Making decent solar panels part 3

[oztules]

I just thought of some questions, Oz;

The spacing of the cells - you mention in the previous part of this - but you didn't mention where the EVA squeezed out, how much, and so on after curing.  If there wasn't much of it squeezed out, for example, would it be practical to tighten up the spacing of the rows of cells to make the panel just a bit more compact?  If there was lots and lots of extra EVA would you suggest using a thinner sheet of EVA (if that's available)?

Your procedure is hardly any different from vacuum-curing fiberglass panels or other composites, so many of the techniques and supplies carry over.  The "breather cloth" for which you used a "duvet"/"dooner" can be bought for pretty cheap from suppliers of commercial fiberglass.  So can a release film that helps separate the layers when you take it all apart.  I suppose at some point it doesn't matter (this is backyard DIY after all), but maybe you'd have some thought on it.

Thanks again!

Hmmm..... The cell spacing can be whatever your comfortable with soldering together, and not making the tabs bend too severely between the next cell and the first... otherwise you may fracture the edges when the pressure comes on. My cell to cell spacing in a string is very short.... maybe 2-3mm. My inter string spacing could be anything I was comfortable with too. In this current case, the glass has certain measurements, and you work with that. You cannot cut toughened glass without a very high temperature oven (900C and up) to take the tension out of the pane..... cut it and then re tension it again..... or you can simply space the strings symmetrically.... seems simpler.

The EVA will migrate to wherever the pressure is less..... so in this case, the stuff in front of the cell will migrate towards the back of the cell and out the sides if it can to get away from the pressure. Fortunately, the plastic bag seals the edges very well with the air pressure, and the eva  stays mostly where it was put originally..... but more will be on the back of the cells than the front in my cases......hardly any  escapes past the tyvek or whatever your using there.... enough escapes to annoy you into unwrapping it early so you get a chance to clean the small bits up.... but for practical purposes it is no biggy. I would not change the EVA thickness on purpose.... I would use what I can get, and not get fussed..... main thing is to get commercial EVA designed for solar......eg  I don't think hot glue would have the same uv stability or transparency.

Compact panels will only occur when you can cut the glass to size.... or you find a size that fits your cell pattern and voltage.

Tis true that this is very similar to vacuum forming as I understand that process (very adumbrate for me)..... but for DIY island style....... use what you can get. There must be very good material available in the USA and Canada..... but thats not the same as making do and getting as good a result. I try to make it so that anyone can see the simplicity, and ease of a project, and not be put off by the non-availability of stuff in their lacale. The shade cloth was here (works but not reliable) the dooner/duvet was here (works very well) and for the release film, I will ditch the tyvek and try the grease proof paper.... and it's here too.

Look forward to seeing the Sparpanels in future.


..........oztules

[oztules]

Harold and Phil,
Lets not loose sight of what we are trying to achieve..... we want power and we want it cheap. If we have to buy too much exotic stuff, we may as well by commercial panels as the cost spirals away very quickly.

The output difference will have more to do with the quality of your cells (when you sort them out) than the quality of the glass substrate. My tests showed that a 10-15% loss would result in using iron free to normal window glass... Now if one is free (say window for instance) and available, then it beats the bonox out of buying glass that may give you less improvement than buying and sorting the cells properly.

If you bang the cells in without sorting you may degrade performance of a panel by more than 30%....... and waste the better glass.

So, even without the iron free glass, we can make panels within 10-15% of a commercial variant, and there will probably be a no-cost component for the window glass. With the money not spent on exotic glass we can probably build another panel, and have 170% more power for the same money.... even using crap glass...... now that is more useful than spending your hard earned on the glass bloke..... remember if he has to order it.... more transport cost.

In short,I think you will be better to use free window glass than buying iron free glass.  The cells are only 38c/w (I just bought 1kw from fred480v on ebay including tab and bus wire.... and the cells were tabbed front and back) and the EVA less than $10/meter (less than $8/m for 60m including shipping from china on the address I gave earlier to Harold).... there are no other costs.... not even transport for the glass..... or for a 60 watt panel... $10 (eva) + $30 (cells) + free glass=solar panel. (in fact these cells are 6x6 so 120 watt panel would be closer, less say 15% for glass loss of window pane.)
Now, not all the cells will give their 8A@.5v or so, so you will build one panel out of the "also rans", and you won't want to spend good money for good glass on that one.... it may be only 50% of the nominal ratings.... but even the last panel made from the dregs with free glass will be cost effective.


