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I have understood that solar panels don't last forever. Warranties are typically a couple dozen years, and you can expect your panel to last for perhaps twice the warranty period.

But what does exactly happen when the panel is failing? Does it fail suddenly like computer hard disks, or does its output degrade like the capacity of batteries? What are the physical principles behind the failing solar panel? Is the failing in some way related to heat?

Do solar cells made by a reputable brand last longer than cheap Chinese cells?

Is it possible to make a solar panel that would last essentially forever given a high enough price is possible? Such a panel might prove useful if it turns out that the low interest rate environment will continue.

Of course, there are many types of solar cells, so the answer may be limited to the most common types, i.e. polycrystalline and monocrystalline silicon cells.

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    \$\begingroup\$ @Chloe That is a good question, but perhaps not for this site. My understanding is that eventually they will pay back the energy invested. That is obviously dependent on the lifetime, so hence this question. According to Wikipedia, payback is from 1 to 4 years: en.wikipedia.org/wiki/… \$\endgroup\$ – juhist Jul 12 '17 at 20:27
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    \$\begingroup\$ @Chloe You can estimate that by calculating whether it takes more money to manufacture a new solar panel than you save in grid energy over its lifetime. \$\endgroup\$ – immibis Jul 13 '17 at 0:44
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    \$\begingroup\$ Someone can go to chop down a tree, make a mistake, and drop the tree on some solar panels. That will cause a failure right there. \$\endgroup\$ – Zach Lipton Jul 13 '17 at 1:53
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    \$\begingroup\$ @Chloe that's just lies (propaganda) fomented by competitors and state actors with a vested interest in our (lack of) energy independence, targeted into a receptive audience (neocons). Feel free to ask on skeptics.stackexchange or Snopes. Of course they're all bought-and-paid-for by Al Gore ;) \$\endgroup\$ – Harper Jul 13 '17 at 2:55
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    \$\begingroup\$ @Chloe A similar question was asked here: skeptics.stackexchange.com/questions/5101/… \$\endgroup\$ – Steve Smith Jul 13 '17 at 10:23
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Reading here and a couple other places makes it sound like solar panel degradation varies widely. Manufacturing origin doesn't appear to be correlated to longevity or if it is, it may be opposite what we expect (China appears to do well). The general gist is that you'll lose a fraction of a percent every year on average. It's likely due to high energy photons slightly changing the structure over time. Weathering is also a concern. Wind-blown sand scratching the surface and dust blocking light are two other ways cells degrade. Most solar installations appear to be able to handle 20-40 years of use without issue, but some don't appear to handle thermal cycling well. In that case, you can have catastrophic failure of one or many cells causing poor solder bonds to break, delamination to occur, or entire cells to crack. Corrosion of the cell and connectors could be another late game failure mode.

I think more of a concern than the cells degrading is the supporting electronics (inverter) dying. The cost of installing a solar installation these days is largely being determined by peripherals rather than the panels themselves. Power electronics to support the system and their failure mode is really what I would be researching if I were in your shoes as I believe the likelihood of catastrophic failure there is much more likely in a much shorter timeframe.

This looks to give a great rundown of many manufacturers and their lifetimes. I've included a diagram from there below: enter image description here

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    \$\begingroup\$ +1 for Power electronics to support the system and their failure mode is really what I would be researching. I'd be a lot more concerned with the power storage system failing. \$\endgroup\$ – Dan Esparza Jul 12 '17 at 17:34
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    \$\begingroup\$ @DanEsparza Good point, but that's not necessarily a part of a solar installation. Most of the large installations don't want to waste money on that when you can just grid-tie. \$\endgroup\$ – horta Jul 12 '17 at 17:36
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    \$\begingroup\$ Grid-tie is far more convenient and cost-effective than storage where the incentives haven't been tilted to the power utility's advantage. \$\endgroup\$ – pjc50 Jul 12 '17 at 21:22
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    \$\begingroup\$ I don't agree that power electronics (presumably sitting in a nice dry box away from direct sunlight) should be expected to fail before solar panels do. Industrial-grade power equipment is often designed for 20-40 years of service. \$\endgroup\$ – Dmitry Grigoryev Jul 13 '17 at 9:56
  • \$\begingroup\$ @DmitryGrigoryev Good points, consider e.g. elevators. Do they need frequent servicing apart from inspections? Also, Toyota Prius with plenty of power electronics has proven to be an extremely durable vehicle. \$\endgroup\$ – juhist Jul 13 '17 at 11:56
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Just to address the "last essentially forever" part. Unlike some semiconductor devices which can work for half a century or more, solar panels don't get the privilege to be used indoors. This means they will suffer from UV and corrosion and will have a limited lifespan.

It also should be noted that mass-produced solar panels are relatively new, which means their lifespan figures (which are typically around 20-30 years) are only an extrapolation from accelerated aging tests and limited statistical data from panels installed 30 years ago. This is important to understand if you're about to make an investment decision based on this data. I would be extremely wary of investing in solar panels if my profits were a bet on whether they will last for 20 years.

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