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[技术] 自制太阳能电池板!

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发表于 2014-7-6 03:39:21 | 显示全部楼层 |阅读模式
自制太阳能电池板!(转)
这件事情我说我并不想自制太阳能电池板,那是因为自制太阳能电池板会有太多难也解决的问题,如太阳能电池板内的冷凝水问题等,都不是很好解决的。在youtube网站上看了很多视频我选择了用钢化玻璃来自制太阳能电池板。

自制太阳能电池板

自制太阳能电池板

 楼主| 发表于 2014-7-6 03:39:50 | 显示全部楼层
It's something I said I would never do..... but now I have.
If you have no value on your time, and want to do your own DIY solar cells, then it has always been possible to cobble some cells together, stick them to a surface, and place plastic or glass over them, measure the output..... and generally feel good.
A fancy frame helps with the karma... but you know in the end it is only temporary.
As the water vapour creeps into the sealed wooden framed ones, or the window glass you scrounged up...breaks because of the heat/cold and localized heating in particular cells, and it all falls in a heap. It can get pretty sad for a lot of devotees that have tried.
There are plenty of youtube stories and how too's...... but all (but the ones using sylgard (or whatever it's called)) are doomed to failure)...... except those who have tried to use EVA (ethylene vinyl actetate).
I viewed a few treatments on the youtube sites, and none of them inspired a great deal of comfort. They all revolved around using a heat gun and a heap of good luck to melt the EVA around the cells, and onto the glass.........
Why I thought, did they make solar cells 30 years or more ago, and still basically the same today...and yet the amature panel maker comes up with lots of bad ways to do it??
I pondered this for a while, and in the meantime, a plumber friend turned up with a few solar hot water panels..... also 25 or more years old..... they were stuffed..... but they did use tempered glass, and it was iron free glass.... and it was free glass ( this was the clincher).

自制太阳能电池板

自制太阳能电池板

So I sat and looked at a few 2 sq meter panels (1x2m).......... yep, had to have a go too.... but it cant be cut!
This is where I decided to look around the world at the current state of play. This was sobering, no real effort at making proper panels like the big boys built without the big boys price tags... why not?
It appears that folks thought you needed a laminator style of machine, which were very expensive, and a barrier to making your own. But if you look at what needs to be achieved, it is really only a few simple steps.... so lets look at the how and why.
 楼主| 发表于 2014-7-6 03:40:06 | 显示全部楼层
Traditionally they use a sheet of glass (iron free tempered if you can get it), a sheet of EVA, the cells themselves, another sheet of EVA, and whatever your having yourself. After the last EVA sheet, you only really need to put something there that will not wick, and will give you something for the very very sticky EVA to bond to that is not your "jig" It can be painted later if you want more protection. Usually they use tedlar, but really any inert permanently waterproof material will do for protection.
The simple theory of what we are trying to achieve is this:
We need to get the cells fully encapsulated in a UV stable envelope, that resists water and air from denaturing the cells. It must allow for differential expansion rates to occur between the silicon wafers, the glass and the medium itself....... and no bubbles.
Ethelyene vinyl acetate is a plastic sheet .5mm thick. It is soft plastic in texture and seems innocuous enough....... however, when it gets to only 65 degres C, it melts. This means that we need not get to very high temperatures to get something to happen.
I'll bet there are plenty of hopefuls ( like me for instance) that grabbed some EVA, some glass, and the wifes oven, and made a prototype cell......but it is filled with bubbles!..... It does stick to the glass and, it envelops the cells well, but it is useless because of the bubble population.
It is at this point that you start to get a bit anxious about where to get a laminator...... but you don't really need one. We just need to emulate what it does.
Next thing we look at is what happens when it melts. To get the EVA to be useful, we need to get enough energy into the stuff to cross link the molecules. It changes the way the material behaves, and increases the melt point considerably as well. At low temp (65C-80C) it melts to itself very well, but is only slowly converted into the final product, so we have to keep it at these temperatures for long periods..... but as we increase temp, things happen a whole lot faster, and 5 mins may be enough at 145C to get it to cross link, and stick very strongly to the glass and the cell itself.
It also needs some encouragement from pressure..... or a vacuum perhaps, and use the air pressure to do the job of supplying the pressing force.
Now we know it works perfectly well without vacuum, but you will have myriads of fine bubbles.... blocking out the sunlight.... well, not so perfect after all.
So we need a vacuum pump. Ideally one that can draw a near perfect vacuum. The vacuum you can achieve sort of directly relates to the bubbles you will get left with. High vacuum.... no bubbles. It's that simple. The vacuum will also press the cells very firmly (200 plus pounds per cell for the 6x3 ones) against the glass, and this will help the glass bond, and make for a very flat cell, with no voids in the plastic envelope.............as always there is a but:... you must have NO leaks at all, or you will get uneven vacuum in the sheets, and you will get bubbles forming.... probably in the inter cell space, but bubbles all the same.
The heating profile I will use is like this:
15 mins at around 50C with full vacuum
15 mins at 65C with full vacuum
70-80 mins at 100C-120C (or hopefully more) with full vacuum
This last bit is dependent on the EVA you get. Low temp EVA is used for window lamination, where electronic components may be incorporated into the glass matrix....
For “normal” EVA if we can get the temp to rise some more.... then good. Even if the containment bag (ok garbage bag) fails at this point, it's work is done for all practical purposes... better if it does'nt.......but we get what we can.
 楼主| 发表于 2014-7-6 03:40:32 | 显示全部楼层
So all in all.......it looks doable.
First step for me was a BIG oven.
An oven that would handle the 2 meter by one meter panes of glass that came from out of the solar water panels. (it turns out that for some quirk of history, there are plenty of these old solarhart type panels laying around over here).

