[Kevin Cudby]

Last year I developed a vision in which direct control of atmospheric carbon dioxide becomes a practical reality. It’s an extension of solar crude oil production, which I first wrote about in my book, “From Smoke to Mirrors”. I wrote an updated analysis of the concept on my blog. That early draft covers a 60-year transition from fossil fuels to a fully carbon-neutral economy. Which means the analysis stopped before the end of the 21st century. Pushing the vision out toward Star Trek territory, I realised there could be more to James Kirk’s Corvette joyride than teenage troublemaking. It’s possible to extend this technology to sea level stabilisation. And, once the world enacts technology that can drive carbon dioxide back to present-day levels, it’s a lot less risky to use solar radiation management for a limited period during the 21st century to reduce peak man-made global warming. Right now I’m busy on revenue-earning projects, so I have not yet finished writing up the DriveSolar proposal in the form of a publishable technical paper. I’ve put the rough draft on my blog to stimulate interest.

[Ian Miller]

In my ebook, “Biofuels. An Overview” I calculated that to roughly replace oil with biofuels using technology not yet available, the land requirements would be such that there would be too much loss of environment, although the exercise would be possible if we used the oceans. Now, admittedly, I have spent much of my career on biofuel research, and on research into algae, so I may be biased, but it seems to me that only the oceans can provide enough area an productivity. However, there is another problem, and that is the rate of glacial melting. If we want to keep our current coastline, I think some start should be made towards geoengineering. Present-day levels of CO2 still lead to net warming, currently in the oceans of about 0.64 W/m^2, so just holding these levels is inadequate.

[Kevin Cudby]

Ian solar crude oil production is quite different from biofuel production. My drivesolar process is very similar to the process used by Sunfire in Dresden. Solar to crude oil thermal efficiency looks to be about 10-14%. Hence the very low land area requirement. DriveSolar is based on 30% area coverage (heliostat to total facility area). Annual production, 20 billion tonnes oil, from less than 2.2% ice-free land area. For comparison, Scion’s energy forestry proposal gives about 0.85% solar to crude oil thermal efficiency. I see no obvious resource constraint, which is why I say anything better would be a bonus. Incidentally, I was first tipped off to the potential for solar crude oil production by an article in Science.

I wrote up DriveSolar because I eventually concluded Sandia and other researchers were trying to run before they could walk. Within only a few months, along came a press release announcing the completion of Sunfire’s pilot plant. Apparently it’s now producing FT crude.

I have more numbers to put up on Techogeny yet. However, please don’t muddy the water by assuming this involves biology. It’s all hard technology.

[Kevin Cudby]

Also, by the way, carbon-negative crude oil production based on DriveSolar would be capable of driving atmospheric CO2 well below present-day levels. My feeling is that habitat engineers would probably go for sea level stability. Once people adapted to sea level rise through the 21st and part of the 22nd century, why lower the sea level? Based on the modelling I’ve seen, atmospheric CO2 in that case would go below present-day levels. Myles Allen a couple of years ago presented the result of a survey showing huge potential for underground sequestration – which suggests that won’t be a constraint either.

[Adam Cherson]

Thank you for these references. The idea of using renewable energy (wind/solar) to drive a drop-in fuel refinery is fine. Could you explain three things: 1) How is the “carbon-negative crude oil production based on DriveSolar” accomplished by this strategy? 2) How is the CO2 for the system obtained?, 3) What is the source of the H2O for the system?

[Kevin Cudby]

Hi Adam

First, I must emphasise that my purpose is not to “design” the future, merely to show the goal is possible. In this case, the goal is to remove two constraints (energy & earth’s climate) on economic development. If someone invents something better that is a bonus.