Glass thickness is also a factor with transmission loss, and the thicker the glass the worse things get..... but again this needs to be balanced out with advantages of strength and availability. The latter is the killer over here. It is just our Government in their wisdom are virtually paying folks to ditch their solar hot water for the new stupid complex heat pump sort. So there are lots of 25 year old panels (and younger too) just there for the taking....with the aluminum back as well.

It is of course up to you as to your final cost per watt... but this can be can be very low if you don't try to use all perfect stuff....


just my thoughts anyway.


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

[Harold in CR]

 I'm going with cheap window glass. I have to buy it, so, cheap is good. The EVA should hold it together if it gets broken.

 I was just offering info for the ones that asked questions. I'm perfectly content with the "Island Method". 

[oztules]

Keep us in the loop Harold.


........ and just to give you some added enthusiasm, it was about 5pm in the afternoon here, and I thought I would check out the losses of the window glass again.... been a while,

A random cell without glass came up at 3.6A short circuit, with window glass it dropped to about 3.38A.... so it can be less than 10%.loss.

 This glass was out of a sliding window, fairly thin (3mm). From memory the 15% drop was with toughened window glass from a car side window. (maybe 5mm or so thick... maybe a touch more.

As I had the meter out, I decided to check the latest panel again for short circuit current .... Just to make sure the meter was pretty close to right (but mostly to annoy Volvo farmer), I used 2 in series as a rough cross check.

There was a difference, but not enough to mess the figure up given previously...... here they are:


They are a bit better than the other day, which was a bit hazy ( big winds seem to get a hazy look to an other wise clear day in the ocean environment)

In this setup. You can see by the shadows, that this was not the noon sun by any means. I did see a few moments of over 9Amps, but this was caused by small clouds near the sun I think.



That should give impetus to your deliberations perhaps......... 10% less than that is still darn good I reckon.



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

[Volvo farmer]

 I'm going with cheap window glass. I have to buy it, so, cheap is good. The EVA should hold it together if it gets broken.

 I was just offering info for the ones that asked questions. I'm perfectly content with the "Island Method". 

I don't know if this is any concern or not, but I'm pretty sure all commercial panels are made with TEMPERED glass. All the ones I made like a double pane window used tempered, and I'm pretty sure Oztules' solar hot water glass is tempered.  So before you go gluing a bunch of EVA and solar cells onto normal old window glass, you might want to consider why the big boys use tempered. 

[Harold in CR]

 I fully agree VF. However, down here, it's near impossible to find tempered glass, especially used. We are about 30 years behind the USA in materials. NO storm doors. Solid Wood House Doors. Plate Glass Storefronts. Metal caging surrounding stores and houses, IN THE CITIES.

  I live out in the country. Have offered to shoot anyone thats on my property without permission, so, I'm not bothered too much. Put the word out to the local gossips, and, it spread like a brush fire. 

 Economy here has spawned LOTS of thieves, especially in the cities.

 Even scrap metal is constantly sold to salvage yards. It's pretty tough to get normal things, here.
 Just have to use what's available. Frames will be as rigid as possible, to keep from twisting the glass.

 It's the best I can do. At least the glass won't shatter into a million pieces, and, I can wipe some thing into any cracks to keep them sealed as much as possible.

[phil b]

Volvo, You are correct about the value of tempered glass. We had a golf ball sized hail storm shortly after I had mounted two newly constructed 4'X8' air to air solar panels on my roof years ago. They were made with new tempered patio glass.  I KNEW the panels were going to be the first thing broken.  I walked outside with a helmet on, during the storm and was surprised to see the hail bouncing off my panels. No damage except for chipped paint! The storm broke windows in houses and cars all over town and I had to put on a new roof.

Oztules, It is easy to loose sight of the objective here. Window glass I have stored is what I will use. It is all about 3 feet by 3 feet. 27 double pane windows for free. They will make small panels unless I can butt the glass end to end to make larger ones. That's a risky idea. IMHO.
Also, you had mentioned separating out the better cells from the not so good ones. How picky are you being on your selection? Are you putting them under a bright light? Thanks


BTW - Sun electric has 55 watt solar laminate panels for $73.70 each, minimum 2 plus shipping. If they are not out and have not changed their prices. An Oztules 60 watt  manufactured panel is ~$40. Information and knowledge to build your own - priceless.

