Making decent solar panels part 3

[DanG]

I tried a clear glass halogen 60w lamp as light source - I could flash it on and see 4+ amps from .55V 3A cells, I figured exaggerating the light source could help amplify differences but full spectrum sunlight under a cloudless blue sky showed even outputs where the halogens showed mismatch. Sunlight is where its at unless you can wrangle a xenon lamp with a 200nm to 1000nm wavelength and 1 to 10 suns brightness

When I was matching cells I had two digital VOM meters rigged for simultaneous voltage and current readings but one had to be reinitialized - switched on each time to make them place nice together so I needed a hands-free setup.

I made up a single wafer holder frame (three sides) I could slide the cell into and swing down a foam covered contact bar onto the dangling tabs, to press them against a wound 12awg copper pickup coil wound round a paint stirrer paddle without deforming them much. The tab are slightly concave to allow solder to pool beneath them and once that is crushed the effect is lost.

The back-plane contact plate readings were bouncing all over just resting on a metal sheet so I rigged a "bed-of-nails" to slap the evergreen cells against. I took braided solder wick and sewed it into a metal plate and then took a razor blade to the outer strands to make them frizzy so there were dozens of copper 'nail' nubs catching the irregular grains of the back-plane conductor compound.

The testing jig is in pieces now but I found the trial test jig and bed-of-nails version 1 contact plate to show y'all...

[SparWeb]

Using artificial light does not seem to yield the same data for me.... I don't know why.
............oztules

I thought you explained this to somebody once.

Artificial light doesn't have the same intensity throughout the spectrum as natural light.  Arc lights and fluorescents especially have only narrow bands of high intensity.  Incandescent bulbs produce a much broader intensity, but the strong points in the spectrum are not as strong as natural light where it counts in the silicon cell.

[Madscientist267]

And unfortunately, the sun can even play games with you.

I'd imagine you'd need some kind of light meter out there with you to do the tests under the real thing.

Sunlight in particular makes significant amounts of heat in a cell, added to the fact that there are minor variations (depending on where you are) in the atmosphere that really screw with your head while you're taking a measurement. Not all of which are immediately visible, or even visible to the eye at all.

The only thing I can think of is some kind of averaging system where current is logged from a given cell over a period of time, and then compare the averages to each other to get your matches?

Eh, it is what it is I suppose. Sigh.

Steve

[Ovais]

Here is my first attempt to encapsulate a solar cell [pls. see attached pics.]. I have done it just a few hours ago.

It went quite well. The encapsulation is very clear, not a single bubble is present.

I have used a gas oven. Temperature controlling is not easy in a primitive manual gas oven with no thermostat. I had to test several flame configurations for temperature controlling. I set the flame at a certain flame height and the temperature rises accordingly. The times of my temperature profile for this test has been following:

35 to 50 C, no vacuum, 5 minutes
50 to 65 C, no vacuum, 15 minutes
65 to 100 C, vacuum, 30 minutes
100 C, vacuum, 60 minutes [the oven temperature stabilizes at 100C, plus-minus 2C]
110 C, vacuum, 5 minutes [The flame had to be increased slightly for 110 C. I was a bit afraid regarding my plastic bag so I gave only 5 mins. for 110C temperature]

Many thanks Oztules for your detailed descriptions and help.


Regards,
Ovais
 

[dimeski]

Hi Oztules,
I have a question for you.
Where exactly in the oven should the heater be? On what position?
Can you get circulation of the air from under and above the panel?
Can the motor that is used for the heater stand the temperature of 100 degrees?
Thanks,
Zvonko

[dave ames]

Ovais,
That test cell looks perfect! and thanks for including your heating profile..looks like you have a winning combination right out of the gate. I'm beginning to think that it's hard to go wrong here as long as we have a good pre-heat and a good vacuum (no leaks) excellent results seem almost automatic.

Hi dimeski,
If we remember, early in the saga, our mentor mentioned changing out the plastic fan blade on the motor he used for his think safety can heater..stole/swapped for a metal one from his welder? also the fan was pushing the heat thru the heater coils (rather than drawing it thru).
...hope it was OK to chime in as your query was for oztules..he must be out in the shed working on the DIY space shuttle

it's all good fun!
dave

[oztules]

Sorry , Guys,


I seem to have missed these posts.