1 & 2. Solar crude oil is made with carbon dioxide extracted from the atmosphere. At least two companies are now building pilot-scale carbon dioxide harvesting facilities: Carbon Engineering, and Climeworks. There is no reason to think the technology will not work. Carbon Engineering has put plenty of tech info in the public domain. To make crude oil production carbon negative, oil companies would be required to extract additional carbon dioxide. With per-capita economic growth of 1.1% pa, I think it would be feasible by 2140 to require them to extract about 3 or 4 tonnes of carbon for every tonne of carbon they convert into crude oil. The extra 2 or 3 tonnes go into underground sequestration. Annual crude oil demand by then should be above ten billion tonnes and growing strongly. At that time, the annual rate of carbon sequestration (assuming the global energy supply is at worst, carbon neutral), should be about 17 to >25 billion tonnes per year. The sequestration rate could increase over time as economic growth makes gasoline and jet fuel ever more affordable, thus allowing the market to stand the added cost associated with carbon sequestration. The DriveSolar reference process shows the energy flows for carbon-neutral oil production. I haven’t drawn up the carbon negative version yet, and I need to post the costings some time.

3. Water is not the problem some suggest. I now have three independent assessments of the expected thermal efficiency of solar crude oil production (including my own calculations). The estimates range from 10% to less than 15%. Process temperatures are high enough for excellent heat recovery using conventional chemical engineering techniques (up to 1000 degrees in the Sunfire process designed by Bilfinger). This means the system could desalinate a lot more water than it consumes (I’m still trying to get a realistic estimate, but conservatively, it’s a lot). In principle the surplus could simply be released into nearby waterways to boost downstream irrigation, town water supplies, even wilderness areas. However, the market price for water is too low to drive this. Communities near solar crude oil plants would need to work something out. (It could simply  be “quid pro quo” for using the land).

I hope to post more calculations on Techogeny.com, however, I am very busy with my writing practice so this might take some time. Meantime, there are some graphs in my renewable fuel course notes (slides 11 & 12)

[Ian Miller]

I am not replying to Kevin’s posts directly, but regarding CO2, there is plenty in the air, but mechanically extracting it is energy consumptive. Plants, however, do this nicely. Part of the reason I am advocating ocean harvesting is that much of the mechanical energy can be obtained from waves, and removal of CO2 from the oceans helps with local ocean acidification as well.

Water is a problem for liquid fuels because sit is the only source of hydrogen, and all chemical processing is somewhat water consumptive, irrespective of what anyone tells you. That is another advantage of ocean cultivation – no shortage of water.

[Kevin Cudby]

The key question is: “How do you create the market conditions to make this happen?” Myles Allen’s SAFE carbon proposal directly targeted net carbon emissions. His idea would drive a smooth economic transition from what we have now to a mix of bioenergy and direct air capture with underground sequestration.

I found that fossil gasoline with air capture and sequestration (per SAFE) would be a smidgeon more expensive than biofuel in NZ (about 2x fossil gasoline). Over a sixty year transition, economic growth and technological improvement would progressively improve the affordability of gasoline, even though the supply was being carbon-neutralised. But then you would have a big jump from there to fully renewable crude oil. I saw (and still see) no other practical option but a global emissions cap, falling to zero, and strictly enforced. This is the one option politicians run away from. That’s why I developed DriveSolar. It was originally designed to illustrate that such a policy would not inhibit economic development. Gasoline still gets progressively more affordable.

It later became clear to me that sea levels would continue to rise for centuries, perhaps millenia, after temperature stabilisation was achieved. I realised, however, that an extended DriveSolar vision could address that, using KNOWN technology.

An important side effect is that DriveSolar leads to energy abundance. This means the supply energy in the 22nd century should not constrain carbon negative technology, whether it’s direct air capture or marine algae fertilisation. The constraint is hard cash, but I don’t think it is a serious constraint. I have no cost data on marine algae. That doesn’t matter. DriveSolar convinced me that one method of reducing atmospheric carbon dioxide would be affordable. If another method happens to be more cost-effective, bonus! (More money for space development! I want to come back as my great-grandson)

Under hard carbon caps, and nothing else (except anti-smog regulations), the auto, aviation, and marine industries would be free to adopt whatever technology they choose. DriveSolar merely shows it does not matter it hydrogen and battery vehicles never dominate the market.

What kind of policy would take the world beyond carbon neutrality? How can future generations drive atmospheric carbon reduction, without ruling out any particular technology?

Does it matter right now?

(I say the answer to the second question is probably “yes”, because I strongly suspect the world will need to use SRM for some decades, perhaps a century or so, during the interim. That can’t go on forever.)

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