Remember to use thick wire instead of your thin multimeter leads if your using a DVM, if your using a analogue meter you probably already are using thick wire. (voltage and current drop in the wire is exreme with those little DVM leads.)

Pics???

...........oztules

2011solarking · « **Reply #219 on:** October 21, 2011, 10:15:27 PM »

I cannot be sure if not broken during vacuum.

Could be the electrodynamic forces when 4A are generated instantly?
Two of four cells were broken.
I put the temperture (60 degrees) BEFORE the vacuum, thats different of what you recommended. You said to put vacuum before temp during 15 min. Could be that?

Thx again.

oztules · « **Reply #220 on:** October 22, 2011, 04:48:35 AM »

60 degrees should be still fine. Is the glass 60 or only the oven. Where are you measuring the temp.... although I still don't see that as the reason. Don't know what went wrong..... guess just try again.
Only testing will show.... whatever we say.

...............oztules

2011solarking · « **Reply #221 on:** October 22, 2011, 10:38:10 AM »

We put the glass inside the owen, then turn on the owen, and only when temp rise to 60, we turn on the vacuum.
We put a thermometer in the middle of the owen.

Now Iam thinking other cause: when cooking was done, we turn off the heating element but leave running the fan, to acelerate cooling.
That maybe provoke cooling too fast, and because all materials forced to cooling change temp with different speed, it could damage the cells.
We note tbat the broken line is always along the tabs.(metal!)

oztules · « **Reply #222 on:** October 22, 2011, 10:13:58 PM »

Ahh...... that tells me that your soldering is a bit thick.

You must make tabbing as neat as possible. There must be no solder "bumps or lumps" as the cell will have to try to "bend" around them to meet the glass. They don't bend.

The cooling co-efficients are so similar, that I don't think that is the problem. I think it is your soldering technique.... possibly the iron was not hot enough for the solder to "run" nicely.

Cells don't bend. The strip you solder on must be as thin as possible, so it can sink into the EVA.

..............oztules

2011solarking · « **Reply #223 on:** October 23, 2011, 03:06:32 PM »

Oz
Soldering was perfect, it didnt grow the thick of the tab.
I think that cooling speed of glass is not the same that of the tab (cooper or aluminum?)
Maybe, other chances are that we leave cooking very long time, so Eva could almost disappear, so there are no material to absorb the thickness of tabs.
We will make another panel, with same cells, same soldering, same tabs, less cooking and natural cooling.
We will tell you the results.

Thanks a lot!

Finfan · « **Reply #224 on:** November 09, 2011, 04:46:04 PM »

Oz:
Sorry if this question has been asked before but there are a lot of pages of replies now and I might haven't read them all. Is there any reason why you have to build the large oven and encapsulate the entire panel in one shot? Couldn't you just pick an appropriately sized group of cells for the panel you want to build, seal that and then wire them together in banks to produce the voltage? After all it's the cells that are vulnerable not the wiring. Just trying to figure out how to do this. Thanks!

oztules · « **Reply #225 on:** November 10, 2011, 02:14:52 AM »

I can't see a good reason to do it..... but there is no reason that it would not be as effective as all in one go. The oven will still need to take the entire glass panel.... whether it is completely populated or not

...............oztules.

dave ames · « **Reply #226 on:** November 10, 2011, 02:48:40 AM »

....or, Finfan may be thinking along the lines of making smaller panels with a lower cell count and then series them up externally to achieve his desired nominal voltage? like what Kevin did with his 18 cell modules (page 5). you could even make a dozen 3 cell 8 1/2 x 11" picture frame sized panels and series those up

Recently I've thought about the folks who got caught up in the 32 and 34 cell "self regulating" panel fiasco and see no reason why a small two or four cell helper module (with a matching IMP) in series with one of those might make it a more useful battery charging setup....could even add a few volts to a string with a long wire run in hot, hot conditions to make it do what we want?

Oh the fun of DIY

Cheers, Dave

Finfan · « **Reply #227 on:** November 10, 2011, 09:12:13 AM »

Actually I was thinking about making groups of for example 6 cells sealed to the proper sized piece of glass then mounting these to a rigid backing and wiring them together to form a panel inside of a more standard design type panel box. My main concern is that the inside temperature of the box might exceed 65Â° C. What would happen then?

jaskiainen · « **Reply #228 on:** November 10, 2011, 11:04:41 AM »

Probably the only thing happens is that the panel output will go down as the heat increases.
Once the EVA is melted it needs quite a lot heat to melt again. Yes, it might soften a bit but nothing to worry about...

oztules · « **Reply #229 on:** November 10, 2011, 04:30:29 PM »

ok... make your 6 cell panels and just treat them as small panels.... don't put them under more glass etc.., as heat and more losses due to extra glass will make it less useful.

Make them small and hook them in parallel or series parallel or series..... whatever, as you would for normal size units.... just more of them.

.................oztules

fabricator · « **Reply #230 on:** November 30, 2011, 06:58:27 PM »

When the fiberglass crowd does vacuum bagging they use tape caulk to make bags, the stuff comes on rolls, it's like sticky putty, you put it around the edges of your plastic sheeting and just press it together, it makes for perfectly leak proof bags, of any shape or size.

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Author Topic: Making decent solar panels part 3 (Read 101753 times)