The fact that there exist in our world flat rocks that make lightning when you point them at the sun is one of the most unappreciated bits of wizardry in this modern age. As hackers, we love all this of techno-wizardry–but some of us abhor paying full price for it. Like cars, one way to get a great discount is to buy used. [Backyard Solar Project] helped a friend analyze some 14-year-old panels to see just how they’d held up over the years, and it was actually better than we might have expected.
The big polycrystalline panels were rated at 235 W when new, and they got 6 of them for the low, low price of “get this junk off my property”. Big panels are a bit of a pain to move, but that’s still a great deal. Especially considering that after cleaning they averaged 180 W, a capacity factor of 77%. Before cleaning 14 years worth of accumulated grime cost about eight watts, on average, an argument for cleaning your panels. Under the same lighting conditions, the modern panel (rated to 200 W) was giving 82% of rated output.
That implies that after 14 years, the panels are still at about 94% of their original factory output, assuming the factory wasn’t being overoptimistic about the numbers to begin with. Still, assuming you can trust the marketing, a half a percent power drop per year isn’t too bad. It’s also believable, since the US National Renewably Energy Laboratory (yes, they have one) has done tests that put that better than the average of 0.75 %/yr. Of course the average American solar panel lives in a hotter climate than [Backyard Solar Project], which helps explain the slower degradation.
Now, we’re not your Dad or your accountant, so we’re not going to tell you if used solar panels are worth the effort. On the one hand, they still work, but on the other hand, the density is quite a bit lower. Just look at that sleek, modern 200 W panel next to the old 235 W unit. If you’re area-limited, you might want to spring for new, or at least the more energy-dense monocrystalline panels that have become standard the last 5 years or so, which aren’t likely to be given away just yet. On the gripping hand, free is free, and most of us are much more constrained by budget than by area. If nothing else, you might have a fence to stick old panels against; the vertical orientation is surprisingly effective at higher latitudes.
Reminds of an article showing the popularity of used panels in other countries. Kind of like what happened with used clothes.
And used tires.
and second-hand tobacco (https://en.wikipedia.org/wiki/Here_Come_the_Warm_Jets side b track 2)
Remember, the lifetime given by manufacturers and installers is not a drop-dead date. It is the age at which x% of panels will lose >y% of their capacity.
I think the take-away is that you should expect to keep using your solar panels well beyond their “lifetime”. The marginal improvement from replacing an old panel is probably never worth the expense.
If building an array from older used panels, I might lean towards microinverters instead of string inverters, so that the total output of the array is not limited by the most-degraded panel.
The flip side is, your roof will have a finite lifetime so if they’re installed on a building, that’s probably when they’ll be replaced (and i’m guessing is why there’s already a good supply of used panels being thrown away).
My friend uses a good trick to get use out of a single damaged panel he got for free.. Instead of using it to cut his electric bill, he uses it just to charge a 12V lead acid car battery, which he uses just to run his modem, router, wifi, and maybe a little NAS box. Where he lives, power outages are somewhat more common than telco outages so it gives him more reliable internet. And one 200W-ish panel is plenty for keeping a battery topped off even with a number of small computers on it.
Meanwhile nuclear output level is the same for decades.
Kudos for inventing an industry which degrades over time as energy demand increases thus you need to keep making more panels to keep up.
It’s like you created supply and demand for shareholders.
Good thing the world is being forced onto your business model, by….. shareholders.
Nuclear power plants maintain output for a few decades, then it drops to zero when the plant is retired. Building a new one is very expensive.
For solar, replacing the panels without rebuilding the rest of the infrastructure would cost a lot less than a whole new array.
I’m all for nuclear power but, in fairness, nuclear power plants have a lifetime, as well. Many of the plants in France are reaching end-of-life and apparently they don’t have plans to bring up enough replacement power.