I received an email today that I really enjoyed fielding:
From: "James" firstname.lastname@example.org
Subject: Building Solar Panels
I have been wanting to go off grid for some time now and was wondering if you knew anything about the broken solar cells people are selling and if they are any good?
The broken and chipped solar cells you see online are usually pretty decent deals but you have to be careful. A solar panel is only as strong as its weakest cell, chipped cells are weaker and thus bring down the entire output of the board. However, of course there is a solution.
First you are going to need a light source with a very bright incandescent light, a volt meter, and a permanent marker
Take each solar cell and place it under the light, measure the output in amps and write the number on the back of the cell. Group your cells into similar outputs and build your panel! The solar cells I buy are 3.5 amps on average at .5 volts (volts x amps = watts). A good rule of thumb is to group your cells into 3amps, 2amps, 1amp etc... and build panels from each stack.
New cells generate 1.75 watts each so you need 36 of them to build an 18v panel (for charging 12v batteries)
A chipped stack that generates 1.4 watts each would need 45 cells to make up a panel that generates the same 18v as the 1.75 watt cells.
Here is where I say it is a decent deal, depending on who you buy from and how much you pay, the majority of your cells may not generate any more than .7 watts, meaning you need 90 cells to generate the same power as the new cells. If you paid any more than half of what the new cells sell for you paid too much, and you have poor quality cells. I prefer to stay in the $0.30/watt range and I have had great results.
Some notes about solar cells:
As long as the solder is intact on the front of the cell, it can be broken in half and still work fine.
Cracks that go horizontal along the cell are better than vertical cracks.
Although there are two leads coming from a cell they are both the same polarity (positive or negative)
The back side of a cell is usually positive and the front is usually negative.
Building shingles out of solar cells would be a wicked awesome roofing idea!
So is it worth it? For the large part yes, but you get what you pay for so don't be disappointed when your super cheap cells are all super broken. They sort these cells at the factory and price them accordingly when listing them.
Is there any way to know exactly what you are getting when ordering these cells?
Actually, coming up here in the next few weeks we will have a shop up where you can order damaged cells directly from us! We are going to group the cells by weight and offer them to you all so you can select what you need for your system. The reason we do it by weight is because the power generated by the cell is dependent on the amount of surface area. Less surface area, and thus less weight, translates to less power.
You can even make a solar panel using shards of solar cells like this guy: (although instead of using wire I would use tabbing wire because it is already soldered, making my life easier.)