When I first heard about using particle accelerators to create solar panels I must not understand how solar panels are made or how particle accelerators work? And yes, there’s a key, unglamorous step that unless you’re fairly familiar with solar manufacturing technology you probably wouldn’t think of, and it’s in this step where a particle accelerator turns out to be useful: cutting silicon into the really thin wafers that are the key component of a solar panel.
However, even this wasn’t at all what I first thought, which was something like slicing through the crystal with a super powerful particle beam. That sounds awesome, but the actual technique is much less insane and much cleverer. So a typical solar panel cell begins as carefully grown cylinder of silicon atoms arranged in a regular crystal lattice, which are then trimmed and cut into wafer-thin…wafers. Some of which retain curved corners as hallmarks of the original cylindrical crystal.
Then the wafers get covered with other metals, anti-reflective coatings, and electrodes, and so on, to be able to capture the sun’s energy but the part we want to focus on is the cutting. Because when you cut something with a saw, like silicon wafers normally are, there are two problems:
- one, you can’t cut a slice too thin otherwise it might get broken – typical solar panel wafers are cut to about 0.15 millimeters.
- And two, unlike a knife which cuts by separating and wedging two pieces of material apart, a saw cuts with teeth that gouge and eat away at the material, turning it into saw-dust and leaving a gap called a kerf.
In the case of silicon wafers, the gap is roughly the same width as the wafers themselves, which means about half of the original material, goes to waste! This is where particle accelerators come in: not a high powered ablative cutting particle beam, but by taking advantage of the physics of crystals. If instead, you shoot protons with certain energy at the flat face of the silicon cylinder, those protons will embed themselves into the silicon.
The depth depends on how much energy they have, and the thinner you want, the less energy they take, so you can easily pick something super thin. But whatever thickness you choose, once inside the silicon crystal lattice, the protons kind of push it apart and create stress; if you heat the whole thing up, a wafer will break right off, cleanly cleaving along the crystal lattice lines where the protons were. So, if after the protons are embedded, but before the heating, you glue this proto-wafer onto a piece of glass or plastic, and then heat it up, you end up with a nice thin wafer of silicon attached to a durable (and possibly flexible) material, with no waste silicon whatsoever.
To me, this is clever physics engineering! Of course, a particle accelerator is much more expensive than a saw, so there must be some upsides to it – the biggest is that, by using significantly less silicon per wafer and not losing any silicon in the cutting process, it’s possible to justify using much more expensive silicon that’s better at capturing sunlight, meaning the resultant solar panels for a given power output are smaller and need less other material to make them and hold them up, hence they’re cheaper.