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The Carbonate Solution, Part 1: Brute Force

Limestone Quary

This week I want to expand on the potential role of carbonate minerals for fighting rising CO₂ levels in the atmosphere. Previously, in Treasure of the Sierra Nevada and Cruising to Vegas I had explained how moving some of the stranded products of chemical weathering of the Sierras from the Great Basin to the Pacific ocean could offset some of the fossil carbon we’re pouring into the atmosphere. It could even help to reduce atmospheric CO₂ levels once we’ve brought our carbon emissions under control. The key was in the chemistry of soluble carbonates present in the alkaline clay and mineral deposits formed from weathered rock. But there are other sources for carbonate minerals and other ways of using some of them. Could they help?

Ubiquitous resource

The Great Basin is hardly the only place where rich deposits of carbonate minerals reside. Indeed, there are vast deposits of calcium carbonate — the predominant ingredient in chalk and limestone — all around the world. They are found wherever land that was once shallow seabed has been uplifted. Many of those deposits are close to existing shorelines or still under shallow seabeds not yet uplifted. Couldn’t they be used? They’d certainly be easier to access and transport to the ocean. Limestone has a carbonate mass fraction that’s several times higher than the alkaline clays of the Great Basin, so in addition to being closer to the ocean, less material should be needed.

The answer is complex. What distinguishes the carbonates in the Great Basin is that a good fraction of them are soluble evaporites. Solubility is important, because it’s the conversion of a dissolved carbonate ion, CO₃²⁻, to a bicarbonate ion, HCO₃⁻, that makes the parent solution more alkaline and enables it to absorb more CO₂. Calcium carbonate, however, is not soluble in plain seawater. In that sense, the answer would be “no, they can’t be used” — at least not in the same way as the soluble carbonates from the Great Basin deposits.

If one is willing to look beyond the issue of easy solubility, however, there turn out to be several ways that the ubiquitous nature and high concentration of carbonate in chalk and limestone could be exploited for CCS.

In all of what follows, bear in mind that the real issues are economics and scalability. It doesn’t matter if an approach is technically feasible if it can’t be implemented at an acceptable cost or scaled to a useful level. Indeed, it’s the limited scalability of the transport leg of the Great Basin project that leads me to consider other options. The economic feasibility of transporting clay from the Great Basin to the Pacific depends on collateral benefits of the proposed canal: pumped hydro energy storage, recreation and environmental benefits, and tourism. I think those benefits saturate at near the scale of what I proposed. A larger canal, able to transport more material, wouldn’t bring in more tourist dollars or satisfy a market for energy storage beyond what the smaller canal would already supply.

With that in mind, let’s look at some of the ways other natural carbonates might be used. But first, a short digression about the “storage” element of CCS.

Storage conundrum

In all discussions of CCS, the issue of how and where to safely store captured CO₂ invariably arises. Most petroleum geologists insist that there’s adequate capacity in depleted oil and gas fields. The existence of oil and gas in these fields has already proved that they have impermeable cap layers that have held over millions of years. But even accepting that, if storage were limited to depleted oil and gas fields the cost would be high. We’d need a huge network of long-distance CO₂ pipelines to transport captured CO₂ from power plants in parts of the country that don’t happen to be near any depleted oil or gas fields. That’s why there’s interest in deep saline aquifers. They’re widespread, easing the transport problem, but their safety is also more controversial.

There are three approaches that I know of for storing carbon dioxide whose safety, scalability, and long term security are not in question. One is mineralization. I’ll say more about that in a minute. Another is injection into offshore sediment beds at depths of several hundred meters. The ocean temperature there is low enough and the pressure high enough that any CO₂ diffusing upward through the sediment bed would combine with water to form clathrate ice. The clathrate ice would fill the pores of the sediment and serve as a permanent, self-healing cap layer for gas further down. The third approach stores CO₂ as dissolved inorganic carbon (DIC) in the oceans. That’s what the soluble carbonates from the Great Basin are all about.

Mineralization is nice because CO₂ becomes chemically bound into solid carbonate minerals. It forms minimum energy mineral states that are very stable. It’s “nature’s way” of removing CO₂ from the atmosphere over the long term, but it’s a slow process. Early studies of how it might be accelerated considered giant reactor vessels in which crushed silicate rocks would be reacted with water and concentrated CO₂ at elevated temperatures to form carbonate minerals. That works, in principle; suitable silicate rock is very common. However, the energy, equipment, and material handling requirements were deemed too high for economic feasibility.

There’s a shortcut to mineralization that has been theorized and recently tested. If pressurized CO₂ is mixed with water and injected into the porous basalt of old lava flows, the acidic solution of water and CO₂ will react with base minerals in the basalt. The CO₂ content of the injected solution will be mineralized in a period of weeks to months. That was confirmed in a field trial recently conducted in Iceland.

That sounds well and good; there’s no shortage of old lava flows that should serve. But how to capture the CO₂ and distribute it to the injection sites remains problematic. It’s hard to work up much enthusiasm for any of the point source capture methods currently available. The equipment is costly, and its operation takes a heavy toll on power plant output. And aside from pipeline construction contractors, nobody likes the thought of all the CO₂ pipelines that would need to be laid. On top of that, there’s the fact that large point sources (like power plants) account for less than half of fossil carbon emissions that need to be curtailed. If it could be done economically, air capture — and especially capture via enhanced ocean uptake — would certainly be preferable.

Brute force approach

There are several ways that carbonate chemistry could be exploited to use calcium carbonate in chalk and limestone for CCS. One is what I’ll term the “brute force approach”. It is not subtle and not efficient in terms of energy expended per tonne of CO₂ captured and stored, but it’s simple and relatively “bulletproof”.

