Slowing down winds by stirring the ocean would be equivalent to increasing surface roughness in a model. This would be fairly easy to test, I think.
I'm not sure whether the below idea has been suggested before, but using membrane polymers for DAC means that these materials could be adapted to make kites. DAC Polymers - https://doi.org/10.1016/j.clet.2021.100145 Wind energy kites - https://www.powerengineeringint.com/emissions-environment/the-energy-kite-innovation-to-harness-maximum-wind-power/ The temperature difference between the ocean surface and the high altitude winds may be enough for low temperature temperature-swing DAC to be viable, meaning that the desorb step could be passive (or nearly so). On Thu, 30 Sep 2021, 19:45 Renaud de RICHTER, <[email protected]> wrote: > I forward to you all a message from my friend Denis Bonnelle > > > >>> Le mer. 29 sept. 2021 à 14:31, Denis Bonnelle <[email protected]> a > écrit : > > This email is to show some possible synergies among DAC, renewable energy > production, and another geoengineering issue: hurricane control. > I am not claiming that DAC is a realistic solution to fight climate > change, I am just assuming this, as a hypothesis, whose consequences I try > to investigate. > If DAC is realistic, this means that it can withdraw several gigatons of > CO2 per year, i.e. that it can process even more millions km³ of air, i.e. > not far from 1 km³ of air per second (1 y = 10^7.5 s). With air velocity up > to 10 m/s, this means a cross-section around 100 km². (The 22th of > September, I participated in a seminar about NET ("NET-Rapido") with the > think tank Climate Strategies, and such orders of magnitudes have been > emphasized by a speaker). > Air can be pushed through this cross-section by fans, hopefully > carbon-free powered, e.g. by wind energy. This advocates for a direct use > of wind energy, i.e., in windy regions, letting the wind into the DAC > devices, without any fans nor wind turbines dedicated to power them (some > other energy would be needed for the physico-chemical reactions needed to > separate the CO2 from the air). My friend Renaud de Richter tells me that > this is Klaus Lackner's choice, maybe among others. > A 100 km² cross-section could be broken down to, e.g., 10,000 cantilevered > structures, each one having a 100 m x 100 m cross-section, or even to 1,000 > ones, each 300 m x 300 m. So, my hypothesis that DAC would be realistic, > implies that building such cantilevered structures could be seriously > considered. > A related project has recently been proposed, and illustrated by the > following drawing: > > > ( > https://www.rechargenews.com/wind/futuristic-multirotor-design-could-make-floating-wind-competitive-as-soon-as-2022/2-1-1021312 > - notice that for French people like me, the Eiffel tower is a convenient > reference for measuring a 300 m height) > > Of course, there are some differences with DAC: here, this structure bears > relatively few wind turbines, not DAC devices ; and it is floating on the > sea - by the way, I had never assumed that the 1,000 DAC structures would > be built onshore. > Offshore wind energy develops strongly due to various reasons, among which > social acceptance and the possibility to reach better winds (stronger and > less time-dependent). Both reasons reinforce each other: there are two ways > of getting better winds: being at a higher altitude, and being over the > ocean. But taller onshore wind turbines face more opponents, so that going > offshore makes twofold sense to make wind energy at scale possible, even if > it is quite more expensive by the MW (but, due to these better winds, not > that more expensive by the MWh; and with a larger economic value as it > needs less power back-up, or as it enhances the capacity factor of > conversion devices which would use this power, such as electrolysers). > Offshore wind energy can be either "near offshore", linked to the shore by > electric cables, or "high sea offshore". The mainstream idea is that the > latter would be useful only through on-board "power-to-liquid" > transformation, i.e. water electrolysis and use of the hydrogen to > synthesize ammonia, methanol (using CO2), or synthetic jet fuel (using CO2 > through Fischer-Tropsch reaction). The latter two are included in the "U" > of CCUS that you, as CDR and DAC specialists, know well, at least for CCS. > Of course, such on-board chemical plants would be strongly characterized by > economies of scale, which is another argument on behalf of very large > scales such as the 300 m x 300 m cross-section of the above drawing. > But why wouldn't wind energy developers design wind turbines with, at > least, a 150 m radius and a 200 m tall tower, just extrapolating the > current trends, and benefitting from the fact that, offshore, you no longer > face the same political oppositions which, onshore, prevent them from such > bold extrapolation? > The answer to this question is, again, about scale economies. So far, > larger and larger wind turbines have proved cheaper by the MWh, but this is > only thanks to the reduction of the relative part of some costs such as > development costs, maintenance, balance of power, etc. But the hard physics > of the wind turbine per se shows the contrary of scale economies. To > harvest the wind from a x4 cross-section, i.e. from a x2 radius, you might > think that a blade with a x4 area would be enough, but this is not all. > This blade must also be thicker just to keep an unchanged geometry, and it > must be even more mechanically reinforced, as all of the forces it endures > are converted to torques by being multiplied by a "r" coordinate which now > varies up to a doubled maximum radius. All this multiplies the required > materials quantity by, at least, a x8 factor, and probably even more. > Until now (i.e. the record ≈ 10 MW wind turbines, with their blades > slightly longer than 100 m and their towers above 150 m), the cost of this > material wasn't the main part of wind energy's costs, but if you'd aim at, > say, 200 m or 250 m long blades and a ≈ 300 m tall tower, this could be no > longer true, which is a first reason why such a structure with "small" wind > turbines would make sense. > The other reason could be that small wind turbine factories would face a > shortage of clients, while being fully depreciated from an accountancy > point of view, so that they would be able to propose wind turbines at very > attractive prices, overall if somebody offers to buy them by the hundred. > What is the relation with DAC? > First, it proves that such giant cantilevered structures can make