Evaluating a used solar panel & controller?

I was figuring that since he is asking $100 I would offer 50 if it looks ok, and go up to maybe 75 if everything seems to be in very good shape.

Does that seem reasonable?

My experience on CL is that people ask for more than they expect to get -- and quality is all over the map. Some stuff is like new, some is total crap. Did I tell you all about the composting toilet with a turd in it? AND it had been under a roof leak for years and -surprise- the electrical bits would not even turn on. But I got a nice deal on a vintage cabinet, from another seller :).

To give you an idea of how to value for this deal.

You can get a new 100 watt panel for $125 from solar blvd ($150 with shipping), and a 10 amp controller for $10 on e-bay from China.

Doug

Thanks so much for the advice! I finally heard back from the seller; turns out he is out of town and will be back this weekend, so I will meet him then.

You should not be talking more than $1 per watt for a new panel and they do have a limited life expectancy and if the controller is of similar age...

Examine the back of the panel for any 'burned' spots. That indicates the panel has gotten hot and possibly shorted, or is about to short. I'm sure your voltmeter would reveal less than Voc if that had happened.

It's not all that common, but it happened to me.

I'd also measure the open circuit voltage and compare to the Voc spec. More involved to test the controller. Check panel and controller model specs.

I guess what I'd want to see is the output of the CC to a battery. Beyond that, the price is low enough to just grab it and figure out any issues with the CC in the future.
Panels are rated to 80-90% over 25 yrs. so age doesn't really mean that much except not to have your first module being of an ancient variety that has a weird voltage/current output. In case you want to add more panels later, a close match of output is a good thing.
I'm guessing but the output voltage of a 12V nominal module of 100W would be in a range of 15V to 22V. Current could be very variable depending on sun value and orientation.
Bottom line--if it works, grab it.

Hi,

It should have it's factory rating stamped on the back of the panel, and recently panels started to come with factory production dates, more for warranty reasons than any other. I have a pair of 45 watt panels that cost $600 back in 1994, but are only worth about $100 today. I have not checked the amperage output, but most warranties state that they should have 80% of their normal rated output when 20 years old, or they can be replaced as defective.

I don't think that the solar panel should degrade that much over time. The normal 12 volt panel will have a 19 - 22 volt 'open circuit' rating, and you should measure that voltage when it is in full sun and no wires attached.

If you hook up a headlight to it, then you will get the voltage under load. Most car lights are in the 55 watt range, so it might still produce 14 volts with a 4 amp load on it, and make that headlight shine bright! Or two headlights and it should load up the panel to the max wattage, you might get anything from 10 volts to 14 volts (depending on the headlight wattage rating, and how bright the sun is, and how many amps are going into the light bulbs).

Clamp on meters that read DC amperage are very rare, but Sears used to sell one for about $100. IT will clamp around a DC wire and measure it's amperage. Most clamp on meters only measure AC amperage, as it is easy to pick up the influx of power going through a AC line.

You can print out the prices at this website (for panels without a frame cost is around $1 per rated watt new) and give them the print out, and perhaps get this panel (with a frame or it will be practically useless to install on a RV) for around $75.

SunElec.com

If you do not buy this panel, you can look for 12 volt 'nominal' panels at this website, and look for ones with a frame. Normally aluminum frame that you can bolt to brackets mounted to your roof.

I made my brackets out of 2" aluminum angle that have 3 holes 3/16" into the roof and 5/16" hole for a 1/4-20 bolt into the aluminum frame of the panel.

Good luck with your project!

Fred.

Hi,

If the panel is brown colored it is pretty ancient and won't meet the output specifications.

Look for other physical damage--scratches or even cracks.

Look for panel AMPERAGE rating on the label. If you handheld mutimeter can take the amperage using the high amps DC scale, connect the meter leads and switch the dial to amps.

Take the panel out in full sun between 10AM and 2 PM

Nothing should be connected to the panel. Connect your two meter leads ACROSS the panel positive and negative electrical connections. Aim the panel right at the sun.

What does the meter say for amperage? Does it closely agree with the short circuit "I" listed on the panel decal?

Others will want to contribute here.