[DanG]

How about checking the water-white vs. standard glass at less than optimum angles for non-tracking panels?

[oztules]

DanG
I am not smart enough to know the difference between these glass types you mention. I don't bother with trackers myself, as they are a waste of money and time here. I'd rather have built more panels with the time and money. We have two things working against trackers here.

We seem to get more than our fair share of light clouds in the summer skies. This does not diminish the output that much, but it diffuses the sunlight to make it seem to come from a larger part of the sky..... so a pinpoint tracker will give not much better results in this weather. The other ove riding factor is the winds we cop over here. This means very solid tracker construction..... so it is simpler to ignore the possible 30% increase due to tracking (less here i think) and double the panel size instead.... win win.

Phil,
I'd stick to smaller panels. I see no point in making them big like mine....  I can't cut the tempered glass to anything smaller. Volvo is right, you can damage panels with rough weather, but the EVA makes the glass less likely to suffer catastrophically.... a cracked cell works the same as an un cracked  using normal glass (think laminated windscreen), the tempered ones are finished if they are hit (think side and rear windows in cars )..... mine are tempered..... if they go thats it.

Cell testing..... interesting question.
The strangest things happen with new cells. I built a quick and rough cell tester from a 150w flood light etc etc. I sorted the cells, and was disappointed that there were so many less than good ones.... ie 2.0-2.8A cells.... a good amp less than the "normal" 3.8 + ones. Now putting 2A ones in series with 4A ones gives you a 2A panel... bummer... so thats why we test them.  We want to see mostly full power panels, and all the duds in a feeble panel.... not mixed.

The odd thing is, when taken outside into the real sun, strange things happen. Most all of the 2A+ cells came up to 3.4-3.9A The really good ones didn't change at all, the reasonable ones improved a bit.......... but the baddies mostly came up to spec or close. There are still some that didn't, and will be made into window glass electric fence panels.....

So now I always test the cells in true sunlight.... twice..... lab conditions does not seem to tell the real story..... I don't understand this at all.

If we had cheap panels like those you mention over here I may not have gotten into this.......

So it is the same old story, what is good practice in one region, may be undoable in another.... luck with it Harold.



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

[imsmooth]

Very impressive work.

You may have mentioned this in your comments, but how much would a similar panel cost to buy, and how much (not including your time) did this cost for you to make?

[oztules]

For that panel, there is about $150 in it.
Your second question .... depends where you are. I believe in the USA, you can get solar for $1/w..... so 250 bucks saves you the work... over here probably about $800 would get the equivalent in real watts.

Here (AUS) we see 200 watt panels on Ebay,for $550..... but when you get them, (neighbor bought 6) they are no where near their specs. eg Ipwr= 11.3A...... but the best we found SHORT CUIRCUIT was a tad under 10A.... so the vendors make the figures up for the cheapies.. Generally about 2/3 seems to be the ratbag mark up.... buy 960w.... get just over 680w for real ( ones I bought were supposedly 4 x folding 240 watters.... baloney.... and they are marked as 13.5A Ipower .... only ever saw just over 10A out of them short circuit

These panels home use 2sq metres for only 250 watts (about 12%) which is believable,  but I cant see how these small chinese panels can get 200 watts for less than 1 sq meter..... those boys are good .... but not that good.


Thanks Imsmooth

..........oztules

[Ovais]

Hello Oztules,

I few DIYers crimp the tab ribbon between the solar cells to cater to expansion and contraction. Do you also use this technique? Is it important in increasing the panel life?


Thanks,
Ovais

[BrianSmith]

Oz,

I think the mystery of why a solar panel will give a different reading when put in front of a bulb vs real sunlight probably has to do with the intensity of the colors coming from the bulb vs the real sunlight.  All bulbs have a different characteristic of the light output they produce with some having more blue, other more yellow, etc.  That distribution of light color is also a distribution of light energy at different wavelength (colors).  Its likely that some solar cells were more sensitive to some colors than others and converted the shop light bulb colors to electricity better than others.  The sun is pretty broad and full spectrum light where as bulbs are concentrated in a few colors more than others.

At the end of the day its the suns energy that really matters unless your going to put them in front of all the lamps and try to reclaim all that wasted light power ...