Great to see excellent results from the get go there Ovais.
If you have good adhesion as well, you have it conquered it.

Excellent to see another heat profile..... as Dave says, it seems pretty fool proof. This shows I'm not that smart, but the EVA certainly is.

Zvonko.... yes the 100-120C seems to not upset the motor at all... it really is not much above boiling water, so you would expect the bearings and wire to easily suffer this temp... and they certainly seem to..... beware of plastic blades though in near proximity to glowing wire...... if need be make your own from the lid of a large coffee can or something.... as Dave said, I pinched the blades from the MIG welders fan which were aluminum, and put the plastic one back in the welder.

Your position in the oven is only important if you have no air flow.....in a fan forced oven it should be reasonable uniform throughout the volume..... particularly if the heat source only heats the volume up slowly... it will be very uniform if the fan moves a fair bit of air.

I place the temp probe of my multimeter between the glass front and the wooden rails holding it up... so I am measuring the glass temp only.


My oven allows circulation on both sides of the panel.... although in truth, the glass side is the only one of importance.... the rear is heavily insulated by the cells, EVA and most notably the wicking material which in the last 10 panels for me has been the insulating material from the water solar panels.... so I don't think much heat gets to the matrix from the rear.

It is the hot glass that really does the heating.... and it is where we want the bonding to really take place.... sticking the EVA to the cells and the EVA to EVA is the easy part.... the glass bond is the only part where we can fail if any where.  This is where it sinks or swims long term.....where it counts.

Good vacuum (no leaks), reasonable temp, and time = success.

It really is that simple. I'm glad it has worked as described for you...... we want to see pics of the  real panels...... soon?

Thanks for trying it out too, and Dave for helping out as well.


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

[Ovais]

Oztules,

Thanks for your reply.

If I pull the EVA with force, it does start to peel off. Is this normal? If not, should I maintain the 110C temperature longer? Is the higher temperature key to very strong adhesion?


Thanks,
Ovais

[jaskiainen]

No,
it should not peel off. Maybe if you can keep it in oven for a bit longer time?
And remember to clean the glass surface really good before putting it in oven.

Do you know the EVAs storage time before you used it?
May it be out dated?

[oztules]

You should have to tear it off...... more time or temp or both.

If the plastic bag fails after the main curing, then it should not lead to bubbles from there.. so you can extend the 5 mins@110C or even higher. My hodgepoge oven gets up to 120 degrees some times (and a bit more I suspect in some areas.... 2sq meters of glass is not easy to control evenly), and when I do this, the plastic bag fails, but too late in the process to allow bubbles to reform.... the bags fail gracefully as a rule.

 If you over heat, there seems to be a stage where the eva out gasses, but I cant prove this at this time, but I recall someone else mentioning this (Richagen?) I think over 140 might be too high though.


more testing.



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

[kill_seth]

oztules,
I'm looking into buying a some cells for a home project and would like to ask you a few questions.

What I would like to accomplish is having my ac "evaporation cooler" running off solar power.
I know it takes 110 watts to power the ac on low. If I'm not mistaken most solar cells put out about 1.5 - 1.75 watts.

If that's the case could I wire together say 80 cells producing around 1.5 watts each and get about 120 watts produced?
I understand I will loose some power so what would you suggest for trying to power a 110 watt ac.

If you could link me to some cells that would be great!

I have been wanting to purchase some of these:
http://cgi.ebay.com/36-3x6-Untabbed-Solar-Cells-Diy-Panel-Kit-w-Wire-Flux-/120708247969?pt=LH_DefaultDomain_0&hash=item1c1ac5b1a1

[oztules]

..... hmmm
Not quite sure I'm qualified to answer this for you, but here are my thoughts..

If you want to keep your ac motor, then you need batteries and inverter and at least twice the panel you are considering.... and then some electronics to protect your battery investment as well. At least you can charge when not using, and get steady results.

I would look into putting a brush motor in to drive the fan (car heater fan perhaps?). Then you could drive it direct from the solar panel via a pwm controller with a zener and a few opto isolators ($2 maybe).

