First, I’ve ordered 36 0.5V, 4.54A cells, tab wire, bus wire, liquid flux in a set from eBay for $47.99 after shipping.
When I received the package there was actually 40 panels in it as the seller threw a few extras in just in case any were damaged in shipping. They were not. Score.
Time to start tabbing. If you’re going to do this ever yourself, make sure you use at least a 40 watt iron. Tabbing wire melts beyond 680F and if done correctly, no solder is required to tab the cells.
One by one until they’re done… note that the tabbing is happening on top of a 3/8″ thick piece of tempered glass. The glass protects the cells as it dissipates the heat from the iron instead of injuring the silicon.
Done and done… The entire process took about an hour. It definitely started going more quickly once I got the hang of it. Note that the tabbing wire runs across the top of the panels and extends about 50% the length of the panel beyond the edge. Next time I’m going to make it 100% and you’ll see why later.
Now it’s time to mount them. I purchased a 4’x8′ piece of plexiglass from Home Depot for $18. This gave me much more surface area than I needed, but I wanted to make sure that as this was my first panel built from scratch I’d give myself a little room between each to work with. This turned out to be a genius decision later on. Each cell is 4″x5″ so I laid them out in a 5×8 pattern with 1/4″ between on all sides with a 1.25″ margin. Large margins, extra space between lines. How I survived writing papers in high school… Once positioned, white electrical tape was used to hold them in place.
An added benefit of the plexiglass is that it actually increases the efficiency of the cells because the chemical construct of the plastic actually deflects the photons towards the panels and also creates a sort of photon greenhouse effect with any that are deflected off of the cell on initial contact.
This is the poorly drawn gist of what’s happening.
Because the chemical makeup of the doped panels and the thinness of the cells to allow the field effect to occur, a very low voltage difference is generated. However, a relatively high amperage is created because of the sheer number of electrons getting flung around. So each cell is ~2.2 Watts but 0.5V. This ratio is going to make measuring the actual available amps a pain in the ass. Later.
In order to build up the voltage to something usable I’m wiring each cell in series. This puts a lot of pressure to perform on each cell as there’s no redundancy whatsoever, but it’s a prototype so who cares if it works. To build up to usable voltage, the tab wire will fold from the top of one cell to the bottom of the next all the way down 5 columns of cells. This will give me 5 rows of 4V. Bus wire will be run up along the gaps between cells and continue the series, giving the upper left and lower right cells the ends of the series. You can see the bus wire is under the black electrical tape:
Front after wiring completed:
Also, I’ve got wood:
It’s a 4’x8′ piece of plywood spray-painted white. Any exposure of the panel that could reflect instead of absorb light is good for two reasons. One, it might get somehow bounced onto one of the cells. Two, cells are very temperature-sensitive. As they heat up, the amperage declines. I still have to crunch the numbers to see if it’s possible to addd peltier cooling that would be efficient enough to result in a net positive gain.
Mounted and sealed. Note that solar cells are subject to oxidation when exposed to air, so making them as air-tight as possible is essential. These are designed for a service life of at least 20 years. I doubt I’ll let them live that long.
And powering a simple inverter. This is very lossy as there is no transformation/regulation to 12V so 8V+ is being lost to heat dissipation. I should be able to push the voltage down to ~14V and increase the amperage 20-25%.
Next step, regulating voltage, smoothing spikes, building a base for it, and implementing a microcontroller-based light seeking/tracking. Then battery charging/management. Then probably something else. Maybe a toaster bath.
So the goal was 100 watts for $100. Total cost of materials:
Solar cells + tab wire + bus wire + flux: $48
Spray paint: $7
Electrical tape: $4
Wood support beams: $3
Screws and washers: $5