Nice panel by the way.

[oztules]

Thanks Brian,
That explanation  had crossed my mind as well, but it did not explain why some cells achieved similar results under both lighting regimes, and some quite different. If it was a spectrum thing alone, then I would expect a fairly linear result.... all showing the same anomaly.... but this did not appear to be the case.

I still don't have a sensible explanation, but maybe it has something to do with the anti-reflective dye, and how thick it is, It may be that some cells have differing coatings ( they seem to come from very different batches in the same parcel of cells), and treats the UV and IR wavelengths differently to some of the others.. ( eg clothes powder that makes your clothes whiter than white, by retransmitting the UV at visible frequencies.....  I don't know......

Ovais,
I did that for the first panel, but on closer inspection of commercial panels, I could not discern any sign of crimp etc. In fact some cells had nearly no gap between cells to put an expansion link in...... so I skipped it from the second one on.

Short answer....... dont know.

 If you find a sensible answer from a commercial panel manufacturer, please share the results, but at this stage I think it seems unnecessary. It is also worth noting we don't get huge temperature differentials here either, so I am less likely to consider it than those living with wide temp variations..... ie where expansion/contraction is a constant problem for even the rocks.




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

[dave ames]

 Hi Crew,

All to often these days we run into things that just sound too good to be true. then again on the very rare occasion the "too good to be true" proposition turns out to be REAL! ........this is one such case!!!

hats off to oztules, i believe the full impact of your tutorial has yet to to realised.

we are hesitant to clutter your thread showing such fine craftsmanship with my hacked up foibles, but will confirm great results following your straight forward instructions- right out of the gate! .... .. albeit on a much smaller (1/16th) scale.

your claims of  making "decent" solar panels with your methods are an understatement! you have removed the final obstacle of DIY pv solar modules for the backyard builder.

the little projects i tend to play with here are always in need of smaller wattage modules in the 5 to 20 watt range, we do save a bit on shipping with these smaller sizes. but the cost per watt can put a dent in the wallet. a 5 watter at less than 50 bucks is a win..with "the oztules recipe" we just took a little 5 watt module out of the oven that cost less than $5. to make!! 

i would urge anyone still up in the air about giving it a go, to have at it  .....if a connecticut yankee can get on with it, anyone else should not have any difficulty.

THANKS OZTULES !

cheers, dave

[oztules]

Yes folks I paid him to say those nice things

Thanks Dave,  there are a few other foibles I have found for larger cells.
When using 6x6 cells (like the ones fred380v sells) DO NOT pre vacuum at room temperature. If it is cold where you live, then the cells will fracture along the tab lines.

Over here it is just into autumn, and with testing I have found the colder/cooler weather makes the EVA a bit stiffer, and the room temp 15 mins thing will likely crack 6x6 cells.
 If you pre heat to around 50 degrees C, it seems to stop this from happening, and so I will try a full panel soon and do a 4th part of the saga.

6x3 cells are very tough compared to the very flimsy 6x6 and seem not to be too bothered with the room temp vacuum stage, but it may be in cool climates, that it would be advantageous to at least get it up to 50 degC before pulling on the vacuum.

The softer EVA at this temp is still not melted, so the air can still migrate, but is soft enough for the tab wire to sink in and distribute the massive weight over the plastic more evenly. With cold EVA, it appears to not sink enough, and so give a "ridge" which is enough to fracture the 6x6 silicon wafer.

On a 5w panel this would not be a problem you would encounter I suspect.



A picture perhaps??


.........oztules

[dave ames]

Cheers Oztules,

a few pics and perhaps a belly laugh at the morning (mourning) activities...

three 3x6 cells chopped into 12, six cells cut into 6ths and nine cells in quarters. all are 36 cell panels:




back landing zone:



some suspended debris but no air bubbles:


some good sun here this almost spring morning and time for first light with our newly minted toys! VOC is fine in ambient room light ~20ish..as soon as we put them in the sun 2 out of 3 go to ZERO!...well how can that be?..we now get to test how well the EVA sticks to glass...after some real tough cutting with a razor knife we get the EVA and backing pulled away enough to see whats happening:


we have found a fatal flaw in our construction techniques!  can you see it?  we dutifully insulated where the bus wire crosses the tabbing wire..but ran it right along the back of the cells in places where there was no crossing..WOW the little pads on the back are for the solder connections but the whole back is conductive..sooo.. as soon as any current tries to flow it goes full short ->now that's funny....gonna dig around a bit more, we may be able to cut the bus connections further and take the power off with some leads where the crocodile clips are? i think we may get to see how this laninated green float glass acts when it breaks.