sense, > notably when it comes to facing strong winds. The same about floating on > the sea. > (I had made some further comparisons with a classical wind turbine, whose > tower undergoes a strong torque due to a force parallel to its shaft. > Having two towers arranged in sort of a quite vertical triangle, would be > cheaper, provided that this triangle could always be in a plane including > the wind's direction. This is impossible onshore, as the wind's direction > isn't constant. But a floating structure can be oriented so that it always > quite faces the wind. Maybe the figure above is also derived from such a > comparison.) > Forces parallel to the wind would also exist if some or all of the wind > turbines were substituted by DAC devices. Then, you can choose between two > possibilities: being strongly anchored to the undersea ground, of being > pushed by the wind and slowed down by a hydrokinetic turbine under the > hull, which could produce some power, maybe cheaper than wind energy, as > the water is denser than the air so that smaller "blades" can be used. > When such structures are dedicated to power production for usual onshore > needs, either case (anchored structure or hydrokinetic turbine) but even > more the latter, imply on-board conversion of this power. I have already > discussed power-to-liquid, through water electrolysis and synthesis > reactions, but DAC could be an interesting use of such power, with liquid > or solid CO2 as an output. Notably, it could be useful as a first "proof of > concept" of the idea of producing offshore power from high sea winds, and > using it onboard to generate dense chemicals, with no need of handling them > too often to their final users. > When such mobile floating structures are pushed by the winds, a force > appears, which means a momentum exchange. In the global momentum balance, > this exchange is between the air and the water. This could be useful for > hurricane control. > A basic idea for hurricane control is that tapping some wind energy from > it reduces its kinetic energy, thus its devastating power, and this idea > has been developed in, e.g., "Taming hurricanes with arrays of offshore > wind turbines", a very interesting paper by Cristina Archer, Mark Jacobson > and Willett Kempton, which compares the economic values of the power > produced by these wind turbines throughout the year, and of the reduction > of the hurricane's damage. > However, this paper only deals with near offshore wind turbines, built on > shallow undersea ground off the US southern and eastern shores (so that no > control of the hurricane farther from these coasts is possible), and it > only deals with kinetic energy exchanges, not momentum ones. > Momentum exchanges are not interesting per se, but because they control a > much more powerful lever about hurricanes: angular momentum exchanges. > Even if the physics of hurricanes is very complex, the idea of reducing > their angular momentum exchanges to control them is emphasized by the fact > that they can't appear too close to the Equator, which proves that angular > momentum is vital for them, and this is logical: a very powerful hurricane > needs a very low pressure in all its quite central air stormy cylinder, > which must attract new air only at its bottom in order to harvest the > ocean's latent heat; at all the other altitudes, there must be something to > protect this low pressure cylinder from anarchic air inlets from the > outside, and this something is the centrifugal force (and an increased > Coriolis's force) which is generated by the rotation of the whole > hurricane, proportional (and even squared) to its angular momentum. If it > weakens, the whole thermal machine will be weaker even if the water > temperature is still the same. > I'm quoting this temperature, as a hurricane relies on two positive > feedbacks. The latent heat one is as follows: > "more latent heat --> more air buoyancy --> a deeper low pressure near the > hurricane's center --> stronger attraction of the winds by the hurricane > --> more heat exchanges due to friction at the ocean's surface --> more > latent heat in the whole machine". > It is quite difficult to act on it with a powerful lever, but it might be > less difficult to act against the other positive feedback which hurricanes > desperately need: > "rotation --> strong centrifugal forces --> the inner low pressures being > protected at quite all the altitudes against anarchic air inlets --> this > inner low pressure cylinder strongly attracting air from far outside at the > ocean level --> this radial inwards air undergoing Coriolis's force along a > quite long way and turning tangential --> this Coriolis effect reinforcing > the strong rotation which was the first step of our positive feedback". > And if "acting" on it would mean having a large floating structure being > drawn by the rotating winds so that (angular) momentum is transferred to > the ocean, it would be interesting to look for synergies with the mere > existence of such a floating structure being subjected to such winds and > being designed to generate something else useful for the climate. You can't > bypass the idea of something like "power-to-liquid" happening on-board, but > this "liquid" (or dense) material being CO2 could be the technologically > simplest idea to begin with. > Such a device could be used to control many hurricanes by rotating around > them for a large part of the hurricanes seasons in both hemispheres; for > the rest of the year, they would just capture CO2 on windy oceans, e.g. > being anchored not far from the Patagonian coast. > Anyway, I hope that studying such synergies more thoroughly could be > fruitful for all the approaches of such an idea: DAC; hurricane control > through angular momentum; and the broader trend about wind energy being > harvested over high seas and converted through power-to-liquid schemes. > > Best regards, > Denis Bonnelle. > [email protected] > > -- > You received this message because you are subscribed to the Google Groups > "Carbon Dioxide Removal" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To view this discussion on the web visit > https://groups.google.com/d/msgid/CarbonDioxideRemoval/CAHodn9_KAy9K1PkFMxT2pwAKDD5rXkLmYWu1AwzM1S8s3qxjVA%40mail.gmail.com > <https://groups.google.com/d/msgid/CarbonDioxideRemoval/CAHodn9_KAy9K1PkFMxT2pwAKDD5rXkLmYWu1AwzM1S8s3qxjVA%40mail.gmail.com?utm_medium=email&utm_source=footer> > . > -- You received this message because you are subscribed to the Google Groups "geoengineering" group. 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