The brute force approach is an indirect air capture method. It uses enhanced alkalinity in ocean surface waters to counter ocean acidification and increase uptake of atmospheric CO₂. The “brute force” aspect come into play in how it creates the enhanced alkalinity. It does it via large scale calcination of calcium carbonate — the primary constituent of limestones.

Calcination of limestone is a very old technology. Lime kilns were built and used in early civilizations to make quicklime for plaster and for stabilizing mud as a building material. Today the largest use for calcined limestone is in production of portland cement. The fossil fuels burned to fire production kilns plus the CO₂ released from limestone in the process are estimated to account for 5% of all anthropogenic carbon emissions. Developing alternatives to portland cement with lower carbon footprints is a thriving category of the green technology movement. So how could calcination of limestone over and above the needs of portland cement production possibly help?

The problem with production of portland cement is that all the CO₂ from firing the kiln, along with the CO₂ evolved from the thermal decomposition of CaCO₃, are released into the atmosphere. That’s by far the cheapest way, so long as capture of CO₂ is not rewarded and dumping to the atmosphere is permitted. But if the CO₂ were not dumped, then portland cement, along with plaster and other  products made with calcined limestone, would be very green. They ultimately absorb as much CO₂ from the atmosphere as was evolved in producing the quicklime that went into them. Hence calcination of limestone is a handy way to get a nearly pure, “sequestration ready” stream of CO₂ right at the injection site, while producing a product that will absorb CO₂ from the atmosphere.

The heat source used for calcining limestone is irrelevant to the process itself. For existing installations, it’s almost always combustion of wood, coal, or natural gas. However, it could be anything capable of delivering the required temperatures of at least 850 °C. Highly concentrated solar energy could be used, or even electrical resistance heating if electricity were super-cheap. But for large-scale operations of the sort needed to seriously address CO₂ emissions, the ideal heat source would be a small nuclear reactor. It would need to be one of the high temperature designs, using molten salt or lead. But it would only need to produce heat, not power, so it would be much simpler than a power reactor.

If this approach were used to sequester CO₂ at the current 9.8 gigatonne (GT) rate of fossil carbon emissions (40 GT CO₂), the production rate for limestone calcination would need to be roughly 50 GT of CaO annually from just over 90 GT of calcium carbonate. Large as those numbers are, they’re not utterly impossible. Availability of limestone is not a limiting factor; there are millions of gigatonnes of accessible deposits around the globe.

The big hurdle is thermal energy. 50 GT of CaO is roughly 40 times more than the cement industry consumes annually, and the energy needed to produce it would nearly double the world’s primary energy consumption. However, it’s thermal energy, not electricity. If it could be supplied by a new generation of cheap nuclear reactors that consumed 100% or their uranium or thorium fuels, it would not put a noticeable dent in the world supply of those elements. But how could so much caustic CaO be economically distributed and used to pull CO₂ from the atmosphere? That’s where enhanced alkalinity of ocean surface waters comes in.

Ocean Alkalinity

Enhanced alkalinity of ocean surface waters is the same mechanism that would be used for carbon mitigation in the project I wrote about in “Treasure of the Sierra Nevada” and “Cruising to Vegas”. The procedure is simply to load freighters with alkaline material and send them out on long looping courses to dispense alkalinity into the sea. The freighters would be equipped with filtered input ports to suck in seawater (and no fish). The filtered seawater would be used to dissolve controlled amounts of alkaline material, The resulting alkaline seawater would then be pumped through spray nozzles at the stern of the ship. The nozzles would function like giant lawn sprinklers, spraying a rain of alkaline seawater over a 100 meter wide swath of ocean in the ship’s wake.

The extreme dilution of the alkaline droplets upon hitting the ocean surface would be sufficient to insure that the pH of ocean water behind the ship remained safe for sea life. The pH would of course be raised slightly — that being the whole point of the operation. But the rise from a single pass of a single ship would be minute. For CCS, that doesn’t matter; concentration of alkalinity is largely irrelevant to the amount  of atmospheric CO₂ that can taken up. To a first approximation, only the total amount of alkalinity added matters. The more uniformly the added alkalinity is spread, the more closely the approximation holds.

That’s not to say there are no potential environmental consequences to this approach that would need to be understood and addressed before it it could be implemented at scale. In particular, it would be nearly impossible to ensure that nothing but alkalinity were added to the seawater. Limestone is far from pure calcium carbonate, and the products of calcining it are far from pure CaO. The alkaline solution produced aboard the freighter would inevitably include colloidal particles of silica and iron-aluminum silicates of the sort found in common clays.

That would  probably be good. Those minerals are normally supplied to the ocean from dust blown high into the atmosphere and carried thousands of miles. Their scarcity in ocean waters is a limiting factor in bio-productivity. Increasing their availability as a byproduct of CO₂ mitigation efforts would be a boon to both calcareous and siliceous phytoplankton. That, in turn, should produce consequent benefits on up the food chain, for the health and productivity of the ocean ecosystem as a whole. But it’s not guaranteed. Carbon sequestration by this method is full scale geo-engineering, and unintended consequences are possible. The method would need to be studied and approached gingerly, working up from small tests.

Prognosis

As I said, the brute force approach of limestone calcination is not energy efficient. Energy efficiency, per se, may not be as important as economic efficiency, and the fact that calcination is simple and requires only thermal energy, rather than electricity, does matter. But given a cheap source of high grade thermal energy, it’s not that much harder to produce electricity. So even if cheap nuclear technology of the sort that would enable the brute force CCS approach is developed, its development would also reduce the volume of emissions needing to be captured in the first place.