In this case it would run hard when the sun shone, and run slow when it does not. It will probably get the best reward for installed watt, as it does not need an mppt controller to match the panel to the load, the pwm controller with the voltage step off does this instead (input caps suffer a bit.... but thats what they are there for anyway... sort of)..... I pump water this way.... no different than pumping air.

Try for tabbed cells. Less work , and more likelihood of good cells. As a rule, untabbed means not good enough for the manufacturer to bother to tab them in the first place. If they tabbed them, they thought they were good, but probably suffered a breakage in the string and discarded the lot.

Mlsolar seems to have a bundle of tabbed and strung ones on ebay at the moment... very little work with those. It's all done for you.




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

[Algie]

Morning guys

Im new to this forum and i shall give my past 1 month and half expierienceof making a decent solar panel i would like to introduce myself im from MALTA ( europe ) and we are full of sunshine almost all year round and it never snows here :-) i shall post my expierence and pics taken shortly

[oztules]

I for one, am looking forward to it Algie.


........oztules

[Algie]

Hi oztules

well im must congratulate you for your idea my idea was taken from you here are the pics of the oven which i created with my hands i made it of aluminium and 4 heating elements connected to a temperature controller it took around 60 mins of 100 deg C to make the EVA transperent and not dotted

[Algie]

this my oven open at the moment it has 2 elements dint take a pic with 4 elements btw the elements are 1000W each

[Algie]

I installed an oven fan on top of the oven to circulate the hot air but had to disconnect it due that the air produced starting moving the cells and the EVA

[Algie]

hey oztules

im in the vacuum stage

i need to ask regarding the plastic after you finished did the plastic melt and attach to the panel?? did you tear it up after you finished if so how did you do for the back side due thatthe plastic attached to the back panel

[oztules]

I use a plastic sheet on the back of the eva instead of tedlar...( although it is widely available.) The plastic or tedlar bonds to the eva and they become one... quite sturdy too.

Between that plastic backing,you will have the sheets. towels, doona or whatever you are using to allow the air to move through . This shouldn't stick to the backing plastic... unless you get so hot as to melt it to the sheets/towels etc.

I generally just cut the plastic bag off the panel, and it does not get used again.... disposable bag if you will. I find the plastic bag gently adheres to the front glass if you heat it up very hot, but it always just pulls off the glass, the bag does not seem to stick to the sheets etc, although if your going for high temp, perhaps use silicon bags. I avoided this by keeping the temp below 130C.... garbage bags work fine for smaller panels. I had to make my bags as they were 2sq meters.


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

[Algie]

Did you ever use TPT do you know if it works like EVA heat shrinkable??

[oztules]

no...... but maybe someone else has those answers.

If you spend too much on the bits, it may be as well to buy panels.

Cost spirals rapidly when you pay for the glass, the eva, the tedlar, the frame etc etc.  Unless you can source most of it free, it may not be worth it.... except for the experience.

Have fun with it.



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

[Algie]

Well mate

im doing this for the nice expierience secondly the cost for a 240 panel is over 600 euro ( $ 850 ) and limited you find only 30 volts + and not 12V  for battery connection we are an island on our own surrounded by sea so frieght is very high so i dont think i shall cover the original cost

[Algie]

TO oztules

this is my final stage " the vacuming " and looks it came very bad i shall upload some pics maybe you can give me your feedback

[Algie]

[oztules]

Can you describe exactly the method you used... step by step. The glass then the eva then the cells (face down on it) then the eva then the backing (plastic you used for your bag should be fine)........ then your wicking material, then your bag.

Then show/describe you vacuum pump sysem, and what pressure you got down to.

It looks all the world to me that you had no vacuum. Your bag shows bubbles that cannot exist if it were forced down against the cells. The bubbles in the plastic tells me that this has already been heated.... (it appears that the front and back of the bag has adhered together).

At this time it looks as  no/very little vacuum.. is the culprit.........Also is there any foreign substances on your cell faces (wax or any other stuff).

What pressure did you get down to .... 0 atmospheres is you goal.... what was yours. If your vac gauge said zero or close, did it's hose get stuck to the plastic bag, and did not suck the contents out.

The vacuum must be on while it is cooking..... just in case.

I haven't seen that effect before except when I did the first on in test piece in the wifes oven just to see how it melted ... no vacuum.. just to see.

