Recycled silicon used in 19.7% efficient PERC solar cells | Hacker News Reader

Recycled silicon used in 19.7% efficient PERC solar cells

pv-magazine-usa.com

87 pointstaubek34 comments

Why bother? It’s not like silicon is some rare element that needs to be mined in distant, war-torn countries.

It’s literally sand!

The hard part is purifying it. Starting from already manufactured electronics seems like an uphill battle because the silicon is already contaminated with precisely those elements that need to be removed from it to control its electronic behaviour!

The Fraunhofer Society is a research organization (tending towards the applied/engineering end of the spectrum), so the answer might be simply "because they can?".

Beside that: if they can work out the economics of the process, why not? Waste disposal costs money which might shift the economics in their favour (as people would have to pay someone for disposal anyways, so they could as well pay the people who make new panels from old ones).

We as a society cannot keep disposing of things forever. We need to be making as many production streams cyclical as possible, or we will eventually run out of the easy-to-aquire resources

The earth's crust is 60% silicon dioxide. I don't understand how we could possibly run out.

I mean, I get the value in recycling the panels. It's presumably easier to start with almost pure material than 60% pure. Still, if it were cheaper to start with a chunk of feldspar than an old panel, I don't think we'd have to worry about the lack of virgin materials.

This is precisely my point. So many people automatically assume that everything is scarce and recycling is automatically “good”.

Chances are that the process described in the article uses more resources and produces more pollution than simply starting from sand.

This comparison is incomplete without thinking about what happens to the disposed-of panels. Panels in landfills are pollution as much as anything else

Solar panels are glass and silicon. Just crush them an mix them into concrete…

It's also not clear if recycling the silicon in PV cells into new PV cells is the best way to recycle it. The world also uses silicon in silicon steels and in the manufacture of silicones. As PV is further scaled up these may not be large enough markets, granted.

The air is 21% oxygen and hospitals were running out of oxygen in some places during the COVID pandemic. Hydrogen is the most abundant element in the universe, and yet, the supply of hydrogen is one of the biggest hurdles to the adoption of hydrogen cars.

Just because a resource exists nearby doesn't necessarily mean it can be harnessed economically or within the other constraints that the world and society imposes on us.

Silica mines are mostly (all?) surface mines, we don't explore anywhere into the crust to get it now because it isn't economical to do so. "Running out" of supply doesn't necessarily mean that the element doesn't exist, it could mean that it is inaccessible for other reasons -- like it could be the beach in front of someone's house, or a protected park.

Would be more concerned with pollution and side effect before resources scarcity.

> We as a society cannot keep disposing of things forever.

Of course, because the Earth won't be around forever. But we can dispose of a lot of stuff for a very long time, because the Earth is a really big place.

Geology is all about massive quantities of stuff just being left in piles and solidifying over millions of years. If the stuff isn't that toxic, this could happen to anthropogenic stuff too.

The world is producing vast quantities of solar panels, which will eventually end up in landfills. What they are doing is essentially just what say: removing sand from panels and separating the contaminants which can then be dealt with separately.

Sand mining causes significant environmental damage, and there's a shortage of sand from the less-delicate sources.

Also, I imagine it takes a lot of energy to go from "we found this on the beach" to "this is ultrapure silicon for use in solar cells". We have essentially unlimited aluminum too.

The purpose of recycled cans is saving energy and reducing pollution from extraction. I do wonder whether it's easier to start with glass from beverage bottles than from solar panels though.

Silicon is purified by conversion to trichlorosilane, followed by distillation. One doesn't need extremely pure silica as the input. An intermediate step for this is reduction of silica to metallurgical silicon which is not anywhere close to semiconductor grade (it's about 98% pure).

Where one DOES want pure silica is in making the crucibles where silicon is melted. There's a particular mine in North Carolina (Spruce Pine) where this very pure silica is mined. We could make artificial pure silica, but this stuff is cheaper.

> there's a shortage of sand from the less-delicate sources

I thought the only sand shortage to speak of was the specific type required for making concrete, because wind-blown sand is too rounded off for producing strong concrete. So those endless dunes of wind-blown sand everyone envisions aren't applicable.

But when you intend to melt the sand I presume there's an abundant supply.

All sand is not equal, and it is slowly becoming more scarce. There are already sand mafias popping up due to certain types of sand (used in construction) becoming hard to find. There are black markets, and shady practices already happening. Maybe the sand needed for semiconductors doesn’t fall into this category yet (I don’t know, maybe it does), but it doesn’t hurt to start thinking about it.

We are already running out of one type if sand mostly due to the amount of concrete we make.

Your answer is in your penultimate sentence ("The hard part is purifying it.") and at the end of the article.

>>The German scientists said the cells were fabricated only with wafers relying on recycled silicon and that no commercial ultrapure silicon was added during the manufacturing process.

>>The performance of the first trial PERC cells was tested and the devices were found to achieve a power conversion efficiency of 19.7%. “This is below the efficiency of today’s premium PERC solar cells, which have an efficiency of around 22.2 percent, but it is certainly above that of the solar cells in the old, discarded modules,”

Yeah, just like fresh water and trees are everywhere, so why bother conserving them.

Environmental destruction is a huge problem and usable sand is a limited resource and often in delicate environments. It’s not the 19th century anymore—people today are more aware that taking resources has consequences.

