> why extract from the air when you can just put a device on the smokestack of an existing coal or natural gas plant?

So you have spare available energy you can use to run the converter, and you also have a demand for energy that you're satisfying using a hydrocarbon powered generator. Why not reduce your hydrocarbon use in the first place, by substituting in the energy you were going to use in the converter? That seems to me to be an awful lot more efficient.

IMHO this technology really comes into it's own when you have available spare renewable energy, and want to find a way to store it in a dense, portable and easily reusable form. I think it's best thought of as a competitor to battery storage, but with the added benefit of extracting atmospheric CO2.

"why extract from the air when you can just put a device on the smokestack of an existing coal or natural gas plant? "

The process uses clean electricity to reverse the CO2. I suspect here we have a timing issue. When the sun shines, the gas plant will be idle, and that's when the spare electricity is available is used to reverse the process.

And the physical position - the gas plant is likely to be where the sun shines less.

As ever we have a storage buffer problem.

That storage buffer problem leads to one possibility. (excuse my english!)

I think there are really two major business cases for Prometheus. One is in earning back carbon offsets (reducing net CO2 production from a polluting source) while producing a valuable byproduct. The other is as a way to ethically and profitably use local excess energy to create that same byproduct.

I think it makes sense for the Prometheus apparatus to be paired with electrical load balancers (aka industrial battery banks) built for renewable energy. Allow me to expand:

1. Renewable sources like solar collect electric energy on an inconsistent basis.

2. Depending on local energy demands (a factory, the neighboring town, etc.), the grid will either use or store the electric energy. Storage for large businesses and nations nowadays occurs through industrial battery banks (i.e. BYD's).

3. Usually, those who use battery capacity battery stored energy can be used before conditions are right for collection again. However, if local energy demands less than can be stored and used in the next collection cycle, that "buffered" energy is wasted.

This is a prime use for that wasted energy. I imagine it only becomes viable at scale. And there is one other issue to address...

Companies like BYD who do national-scale renewable grid storage usually undershoot the amount of battery storage they provide because over-storing is costly (the energy isn't used or is distributed less efficiently and the batteries incur both capital, installation, and maintenance costs).

If Prometheus reaches cost effectiveness, a renewables/storage company could start over-providing energy generation and battery storage and pair it with CO2 factoring to a) reduce costs associated with wasted energy b) earn carbon offsets for large companies and c) create valuable byproducts.

The co2 could be stored underground? I guess that could deal with the timing issue at least?

You're mostly right, in that a timing issue could be resolved through a temporary storage unit, though probably wouldn't have to put it underground.

Likewise, batteries/capacitors/whatever would probably be set up on the electricity. A plant design would seem to want to control the flow rates of both.

Overall, the parent comment's unlikely to be correct in its speculation that the reason for open-air capture is related to timing issues.

You'd have to separate pump and store it, when electricity is expensive.

I suspect the advantage of this system is that is doesn't need pure co2 to work

And if you were storing CO2 I suspect the first question is how do we liquify it. So the advantage fades away.

edit: You'd probably want to store the electricity on-site instead for this. At least if there's no CO2 to consume you can be in the electricity storage business.

We want to replace fossil fuels with renewable fuels, at the largest possible scale, over 300 billion gallons of fuel per year. Point sources of CO2 and biofuels can't scale to this level.

But first you have to cross the valley of death. Elsewhere you refer to having to limit capital spending, wouldn't getting CO2 from a 3rd party instead of building a massive air capture facility do that? Everything I've seen says that its cheaper to capture from a point source than from the atmosphere, why would you make your costs higher than they need to be? You can of course build air capture down the road but I'd guess that you'd want to get off the ground as easily as possible.

Yes, we're actually agnostic on CO2 source. To get to scale we'll need to use CO2 from direct air capture, but we could by the collection from someone else.

I can completely see the logic. If this only works for point sources it may not scale sufficiently to be viable long term. So that capability needs to be proved out early in order to demonstrate it's long term value to investors.

how many point sources do you need to make atmospheric extraction viable? i'm thinking it's like a million

> 1. why extract from the air when you can just put a device on the smokestack of an existing coal or natural gas plant? The higher CO2 density of the effluent will make things more efficient.

That was my big question, too. Asked and got a response here:

https://news.ycombinator.com/item?id=19844578

But then, why to use solar energy to convert CO2 into fuel when you can convert the solar energy into electricity directly and remove the need for the fossil fuel based power plants?

This question is probably answered literally more than a hundred times in this comments section!

We have a huge fleet of cars, trucks, planes and ships that are all very carbon-positive. We also have a huge amount of existing infrastructure for delivering fuel to these things.

Sure, cars and trucks could go electric, but large airliners probably never can, and it's difficult for ships. But even for cars it will take decades to fully transition to electric. An economically viable, carbon neutral fuel that could be brought to market and scaled up quickly would be a huge win for the transition. Especially if it's cleaner burning (no/very low sulfur, aromatics etc.).