The bubbles in the clear parts point to vacuum too.

Hopefully Dave and some of the other experimenters will have something to add..... but it looks sad to say the least.



Can only get better I guess, so explain it as best you can.



On my island you can't even buy glass of any type. Your on a populated island from memory, at least you can buy something. Our 4 shops are good only for food and provisions for cattle and sheep really.



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

[klsmurf]

Hi Algie,
 As Oztules said, check your vacuum. That's the most important part for having no bubbles. Looking back through your postings, I see you noted you removed the fan you used to disperse the heat. Is this still the case?  I really like the idea of the oven heating elements also, especially if they are controllable. With your box/oven being only a few inches in depth, I would have a concern about "hot spots" directly above the elements.  I posted a picture earlier in the thread of what happened when I forgot to put my deflector in between my heat source and the panel. Your pics look to have very similar effects. Keep at it, You'll get it all sorted out.

Kevin

[Algie]

Hi mates

The method i used was glass eva cells and then eva i enclosed it in a bag the thickness of bag is 250 microonns and sealed the whole bag with a hot blower leaving just the hole for the pipe to come out ( i think that is the problem the seal from pipe to bag ) and no i had no full vacuum the vacuum gauge arrived to just the middle of vacuum i shall add a pic of the vacuum pump should do the job i left the pump running while the bag was in oven the fan was running while the oven was onn so i should have had hot air running as well yes the heaters are connected to a thermostate with temp setted at 100 deg C.
The cells were new only soldered
i need to seal the bad were the pipe is running through any ideas??

[dave ames]

Hey Algie,

Sounds like your assessment of the air leakage between the hose and bag is right.

We need to get that sealed up good.. many here have found that using several zip ties work well. I've had some luck just tying many wraps of twine around the hose to get a seal.. also found that we can hear any areas that are leaking (a faint whistle sound) we can hear the pump sound change as well when it's loaded down with a proper vacuum.

I could not see what we have for an airwick? the vacuum hose wants to be embedded deep into the wick so as we have a free flow for the vacuum to spread.

keep at it! these initial test runs are the key to success 

all the best, dave

[oztules]

ok
It seems from here you had no wicking material to move the air inside the bag, and had leaks.

This results in very very uneven vacuum distribution as the plastic sticks and precludes air movement.

The idea....
Your pump looks the goods. I think it does not matter absolutely if your pump is designed for only say 90% vacuum.... so long as it gets to it's limit... whatever that is.

If it does, it means no leaks, that means if you have a wicking material, the negative pressure within the bag will be even.... yours is not.

What wicking material did you use?

I use plastic wire ties to compress the bag opening around the hose. You may need a few, and also an extra when the bags gets very pliable, as it will have to compress all the folds of plastic around the hose to seal.


So.... sealing and wicking are the two most important things for this to work.





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

[Algie]

i shall try to make a more secure end from bag to hose with tie wraps see what happens

may i ask what you mean by "wicking  material " cant understand the meaning !!!!!

[oztules]

wicking material is that materiel that you put in the bag to allow the air to move freely in. Without this, the bag will stick to the plastic backing impeding the air movement required to let the air be evacuated from the bag. There must be this in place or it won't work. It can be towels, rags, glass fiber etc. anything to allow the air to move between the backing plastic and the bag proper into the hose from the vac pump.


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

[Algie]

ok mate
thanks foir ur explanation well what i used i think is quite original hopfully in case i will change it
in agriculture there is a pipe for irrigation which is pourous its full of holes its made for water to come out from everywhere well i changed its job and used this type of pipe INSIDE the bag and turned it in all the lenght of the bag

hopeing u understand i will post u pic soon so u see how i made it if you have another idea pls express urself

[Algie]

I trid another experiment with no success again

i got the bag at almost 80% vacuum when i inserted bag into oven after 30 mins no time for eva to stick to plastic on the bag, air started going in vacuum gauge started decreasing and finished up with all AIR in so i guess the bag bursted.
bag im using is 250 micronns, what are your ideas oztulles shall i raise the height of the OVEN which is 4 inches to 8 inches or increase the thickness of the bag which i cant find more thick !!!!!!!!!!

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