自制太阳能电池板

自制太阳能电池板

We know that the temperatures involved are not terribly high in order to achieve the bonding and cross linking that is required to get the cells to be protected, and pressed against the glass without any bubbles..... so I started with a wooden construction..... yes for an oven.
I had recently pulled down a wool shed for a fellow, and I was given the wood.... lots of old 4x2 hardwood.... so this was to be the frame
It looks like this >>

自制太阳能电池板

自制太阳能电池板

I was also given some packing material in 8x4 foot sheets of low grade 3/4" pineboard.(someones kitchen apparently turned up in them). These would serve for the bottom and lid of the oven. For the sides I just used some of the old floor boards from the shearing stand.....
 楼主| 发表于 2014-7-6 03:40:58 | 显示全部楼层
The whole thing is lined with ceiling roof bats insulation and then all held in the walls with a sheet of TYVEC building wrap material.... could be anything really.... even paper.

自制太阳能电池板

自制太阳能电池板

Ok, that gets us the oven walls and floor, and the lid was just a sheet of the 8x4 pineboard with insulation laying on the top.... Now we have an insulated container that will take our panel.

自制太阳能电池板

自制太阳能电池板

自制太阳能电池板

自制太阳能电池板

What this means to the 60watt panel builder.....is that even an insulated cardboard box will do for an oven (I used one with a fan heater blowing from in front for the initial trial, with blankets and dooners for the insulation...... perfectly good for a 60 watt panel)
Next step is a heating element.
This was simply solved by destroying a fan heater/radiator. These things draw about 2000 watts and incorporate a fan and a nichrome heating coil. They spill out a fair stream of not too hot air, so are unlikely to melt our plastic bags (comes later) when we bring the oven up to temperature.
I built the heater body out of a "think safety" sign (ironic really), which housed the heating element at one end, and the fan motor at the other. The fan blades were plastic, and would melt in this environment (proximity to the glowing element), so I stole the aluminium blades from my big MIG welder, and put the plastic ones back in that.
 楼主| 发表于 2014-7-6 03:41:18 | 显示全部楼层
This gives us a 2000w heater that blows warm air..... but not too hot,and will allow us to gently heat the oven up to about 100-120 degrees, without any cunning trickery required to temp control it. Because the oven is so well insulated...... we just keep adding watts from the heater until we get to where we want.
Finished it looks like this:

自制太阳能电池板

自制太阳能电池板

自制太阳能电池板

自制太阳能电池板

Perhaps finished was too strong a word to use...... but it does work.

自制太阳能电池板

自制太阳能电池板

 楼主| 发表于 2014-7-6 03:41:44 | 显示全部楼层
Sober reflections:
Eva onto toughened glass has a track record, and most folks know of panels that are at least 1/4 of a century old and still running fine. The EVA of today is better than the EVA of yesteryear, and will be less likely to change colour than the older material. I have some BP panels 15 years old, which have clearly changed to a brownish tinge over the cells... from the heat, not the UV alone. The inter-cell spaces are still clear, as are the last 1/2 inch of the outer perimeters of the cells.... but even then, the performance is probably only 10% less than stated on the stickers.
If you build the panels for 50c per watt, and they only last a few years.... then it would have been cheaper to buy them made.... as they should have lasted at least 12 times longer.... so to keep replacing is $6.00/watt......??
To reiterate the preliminary vacuum stage.
With large cells, the metal tab on the front will try to take the pressure of the air when the vacuum is pulled on. It can then try to push the tab wire into the eva, to spread the pressure load. When the air temp is cold, the EVA won't give easily enough, and the silicon cell will try to wrap around the tab wire so it can press against the eva as well.......not being flexable, it will instead split along the tab.
This is easily mitigated by raising the temp up to 50C or more (less than 65C though) for the prevacuum, rather than room temp.
I found room temp fine on a hot day, but too cold at night...... so now use the oven to get 50C. This softens the eva, and makes it easy for the tab wire to sink into the eva, so the silicon presses evenly against the "glass".
Moving right along, we now have an oven to cook the panel in.... we have bought the vacuum pump, and are now prepared to make a test panel/cell..... just to see if it is true.
I decided that it would be best to do a show and tell for a single cell at this point, in a step by step approach.
So here we go:
First get a piece of glass that will fit your cell on.
Wash/dry the glass with alcohol (Methylated spirits).
Grab the bit of your EVA your going to use, I have chosen to build a single 6x3 cell, with some other bits thrown in just to give an interspace between cell and cell bits..... like this:

