It's such an easy, relevant question to ask that it boggles the mind that investors don't have their own engineers to ask it. I know you're money people not tech, but how do you know you're not being ripped off if you can't check figures that basic?

Anyway, apparently 3 MWh/tonne is a not-unrealistic claim, so they're only demanding 1.5 MW (on average, though if solar-powered it would make sense to oversize) and a km2 of solar panels could reasonably generate 50-100 MW on average (this is conservative for most places, though not for Iceland). A km2 of tress, by their calculations, gets 1,000 tonnes, so DAC comes out ahead, although you're right to observe that trees do have a synergistic use for the carbon they capture.

Welcome to planet Earth. If you can do napkin math, and bother to do it, you can be an extremely successful in engineering domains, because almost everyone else is completely useless.

Napkin math is an underestimated skill indeed.

Early investors, it seems, don't care. All they care about is whether or not they can sell their shares to some greater idiot down the line.

Heck, those money people don't even care about money questions.

Examples of non-existing due dilligence include: WeWork, Theranos, Nikola, FTX. Just from top of my head.

For context, 4000 tons of CO2 is roughly the emissions of a full 777 flying from San Francisco to London and back twice.

That doesn't sound right, 4000 tons is more than 10 times the maximum takeoff weight of a 777.

Jet fuel is comprised mostly of hydrocarbons with 8 to 16 C atoms, and a large fraction of these hydrocarbons are straight-chain alkanes.

Combustion of dodecane (a C12 straight-chain alkane) makes 12 CO2 molecules. A 747 jet consumes about 4 L of jet fuel per second when in flight. Based on the density and molecular weight of dodecane and the stoichiometry of its combustion reaction, you'd arrive at something like 0.01 ton of CO2 emitted per second of flight time.

4000 tons is a good estimate.

Back of the envelope...

Ah, so you're saying (if I'm reading this correctly) that the plane only carries the carbon portion of the CO2, and the oxygen comes from the air itself. That's how it's emitting more CO2 then it's fuel mass.

Is that right?

Correct. Fuel is around 16/36th of the CO2 mass it emit when being burnt. A 777 carries around 120 tons of fuel for a SF/LON flight, so that's around 300 tons of emissions per flight.

It looks about right to me (I used https://www.atmosfair.de/en/offset/flight/)

It’s about 850 US tons per full leg * 4 legs to make up the two round trips

(388 pax in a -300ER)

You have to account for the mass of the oxygen that gets bonded to the carbon in the jet fuel to form CO2. i.e. most of the mass is coming from atmospheric oxygen, not what the aircraft is carrying onboard.

TIL, thanks for the explanation.

I tried calculating it two ways to see.

Firstly, based off two full fuel tanks for a 777. Apparently a 777-200 has a 117350 L fuel tank, and the density of jet fuel is approximately 800 g / L.

The emitted carbon dioxide combines oxygen from the air with carbon from the jet fuel. Apparently the average chain length is 12, so it would be C_12H_10 for a straight hydrocarbon.

Factoring in the molecular masses, the amount of CO2 from two full tanks would be: (12 * 12.011 + 212.01115.999) / (1.0080 * 10 + 12 * 12.011) * 117350 * 800 * 2/ 1E6 = 643 tonnes.

Now, they might not use the full tank. Another estimate is that long haul flights use about 0.1 g / passenger / km. Apparently it is 4308 km in a straight line from SF to London, and a 777 seats about 350 people depending on the configuration, so multiplying by 2 for a return trip comes out at 302 tonnes of CO2 (that's probably an underestimate since it is a straight line).

So I think 4000 tonnes is an overestimate (and they said tons, which is even more than a metric tonne, at 4480), but the emissions of such a flight is still significant (and the global warming impact is higher because combustion also disperses water, which also has a warming effect at that altitude).

The entire aviation industry emitted 619 million tons of CO2 in 2019 [1]. So about 155 thousand of these plants would be needed just to offset air travel

[1] https://www.iea.org/reports/aviation

I mean, that's not a lot compared to trees. There are >3 trillion trees in the world.

How much carbon is produced by the transportation and storage of the carbon that is captured? I want to see their carbon math for the whole process (including electricity) to prove this is all truly carbon neutral, seems like something that should be front and center on their website but they only vaguely discuss the carbon footprint of the plants.

Having a business saying their product is carbon negative when the actual end to end process isn't seems par for the course, especially one with VC backing...

There is no transportation, they site the plant where they are going to store it. That's one of the advantages of capturing from the atmosphere.

And the land for the solar panels that substitute the energy you'd harvest from the trees while turning them into highly concentrated CO2 for storage. And the land for the batteries you'd have to add to achieve the same dispatchability as the burn trees (or faster-growing plants!) and work on that CO2 alternative. DAC is a joke.

> Also what's the carbon waste that this generates? Is there a synergistic use for it?

I've wondered the same about these carbon capture plants. Is this literally just elemental carbon in some kind of dust/sand at the end of the day? Could this be a raw material input for carbon fiber production?

Elemental carbon is a valuable industrial material -- and even low-quality carbon, like "carbon black" soot, ain't cheap!

Nah, separating carbon from oxygen in CO2 and CO is too expensive and energetically demanding.

To simplify things a little bit, what they do here is inject CO2 into water at high pressure, which results in highly acidic H2CO3. They then pump H2CO3 into basalt rock, which chemically reacts with the acid -- in fact, it is partially dissolved. Then there's a second stage reaction between the partially-dissolved basalt and the remnant HCO3-, and it recrystallizes as carbonate minerals, e.g. FeCO3 or CaCO3.

