Second-hand solar panels: Are they worth it?

People put up their solar panels for sale for different reasons. Some have broken their panels and want to get at least something out of them. Others want to replace them with more modern and efficient models. Finally, some people just don't want to have panels anymore and decided to sell them.

There are lots of cheap used solar panels for sale on the internet. The discount on them is around 60%-80% of the original price. Pay attention: it doesn't mean that these are 60-80% cheaper than new models. The price mostly depends on the age of a panel and the damage it suffered.

When looking for second-hand panels, you have to accept beforehand that they are likely to be damaged. Some defects are easy to identify, others can be revealed only with the help of an expert or special equipment. For example, a broken junction box is self-evident, but microcracks can't always be found with the naked eye.

The damage to a PV module isn't always critical, but can be troublesome nonetheless: the output of a solar panel drops and, in some cases, the lifetime of a module decreases. Some problems you can fix yourself if you are up for it – for example, replacing a broken bypass diode is rather simple. However, sometimes it is not just worth it. Moreover, if you've bought damaged panels from someone, getting warranty support for them is usually a pipe dream. So, while purchasing old PV modules might save you money, it's a risky move overall.

Looking at the big picture, the rapid growth of the solar industry is another reason against used panels. Solar panels lost around 82% of their price over the last decade, according to the International Renewable Energy Agency (IRENA). Modern panels are simply cheaper than the old ones were, which suddenly makes the discount on used modules less appealing.

Modern panels are much more efficient than they were back then. They've become more tolerant to high temperatures, cloudy weather and shading. What's more, the performance of used panels will be much below their rated power output. On average, a panel loses 0.5% – 0.8% of its power output per year, so a panel manufactured in 2010 is going to perform at around 90-95% at best. Thus, a PV system out of old panels is going to take up much more space than a brand new one of the same capacity.

The bottom line is that new panel technologies and rapidly falling prices for PV modules make it unreasonable to go for second-hand options.

While building a whole residential installation out of used panels is ill-advised, just a couple of used panels can come in handy. For example, buying a few used panels can be great for a small DIY project in your garage. So here are a few tips on choosing an old solar panel:

• Look for a model without any visual signs of damage.
  
  
• Check the power output of a panel with a voltmeter and compare it to its initial rated output to see the difference.
  
  
• Burned out bypass diodes are common among old solar panels and can be replaced. You can get a panel with dead diodes for a really low price, purchase new ones and make yourself a nice module.
  
  
• Check the connections of solar panels as they often pose a problem. In some cases, broken connections can be repaired with solder or conductive epoxy.
  
  
• Don't be too afraid of the brownish hues of old solar panels – it often doesn't say anything about their performance. If the appearance of panels isn't a dealbreaker for you, you can get decent panels for a very low price.
  
  The subject has been discussed on Reddit as well. Some solar fans found used panels to be an okay choice for a home system, as long as they are not too old and the dealer has good reputation and quality control. However, the user under the nickname ‘mildlyinfiriating’ wrote: “Double check the permitting side of the process. The used panels that I have while I'm sure once were UL certified technically aren't any more because their labels have been removed. Having UL certified equipment might be a requirement for you”.
  
  

Alongside panels, you might stumble across other used solar equipment. Keep in mind that it isn't as long lasting as PV modules. Here are approximate lifetimes of solar system elements:

• Solar panel – 25+ year
• Charge controller – 10-15 years on average
• Deep-cycle battery – 2-10 years, highly depends on the type of battery and maintenance.
• Inverter – 10-15 years, while being the most fragile part of the system.