[carbonguy]

This concept is not quite smoke and mirrors, since there's nothing wrong with the science, but this article definitely reads more like a breathless press release than something truly ground-breaking. More notes below:

> Synhelion was founded in 2016 as a spin-off from ETH Zurich, sparked by what the company founders describe as a crazy idea they had: what if they could reverse combustion and turn carbon dioxide and water back into fuel?

This is not a "crazy idea", but rather a straightforward description of the chemistry involved. We call one implementation of this process "photosynthesis", but there are others.

> The technology they’ve developed relies on four key components. Mirrors – known as heliostats – that track the sun to focus its energy on to a solar receiver. This in turn produces very high process heat at temperatures exceeding 1,500°C. This heat powers a thermochemical reactor that turns CO2, water and methane into syngas, which can be processed via Fischer-Tropsch into fuels.

Again, this is well-understood industrial process chemistry - absolutely a good thing, in my opinion, but not new and sexy by any stretch.

> And finally, a thermal store to release energy when the sun goes down to allow the solar-powered facility to operate around the clock.

This actually IS new and interesting in this application (or at least, it is to me) - a shame that this isn't fleshed out more in the article. I tried to see if there was more about this aspect of their process on the Synhelion website, but their pages were loading slowly and I lost patience. Sorry, team.

> The company says the design of its ultra-thin hexagonal mirrors are key to achieving such high process heats.

Any physicists out there who have a speculation about why the thinness of the mirrors makes a difference here? My understanding is that the maximum temperature that mirrors can get you is limited by the surface temperature of the sun, rather than the mirrors themselves, but I'm certainly no expert on this point.

> It uses an AI-based method involving drones to calibrate the mirrors 200 times faster compared to traditional techniques using cameras, Synhelion says. Precision is key to ensure the mirrors track the sun and efficiently reflect its light into a solar receiver at the top of a 20 m tall tower.

This bit smells like trying to shoehorn in an application of "AI" where it's not really needed - what's the actual improvement using "drones and AI" over just pre-calculating a tracking curve based on latitude + time of day/year? Or just putting down twice as many mirrors and not bothering to make them track?

> “... The inauguration of DAWN marks the beginning of the era of solar fuels – a turning point for sustainable transportation. Our founding dream of producing renewable fuels from solar energy is becoming a reality.”

This is hyperbole, as eg. Prometheus was doing this two years ago. Additionally, Synhelion will be hamstrung on growth as long as they depend on biomass methane as a feedstock, but they can solve that by buying methane from Terraform :)

[fl7305]

>> And finally, a thermal store to release energy when the sun goes down to allow the solar-powered facility to operate around the clock.

> This actually IS new and interesting in this application

Yes, it's a nice thing to have. But it is a major research and engineering project just in itself. It is by no means a solved problem where you can buy a working solution from someone.

> This bit smells like trying to shoehorn in an application of "AI" where it's not really needed - what's the actual improvement using "drones and AI" over just pre-calculating a tracking curve based on latitude + time of day/year? Or just putting down twice as many mirrors and not bothering to make them track?

Open loop (just pre-calculate) is pretty inaccurate in a system like this. Especially over time as the mirror positioning degrades with accumulating inaccuracies.

So there might be a business case for their AI drone calibration system. But just that part in itself is also a major undertaking that requires a significant investmet over a long time to make it a production system.

"Just add more mirrors" sounds like a better business proposition, coupled with a much simpler autocalibration. Perhaps an off-center bullseye target where each mirror periodically aims itself, and a central vision system figures out the azimuth/elevation offsets?

> This is hyperbole

I agree in that I'd be very surprised if they ever get to the point of mass production.

But I agree with the point that generating synthetic fuels from the sun in a 100% renewable way would be very significant.

Sure, in 30-50 years electrical transportation might meet 99% of our needs. But we're not there yet.

[leetnewb]

Couple of points, but not a physicist or scientist.

1. I believe most existing concentrating solar plants operate below 1,000C. 1,500C might be well understood in producing syngas using other energy sources, but operating a CSP at that temperature is not. To the extent that a company is bringing a CSP plant to market with 1000+ temperature operation, that is novel.

2. Heliostat design seems like a core focus of improving CSP performance. A lot of research direction is on lowering the cost and complexity of deploying and maintaining the mirrors. See: https://www.nrel.gov/csp/solar-fields.html and https://www.energy.gov/eere/solar/heliocon

[fl7305]

1,500 C sounds like it's way past what any normal metals can handle?

But in this case, maybe it is enough to have just a small part of the central reaction vessel handle 1,500 C? Maybe using ceramics?

Or can you 3D print an Inconel chamber with builtin cooling channels that makes it possible for the Inconel surface to handle the incoming heat?

[leetnewb]

I think you nailed it on the ceramics. Pretty sure they are looking at falling ceramic particles in the tower to capture and transfer the concentrating solar.

[pfdietz]

Silicon carbide would work up to 1800 C. Various refractory oxide ceramics could also work.

This whole approach needs direct sunlight, so it's not great for a place, like Europe, where it's often cloudy. It would be better for deserts, like in Chile, Namibia, or maybe the Arabian Peninsula.

[fl7305]

It's not great for a production site. But for engineering tests, you can do a lot of stuff with no sun, and the occasional clear skies are used for sun testing.