There's a widely-held belief that the energy cost of PV production is largely outweighed the benefits from PV usage.

This may have been somewhat more true in the past, but I believe the energy payback period is now less than 24 months, on a PV device that should last over 20 years.

We must pay attention to weighing up the relative costs to environmental destruction by one cause (production and disposal of PV) against its most common alternative (continued fossil fuel usage).

Nobody is arguing that the material usage from non-recycled goods is a big enough issue to stop selling solar panels.

But maybe this technique makes the payback go from 24 months to 22 months. Maybe even just to 23.5 months! It’s still progress!

>> Nobody is arguing ...

Nobody here is arguing that. FUD is a real thing. Be careful not give them ammunition.

What? You somehow implied that people hate renewable energy when the only thing is people are saying that in addition to that, recycling is good.

FUD isn't even an applicable term.

Because we are increasing solar panel production on an exponential curve. This is amazing for sustainable energy, however 30 years from now amount of trashed solar panels will be increasing on an exponential curve. Recycling them into more solar panels sounds like an amazing solution.

How long would they last?

A lot of record breaking cells are lab only due to them degrading so fast that it precludes any practical use.

General rule, the purer the silicon, the less doping, the longer its life, albeit at low efficiency.

Silicon cells above 20% were in labs decades ago, but practical designs with long life only appeared last decade.

To my knowledge, having a couple years working photovoltaic research, degradation is only a significant issue in the perovskite solar cells (basically organic molecules that react with or at least see property changes with adsorption of water). Others get maybe a bit of degradation (a couple percent maybe) in the near term, but what they are is what they are. Solid state devices are pretty stable, which is also why CPUs can work for long periods of time (same basic building block, the PN junction, and yet much more complicated).

The problem with solar cell efficiency as being the top-line metric is that is that it outright ignores a very complex system. Never mind you got to string them together for panels. Nevermind you just spent $10k making that one cell and your yield is pretty garbage. Never mind that an incrementally more efficient cell doesn't move the needle much when a large fraction of the cost is delivery and installation. Nevermind intermittency is a huge problem for the technology in general.

Another important thing to look into for the photovoltaic problem is the Shockley–Queisser limit [1], which shows that we don't even have a lot of room to run in terms of basic efficiency improvements (~50% for Si). That's a fundamental physical limit for single junction cells.

In terms of scientific advancements, I would get much more excited to see improvements in energy storage technology. Photovoltaic deployment is probably also going to see more advancement based on improvements in manufacturing, logistics, and building construction. At this point achieving cell efficiency records is more just for the sci-peen.

[1] https://en.wikipedia.org/wiki/Shockley%E2%80%93Queisser_limi...

Greatly informative comment!

I take that to read this as a way to make a solar panel with an acceptable efficiency rate.

> I would get much more excited to see improvements in energy storage technology.

This whole thread is about silica, so... energy storage with sand! $2/kWh(t) capacity cost, 54% round trip efficiency, baseline scenario $0.05/kWh-cycle cost of storage.

https://arpa-e.energy.gov/sites/default/files/2021-03/07%20D...

>That's a fundamental physical limit for single junction cells.

That sentence contains its own objection.

If your implication is that one can simply stack more junctions, that is fine to try from a research standpoint and for mass-constrained applications like space exploration, but the economics get substantially worse for normal applications. It's also the case that multi-junction cells (at the infinite limit) have a max theoretical efficiency that is about double the theoretical max of the best single-junction systems. That also ignores recombination effects at the interfaces between systems, which are also almost pretty gnarly.

That's my point, it's an economic limitation masquerading as a physical limitation.

Given the definition of economics, I'd say whether it is technically one or the other is kind of meaningless. If you throw enough resources at something, you can achieve all manner of things that don't make any practical sense. Whether such a situation can be more properly understood in terms of "just needing a lot of money," or "having physical limitations making it impractical" is a pants vs. trousers type question.

ETA:

I didn't follow up my point very strongly earlier, but "double" is important here. Spending many multiples of resources to get cells that at most have double the efficiency of standard single junction cells is not what we usually think of when we think scientific breakthrough. It's certainly not scaling on the level of Moore's law, the expectation that the economy grow something like 3% a year, or various other exponential growth patterns we have come to take as normal.

A fun chart to look at for efficiency is provided by NREL [1]. Half the talks on photovoltaics seem to add it somehow. An important point is technologies can get stuck in a particular parameter space for large amounts of time despite tons of money being poured in. Efficiency improvements are not guaranteed, they cost a lot, and they are often tiny when they occur. My macro point, if I have one, is society is best off trying to grab low hanging fruit from multiple disciplines that feed into photovoltaics, and media should try to emphasize that effort rather than pushing cell efficiency improvements, which are not going to do a whole lot by themselves.

[1] https://www.nrel.gov/pv/cell-efficiency.html

I have seen some Chinese monocrystalline modules being offered with 30 year warranties. This means with < 1% annual degradation (as specified in warranty) no reason well maintained installation can last even longer. I think life of a silicon based cell is no longer an issue, it is the perovskites that are a problem. If perovskites can be made to last longer, we can have very good tandem cells. Another issue is the thin film printed cells, which if they can last even a decade may become a game changer if can be manufactured cheaply enough and have > 10% efficiency.

but how many would really honor that 30 year warranty?

In past, I've had some pretty bad experience getting my alibaba seller to even acknowledge a problem.

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