So they're turning CO2 into a liquid acid, and then injecting it into rock where it reacts with basalt and crystallizes as carbonates.

Great explanation that I've never seen on any of these carbon capture sites. Thanks.

Plants/trees waste product is oxygen. And plants only need water and sun. Plants can also reproduce themselves. What we should concentrate on is to make artificial systems that get water to areas where it doesn't rain.

> How much land, in solar panels for example, is required to power this?

It says "The CO₂ can then be safely and permanently stored underground by our storage partners — Carbfix in Iceland."

So my assumption was that the collectors are located there as well and using Iceland's abundant geothermal electricity.

I remember watching something about Carbfix on TV: they inject the CO2 into underground magma and it is then incorporated in the rock formation (carbonate rocks?)

So, yes, it would make sense to use local geothermal electricity or even to produce it at the same time as the CO2 injection process if that's possible.

In other words: it definitely will not scale.

But it looks good on a pitch deck. I just wonder if it cannot be combined with those particle emitting start-up that wantsbto creat artifical clouds. Both ideas sound like they are ment to be combined in the same company just before an ICO or a SPAC.

>The energy usage: We're committed to driving down energy consumption as much as possible. We only use renewable energy, energy-from-waste, or other waste heat to power our plants.

They make it impossible to do the math. Energy consumption, lifetime capital cost per ton, are what make or break this scheme.

Unit economics are so unsexy, they did with e-scooter rentals and fresh food deliveries.

1000 kWh/ton (found it on google):

166 kW/ton in a sunny place:

1000 square meters/ton in a sunny place:

4 million square meters = ~1000 acres of PV to power. One unit.

Yeah, that’s going to happen. /s “We’re too ashamed of our energy requirements to post them on our page and are well aware they’re dooming this technology until cold fusion comes out” is what I read between the lines on their fluff page.

1000 kWh/ton to sequester, and how many tons per kWh to generate?

EDIT: Apparently, one ton of CO2 is released by 1000 kWh of electricity:

https://www.eia.gov/tools/faqs/faq.php?id=74&t=11

So you have a coal plant generating energy and emitting CO2 just for this factory next to it to capture all that CO2 again. Seems more efficient to just not run the coal factory.

It seems like this idea will be worthwhile when the last coal factory closes.

It'll always be more efficient not to emit carbon.

Imagine you have a teaspoon of salt and a cup of water.

Adding salt into the water is dead simple and requires little energy. Now how hard is it to remove that teaspoon of salt?

That's effectively what's happening with the atmosphere.

two comments: they claim to sequester 1000 tons (1e6 kg) vs 22kg, so the sequestration space difference is on the order of 200000 difference. They may include the solar panel area in their stated efficiency calculation.

Secondly, the solar panels are a bit more liquid than a comparable area of trees, when industrial demand is high, you can route it there, when it's low, it can be working on sequestration. There are some advantages there. Especially considering the atmosphere is fairly homogeneous, but soil in proper condition for forests is less so.

Their plant is in Iceland and runs on geothermal

Geothermal is not good for global warming bc it is an additional source of energy which would normally be contained. The sun gives such amount of wattage and the earth can give so much wattage back to the universe. Nuclear, geothermal and fusion is stored energy like fossil fuel which adds to the heat in the atmosphere. Today that only amounts to 5% of global warming but if it's the only source of energy it could add more. CO2 is the focus right now bc it is continuous warming potential but the other energy forms have it too. Wind and solar is just "saving" sun energy from being instantly converted into heat and can be so used for our pleasure as it doesn't add to the input/output equation.

Heat waste is absolutely miniscule compared to the amount of energy the Earth receives from the Sun. As in, the Earth is continuously bombarded by 173 petawatts of solar radiation. So you can see why it would be worth trading some waste heat to reduce the retention of solar energy in the atmosphere.

This doesn't make too much sense in this case, the geothermal energy is being stored in chemical bonds in the carbon sequestration process and returned underground

Too late to edit, but I should qualify this:

They claim 4000 tons per year, I did the math on 4000 tons per day. So ~3-4 acres of PV to power, not 1000 acres.

To completely counteract the 37 billion tons per year produced worldwide, and do it with PV only, assuming desert southwest conditions, would require ~30 million acres of PV. That sounds impossibly high, but is only about the size of the US state of Mississippi. 20% of the land area of Texas, on the El Paso side, would be sufficient to keep pace with the entire world's carbon dioxide emissions.

I remain skeptical that this is the most cost-effective approach, as well as skeptical of its ability to scale, but I apologize for crapping on it at first gloss.

A better use of CO2 is generating fuel, I suggest.

https://terraformindustries.com/

4000 tons of CO2 removal per year is at best a proof of concept. If it was one of the industrial giants, with the muscle and budget to scale it and the sales channels to sell it, I would be more optimistic about that.

But than I became so jaded regarding start-ups, especially "ddep" tech ones, lately that I tend to see even more negatively than I already do in general.

Ummm, seems to me that 0.42 acres of trees would sequester a lot more that 22kg of CO2 per year. Let me guesstimate from my typical annual hedge clipping - we have a (appx) 1.5m wide hedge that is (appx) 120m long equal to (appx.) 180m^2=0.044 acres. The annual clipping produces 10 hefty bags (the big bags used to carry e.g. 1 ton of gravel or stones), so maybe a total of 300-400kg for my hedge. Multiply by ten for 0.42 acres, yields about 3000-4000kg.

Sanity check anyone?

Unless it was edited...that sentence says 22kg per year each. So it's 22*220.