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Solar panels come in all shapes, sizes, ratings, and prices. You can spend a bunch of money but don't need to if you're an educated shopper. We're keeping it thrifty remember?

Amorphous Vs Silicon.

Amorphous solar panels (pic 1) are what's usually found in little solar powered yard lights and trinkets. The panels have a brownish look. This is a low cost technology that is the most inefficient (requires more panel to produce the same power when compared to silicon) and has a shorter lifespan. There are some discount tool vendors that sell solar kits made up from amorphous panels. They do have one benefit which is they perform better in "shaded" applications, cloudy days for example. Pass on these unless you got them for free or darn near free. The one benefit doesn't outweigh all the negatives.

Silicon panels (pic 2) have a blue look to them and that's what you want. Silicon solar cells can be made from mono or poly crystals. This results in a dark blue even color or a blue color that seems to be made up of slivers. Either one is fine for our needs. There is a difference in mono Vs poly crystal panels but for our purposes either one is fine. Mono crystal panels tend to produce more power per square inch but it's a minimal difference on the scale that we're working at.

So we're looking for silicon cell panels, what else do you need to physically look for?

GECONA SOLAR contains other products and information you need, so please check it out.

Solar panels can be framed or unframed. They can be rigid or flexible. they can have a glass face or an epoxy sealed face. Aluminum framed, glass faced silicon panels have the longest lifespan. It's not uncommon for one to last 20+ years as long as it's not physically abused.

Unframed panels need to be framed to protect them and give you a way to mount them. Epoxy faced panels work well for a few years but the epoxy sealant will slowly begin to darken over time and diminish the panels output. Eventually the epoxy gets so dark, the panel is useless. Flexible panels are convenient for portable installations but have short lifespans due to the flexing of electrical contacts and the epoxy sealer they use to keep the whole assembly flexible. Glass faced aluminum framed silicon is the way to go.

Solar panels come in many different output variations. In order to keep it simple, stay with panels that have an open circuit voltage in the 17-20v range. These would be considered 12v system panels and will match up nicely with the ultra cheap regulators we'll be talking about later. Can you use panels with higher voltages? Yes but it will require a more expensive MPPT regulator. Can you use panels with lower open circuit voltages? Not without some electronics ingenuity that is simply not worth the effort. The exception is if you have multiples of the same panel and you connect them in series to raise their operating voltage. There's an additional electrical spec to worry about but we'll come back to that.

New or used?

New is obviously better as solar panel tech is improving constantly. A panel that was $4 per watt 20 years ago is now $1 or less a watt. Solar panels live outdoors, cook in the sun, get rained on, and depending where you live, freeze on a cold night. In short, they have a hard life. $100 shipped for a 100w glass faced silicon panel for a 12v system on ebay is not uncommon. For a two 10w LED light setup in a sunny place, 60w is about ideal. If you can afford new panels, go that route.

Going used?

There's a few things to look for. Skip the epoxy faced panels unless they are darn near free. The epoxy has a limited lifespan before it starts to darken and diminish the solar panel's output. If the epoxy sealant is visibly turning a honey color, it's on it's way out. These epoxy panels can be identified by simply digging your fingernail into the face of the panel. Epoxy panels will have some give, glass won't.

Amorphous panels are not worth getting used unless darn near free. Just like epoxy faced panels, they have a limited lifespan. As they age, the output will diminish. Expected useful lifespan for amorphous panels is about 7-10 years. With the prices coming down on silicon, the limitations of lowered output and decreased lifespan make amorphous panels almost not worth dealing with.

This leaves us with glass faced silicon panels. These are clearly the best option for any solar project. A well built glass faced aluminum framed silicon panel can easily last you 20 years. When buying these used skip any with glass damage. They may still produce but not for long. Bent aluminum frames can usually be fixed by disassembling the frame and straightening the rails. One other defect to look for on silicon panels is humidity damage. You can get humidity inside the solar panel assembly if it's seal has gone bad. This will look like a white haze over the solar cells (pic 3). While not an immediate killer, it will shorten the life of the panel and definitely lower it's output.

What about electrical testing of used panels? If your looking at panels of less than about 400w each you can do all your testing with a common multimeter. Your meter should be able to handle up to 10a of current (most do).

Place panel to be tested in direct sunlight. Set multimeter to DC voltage and measure output. If panel is in direct sunlight the voltage reading should be very close to the open circuit voltage on the manufacturers label located on the underside of the panel (pic 4). Next we will test current output. Set your meter to amps (some require moving leads) and test just like you did voltage. When a test meter is checking amps this places a dead short across whatever you're testing. This is a big no-no on most electronics but ok for testing solar panels providing your meter can handle the output of the panel. The amp reading you get should be close to the max amps rating on the panels label. If you get zero, check your meters internal fuse before condemning the panel. It's not uncommon for folks to accidentally blow those fuses and forget too change them.

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