Ask HN: Sequester Carbon with Wave Power? | Hacker News Reader

Ask HN: Sequester Carbon with Wave Power?

3 pointsncmncm4 comments

Picture a fabric structure floating, anchored, in the ocean, roughly tube-shaped. At the surface, the edge is supported a few feet above average water level, positioned so waves wash over the edge into it. Once in, the only way out is down to the bottom end of the tube, say a thousand meters deep.

In the tube, where it narrows, is a flow meter and a pH meter. Water at the surface has atmospheric CO2 dissolved in it, which in water becomes carbonic acid, so the metrics report the exact quantity of atmospheric CO2 being driven to the deeps. Certified, transmitted by satellite, I think this should be able to be sold as carbon credits.

High waves are a shallow-water phenomenon, so the tube would need to be slanted to exhaust out in deep water, and probably best situated near an underwater cliff. The amount of wave water that can be collected depends on the perimeter, so the overall shape needs to be like a funnel, very wide at the top, but narrower below so the total amount of fabric needed is not extreme.

(Some may question whether this would acidify the deep ocean. A bit of calculation shows not, provided we cut carbon emissions in coming decades.)

I imagine thousands, maybe ultimately millions of these installed worldwide to draw down atmospheric CO2 using the whole ocean surface to collect it.

Is there anything I am misunderstanding about how carbon credits are awarded? How does one get metrics certified?

I think you can get the carbon credits if you can make the system work.

You should work out the economics: the volume of water one of these tubes can transport per year times the amount of CO2 dissolved in that much surface water divided by the installation cost per tube. The flow rate may be low because the relative pressure is very small: only a few feet of water.

I suspect the tubes will be very expensive to install. They need to be long (many kilometers) and the ends need to be anchored, so it probably costs a lot to install each one. You can look at other things installed underwater like pipelines and telecom cables to get a ballpark estimate.

If you can remove a ton of carbon per year per $1000 installation cost, you might have a viable project.

Since the real goal is to move carbon out of the atmosphere, it doesn't need to be especially profitable, but if it were, I hope that would drive a large number of them to be placed.

More worrisome is

https://earthobservatory.nasa.gov/features/OceanCarbon

which seems to suggest that deep water already has more carbon than surface water, so that moving surface water down might have no, or contrary effect. At least, you would need a pH meter at the exit to show exactly how much more acidic is the water leaving than the water already there, and of course you would need to be careful to place the system where there is such a difference.

Facts are inconvenient.

Anything that floats creates surface area for life to cling on. Water flow can then provide food and oxygen. Puzzlingly oxygen is not a requirement, there is even multicellular aneorobic life with methane as the CO2 equivalent.

Your system would have a significant impact on life and could cloque up, or become very heavy and sink to the ocean floor.

Based on the conservation of mass, Stoichiometry helps you to calculate carbon storage. In sea water calcium is present, corals and mollusks or snails use it to build their shells out of calcium carbonate, which is insoluble in water. Forming the white cliffs of England and many other things over millions of years.

The calcium concentration varies alot over the oceans and depth.

If the CO2 concentration is high calcium bicarbonate forms, which is soluble in water. Rising levels of that stuff are the cause of ocean acidification. Otherwise calcium carbonate will precipitate out, trapping the CO2.

You could calculate the excess mass you are producing this way, in form of calcium carbonate, by Stoichiometry. Just farming snails and mullusks and weighing their shells, you would do the exact same thing. Noting that CO2 is 44 g per mol and calcium carbonate is 100 g per mol 1 kg of sea shells produced is 440 g of CO2 removed, roughly.

To certify your metrics you have to calculate a stoichiometry of your complete processes of production, deployment of sattelites, data aquisation ,...,... . If you only use green energy you can cheat a lot here. From this you can then remove your sea shell production offset, with the mentioned mass reduction.

This total is your certifyable CO2 reduction, which you can sell to somebody to fudge his certificate.

I don't think most people understand how much CO2 is produced when burning a gallon of gas. 1 gallon produces about 20 pounds of CO2. And that's without accounting for the fuel used to produce it and transport it.

https://www.fueleconomy.gov/feg/contentincludes/co2_inc.htm

Your solutions seems nice but it's so much more productive to find ways not to burn any more CO2 producing fuels. That's something we can all do now and we can do it with out any special technology.

I get it something is better than nothing but we need to find ways to reduce the cost of alternative energy to be so inexpensive that we can begin to remove c02 from the atmosphere. Right now it costs $600-$800 ton or 6 to 8 dollars per gallon of gas to remove CO2. If you can quantify the cost per ton that's way lower then your solution has value.

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