That level of nuclear technology would even reduce fossil carbon emissions from liquid fuels in the transportation sector. Cheap, reliable electricity would make electrification of transport more attractive, while simultaneously making synthesis of fuels from CO₂ and hydrogen competitive with fossil hydrocarbons. Hence calcination of limestone — the brute force approach to CCS — is unlikely to ever expand far beyond its current market for making portland cement. It could rise to a few gigatonnes per year as part of efforts to roll back CO₂ levels once fossil carbon emissions have been curtailed, but is unlikely ever to become our front line of defense to hold back global warming.

Now suppose that cheap nuclear technology is not successfully developed any time soon. Where would that leave us? We’d be forced to depend on conservation, energy efficiency, and diffuse and irregular renewables to cut fossil carbon emissions. Some feel that that would not be a bad thing at all. But what of rolling back the disastrously high atmospheric  CO₂ levels we’re certain to be stuck with before we can get to zero on the fashionable RE pathway?

The Great Basin project that I wrote about in my last two posts might deliver a few hundred megatons of CO₂ capture capacity per year. It probably doesn’t scale well beyond that. But there are energy-efficient ways to exploit carbonate chemistry for CCS that are worth exploring. I had intended to write about them here, but I find I’ve used up my allotted schedule time and word count already. So that discussion will be deferred until next week.

In the meantime, patient readers, happy pondering!

Roger Arnold's picture

Thank Roger for the Post!

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Jim Baird's picture
Jim Baird on June 21, 2016

Roger I am not getting the ta da moment.

“The extreme dilution of the alkaline droplets upon hitting the ocean surface would be sufficient to insure that the pH of ocean water behind the ship remained safe for sea life. The pH would of course be raised slightly — that being the whole point of the operation.”

National Geographic says over the past 300 million years, ocean pH has been slightly basic, averaging about 8.2. Today, it is around 8.1, a drop of 0.1 pH units, representing a 25-percent increase in acidity over the past two centuries.

In “The Treasure of the Sierra Nevada” you go through the steps of how

2H+ + CO32- ⇀ H+ + HCO3–

Then that reaction consumes H+ ions, so their concentration is reduced. The seawater is made more alkaline, with a higher pH.

The effects don’t stop there. The reduced concentration of H+ ions slows the reactions that consume H+ ions and accelerates those that produce them. So:

H+ + HCO3–(aq) ⇀ H2CO3 (aq)

is slowed, while its counter reaction is accelerated. The net result is to reduce the concentration of H2CO3 (carbonic acid). But then that increases the speed of the reaction that produces H2CO3 and consumes dissolved CO2:

CO2(aq) + H2O ⇀ H2CO3(aq)

And ta da! CO2 absorbs atmosphere from the atmosphere.

The problem is H2CO3(aq) is an acid.

Don’t we have to have a cation to react with the acid to produce the carbonate or bicarbonate and to balance the equation?

And then doesn’t this cation then come with its own baggage?

Maybe this is to come in the next segment but I am missing something in the reaction between the two streams, maybe it is just me?

Roger Arnold's picture
Roger Arnold on June 21, 2016

There are three approaches that I know of for storing carbon dioxide whose safety, scalability, and long term security are not in question

OK, that’s going to ruffle some feathers. I didn’t include bio-oriented approaches: bio-char, increasing forest cover and standing biomass, and redirecting agriculture away from shallow-rooted annuals to deep-rooted perennials.

For the record, I’m strongly in favor of all of those. They all have significant potential, especially over the long term. But that’s the problem: they’re long term strategies and can’t help much (or enough) in the near term. If we could stop burning fossil fuels tomorrow, those approaches should allow atmospheric CO2 to slowly return to safe levels before the worst effects of rapid warming bit. But we’re talking 50 – 100 years, and that only afterwe’ve drastically reduced burning of fossil fuels.

I used to consider myself a “moderate” on global warming. I knew it was a looming problem that would need to be addressed, but I didn’t expect we’d see drastic effects this soon. But the rate of increase in global average temperatures and sea level rise have become alarming. I think we may already be into territory where full-scale geo-engineering may be necessary.

Roger Arnold's picture
Roger Arnold on June 23, 2016

Jim, H2CO3 is carbonic acid, all right, a hydrogen donor. It can contribute H+ ions to a solution, or supply an H+ to neutralize a hydroxyl ion (OH-) in the solution. After doing so, it has become a bicarbonate ion. But H2CO3 is a weak acid — meaning that it doesn’t fully dissociate into H+ and HCO3- ions in solution. The neutral molecule exists in equilibrium with hydrogen ions and bicarbonate ions. Reduce the concentration of H+ by adding alkalinity — i.e., a base whose anions are H+ acceptors — and the rate at which bicarbonate ions combine with H+ ions to (re)form neutral H2CO3 will drop, while the rate at which neutral H2CO3 loses a hydrogen to (re)form a carbonate ion is unchanged. So the concentration of H2CO3 drops. But that means that the rate at which H2CO3 splits into a water molecule and neutral CO2 molecule also drops, while the rate at which CO2 molecules enter solution from the atmosphere remains unchanged. Result: a net flow of CO2 from the atmosphere into solution.

Just remember that equilibrium is a matter of balance in concentration-dependent reaction rates. At equilibrium, the reaction and its counter reaction are still ongoing, but they’re rate-balanced.

Clear as mud? Sorry, but I think that’s the best I can manage.

