A used solar panel that has a chipped or broken surface, as well as a solar cell peeling from the glass, is worthless. By buying a worthless solar panel, you are at a loss, no matter how cheap the panel might be.
Never buy used solar panels without having a look at them! The first thing you are going to notice will be some kind of obvious damage — cracks, scratches, etc. Above all, you should check whether the panel surface is chipped or broken. You should also watch out for cell damage, which is a typical consequence of improper handling during mounting, unmounting or transportation. Broken terminal connections are not terribly important, as they can be fixed by soldering.
Check whether each connection is fixable — this is one of the reasons that you should bring a fellow electrician or technician with you. You should also check for water condensation between the glass and the silicon. Moisture has a detrimental impact on the panel’s efficiency. Check for any indications of delamination.
Delamination describes the detachment of solar panel layers because of humidity entering into those layers, and appears in the form of bubbles in the panel. Not all solar panels are resistant to long-term exposure to humidity, so you could ask whether the panels have been tested against humidity. If the panels lack such a certificate, do the following:
- Check for any openings between the inner side of the frame and the back
sheet. There should be no openings and the glued edge between those surfaces should be smooth.
- Check for any visible slits between the upper side of the panel and the glass.
The solar cell should be steadily glued (sealed) to the glass.
Avoid secondhand panels used in marine environment. The reason is that such panels might have been exposed to much tougher conditions than their land counterparts — wind, storms and, above all, seawater cause much faster corrosion than normal.
Mind that if even one cell of a panel is damaged, all the other cells in the same string are useless. This means that its power rating will drop severely, down to between 25% and 50% of the stated value. Broken panels are a fire hazard. You’ll hardly be able to find any electrician eager to mount anything broken in an electrical network, let alone connect that network to the utility grid! Older panels were manufactured on a plastic substrate, and not on a glass one. Plastic might turn brown after years of exposure, but this is not necessarily a problem. The important facts are the power and voltage readings of the multi-meter upon the panels’ exposure to sunlight.
For solar panels, efficiency is as important as lifespan! If you buy a branded secondhand solar panel, it might be operational for years to come. At the same time, however, panel efficiency is a key factor in any solar panel system evaluation. If you don’t know the efficiency of your panels, you will know neither how many panels will meet your energy target, nor how much area you need to install them.
Solar panel measurements
You should test the panels using a multi-meter not only to determine whether a panel is operational upon exposure to sunlight, but also to measure the generated voltage.
1) Measure the voltage across the panel terminals. This should read a steady voltage. For example, when exposed to maximum sunlight, a 12-volt panel should show a fairly steady (not fluctuating!) reading of 21 volts between its terminal connections. Then you should measure the voltage across the panels at less sunlight. In total darkness, the voltage should drop significantly, but there should still be some voltage. In shade, the voltage should drop only a little.
2) Examine the current. Change the multi-meter to ‘DC current’ mode and select the highest amperage scale. Similar to voltage measurement, examine the current across the panel in clear sunlight, in total darkness and in shade. The current could vary a lot more than voltage does. What you are measuring is the short circuit current of solar panels since the load resistance of multimeter switched to a current measurement mode is almost zero. Different panels behave differently. For polycrystalline panels, the cells are connected in a series, so if just one cell is shaded, the current drops significantly. This means that any potential shade is detrimental. Amorphous panels do not have this same problem. What we are interested in is solar panel output. Power is dependent on the amount of sunlight. To get higher power, you need more sunlight.
Warranty and warranty support
Usually, secondhand solar panels do not come with a warranty.
New cheap solar panels, however, normally come with some warranty, although it’s much less than 25 years. Therefore, you should check to see how the warranty would be applied. This means that you need to ask who will take care of the panel in the event of a problem (malfunction or damage) — a vendor’s representative or you personally.
Furthermore, if a panel gets damaged, it is important to know:
- Whether the vendor is going to bear the expense of transportation and repair,
- In what time they can do that.
Remember that, regarding warranty issues, big solar suppliers are more reliable.