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Post-apocalypse how well would photo-voltaic solar cells hold up? They are solid state so I expect they would do okay for a while, but would they remain functional for 100+ years.

I know that dust and grime would stop exposed arrays functioning, batteries will rot and that inverters and smart meters are prone to failure, but would old cells be able to be reconditioned and put to use? Would scavengers be able to find rooftop solar arrays, or would they need to find sets that for some reason were never installed and kept in safe storage?

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  • $\begingroup$ Related: electronics.stackexchange.com/questions/317028/… $\endgroup$ – juhist Sep 9 '17 at 16:17
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There are three big problems and one that is far less serious.

One, encountered by a Peace Corps volunteer I knew who worked in the Sahel region in Mali, and also brought to my attention by someone who had been a U.S. consul in Tanzania, is that photo-voltaic cells are theft magnets in places where there is lots of extreme poverty. It is a form of wealth that cannot be hidden if it is to do its job and can't be carried on your person. Efforts to install them to run village well pumps would generally fail unless a 24 hour guard crew was assigned to protect it by the village. Post-apocalypse, I would expect that similar concerns would arise.

A second is that photo-voltaic cells usually have fragile glass panels incorporated in them and aren't that sturdy at the silicon level either. While they don't have moving parts - yay! - any decent hail storm, hurricane, or dust storm vigorous enough to stir up gravel is going to do a lot of damage. Even a proximity too close to a nut or pit-fruit bearing tree could be a problem in the presence of severe windy storms. High winds can rattle them if they aren't installed tightly (slowly loosening the connection of the mounting to the surface it is mounted upon over decades) and if severe enough, high winds can blow them off a roof like shingles. In places where hail happens with some frequency, it isn't uncommon to have to replace a roof due to hail damage every 10-25 years, which is considerably less than the expected useful life of the cells. Unless someone is covering the cells with shutters or some other kind of cover in windy, stormy weather, it is likely that most will be seriously damaged over the course of a century or more.

A third concern is that photo-voltaic cell installers don't always pay a lot of attention to the materials in the frame and mounting. Iron and copper corrode, and over time, even coatings designed to prevent that from happening will wear off.

Another kind of issue would be bird poop, leaves and dust, but these would merely temporarily degrade performance until the panels are cleaned.

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    $\begingroup$ Plus PV panels are rated to have 80% output after 20 years. Good quality ones have averaged 90% ish. If it keeps linearly losing 20% every 20 years, it probably won't last a hundred; and that isn't considering whether the loss is exponential. $\endgroup$ – nzaman Sep 9 '17 at 8:52
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    $\begingroup$ @nzaman Good point. A non-linear decline would leave a higher output after 100 years than a linear one, but it would still be lousy. $\endgroup$ – ohwilleke Sep 9 '17 at 8:55
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    $\begingroup$ @N2ition There's a section of solar panel road that isn't actually a road, it's a sidewalk, doesn't produce as much power as it consumes, suffers frequent breakdowns even with constant maintenance, and hasn't been mentioned in the news since it caught fire... $\endgroup$ – Perkins Sep 9 '17 at 19:18
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    $\begingroup$ @N2ition Unless the panels have a comprehensive, robotic self-cleaning and security-guard style anti-theft system, the way to disable it is basically, "throw a blanket over it and wait for the battery to run down." Assuming the battery is even still good after 100 years. $\endgroup$ – Perkins Sep 9 '17 at 19:29
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    $\begingroup$ I don't know about that, I have a cheapie eBay panel in a location where it gets beaned by tree branches on a constant basis, and no "fragile breakage". The people building these panels are not idiots. $\endgroup$ – Harper Sep 9 '17 at 19:49
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If panels are kept reasonably well (and are not stolen, of course) yo can expect a mean degradation < 1%/year for reasonably good quality panels (the whole story is here).

This means you may expect to get about 1/3 power out of the panel after 100 years.

This figure already includes small damage due to "normal" wear and tear (temperature stress, cleaning, ...) but does not include major events (e.g.: a tree falling over the panel or it being stolen).

Note this figure is constant for a certain number of years (dependent on quality, but surely >= 50y), then will start to increase due to other factors collectively labeled "corrosion of cell and interconnect" that can be disregarded for a certain period, but later become prevalent and depend heavily on maintenance (especially waterproofing as sealants fail after a number of years of sunshine exposure).

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Solar cells works roughly on this way:

enter image description here

The here important part is, that the photons of the Sun push the electrons out of the base plate. These electrons can find their way back only after they made some work for us.

To make this possible, that base plate should pass very strict constraints (in its crystall structure and materials what it has).

Furthermore, it depends also the energy of photons:

  1. Photons with too small energy (infra-red) are incapable to do anything, they are reflected back or they heat the solar cell.
  2. Photons with the needed energy do as we want from them.
  3. Photons with too much energy (they are mainly ultra-violet) can damage the base plate: they disorganize the crystall structure and the plate coating.