Roger Arnold's picture
Roger Arnold on June 23, 2016

Jim, H2CO3 is carbonic acid, all right, a hydrogen donor. It can contribute H+ ions to a solution, or supply an H+ to neutralize a hydroxyl ion (OH-) in the solution. After doing so, it has become a bicarbonate ion. But H2CO3 is a weak acid — meaning that it doesn’t fully dissociate into H+ and HCO3- ions in solution. The neutral molecule exists in equilibrium with hydrogen ions and bicarbonate ions. Reduce the concentration of H+ by adding alkalinity — i.e., a base whose anions are H+ acceptors — and the rate at which bicarbonate ions combine with H+ ions to (re)form neutral H2CO3 will drop, while the rate at which neutral H2CO3 loses a hydrogen to (re)form a carbonate ion is unchanged. So the concentration of H2CO3 drops. But that means that the rate at which H2CO3 splits into a water molecule and neutral CO2 molecule also drops, while the rate at which CO2 molecules enter solution from the atmosphere remains unchanged. Result: a net flow of CO2 from the atmosphere into solution.

Just remember that equilibrium is a matter of balance in concentration-dependent reaction rates. At equilibrium, the reaction and its counter reaction are still ongoing, but they’re rate-balanced.

Clear as mud? Sorry, but I think that’s the best I can manage.

Jim Baird's picture
Jim Baird on June 23, 2016

Roger I understand that H2CO3 is carbonic acid. My problem is the point of mineral weathering is to neutralize this acid with something that precipitates a carbonate or a bicarbonate or something else. To my mind you are not showing us this reaction.

eg. Greg Rau uses the following :

4CO2g + 4H2O + Mg2SiO4s + Vdc —-> 2H2g + O2g + Mg2+ + 4HCO3- + SiO2s.

What is the formula you are using?

Jim Baird's picture
Jim Baird on June 23, 2016

Roger what I am saying is that adding a bunch of minerals to the ocean doesn’t get you anything without Vdc. Power is the key ingredient and when you add Vdc to saline water you end up with H2 and then the O2, Cl dilemma .

Roger Arnold's picture
Roger Arnold on June 23, 2016

In the case of using soluble carbonates from Great Basin deposits, the overall descriptive formula you’re asking about would just be:

CO2 + CO3– + H2O –> 2HCO3-

In words, a CO2 molecule from the atmosphere and a doubly charged carbonate ion plus a water molecule end up as two bicarbonate ions in solution. That’s the end result; it doesn’t reflect the actual reactions that are occurring at a micro-level.

The formula that you give as an example is the overall descriptive formula for Greg’s carbon-negative electrolytic hydrogen production. It’s valid as an overall description, but, as above, doesn’t really reflect what’s going on at the micro-level.

Roger Arnold's picture
Roger Arnold on June 23, 2016

Doesn’t get you anything? Sure it does. Natural weathering or rock is capturing and sequestering CO2 as dissolved bicarbonate minerals all the time, with no help from any external Vdc.

Application of power in some form is needed to greatly accelerate the natural weathering process, and Greg’s carbon-negative electrolytic hydrogen is one way to approach it. The thermal decomposition of limestone that I characterized as the “brute force approach” is another. It doesn’t involve any external Vdc, but I guarantee that broadcasting a solution of slaked lime onto ocean surface waters will raise their pH and cause increased uptake of CO2 from the atmosphere. It’s just not an energy-efficient approach. It’s only practical if one has a very low-cost source of high grade (>859 C) thermal energy.

There are more energy-efficient alternatives that I’ll be writing about next week.

Jim Baird's picture
Jim Baird on June 23, 2016

I stand corrected. Natural weathering of course does occur but it doesn’t happen fast enough to get out of us our current climate fix.

Maybe I am jumping the gun and will eagerly look forward to the next installment.

Helmut Frik's picture
Helmut Frik on June 24, 2016

I do not think a small or big nuclear reactor will be a reasonable solution. With expanson of renewable power generation, and with development of market mechanisms to get them payed (payment based on variable costs as in todays energy only makrets does not work with renewables like PV and Wind, which is not a fault of PV and Wind, but of wrong market design) , there will be a permanent overproduction of electricity by some percent, perfectly suitable for tasks like procucing cement or aluminum in low cost (per production unit) facilities, which can be switched off any time when suply gets smaller compared to demand. Nuclear is far to expensive in comparison, with or withour turbines.

Roger Arnold's picture
Roger Arnold on June 25, 2016

Nuclear is far to expensive in comparison, with or withour turbines.

If you’re referring to current generation pressurized water or boiling water reactors, it’s a moot point; they’re limited to the temperature of pressurized steam, which isn’t nearly sufficient for calcining limestone. They’d have to generate electrical power (at around 35% efficiency), which could then be run through resistance heaters to generate the required temperatures. I agree that that would be far too expensive.

If you’re making a general statement about any future high temperature reactor that might be developed, well, your assertion is noted. But if you want anyone who’s technically literate to take it seriously, you have work cut out.

You certainly can’t justify the assertion on the basis of fuel costs. Even current generation reactors, with fuel burn-up of around 1%, typically have fuel costs in the range of 0.5 to 0.7 cents per kWh (according to the EIA). And that’s for electrical output. Cut that by a factor of 3 for thermal output. Then add the fact that the possibility of nuclear fuel burn-up close to 100% have been proposed and validated, and we’re looking at nuclear fuel costs of $1.60 to $2.30 per megawatt-hour of thermal output.You need to somehow make the case that for any future nuclear technology, O&M costs plus amortization of capital will always be hundreds of thousands of times higher than nuclear fuel costs. That would be an interesting case to see.

On another point, you say that surplus power from cheap wind and solar would be “perfectly suitable for tasks like producing cement or aluminum”. That’s actually not true. To be perfectly suited it would need to be reliable enough to allow close to 100% duty cycle on the production equipment. The capital cost of the equipment doesn’t drop just because it’s only run when surplus power is available. Cement production has the added complication that the kiln requires a length warm-up period, while aluminum production has the complication that the pots of molten cryolyte freeze up if the production rate drops below what they’re designed around. They need power that’s guaranteed to stay within a specified range.

Intermittency sucks.