It's back to the goodwill store for a few more 50 cent aluminum picture frames. and chock this first volley up as a learning run.

still counting this as a success (the lamination process)..it's my other skills that need work.

kind regards, dave

[oztules]

Nice work there Dave.
How did you so successfully cut the cells up If I may ask.

Look forward to the next iteration.


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

[dave ames]

that's very kind of you to sift through this mess and find something redeeming to explore.

there was a time that a mistake like this would have taken all the wind out of my sails. and i would certainly have never talked about it in public..not so much these days. of course we never want to screw a project up. but now, in life's later chapters.. i find blunders such as this more amusing than upsetting..and it does go a long way in helping to keep ones ego in check, that's for sure!

about cutting the cells: this exercise provided a fair amount of amusement as well. the very first two cells were total losses..turned to chard's of confetti as soon as the handheld dremel came near them..was never sure if the tool had actually even touched the cell? ..of course it must have but you could not feel it in the tool.

things improved (we can't get worse than 100% scrap) when we worked up a fixture using flexable magnetic strips. the jig essentially traps the cell and protects the portions we want to save and lets us "destroy" a line we want to remove. more improvement was to be had by covering the cell in tape (removal proved difficult) then tried and went with a food cling wrap for our trapping and destroying operation. ended up with a final scrap rate of about 25% still quite high! with that 25% scrap from the larger cells we cut them further for ever smaller cells/panels..total full cell count was 23 cells including the first two turned to sparkly chips.





we have since obtained some lapidary gem cutting saws that are rated for cutting quartz crystal. everything read seems to indicate that the mohs hardness and lattice structure of the industry grown silicone is very close to natural quartz? hoping to get a mini table saw rigged up to give these thin .008" kerf and 4" diameter blades a go. it would be nice to get a true cutting action, rather than the semi controlled amputation method.

a big surprise, (besides the grey powder coating being conductive). was the amount of debris in the EVA interlayer. we have inspected with an eyepiece and it is clearly dross of cell material. this says we need a much better cleaning method-perhaps even a way to seal the cut edges.. for i fear that these flaked bits are coming off the edges after my best efforts to clean them up. any ideas there?  think a corona dope or varnish might do?

i see some familiar names in the EVA supplier comments section so we may get to see some more results with the "Oztules recipe" soon?

thanks again!
it's all good fun,
dave

[oztules]

Thanks Dave.

Was the tape better than the cling wrap.... and the difficulty removing the tape made you use the cling instead of the tape?
If so perhaps use insulation tape (Nitto etc) and then a heat gun to remove it easily.

I have now built panels with the 6x6 cells, and they are fantastic to work with, and perform very very well.
I have seen well over  9.5A short circuit, and direct into a 24v battery bank from a single panel over 200 watts....



No that was not the max reading, but was what it was doing when I finally remembered the camera.
It had gotten to 7.5a@ 27.8v..... but the current dropped a tad when it got over 28v This is only a 66 cell panel (6 rows of 11 6x6 cells)


I have run out of Tyvek, and now use the same plastic sheet I use for the bag. It makes for a nice clean back, which is transparent and very tough as well.



and a close up picture.



Here is the layer formation:
Glass-eva-cell-eva-plastic sheet.



I expect to see an updated Dave panel in the near future...... with the better designed buss system

I now have over 2kw done for home use (not counting the water pumping ones... they are installed)...... just have to find a place to install them here around the house.

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

[Harold in CR]

 No surprises with those 6 X 6 cells ??  I was going to have my son pick up some tyvek, when I talk with him, tonight. Might just skip that and buy plastic on a roll at the local hardware.

 I'm about to re-side the house, and figured Tyvek would be used there, also. Down here, no one puts a wrap on a framed wall house. Wood on both sides of the studs, and, they are 33" on center. Might just wrap the house in plastic and" fork" it occasionally.

 Hope to get my crate down here within a month from now. Keep adding to the list my Son has. 

 Once again, you have raised the bar, Oz   

[howlet]

Oz, Nice panels and great advice!