Obviously the solar cells on the Earth are tuned that the most solar photons fall into (2). But not all of them.

To prevent the problem of (3), typically the antireflection coating has also a filtering function, to filter out the possible most harmful photons. But this is not perfect.

The result is that the effectivity of the solar cells still decreases with time, and slowly they will become unusable. How long they last, it depends mainly on manufacturiing details, but none of them would last forever.

As the large-scale solar cell manufacturing is a young industry, there is yet not enough practical results. Different estimations around the net say some decade. Here is a detailed list of the typical degradation of the solar panels. This list is for the currently most common application, their real timeline likely significantly depends on the anti-UV coating, too.

It could be tuned, but it would require to make the antireflection/ultraviolet protection layer much more costier now. It is un-economical for the sake, to make them lasting longer decades later.

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  • $\begingroup$ Do you know any reference for (3), that ultra-violet radiation which isn't filtered by the Earth's atmosphere can indeed damage the crystal structure of silicon? I know it can damage the human DNA, but in my understanding the crystal structure of silicon is far more robust. And also, the Earth's atmosphere filters away the most harmful radiation. $\endgroup$ – juhist Sep 9 '17 at 16:33
  • $\begingroup$ @juhist The most, but not all. If you put a color photo into direct sunlight, it will fade in days. Also clothes let to dry under the Sun lose colors faster. Behind glass windows, the same effect it much lesser, because glass is nearly opaque in ultraviolet light. Also we don't become browner sunbathing behind glass windows. Here is a detailed list of the typical degradation of the solar panels. This list is for the currently most common application, their real timeline likely significantly depends on the anti-UV coating, too. $\endgroup$ – Gray Sheep Sep 9 '17 at 16:44
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Solar panels are more durable than they are being given credit for here.

Regarding fragility and susceptibility to physical damage consider the potential damage from hail. All panels are tested to survive at least 50 MPH hits from hail, most are up to higher standards, and a few manufacturers even build and test to 250 MPH (I'll leave that to you look up as I don't want to promote any brands). For reference, one inch hail stones (considered severe and only likely to hit 0.5% of panels in a 20 year time frame) travel at 45 MPH (Another source, NASA JPL from 1978). As far as nuts falling from a tree go, they have significantly less impact than hail. Also, I'd recommend against putting your solar panels in shade but I'm no expert. If you want to see an example of a severe storm having little impact on a PV system, here you go. Mechanical stress is unlikely to be a factor in your scenario.

Degradation is really the only significant worry. Modern solar panels are better than older panels, though. They degrade at approximately 0.5% per year linearly. Older panels averaged 1% per year over 20 years and often followed a bell curve (so they'd get worse faster). After a hundred years of use the median panel will still give you 50%. I imagine that's not going to be your biggest worry in a post-apocalyptic world.

All this is assuming you are finding panels that have been used for a hundred years. If you're talking about panels that have been in storage or have only a few years of use things are better. Corrosion comes from the environmental conditions, namely humidity, wind, and heat. A new or shielded panel will have very little of this. Degradation comes from the heat around the panels as solar panels get very hot while under the sun and generating electricity. Again, this won't have taken much of a toll on new panels or panels in storage.

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As others have pointed out, modern silicon solar panels degrade about 1% per year assuming no physical damage. So the odds of them producing a significant amount of power after 100 years of actual weathering aren't that good (unless maybe they got buried in dry sand or something and miraculously didn't get broken as it shifted.)

There are other types of solar panel, like black copper oxide, that don't suffer nearly as much degradation from use. But they're much more expensive and much less efficient, so while some of them could last 100 years, you'd be unlikely to find any except in the ruined homes of crazy, old tinkerers. And they'd still be big, heavy, and horribly inefficient.

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  • $\begingroup$ You haven't supported your claim that "the odds of them producing a significant amount of power after 100 years of actual weathering aren't that good". Note that 0.99¹⁰⁰ ≈ 0.366, so more than a third of the original power level may be available. $\endgroup$ – James Waldby - jwpat7 Sep 10 '17 at 5:35
  • $\begingroup$ @JamesWaldby-jwpat7 If you store them perfectly so that the only reduction in power comes from decay of the doped silicon, you're already down to a bit more than a third of the capacity after 100 years. That doesn't include physical battering from bad weather, cell cracking from 36524 hot/cold cycles, thermal damage from when the output leads short to ground due to insulation decay, or anything that various bits of flora and fauna might do to it. Most likely you'll have to disassemble the panels, pick out the cells that are still functional, and reassemble, for 1/3 of the original capacity. $\endgroup$ – Perkins Sep 11 '17 at 19:49

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