自制太阳能电池板

自制太阳能电池板

Next throw on the top EVA piece:

自制太阳能电池板

自制太阳能电池板

Now a piece of tedlar, or even just sheet plastic ( I used white building wrap this time) anything you want the rear of the cells to wear. It must be non-porous, rot proof, water proof and everything else proof. It only performs the role of keeping the EVA away from anything that may want to harm it.... and to allow you to get the panel away from the vacuum bag.
 楼主| 发表于 2014-7-6 03:42:07 | 显示全部楼层
The EVA cross links into something a bit like silicon. It is rubbery, and not especially strong..... although try getting it off the glass once cross linked and bonded properly and you may decide that it is very strong.
Here we are with a piece of building wrap on the back. (The wrap is porous but the EVA will soak into it and fill the pores.... it has been found to be better to just use plastic sheet... the EVA when heated initially will be a runny liquid.)

自制太阳能电池板

自制太阳能电池板

Now we have all the ingredients to make it work, we just need something to allow the vacuum to suck the air through..... an air wick if you will. This can be any porous material you can get hold of. I find for small 60watt panels, that a few thick teatowels covering the back do ok, for bigger panels, it is best to find something a bit better.... beach towels? Glass matting would be good if you have it, I tried shade cloth on the 2mx1m panel, but found that it shrinks a little when it gets heated. Not enough to damage anything, but enough to make the cells not line up as I had placed them. For this show and tell I just folded up a rag that was lying around near me... and it looks like this:

自制太阳能电池板

自制太阳能电池板

Next we need a plastic bag big enough to place our panel in. Unless your into building big ones like I have, most likely a big garbage bag will be the best for the job... cheap, plentiful, and plenty strong enough for the job. Here I used a transparent one for demonstration of seeing the stuff in the bag

自制太阳能电池板

自制太阳能电池板

Next we poke a hose into the bag and seal it up I use plastic wire ties. This seems to hold the bag opening onto the vac hose pretty well.... except for this time. The plastic bag must have a hole in it, as I could not get down to max vacuum......
 楼主| 发表于 2014-7-6 03:42:26 | 显示全部楼层
Do NOT place the rubber suction hose over a cell. It will crack that cell, so just place it between your airwick material and the glass... or inside the folds of the material, but away from the cells themselves, and let it suck from there. Provided there are no leaks, all the air will all eventually seep through the wick. If there is a tiny leak, your wick will need to be very very porous to still work. If it is a bit difficult for the air to move through, a leak will kill this project.... if it is a very free wick material, a leak may be tolerated.... best without though.

自制太阳能电池板

自制太阳能电池板

So I have replaced the clear leaky bag with a trusty black garbage bag....

自制太阳能电池板

自制太阳能电池板

Note the wire ties:

自制太阳能电池板

自制太阳能电池板

Now for this exercise I won't use the big oven, but instead will show just how simple this can be.......
 楼主| 发表于 2014-7-6 03:42:54 | 显示全部楼层
Here is the latest you beaut high tech laminating machine...... or the build it in 1 minute oven..... and it will work every bit as well as an expensive laminator

自制太阳能电池板

自制太阳能电池板

Of course we know there is more to it than this ......like the heater.
For this size ... and up to at least a 60W panel, a fan heater pinched straight from the loungeroom would do to get it up to 80-100C..... or if you wanted to prove a point, perhaps broil it in boiling water.....ie half a 44 gallon drum parked over the camp fire........simmer till cooked.
Well I guess that would work too, but I'm trying to make clear that this does not need to be high tech, to get a perfect result.... just temp time and vacuum.
If you are going with very low temp, then it will take a very long time... ie 80C for 80 minutes, or 140c for 5-10mins
I have toyed with the idea of using the sun... ie use the some of my spare solar glass from the hot water heaters, and make a solar oven... very similar to the solar panel itself... as the oven.... I haven't tried it as yet, but if you can boil water on a hot day with a sheet of glass and the black backing..... then , it can crosslink the EVA easily too.
Note the solar cooking has now been done in Africa to do it similar to this.... but without the vacuum...... they were still happy.
Your trial one will give you an idea of how long to cook it with what equipment you have to get your brand of EVA to crosslink properly and stick to the glass VERY well.
If it has not been left for long enough, you will be able to peel it off the glass, we don't want that..... try just putting it back in and cook some more... noting how many minutes gets the required bonding... if it is too poor this extra cooking may not be enough, but has worked before.
Our trial one looks like this

自制太阳能电池板

自制太阳能电池板

and the whole sophisticated arrangement looks like this:

自制太阳能电池板

自制太阳能电池板

And yes, it got to .....and stabilized at about 112c... so I cooked it for 45mins anyway. Note the improved insulation (brown towel) pushed the temp up another 20 degrees from the picture first showing the box oven without this high tech improvement.
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