Helmut Frik's picture
Helmut Frik on July 1, 2016

Well in a nuclear wonderland Power costs nothing, and reactors fall from heaven without costs, I know.
But in real world, no matter how cheap nuclar fuel is, fuel for wind and solar is cheaper.
Also it is well known forom practice that there is no way for nuclear to undercut wind and solar on operation costs – see above how high operation costs of nuclear real life plants are.

So the last tiny chance for nuclear could come from capital costs. This is capital costs per kWp devided by utilisation rate.
Well located utility scale PV has cpacity factors above 0,2, wind above 0,3 for _modern_ equipment. Average capacity factor for nuclear today is 75% according IEA.. Let’s move this up to 80% for new or mostly new ones.
So nuclear inevitabely and by a long distance looses at costs per kWp which is 4 times higher than PV or factor 2,7 to wind.
Nuclear power under construction today by far exceedes these costs.

Cement production and aluminium production operate at capacity factors well below 1, they usually can never sell all products they could produce in theory. Both products can be stored easily at nearly no costs, this is done already today by these companies. A utilisation factor of 0,5-0,7 as it uis usual, which can be moved quite freely for weeks and mothes means they can make use of solar and wind power which is available >50… >70% of the time. Weather forcasts tells days ahead when to ramp up and down the facility, while a nucleap reactor providing heat could quit within seconds, and then only thermal capacity remains as time for shutdown. So those facilities can work with surplus power from wind and solar on wear and tear costs of wind and solar, which is much below the prices nuclear can compete.

Not knowing how to handle intermittency, and how small intermittency becomes in big grids is what really sucks.

Roger Arnold's picture
Roger Arnold on July 1, 2016

I’m not interested in getting deeply into yet another debate about nuclear vs. renewables. But I do lose patience with partisan rhetoric in the hardline camps. That applies to both factions: “nuclear is awful, we’ve got to shut ’em down” and its opposing “renewables can never work, we’ve got to stop supporting them and just go nuclear”.

I may be a little less tolerant of the former, because, in addition to being wrong, it’s been doing tremendous damage to the environmental cause it pretends to support. The other is also wrong, but I don’t see that it’s been doing any damage. It’s wrong in that renewables — even 100% renewables — can work, in principle. But a workable solution does require a very large investment in energy storage and dispatchable backup facilities that advocates are unwilling or unable to see.

Regarding the specific issues of cement and aluminum production as DR opportunities and the effects of capacity factor:

You’re quite right that both operate at capacity factors well below 1. However, the way they do so sheds some interesting light on the nuclear vs. renewables issue.

For starters, cement production is inherently a high temperature thermal process. It’s not a candidate for DR smoothing of renewable energy at all, unless one is willing to consider electrical resistance heating for firing the production kilns. That’s tremendously expensive compared to burning coal or natural gas unless power is priced down in the penny per kilowatt-hour range. A penny per kWh might seem a good alternative to curtailment, but if the kiln can only operate when there is a such a surplus of RE that curtailment is the alternative, then the CF of the cement kiln would be very low indeed. Only it’s worse than that, because of time factor. Once a decision to fire up a kiln is made, the firing is expected to continue uninterrupted for at least days, if not weeks. So “as available” electricity for cement production is out.

For similar reasons, cement production is not a good candidate for DR based load following for nuclear reactors. But it’s an extremely good candidate application for dedicated high temperature SMRs (small modular reactors) — if and when they are developed and licensed.

Now, aluminum production. It’s an inherently electrical process, and to that extent is a potential candidate for DR accommodation of intermittent renewables. However, it has similarities to cement production in that a production plant has a number of pots, some of which are active and the rest of which are either on idle standby or down for maintenance. And once a decision to fire up a pot has been made, power to that pot is expected to remain available for some time. An aluminum electrolysis pot is tolerant of brief power interruptions, and I believe they can even be throttled to a degree. But a prolonged interruption (> 10 minutes? — that’s a guess) is a minor disaster. So aluminum production is also not a very good candidate for DR accommodation of intermittent renewables.

That’s not to say that there aren’t other applications that are good for DR. I’m actually a fan of DR in general. But without a lot of investment to expand DR opportunities and a willingness to pay the higher costs associated with low capacity factors, I don’t think is a workable solution to the problems that high penetration of RE poses for the grid.

Engineer- Poet's picture
Engineer- Poet on July 1, 2016

in real world, no matter how cheap nuclar fuel is, fuel for wind and solar is cheaper.

In the real world, the cost of solar plants which can’t run overnight are 3x as high per watt as nuclear plants that run 24/7.

In the real world, wind and solar require about 10x as much steel and concrete per average watt than nuclear does.

it is well known forom practice that there is no way for nuclear to undercut wind and solar on operation costs

It is well known that there is no way for any combination of wind and solar to function without almost-100% backup.  Failing to count the backup’s cost, including its fuel and whatever emissions it must pay for, is dirty accounting.  Sadly, that’s par for the course with Greens.

see above how high operation costs of nuclear real life plants are.

A lot of those costs are imposed by silly rules, not the technology.  Stop mandating ridiculous levels of security, and the cost of security goes way down.  (Seriously, nobody’s going to be able to steal spent fuel!  If someone is dumb enough to try, let’s hope they waste their effort there instead of doing something that could actually hurt people.)

Not knowing how to handle intermittency, and how small intermittency becomes in big grids is what really sucks.

Dealing with someone who has no respect for facts or truth and makes up claims on the fly is what really sucks.