 A company named Greco once manufactured sign laminators that, depending on the model #, are large enough to laminate more than 1 panel at a time. They can be purchased, perhaps at auction, for a song. A few years ago I snagged a 30"x 48" for maybe $200 U.S., equipped with a Gast vac pump and an optimum diaphram.

 I'm also a fan of standard tempered glass as I cant justify spending the large difference in cost for marginal wattage gain.

 I shared my progress in DIY panel fabrication but at that time most folks considered such endeavors to be foolish. Imagine that.

 I'm still a "Newbie" according to my profile. Have not met the magical 50 posts required for a membership status upgrade.                                                              howlet

[oztules]

Harold
" No surprises with those 6 X 6 cells ??  I was going to have my son pick up some tyvek, when I talk with him, tonight. Might just skip that and buy plastic on a roll at the local hardware."

Yes!..... Do not pull a full vacuum on these biggies at room temp. They will crack along the tabbing wires..... without exception almost.

I found that if you preheat to 50C, and then start the vacuum process, that all the cells survive perfectly, and the output reflects this. This is also good advice for the 6x3, which seem much more robust, but stll the occasional one broke along the tab if I did it at night and the temp was cool.... so preheating is a must I think for all cells now.

I prefer the plastic to the tyvek. It makes for a very clean an neat backing.... also if you push the temps up too high with the tyvek, it will dissolve into a not so pretty backing.... no detraction from the usefulness, but I find it nicer to use the plastic sheet...... Also, if you get a broken cell it is simple to fix if you can see all the wiring in the back of the cell crystal clear..... a cell bypass is simple then.

Howlet, I tracked down your picture of your panel. It looks the bees knees. How has it weathered... very well I trust..

(hope this is it):


Did you do a story on it someplace?

From the cracks on the second from left top cell, I suspect that the vacuum was pulled on before any temp had gotten into the EVA (but you probably know that by now anyway)..... but the drift exhibited tells me that the broken bit drifted when the EVA went liquid..... as if the backing was not stable? (ie what did you use for the wicking... did it move?)
The big bubbles worry me a bit. Did you hold the pre 65C vacuum on for too short a time?... or is there some other explanation I should know about. I have not seen this in any of my cells (please share any bad experiences and the "fixes" for them for mine and  other folks benefit..... your years in front of me)


I note your disappointment with the reception that most DIY solar efforts receive..... and mostly for good reasons. If yours are EVA  laminates, vacuumed (need the pressure too) and without bubbles....... gee it's hard to see how they could possibly fail (unless someone puts a brick through them). They are sealed up but good.....  for good, and providing you use decent EVA and cure it well , it should not denature.... it is designed for it, and better than the older generation of the stuff..... and the old stuff was pretty serviceable as well.

I suspect that those that deride DIY panels, have taken the wrong path themselves, and or seen others efforts end in tears.... so their skepticism is probably well placed.
In my case, I am isolated, so transport is a difficult thing for delicate big things, and old solar water panels are plentiful here (about the only thing that is). I know how tough the EVA end product becomes, and am very confident in the aging being little different to the commercial panels. In truth, it will be the panel to panel connecting system that will be likely to require the most effort from here.

Those using heat guns will get a reasonable short term result, but they have only melted it.... not cured it and it will likely lift off the glass eventually.........,unless they got it very hot... uniformly, then it just might stick forever.

 If it's not mostly/fully cured under pressure (temp and time tests), it may not bond to the glass long term. If they don't get the glass clean... ditto ( at least the cells will last inside the EVA envelope, but may break if they leave the glass,) or get moisture in front of them. It is not fool proof by any means if done poorly (but nor is anything else)


So even EVA enveloped cells can still come in for some well directed flack.

