Carbon capture buoy scenario

A CO₂ and energy harvester buoy on the way back to the harbour with nanofactories and a connection to the global microcomponent redistribution system. (No point in lugging replication capability around for on-site-selfreplication of these buoys as it's both – less efficient and – less safe). There at the harbour the captured carbon (plus some mined rock) can be used to make more buoys till many billions of them roam the seas and fix our climate crisis in mere decades or even less time. The question at which level to stop arises as we don't want to induce an ice age or even cause troubles for plants depriving them of CO_2.

A CO₂ and energy harvester buoy deployed on the open ocean. Unlike compact when traveling a large area coverage of (highly flexible and robust non-ripping solar cells can be deployed. Of couse still leaving enough light and air openings to not endanger esisting sea life. heck these couls even oxygen enrich the surface waters and provide artificial reef surface as side task (and deploy secondary deep see stuff). There is no need for an air intake as CO2 can be equally filtered from the water and that is probably even more efficient as water is a decent solvent for CO2 pre-concentrating it.

Conceptual sketch of a buoy for collection of atmospheric CO₂. SVG - mobile carbon dioxide collector buoys

Context

CO₂ is a big challenge of our time.
Beside avoiding to expel more of it we also will eventually need to actively take it out eventually.
This will need to be done on an unprecedented hyper enormous scale.
As you basically need to roll back the entire industrial age for the whole world.

Scenario / story

So here's a possible scenario:

In many harbors/shipyards there will be placed nanofactories producing special very robust carbon capture bouys in high quantity.
The size of the buoys may be between 10cm and 1m perhaps.
These buoys get released and spread across the oceans in low latitudes near the equator where there's the most sun to be harvested.
The buoys deploy robust swimming foils of solar cells (leaving some light and air through for sea-life).

They use the solar energy to capture CO2 and convert it into some suitable form.
Possible are e.g. ethanol (being rather environmentally non-problematic) or ethyne (being a good stoock for mechanosynthesis of diamond).
Large scale spills are unlikely if anything they will be caused by a software error or malicious attack.
Fluids might get microcapsuled.

Once they filled their tanks they return to some harbor/shipyard and feed the harvest into the global microcomponent redistribution networks
Some fraction of the harvested carbon will be used right then and there to make more buoys for sending out.
The cycle begins anew.

Dumping excess carbon

Excess carbon will need to be dumped decentralizedly.
We burnt more carbon for transport (cars, freighter ships, planes, …) than what we can ever use for housing and streets (biggest volume sinks of civilizations martial usage).
At least today without mega-structure hive-cizies. (Which may never come considering dropping birth rates in high wealth countries like Japan. Who knows.)

Dumping all on one ginormous pile would get us a mount Everest of carbon
so heavy that it'd cause earthquakes and maybe even deform Earths crust a good bit. Man made volcanoes. Yay!
Not seriously of course. No one would consider making one ginormous pile obviously. Well, I sure hope so.
But it's still interesting to think about is this way to get an intuitive feeling for the scale of the problem.

Bad idea: People might be inclined to code the buoys such that they dump excess carbon right form the capture site to the ocean floor.

Good idea: Combine excess carbon with silicon (of which we have an FAPP infinite amount available)
to make silicon carbide (SiC, moissanite). This is highly fire resistant very unlike many other forms of reduced carbon.

Storing excess carbon as CaCO₃ aka calcite / aragonite / limestone / chalkstone / double spar

Storing excess carbon in safest fully oxidized from yet still uncolled stably solid
requires mining calcium from ultramafic (metal rich) basaltic rock.
Warning! you are moving into more speculative areas.
Or drilling down to record depths tapping the mantles metal riches??

Energy conversion details

After photoelectrical energy conversion (light to electrical current) rather than a following electrochemical like in batteries a two step process
electromechanical and then chemomechanical may be preferable.
Unclear if more efficient optomechanical or optochemical energy conversions pathways options will offer themselves.

Repositioning and recovery

If a buoy drifts too far it undeploys the solar cell foil and reposition itself via some robust integrated probulsion.
Buoys that get entangled somewhere or experience some other failure will report that to be recovered.

Dangers

Overall probably a low risk geoengineering approach.

A viable system would be gargantuan in size but still need years to
change the CO₂ levels significantly.
So there's no risk of a malicious software attack making
CO₂ levels change to dangerously low (or high) levels withing the timespan to deal with the hypothetical attack.

Local on site buoy self-replication

Of course local on site repliation would be possible if each buoy would carry a nanofactory. But that nanofactory would spend most of it's lifetime inactive and pose an obvious replication accident risk. Well catching >10cm buoys is still more managable than (unlikely) grey goo nanobots.

Related

• Abstract without story: Mobile carbon dioxide collector buoy
• Story scenarios
• Carbon dioxide collector
• Energy harvesting
• Global scale energy management
• Energy transmission
• Transportation and transmission