Alistair Newbould's picture
Alistair Newbould on July 2, 2016

This brute force approach seems to be just a means of moving CO2 from the atmosphere to the original sequestering site via a high energy complex route. Would it not be better to site an open air CO2 extraction plant at the storage site. Not sure of the energy reguirements but some of the systems described in the Virgin Earth Challenge:
http://www.virginearth.com/finalists/carbon-sink/
appear to be reaching an advanced stage of development. Loving this series. I am especially excited by the Icelandic study on CO2 sequestering in basalt (CarbFix project). The technology is outpacing the politics.

Helmut Frik's picture
Helmut Frik on July 2, 2016

Hello, we are not in the year 1996, nor in the year 1986, it’s the year 2016, and the world has changed in between.
In real world projects nuclear power needs >10€ct/kWh (e.g. Hinkley Point) for 35 years +inflation compensation, while utility scale solar varies from 6-7 ct/kWh in less sunny germany to 2.7 €ct in Dubai, so the factor 3 today is the other way round.
You promote nuclear to become a bit cheaper if security is decreased…. Well since also Gen II and III stations quit at today’s wholesale power prices when major repairs are necessary obviously you propose safety levels below Gen II. So just nuclear pipe dreams, not worth any discussion.

Helmut Frik's picture
Helmut Frik on July 2, 2016

OK, as it seems we have to go at first a bit to the basics ho a power grid and a power system is built and managed.

To operate a stable grid (so something which is not run like the french grid, which relays on imports to cover peak demand) there is always a surplus of available production capacity over maximum peak demand ever seen in the grid.
How big this margin is depends on the preferences costs grid stability. In germany it was ever, with conventional production between 20-30%, but germany clearly prefers grid stability. (which results in about the most stable grid worldwide)
Other countries have lower reserve margins, but usually they are significant positive, only in France it is significant negative.

This will not change in case somebody operates a grid mainly based on renewable.

Just the area for balance will be bigger than e.g. the borders of germany, so grid safety will be a bit more french in local (states) view, but still with a significant positive margin on whole grid view (North America, Europe/Eurasia etc. )

Difference is that where today these spare capacities stay cold mothballed, to not to consume fuel, with renewable there is no use to mothball this generation capacity, as long as someone is willing to buy the power at or above the price of wear and tear.

The costs of wear and tear of renewable is below a penny /kWh.

So in a average year, and with the power system designed in german radition, you’d have 20-30% + remaining variability of renewables available during the year, but rarely less than 20%. The percentage might be different depending on the preference price reliability.
But there will be a lot of power available around the clock or close to around the clock for tasks where a price of 1ct/kWh or less would be favorable. (10% of 4300 TWh in USA is still 430TWh, and quite sure more power will be available in average years.)
It is known days ahead when there will be low renewable power production, enough time to ramp production up and down, both for cement and for aluminum. Aluminum production can reduce power consumption extremely fast, moving from electrolysis to just keeping the temperature in the pot. (and with days or hours known ahead that less energy is to be consumed, the pot can be emptied) Trimet sells almost all it’s power consumption on the regulation power market, so they offer to ramp down their power consumption within less than 15 min to close to zero, which has the same effect to the grid as if some power station would increase output accordingly. And this is still equipment which was not designed with having demand management in mind.

I do not say nuclear must be shut down in at any costs, but i find when doing the maths that it’s by far not a economical solution any more.

Roger Arnold's picture
Roger Arnold on July 2, 2016

Thanks for the link. I met Dr. Lackner at an energy conference at UCSB about 10 years ago, when we were staying at the same hotel. I’ve followed his work since then, and I consider the humidity swing cycle for air capture that he and a colleague discovered to be probably the most promising technology for air capture that’s around. It’s nice to see that a company using that technology is one of the finalists for the Virgin Earth Challenge.

I notice that “smart rocks” is also a finalist. I talk about that approach in Part 2, which should be appearing on Monday.

I’m not sure what you mean by the “original sequestering site”. The brute force approach captures CO2 from air in contact with the ocean, and stores it as bicarbonate ions in the ocean. The storage is permanent — or as permanent as anything on a geologically active planet can be. Its advantage is that it combines capture and storage. It will never be practical, however, unless a very cheap source of high temperature thermal energy is developed.

Integrating capture and storage could also be also be considered a disadvantage, since it doesn’t produce a pure CO2 stream that can be sold to anybody. It only pays off financially once there’s a price on carbon emissions. The companies producing the quicklime can then claim credits for negative emissions.

Engineer- Poet's picture
Engineer- Poet on July 3, 2016

Hello, we are not in the year 1996, nor in the year 1986, it’s the year 2016, and the world has changed in between.

It’s 2016, and some things have not changed since 1716, or even 0016.

– It gets dark at night over half the entire globe.  A contiguous half, mind you.
– Winds go calm over very large areas.  Right now the winds are too low to power wind farms for at least 500 miles in every direction from me (an area comparable to the size of western Europe).
– Holland, which has literally centuries of experience with wind power for draining its polders reclaimed from the Zuider Zee, did not use it to start its electric grid.  Per Wikipedia, Holland has STILL not even produced 14% of its electricity from “renewables”.  Holland has little nuclear power, so it’s burning fossil fuels instead.

In real world projects nuclear power needs >10€ct/kWh (e.g. Hinkley Point) for 35 years +inflation compensation

In the real world, your solar panels and off-shore wind farms cost far more than €0.10/kWh even before the external costs of the CO2 from the backups are counted.  You need vast expansions of transmission systems to spread power over large distances.  You need huge amounts of storage to buffer the feast-or-famine production of “renewables”.  You have neither, and are still arguing over how to pay for it.  Meanwhile, the planet burns.

You promote nuclear to become a bit cheaper if security is decreased

The nuclear plants were just fine without all the extra security personnel.  They are adding ZERO actual security.  It is a total waste of money.  If the government is going to mandate it, the government should pay for it.  It won’t come close to the subsidies that wind and solar enjoy.