Good looking work Howlet




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

[dave ames]

 Thanks Oztules, and greetings to the group.

round two and a few more chuckles to be had.. a few small air bubbles trapped in this effort but was very happy with the results until......we were moving it about and whacked it into the corner of the table and...you guessed it. 

oops!


some improvement in wiring methods:


a pic of the shorted out version:


we were able to get away from any tape or cling wrap this go. though the tape worked well in the "obliteration" cutting method. improved techniques have removed the cross the fingers and hope for the best with our cutting operation.

with our 4" diamond lapidary blade in a dremel based radial arm saw'ish contraption, cutting these cells becomes reliable and predictable.





an approximate handbook reference for this string ribbon drawn silicon cell pv material might be: dry cut;  5,500 sfm, 0.01" per revolution feed rate with a chip of  0.001"

we used a tool approach at rate and full clear after cut (no stopping and starting please). our flexable magnetic clamp works well (support on top and bottom) though i suspect a single surface vacuum clamping system would yield good results. we do need to take care not to transfer any tool vibration into the cell..smooth running equipment is the rule of the day here.  of course eye protection and a dust mask are a good idea for this operation.

with some digging we have revised our theory of the flakes of cell material being dispersed into the EVA interlayer. i was wanting a way to clean the cells better and seal the edges..however the new working theory is that the cut cell edges must be absorbing moisture after being cut. then when we put them through our vacuum process they may be "sublimating" when they come down through the 29" level of vacuum thus boiling water from the edges (causing cast off) right at our pre-heat 50*c /120*f temperature. we added a pre-lamination dehydration bake for the soldered up cells of 15 minutes at 400*f and letting them cool back down in the oven just before assembling our EVA layer cake .... .. that must have been the gremlin, as we have no suspended surprises! just the cracked kind this time. 

the saga will continue to see if dave can get through this just once without shooting himself in the foot. 

still counts as good fun!
cheers, dave

[oztules]

Well Dave,

Thanks for the cell breaking test. It was successful I see.......well it held together anyway as advertised.
How was the panel output after you tried to pacify the table with the panel?

I found it barely changed it, if at all. Was that luck, or did you find the same thing.
It wasn't a test I wanted to do a lot of.

Must say I'm impressed with the cell cutting you have done.... I had a cursory fiddle the other night and succeeded in making lots of irregular confetti....a 4" angle grinder is not quite the right toy I'm afraid.

When I use the paper as the bus  barrier, I slip some EVA under the paper (same size or bigger than the paper) so that there is not a void in there..... and even between the bus wire and the paper....... in fact anywhere there in an interface of anything, I put EVA between.... just to keep it all tight, and bound together. It may be over the top, but it makes me feel better. I suspect that in your current setup, you would be able to feel movement when you grabbed the output tabs, as they are really floating above the cell backs. Eva between all surfaces will stop that completely.

EDIT: thinking about this, enough EVA will seep through the inter cell spaces and fill the void.... at least mostly and possibly completely  anyway.... maybe I'm off target here, and you were going to be fine anyway.

Good to see that you have solved the detritus problem. I hadn't considered that angle at all. The pool of information is growing.


Thanks for the pics Dave..... and keep at it.



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

[howlet]

Hello Oz, Jeff here. The "rant" that I posted last night (eastern std. time) was due to board policy and had nothing to do with you.
 Its about time that real, practical DIY solar is taken seriously and your efforts are doing just that.
 In answer to your questions about the flaws in my panels, the air pockets along the solder joints are due to poor soldering technique caused by excess tinning of the tabs and cell distortion caused by excessive heat while attempting to repair the solder joints.
 The air pockets in the middle of the cells are the result of a poor consistant vacuum due to buildup of EVA in the pump itself. Periodic maintenance or cleaning of the pump generally takes care of that.
 I have not experienced any diminish of performance on any of the panels that I have fabbed.
 The "rants" or unprofessional behavior exhibited by myself resulted from frustration or embarrasment due to the inability to shrug off uneducated responses from long ago posts.
 I'm very sorry to hear that you could have been affected by my behavior.          howlet

[ghurd]

I saw an old Solarex 60W leaning on a wall tip glass-down onto flat cement and smash.
All the glass went into tiny pieces.
None of it stuck to the cells, or between the cells.

Saw another of the same panel that was hit by something.
Glass smashed into tiny pieces, but most of it stayed on the panel.

Not sure what that means.  Thought it might be interesting.
G-

[Madscientist267]

a 4" angle grinder

LMAO

Immediately Dremel comes to mind, which I see I am not alone in. But am I interpreting the pic correctly? The drum sanding attachment to cut the cells? Or am I missing something...?

I'd think the little cutting discs would be the most effective. Or again, did I miss something?

That pesky 'selective reading' thing might be lurking in the shadows for me again... 

