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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.

juhist
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    I'm curious if solar panels produce more energy than it takes to manufacture a new solar panel. Otherwise you are just burning fossil fuels to manufacture solar panels. – Chloe Jul 12 '17 at 20:25
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    @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: https://en.wikipedia.org/wiki/Energy_returned_on_energy_invested#Low_carbon_power – juhist Jul 12 '17 at 20:27
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    @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. – user253751 Jul 13 '17 at 00:44
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    Someone can go to chop down a tree, make a mistake, and [drop the tree on some solar panels](http://wildfiretoday.com/2013/03/01/sawyer-drops-tree-on-solar-panels/). That will cause a failure right there. – Zach Lipton Jul 13 '17 at 01:53
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    @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 ;) – Harper - Reinstate Monica Jul 13 '17 at 02:55
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    *cheap Chinese cells* - or indeed cheap cells from any country. – Nick Gammon Jul 13 '17 at 06:52
  • @NickGammon AFAIK Mexico and Korea stopped mass-producing dirt-cheap low-quality electronics about 15 years ago. China is practically the only one still in the game. – Dmitry Grigoryev Jul 13 '17 at 09:30
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    @Chloe A similar question was asked here: https://skeptics.stackexchange.com/questions/5101/does-the-production-of-a-home-pv-solar-panel-provide-a-net-benefit-to-the-enviro/11165#11165 – Steve Smith Jul 13 '17 at 10:23
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    @DmitryGrigoryev Mass production - check - dirt cheap - check - but I would not consider chinese electronic product low quality in any general statement. – antipattern Jul 13 '17 at 11:29
  • I would not trust Chinese electrolytic capacitors. Japanese ones? Yes, I trust those, but would still prefer a device with no electrolytic capacitors at all. – juhist Jul 13 '17 at 11:59
  • @Chloe What if all the energy used to produce a solar panel is produced from solar panels? – Michael Jul 13 '17 at 17:57
  • There are many political and economic issues involved with privately owned solar power. What happens to the utility companies? What happens to their investors? In the future, you may see regulations imposed on the solar energy industry, probably in the name of environmental protection. Aren't they partly made of arsenic? – richard1941 Jul 13 '17 at 18:48
  • @richard1941 Actually, the n-type dopant used in solar cells is phosphorus, not arsenic. And even if arsenic was used, dopants are used in extremely low concentrations so that wouldn't be a problem. Some cells used in space applications use gallium arsenide, but then again such cells are not used at all often in terrestrial installations, because GaAs cells are more expensive (but the multijunction cells offer greater efficiencies, more than offset by their high cost). – juhist Jul 13 '17 at 18:52
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    @richard1941 ...and the electricity use peak follows quite well the solar power production peak due to people using electricity during daytime, not nighttime. So, utilities can actually see more stable demand due to solar power. Overall, solar is good for the electricity system. It is especially good because air conditioning is often used: solar production peak equals air conditioning demand peak. – juhist Jul 13 '17 at 18:55
  • Solar power cells have been powering satellites for fifty years and are still going strong. I am not aware of any physics that would cause them to wear out, other than eventual cosmic ray damage. However, weather will attack your wiring and electronics. I would have a look at how NASA and DoD qualify solar cells. – richard1941 Jul 13 '17 at 19:05
  • The notion that solar panels cost more to make than they will ever produce in electricity is easily disproven. Let us assume a worst case scenario in which ALL of the cost of a solar panel went into the energy required to make it. Take the cost of the solar panel, and calculate how many KW/h that money would purchase. Now take the energy produced by the panel, and amortize to determine how long it takes to pay off the panel. As long as the lifespan of the panel is longer than that breakeven point, the cell will produce excess energy. You will likely find it pays for itself many times over. – Byron Jones Jul 13 '17 at 20:56
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    @ByronJones, the dollar-cost of producing the solar panel is not by definition proportional with the energy-cost. For example some company might pay 1500$ to manufacture a 3000$ panel, because they get 1500$ subsidies from the state (whatever country they are in, this is a hypothetic scenario). And the end-user (buyer) might also earn 4000$ in 20 years from the electricity-cost savings, but this might be due to increased energy prices in the future. But this dollar-price is not (in theory) proportional to the energy-cost, which might be 1MWh to manufacture a panel which will produce 800KWh. – Sorin Postelnicu Jul 13 '17 at 22:10
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    @richard1941, as I understood, in Spain you pay a special tax for each kWh of solar energy which your private solar panel produces. So yes, your "hypothetical" scenario is not so far-fetched. :) It seems that in Spain the sun is not free. – Sorin Postelnicu Jul 13 '17 at 22:12
  • In engineering school we learned that the future energy produced by the solar cell system has a net present value that depends on the future value of the energy and future interest rates. Do you think you can predict that? It is a bit more complex than merely comparing the present cost with the energy produced at present day prices. All this has nothing to do with the reliability question, but it is something to consider. I give an upvote to Horta for addressing the failure modes. – richard1941 Jul 14 '17 at 19:31
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    @SorinPostelnicu - here is a link to an actual scientific study. It shows that with modern solar panels, the payback time ranges from slightly less to slightly more than 1 year. Given the lifespan of modern solar panels is measured in decades, they do in fact pay for themselves many times over. https://www.nature.com/articles/ncomms13728 – Byron Jones Jul 15 '17 at 11:46

2 Answers2

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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

horta
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    +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. – Dan Esparza Jul 12 '17 at 17:34
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    @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. – horta Jul 12 '17 at 17:36
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    Grid-tie is far more convenient and cost-effective than storage where the incentives haven't been tilted to the power utility's advantage. – pjc50 Jul 12 '17 at 21:22
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    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. – Dmitry Grigoryev Jul 13 '17 at 09:56
  • @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. – juhist Jul 13 '17 at 11:56
  • @juhist elevators are safety-critical, thus regularly inspected. I have seen a 500 kW power inverter which was designed for a service life of 40 years with a single maintenance after 20 years. The maintenance mainly consisted in opening the cover and checking that none of the screws have loosened due to vibration. Though maybe that kind of electronics is too expensive for solar power... – Dmitry Grigoryev Jul 13 '17 at 12:40
  • @DmitryGrigoryev Perhaps my desire to research the failure mode of power electronics stems from my lack of experience with industrial grade versions of them. Good to know that they in general are known to be reliable. – horta Jul 13 '17 at 15:09
  • From what I gather, the "catastrophic failure" of cells you describe would result in zero power output, correct (or reduced by a factor proportionate to the number of failed cells)? Is it possible for a panel to catastrophically fail in such a way that causes cascade failure or fire (e.g. a defective cell failing short and causing other issues for otherwise operational cells linked to it)? – Doktor J Jul 14 '17 at 13:48
  • @DoktorJ Catastrophic failure of a cell will likely result in an open circuit. The latest setups are fitted with bypass diodes so any cell that fails just lowers the current output. That bypass diode is virtually a short so a short circuit isn't really a problem. It's entirely possible for the inverter circuitry to fail closed and result in a fire, but according to Dmitry, that's not likely. There's also not much to burn in silicon cells as they melt at 2500 deg F. – horta Jul 14 '17 at 14:31
  • @horta thanks for the info. Of course if a cell does overheat enough, even well under that 2500˚ mark, it may be attached to things that combust at lower temperatures... – Doktor J Jul 14 '17 at 18:22
  • @DoktorJ True. I think aluminum or some other metal would be the standard hardware. Plastics would have trouble in the heat of a solar array. – horta Jul 14 '17 at 18:34
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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.

Dmitry Grigoryev
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