A while ago (years ago?) I read something about how carbon capture is so energy intensive that it doesn’t really help much. Is that still true?
I guess if you powered it with green energy, that’d be a net positive?
I guess if you powered it with green energy, that’d be a net positive?
We've emitted more than a trillion tons of CO2 since 1990. If we want to put just that back into the ground (pump it into old oil wells), the final storage will be several thousand cubic kilometers of high pressure CO2. Just the direct air capture will cost more than an Exawatt hour of renewable electricity (currently, humanity produces around 30 PWh of electricity per year from all sources).
You can use some tricks. Turning all agricultural waste, forestry waste and organic garbage into bio char (instead of letting it decompose on the fields or in compost facilities, which emits CO2) captures a few billion tons per year, but that's far more labor intense and requires a lot of automation work.
DAC isn't useful for short term, but could be useful as a very long term cleanup project.
Assuming world wide solar panel production continues to rapidly grow, wait until it reaches a point where we could set aside a number of solar panels for DAC each year equal to the current annual production of solar panels. Let's call this an arseload of solar panels.
Each year use those panels to build a solar farm in a subtropical desert dedicated solely to powering a DAC facility using current commercial DAC technology.
When we've expanded solar panel production enough raise the set aside to two arseloads a year. Keep increasing it when we can.
By the time we have 180 arseloads worth of panels (at current panel efficiency) powering DAC (at current DAC efficiency), we'd be removing each year about 10% more CO2 than we currently emit per year. We'd be using about 1/15th of the area of the 5 largest subtropical deserts.
If we ever got to 1600 arseloads we'd be removing CO2 fast enough to take the atmosphere from 450 ppm CO2 to 280 ppm in 6 years.
All that carbon removed, if stored as graphite and spread out evenly under 1600 aresloads of solar panels would form a layer about 1 cm deep.
Note that I'm not hypothesizing any breakthroughs in solar power or in DAC. The only thing speculative here is that it is possible to build hundreds of arseloads of solar panels over the next several hundred years. I have no idea if there is some consumable needed that is sufficiently limited to make this impossible.
DAC of a ton of CO2 costs around ~2 MWh. Compressing it into a well costs ~0.5 MWh, but low temperature reduction to solid graphite costs ~10 MWh.
Solid storage in soil is much more interesting in bio char applications, because the char is full of nutrients and a good water absorber.
However, places that have 100% clean electricity are often isolated. You need to ship in all equipment, which is made elsewhere, and fly in all personnel. This quickly adds up:
https://heimildin.is/grein/24581/climeworks-capture-fails-to...
Capturing carbon from the source, like a coal power plant, is much easier. But the capture rate is only 50% on average, so a coal power plant with carbon capture is still horrible while also ridiculously expensive, so it doesn't really make sense.