Steve

[zap]

a 4" angle grinder

LMAO

Immediately Dremel comes to mind, which I see I am not alone in. But am I interpreting the pic correctly? The drum sanding attachment to cut the cells? Or am I missing something...?

I'd think the little cutting discs would be the most effective. Or again, did I miss something?

It might be hard to see in the picture but he's using a "4" diamond lapidary blade".
I think the sanding drum is what's holding the blade on the Dremel?

[dave ames]

a 4" angle grinder

LMAO

still, a finer cut than say.........a chainsaw?  

quote author=Madscientist267 link=topic=145004.msg985186#msg985186 date=1300807325]

Immediately Dremel comes to mind, which I see I am not alone in. But am I interpreting the pic correctly? The drum sanding attachment to cut the cells? Or am I missing something...?

hard to see the blade in that shot..mounted on the sanding drum arbour.

an after cut saw position picture shows up better:


been playing hide and seek with the sun this morning and still see 800mA isc with this broken module..then not much change with another piece of 11x16 glass in front. we may go with another layer of EVA and glass over the top and see what happens?  for all it's downside (tempered glass may have survived the table bump better) there may be some advantage in the "friendly" cracking of non tempered float glass?

When I use the paper as the bus  barrier, I put EVA between.... just to keep it all tight, and bound

The pool of information is growing

yes in the final assembly we went that route as well.  amazing how the separate bits of this stuff knits together without any sign of where the join is.

hope everyone knows that i'm trying to make all these mistakes so folks don't feel so bad about sharing theirs!

it's all good fun!
cheers, dave

 ->zap still has good eyes!  

edit: the glass size is 12x16

[oztules]

I saw an old Solarex 60W leaning on a wall tip glass-down onto flat cement and smash.
All the glass went into tiny pieces.
None of it stuck to the cells, or between the cells.

Saw another of the same panel that was hit by something.
Glass smashed into tiny pieces, but most of it stayed on the panel.

Not sure what that means.  Thought it might be interesting.
G-

It means they did not get the curing right on the panel that the shattered glass didn't stick to the cell faces. I expect it was caused by incomplete time temperature  problems. (ie. they didn't keep it in the laminator long enough on that panel, or the temp didn't get up high enough for the time they laminated it for) or the glass cleaning failed on that occasion.

The one that all stuck to the cells was cured mostly right from the sounds of it. All the glass should have stuck to the cell/eva front, and very little would be left on the ground.

....... or as I mentioned above

"Those using heat guns will get a reasonable short term result, but they have only melted it.... not cured it and it will likely lift off the glass eventually.........,unless they got it very hot... uniformly, then it just might stick forever.

 If it's not mostly/fully cured under pressure (temp and time tests), it may not bond to the glass long term. If they don't get the glass clean... ditto ( at least the cells will last inside the EVA envelope, but may break if they leave the glass,) or get moisture in front of them. It is not fool proof by any means if done poorly (but nor is anything else)


So even EVA enveloped cells can still come in for some well directed flack."



Even the commercial blokes can mess it up if they try.

Dave,

Does that mean the panel is still good for 10W or so? If you have the glass handy, then another go in the oven with another EVA layer should yield a still useful panel. You will have achieved a laminated windscreen with cells behind it...... not to mention proved that float glass is not as bad as the guru's say. You may still have a second chance with this stuff...... not so the tempered variety. It will be informative if you do do this. (wonder what will trip us up this time?)

While your at it, you will have to belt the table harder with it  to see how well it holds up...... this product testing can be a tough business.

Jeff,

It's good to see they have performed as expected. DIY panels can be very good, and your out in front proving it.



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




Hmmmm     .... chainsaws and solar cells....... I wonder......if I just get a jig, and .........

[Harold in CR]

 I'm a little confused as to why you are cutting the cells ??  I have some ideas, but, I would rather hear you reasons, first.

 Sorry to see the damage, BUT, you might be the new Pioneer of Broken panels. 

 Good job posting. My Son might get my crate ready to ship in a couple weeks. I'm waiting on Batteries to arrive, so I can start my 103rd project, in the works. 

[Madscientist267]

hard to see the blade in that shot..mounted on the sanding drum arbour

Very hidden, indeed. Camouflage even.

It makes a little more sense now. Somehow I missed the part about a 4" blade. Maybe a subconscious attempt to throw out 'the illogical'... 

Ahh, the human mind and the tricks it plays.

Steve