For that matter, if the government is purporting to reduce GHG emissions, it should give equal preference to all GHG-free sources of electricity.  It does not.  Nuclear would be wildly profitable with the same production tax credit wind enjoys.  A dozen or more nuclear plants would be under construction if nuclear was covered under “renewable energy” quotas.  Nuclear is the best solution to these problems; that is why all the “Green” programs have to stack the deck against it, to keep the problem from being solved.

Helmut Frik's picture
Helmut Frik on July 3, 2016

In your nucleasr pipe dreams, you’re still struck in the last century.
It is 2016, even if you don’t want to see it. Sending 10 GW by two wires over distances of 1500 Miles and more is standard today. So a calm with a radius of 500 miles is far from creating any problem for a grid to balance out wind.

And since transporting power even around half of the world is also just a question which diameter the aluminum wires have, even a 100% PV around the clock power supply is possible, and even comparable economic with fossil power production with todays prices of sea cables. But this does not say that this is the cheapest possible solution or that anyone will build it. It just tells that it can be built, and it can be financed, more easy than a big pile of nuclear power stations.

And yo now you are promoting new subsidies for nuclear, when the subsidies for renewables are just phased out. The subsidies for renewables were to get new technologies runing. Nuclear is far from being new, and it received its own subsidies when being new. But since you never look at the changes in the world keep dream on your nuclear pipe dreams.

Engineer- Poet's picture
Engineer- Poet on July 3, 2016

In your nucleasr pipe dreams, you’re still struck in the last century.

You’re stuck in the 18th century, when entire continents were deforested for fuel and building materials.  Worse, you’re doing it again.  You crazy Germans are clearcutting forests which took centuries to regrow, for “biofuels”.  Neither the energy nor the ecosystems are renewable on a scale of a human lifespan.

Sending 10 GW by two wires over distances of 1500 Miles and more is standard today.

Standard?  Try “never done yet, anywhere”.  Biggest HVDC project I can find is 8000 MW, and needs another 25% to hit 10 GW.  Longest is 2385 km, still shy of 1500 miles (and needs to grow 40% to hit your 10 GW benchmark).

a calm with a radius of 500 miles is far from creating any problem for a grid to balance out wind.

The top post at ergosphere dot blogspot dot com (can’t hard-link it because of mod filters) is a weather map I captured last night.  The map covers the continental US, northern Mexico and a substantial part of Canada.  The ONLY spot on the map with winds above the cut-in speed of normal wind turbines was a small area in southern Texas (roughly San Antonio), and that just barely.  It was also about 1300 miles away from me by great-circle measurement.

You are claiming that wind has the availability to keep a grid running.  That claim is ridiculous.  Even if it wasn’t, the vast rights-of-way through forests and other areas required for such a massive HVDC network would cause so much ecological damage that it absolutely SHOULD NOT be done.  If you did do it, it would be a fragile and tempting target for terrorists.  The bottom line is that you are peddling nonsense, and you would have to be insane not to know it.

yo now you are promoting new subsidies for nuclear, when the subsidies for renewables are just phased out.

Subsidies for wind and solar were just renewed for another 5 years in the USA.

The subsidies for renewables were to get new technologies runing.

Wind power has been around literally for centuries.  The first grid-scale wind turbine in the USA was built before the first controlled nuclear chain reaction.  WHAT “new technologies”?

It is 2016, even if you don’t want to see it.

It is impossible to power a modern electric grid using grossly unreliable sources like wind and solar, even if you don’t want to see it.  This will be true no matter the year.

The more pro-ruinable propaganda I read, the more I get the impression that the advocates fall into two major groups:

1.  The fanatics, the ignorant and the brainwashed.  These people are driven by emotion and cannot evaluate evidence.  Many show signs of mental illness.
2.  The front people for the fossil-fuel industry.  These people don’t care, and they should be held criminally culpable.

Roger Arnold's picture
Roger Arnold on July 3, 2016

Oops. I just figured out what you meant by “the original sequestering site”. You meant the limestone that the brute force approach is calcining. Inexcusable that I didn’t immediately understand that that’s what you meant, since I had the same reaction when I first heard about “accelerated weathering of limestone” (AWL) as a capture and sequestration method.

It is indeed ironic that an effective capture and sequestration method could begin by releasing CO2 from the mineral that is the largest, and in some sense the “ultimate”, geological store of carbon on the planet. I may not have made it clear that a critical part of the brute force approach is that the CO2 released from the limestone that’s being calcined MUST BE sequestered, and not released into the atmosphere. There are various means for semi-permanent use / sequestration of small flows of pure CO2, but the only approaches that are scalable to the gigaton levels needed to make a climate difference are probably those that pump CO2 into deep geological storage.

So the limestone first serves as a convenient local source of a pure CO2 stream that is being pumped underground. Then the lime that calcining produces is slaked and broadcast onto the ocean surface to soak up CO2 from the atmosphere. The net effect is to move CO2 from the atmosphere to underground geological storage. It’s an energy-intensive form of air capture, but one whose capital cost is low. It works IF one has a very cheap source of high grade thermal energy.

More about AWL and other mineralization options coming up in Part 2.

Roger Arnold's picture
Roger Arnold on July 3, 2016

I appreciate the spirit of your reply here, Helmut. You are staying focused on substantive issues. The comments nesting level is getting rather deep, so I’ll continue this reply as a new comment at the outer level. This is just to let you get notified by WordPress that there is a reply.

Engineer- Poet's picture
Engineer- Poet on July 3, 2016

If you have the deep geological repository, you get more bang for your buck if you have any atmospheric carbon capture method that requires less energy (or cheaper energy) than calcining limestone does.  Calcining lime requires about 180 kJ/mol while the thermodynamic limit for concentrating atmospheric CO2 is 20 kJ/mol.

