Well it's time to ramp it up a bit. Yesterday I attempted to show how simple it is to work with the EVA, and make a single cell panel with very little tools at all..... cardboard oven etc.
Today I needed to build a new 250watt panel, so I tried to photograph it as I went..... but forgot to use the camera as much as I would haver liked. You just forget that people may not know how to do some things that I take for granted, and so gloss over it.... eg how to build a 2.5m*2m plastic bag at a moments notice etc.
I will take it as read that we know how to tab cells, (youtube does this well). Once tabbed we are ready to begin..... first we need the glass.
In this case we will be using the iron free solar glass from a disused hot water panel. It is toughened, and the iron free...... this means when you should get 1.8w per cell you will. If you use window glass, then it will be less, but work anyway.
So we get the glass and wash it in water and dry thoroughly. Then wash the cell side with methylated spirits and dry. My glass looked like this:
I won't attempt to detail the cell joining process as it is just soldering cells together, and this too is covered well elsewhere. Suffice to say, keep as much room between cells as your design and glass size can afford... I like 1/4 inch, but never get that luxury. In this case I need 23 cells in a single string to fit in the glass with an inch left at each end. This dictates very close spacing between cells, and can lead to shorts if not careful.
I also use the solar hot water case as a straight edge to build the string in. I use transformer paper on top of the aluminium, and use the side of the case as the straight edge. This way guarantees that the cells don't wander about the place.
It looks like this:
We then carefully (very) pick it up and transfer it to the glass sheet which has the EVA cut to size on it I use some untabbed cells to get the spacial arrangement to make it look symmetrical not very well really, but i did try a little bit.
We keep laboring away until we fill the glass up with cell strings. We then need to place the bus lines in to join the strings. There was not a lot of room to do this here, so I actually placed the output tabs on top of the last cells in the string in some places. I use transformer paper to effect the isolation needed, and EVA strips between any surfaces, so that the whole lot will melt together later. It may be seen here:
From a "looks" point of view, it is more important to get the strings straight, and the gap between strings even. The inter cell gaps in a single string seem to have little impact visually compared to these other two requirements. I see a lot of youtube folks with tile spacers to try to get it right, and they still fail miserably.... so just keep the lines straight, and even between strings and it will look ok. .... I think anyway.
Then it's time to place your second sheet of EVA on the pile. Hopefully you remember to cut it before we get to this point.... unlike me.
Then it's time for the backing material (tyvek for me, whatever else for you).
Later I turned the sheet over ...... with mixed results. It wrecks the visual impact because of the blue and red wirting.... ahh well.
Now the next part is critical to success..... yes the plastic bag and wicking material
2.5m x 1.5m plastic bags don't grow on trees over here, so we need to build our own easily and quickly.... and it MUST be airtight.
I did have a roll of plastic sheet donated from a farmer. It was 2m wide and a million meters long.... so I cut off 2x 2.5M bits of it and laid then on the table one on top of the other.... Now we just need to seam them. We can use a straight edge.... for no other reason than to limit the damage we are about to do.
Place the straight edge about 1" in from the edge of the 2 pieces of plastic laying on the table. Grab the heat gun, and heat the plastic edge, running up and down the straight edge quite quickly. The plastic will start to melt in that 1" zone. Move the straight edge onto the 1" melted zone, and it will cool it rapidly, and seal that zone..... like this:
We then end up with a huge plastic bag, with very little effort. We can seal the open end after we place the cell inside of it.
Here is my plastic bag:
Last time I used shade cloth for the air wick material, this time I found an old dooner, which will allow for reasonably free air movement. This is key to no bubbles... as well as no leaks in the bag. Shade cloth shrinks with the heat and distorts the cell layout, the dooner did not... yippee.
Bagged up, and the vacuum starting to take up the slack, we get to this:
We can see how I have sealed the end of the bag now, and placed the vacuum hose into the dooner cloth. It's all starting to happen about now.
and nearing vacuum condition, the dooner is now flat as a pancake:
Here is a closeup of the hose going into the cloth:
Now we have to maneuver it into the oven
The whole lot was under vacuum for about 15 mins before I started the heater. It slowly climbed up to 105 degrees or so, and so I ran it for 70 mins... better more than less, or glass adhesion may not be complete.... and thats it.
There is nothing more that can be done now.... but wait... and wait.
After about 70 mins, I turn off the heater, pull back the lid of the oven, and let it cool off.
Before it gets too cool, it is wise to get it out onto the table and undress it.... the EVA runs where ever it can, and some may stick to things you don't want it to stick to (the dooner for one)... so rip off the plastic and free the dooner as soon as practical. The eva will still be a bit soft at this stage, and you can remove some from the edge or whatever. When it cools and the curing is finished.... nothing is easy with it. It is tough stuff.
Like I mentioned earlier, I may ditch the tyvek altogether, and use grease proof paper, and try to just get the eva on the back. It needs no protection at all in my application, the solar water jacket protects the rear of the cells from pointy objects, and the EVA is water resistant, uv and everything else resistant. Open panels may need protection .... although I can't really see what from.
This software can't handle more than this, so I will continue with a comment to keep it all together
...........oztules