Buying Used Solar Panels
We don't recommend purchasing used solar panels as most are too small and voltages in older panel are sufficiently different in output causing them not be efficiently combined with newer, larger panels. Many older panels come with brand names no longer heard of and don't have specifications that can be found on the Internet. However, we sometimes hear from our clients that they've purchased their solar panels from someone who is upgrading their system and wants their panels to be of the same shape, colour and form, and prefers to start over rather than to display a mix of panels. Solar farms purchase many pallets of solar panels and sell off cheaply those they did not install. There are deals to be found!
Panels to Avoid
Unless you're willing to take a BIG chance and are prepared to work on them avoid panels with:
Test PV Panel Output
Before you go to see the panel check out what the specifications for that panel are and bring them with you. Bring your multimeter with you, set it to DC volts, and test the used solar panel by measuring across the open-circuit (OC) voltage by measuring across the positive and negative terminals. If you're not going to to the location during the day or on a cloudy day you're taking your chances. A 12 volt panel should produces approximately 17 volts in full sun. A Larger 72 cell panel has an OC voltage of around 47V.
Next measure DC amperes; again measure the short circuit current in full sun between the positive and negative terminals. Watts = Amps x Volts. To determine actual panel Watts multiply the current (amps) you measured by the panel's rated voltage. If you don't know the panel's rating multiply your measured amps by 17 for a 12V panel.
You'll need strong alligator clips on your multimeter, but remember to tap and giggle the panels while you're testing them. Intermittent problems can be difficult to both trace and rectify. Unfortunately you won't be able to check the panel under a variety of temperatures. Some intermittent problems are due to temperature changes.
For a 12 volt panel, multiply your current by 17 volts to get watts. (17 volts is the rated voltage of most 12 volt panels.)
We can't advise you what a good price is for used panels. Just remember that 20 year warranty applies only to the original purchaser. The price had better be a good deal!
Some panels change colour over time. Don't concern yourself about panel discolouration. Measure the actual power output, and make your decision based on Watts.
Of the electrical problems to resolve yourself of, loose connections on the output leads, corroded connectors and breaks within the insulated wire at the strain relief, all causing intermittent problems, are the simplest to rectify. Problems within the panel cells can be repaired but require substantially more commitment and expertise on the part of the buyer.
Bypass diodes will sometimes fail as a result of a nearby lightning strike. If they are shorted out they will significantly reduce the solar panel output. Diodes can be frequently be changed with relative ease with silicon diodes of an amp rating of the panel; look for a voltage rating of 400V or better.
Tricks and tools to repair the panel itself include using the same conductive epoxy used within the heated window glass of cars, electronics grade silver content solder, stained glass silver adhesive tape and epoxy sold as being conductive will help.
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