I had a need to provide power in a remote area without access to the grid, for lighting at night and water pump operation.
Factory solar cells that are available in local shops were very expensive, so I decided to try to build one myself.
Bought a kit of solar cells from ebay:
40/80/108PCS 3x6 solar cells 1.8W/pc cell for DIY solar panel kit 156x78mm - $41.74
Descriptions from seller:
"B Grade with small minorcosmetic defect"
Average Power(Watts): 1.8Wp
Average Current(Amps): 3.6 Imax
Average Voltage (Volts): 0.5 Vmax
"The Voltage ofsolar panel should higher than the voltage of your battery. such as if you wantcharge 12V battery, you'd better do a solar panel with 18V battery."
$0.39 for each watt - sounds like a good deal.
I've found that its cheaper to get tabbing and bus wire with the kit than buy them separately.
Although I already had a soldering gun, this one came handy because it has flat tip which is exactly what is needed to solder tabbing wire to the panel.
So I decided to go with 36 cell panel which according to spec could give 65W.
40 cell pack seems a perfect amount, to have 4 panels extra to cover their accidental damage.
Kit had everything needed to assemble the cells:
40-3x6solar cells
65feet tabbing wire
16 feet tabbing wire
flux pen
60W 220V/240V soldering iron gun
When I opened the case, first cell was already cracked :(
But all the rest were fine. B grade defects were indeed cosmetic, mostly uneven sides.
I recommend this tutorial about how to tab cells
Important thing to learn is the cells are indeed really really fragile.. They are thin as foil and crack like glass.
IMPORTANT!
- use glasses to protect your eyes
- use fan to vent soldering gasses away from your nose
- use rubber glove to protect cells from grease. good to cut and use only fingers from glove.
Good way of joining cells together I've also learned from "greenpowerscience" video
I took the glass from old window and laid strips to it. Thanks to the adhesive tape, it was very easy to perfectly position them
I've decided to cover cells completely with tape. I've used small sponge to gently push tape to the surface.
Now it was time to encapsulate the cells to avoid moisture getting to the cells.
Possibilities are:
- EVA film
- Sylgard
Both seemed very expensive and hard to source.
So I took the easiest way and encapsulated using second glass from the same window and using uv resistant sealant ( PENOSIL Premium All Weather Sealant 4eur/piece) which said to adhere to glass.
Idea was inspired by this video:
I've decided to put a layer of polyethylene foam(sold as underlay the laminate flooring), to push cells to glass and eliminate free air inside to reduce condensation issues.
At first I've used the bus wire to wire out from panel, but later decided to use isolated wire and solder it inside the panel.
The sealant has strong fumes, so make sure to apply it outdoors.
Test results under direct sun:
Voc = 22V
Isc = 2.3A
It turned out the panel gave more voltage than expected, 0.61V per cell.
The cells claimed to give 3.6A, I didn't tested the cells under the sun.
Usable power with 12V load amounted to 30W, more than twice less than specified maximum. Mainly due to improper glass and that some cells in the series are not that good. Still OK for me, but I've expected more.
Two UPS Batteries designed for standby and cycle use, connected in parallel:
BATTERY 12V 7AH VRLA/FGB7-12 EMU - 11,56 EUR
Inspection after 2 months
Wire made a gap and moisture started to get in and condense around:
Good thing I've taped the cells very good and it did not made any higher, the cells looks perfectly dry.
Eventually it will make its way to cells, then I will have to open up the panel, dry it and try to reseal better.
Summary of lessons learned
- Wire lead needs to be sealed better
- Old glass reduces output by 30%
- Weakest cell caps output, screen each cell!
Applications
Quick summary for what I've used the power from the panel:
Lighting
LED 4W 12V Warm White MR16 - Around 3$ piece
I've removed the front plastic and now they give quite wide angle. The plastic part served as a press to keep base in contact with leds, so I've tensioned a small wire. Seems to work well.
Water pump
Micro DC 5-12V Brushless Magnetic Pump High Solar Hot Submersible Water Pump$13.58
If you buy from them directly you can use me as recommender "iTakey" to get 5% discount
http://www.buyincoins.com
I hope you've learned something useful :)
