2D Solar Cells Poised to Set Power-per-Weight Record | Hacker News Reader

2D Solar Cells Poised to Set Power-per-Weight Record

spectrum.ieee.org

32 pointsrbanffy18 comments

On earth, the weatherproofing needed for solar cells by far outweighs the weight of the silicon itself.

In space, we generally don't allow use of anything that can't be tested on earth - that means the silicon has to be able to hold its own weight under gravity. Therefore, it is the mechanical supports that are the weight limiting factor.

One day, when solar cells are built, tested, and deployed all in space, we can probably get rid of these limitations and see 10x or more improvements in power to weight ratios.

Is this actually true for present time satellites? I find it hard to believe that teams designing satellites today would not go for such an 'easy' weight reduction, however limitted it might be.

well it isn't easy... If your foldable solar panels can't be unfolded in gravity because they'd immediately break, then you can't test that they work.

>you can't test that they work.

Sure you can: one needn't test the full exact as-will-be deployed assembly to have confidence a system will work. Systems can be tested in parts or with surrogates.

Will the exact system in the exact conditions have been tried? No - but that's not really the goal; the goal of testing is only ever achieving an adequate[0] confidence of success in actual use.

[0] A situationally defined term.

Test them submerged in a fluid with (approximately) the same density and the material they're made of and they are "weightless" for all intents and purposes. The fluid will add some other dynamics which are not present in a vacuum so the test will not be entirely accurate but it will show whether the mechanism does what it is supposed to, mostly.

Plenty of amazing ground systems aren't flown because they can't be tested. Solar panel tests are usually done with a careful support system that takes the load from gravity and allows the panel to be unfolded in an approximately equivalent environment to microgravity.

And silicon is not the best semiconductor for cell mass. It's an indirect bandgap semiconductor, and requires ~100 microns of thickness to absorb photons (depending on texturing which allows photon trapping.)

CdTe cells, on the other hand, can be just 1 micron thick.

Most panels shipped to space can't support themselves: Google "solar array deploy" and you'll see videos from lots of space missions where there are complex deployment jigs to hold the panels from collapsing under their weight during testing. This isn't the entire story though - launch loads still meaningful contribute some to the weight. A certain amount of mechanical stiffness will still be required even for in-space builds for stability and controllability against slew, solar wind, drag, etc, putting a lower bound on mass. I'd like to see technologies that can avoid coverglass requirements (for atomic oxygen, solar wind), but that's a fundamental physics problem that looks tough to me.

What?

A. just set up a rig that can support the panel in earth gravity

B. Send up a test panel as part of some other satellite. You don't exactly have to spend much of your weight budget.

C. Use your theoretical and practical knowledge of space to determine whether this will work or not.

How do you think they tested the Apollo buggies? Do you think they built it strong enough to support 2 men in earth gravity?

This would be great for all kinds of solar-electric tech where panels can be built into car roofs, buildings, boats, and other stuff! Hopefully we can crank out this, or a derived technology on a mass scale. That would result in a lot less bulk material usage compared to current systems with big aluminum frames and lots of plastic.

There are two reasons for reducing the mass of PV for space.

The first is to reduce the cost of launching PV into space. The second is to improve the performance of spacecraft once they are in space, particularly spacecraft using solar-electric propulsion.

If the goal is the latter, not the former, it could make sense to launch PV with a substantial backing layer to give it mechanical strength, then (after unfurling) remove that layer (say, by allowing it to sublimate, or by oxidizing it with atomic oxygen radicals) before dispatching the spacecraft.

This smells of bad science journalism.

There is no way to manufacture a 2D item in 3D space.

If you read the article, you'd see the end part where they mention that the new design is 4nm thick, making it effectively '2d', versus an existing 100+ micron solar cell.

That doesn't excuse flat out lying. "Thin" does not mean "does not exist in that dimension"

I don’t think anyone is claiming they are truly 2d, and I highly doubt anyone is interpreting it that way.

Claiming it's 2D in the title isn't enough to say they're claiming it is 2D?

What's the threshold?

This seems to have a precise (and useful imho) definition: https://en.wikipedia.org/wiki/Two-dimensional_semiconductor

Do you also complain about 2d or 3d TVs?

(I do, but only because they don't include the time component)

Reply on news.ycombinator.com