If you can hit twice the thermodynamic limit with some thermally-regenerated sorbent which desorbs at 250°C or less (perhaps a tailored zeolite), you can use direct LWR steam to drive the process.  If the Diablo Canyon units are roughly 3.4 GW(th) each and half the thermal output is diverted to carbon capture @ 40 kJ/mol, that’s 85,000 mol/sec or 3.74 metric tons per second.  Off-peak steam from Diablo Canyon could extract several hundred thousand tons of CO2 per day, almost 120 million tons per year.

Multiply this by 50 (roughly the nuclear capacity of the USA) and you get 6 billion tons per year.  Total US CO2 emissions from energy use were only about 5.5 billion tons in 2011.  This appears VERY doable.

Roger Arnold's picture
Roger Arnold on July 3, 2016

(This is in reply to a down-thread comment by Helmut Frik. Nesting level was getting too deep. Not sure if this will work, but if it does, the comment I’m replying to is here.)

First, a reminder. This particular sub-thread started out when you commented on my speculation that small high temperature molten salt nuclear reactors might conceivably be a cheap enough source of high grade thermal energy to make the “brute force” approach to CO2 removal practical, despite it’s energy inefficiency. I had suggested as well that calcination could be a good target application for such reactors, since it didn’t require power generation. You had said, in response that

Nuclear is far too expensive in comparison, with or without turbines.

I then replied that if you were making a general statement about any future high temperature reactor that might be developed and you wanted that statement to be taken seriously, you’d have to come up with some convincing arguments. I don’t think you’ve done that. I’ve yet to hear, from you or from anyone else, any solid arguments as to why nuclear power is and forever will be uneconomical. Regardless of technology or fuel cycle. Basic physics certainly doesn’t support that assertion. Compared to what goes on in a coal-fired power plant, a nuclear reactor is extremely clean and simple. I’m genuinely curious as to how belief in an intrinsic high cost for nuclear power is rationalized.

Now, returning to the points you made in your last comment. I’ve been thinking about what you said about aluminum production as an opportunity to implement DR as a (partial) means for accommodating the intermittency of wind and solar resources. I think you’re right, it can be done. The cost of electricity is a major consideration for aluminum production. The capital cost of plant equipment is high, but not so high that maintaining a near-unity CF is critical. The time needed to re-melt the contents of a pot that has solidified after an extended power interruption is a nuisance, but the capability for doing so is necessary in any case. It’s also true that the system can be fairly easily designed to allow the power level to the pots to be throttled over a fairly wide operating range. It’s just a matter of combining good insulation to keep the pots molten at low power levels, and active cooling to keep them from overheating at high power levels.

The only problem is that there’s not a lot of scope for the application. World wide, aluminum smelting currently accounts for about 3% of electricity consumption. That’s actually quite a lot. However, something like 80% of that is already supplied from low cost baseload sources — a lot of it being dedicated hydropower. So the smelters are mostly already supplied with cheap electricity supporting the highest CF that the plant’s maintenance cycle permits. There’s little incentive to relocate production to areas where surplus wind and solar energy can be had for a penny per kilowatt hour for maybe 10 hours a week.

I actually wrote a series of articles about “coping with variability” that were published on Energy Central about 10 years ago. The second in the series dealt specifically with what I called “responsive loads” — or DR, as we’ve been referring to it here. You might find that one interesting. The second article is here. You can find the others from there.

Engineer- Poet's picture
Engineer- Poet on July 3, 2016

Note, I have a reply to you that’s been routed to moderation and the mods have been AWOL.

Jim Baird's picture
Jim Baird on July 4, 2016

I have been having the same problem.

Jim Baird's picture
Jim Baird on July 4, 2016

In the real world, wind and solar require about 10x as much steel and concrete per average watt than nuclear does.

I don’t know precisely how much more material is required to produce them as an equivalent number of nukes but Nihous estimates that the maximum steady-state OTEC electrical power is about 14 TW (Terawatts) corresponding to 250,000 100 MW plants.

Couldn’t these plants be considered essentially self replicating, at least until all of the necessary materials are produced, if aluminum and the cement are derived from the same plants that produce them. Seem to me this works if some other environmental benefit is derived from this production such as the CO2 sequestration Roger describes or by a reduction of the oceans surface heat load leading to less sea level rise and storm surge?

Engineer- Poet's picture
Engineer- Poet on July 4, 2016

It finally appeared here.

The most irritating thing about moderated comments is that you aren’t allowed to edit them (e.g. for typos) and they disappear after a page refresh.

Nathan Wilson's picture
Nathan Wilson on July 4, 2016

I agree with suggestions by Roger and Helmut that there are several sources of dispatchable load suited to demand response or DR (such as aluminum refining and BEV charging as previously mentioned) that can help to match supply and demand in a zero-fossil electric grid.

However, a few comments are in order:
1) Grids have an intrinsic amount of supply-demand mismatch due to end-use load variation. When wind-power (or solar power in cold climates) is added with their own mismatch, the total mismatch goes up by around a factor of two. It has yet to be demonstrated that DR can supply the matching capability needed by a nuclear-rich grid, even without considering the much larger mismatched by a grid rich in variable renewables.

2) All these methods will trade increased upfront capital cost (or decreased end-user benefit) for a steep discounts in future energy cost. Therefore from power producer’s point of view, they are essentially the same as curtailment (i.e. dumping product at pennies on the dollar is only slightly preferable to discarding it outright). From an investor’s point of view, increased capital cost is a strongly negative attribute.

3) All economic models of demand response force us to accept that dispatchable power has much greater economic value than that produced by variable renewables, with baseload power between the two.

4) Any of these DR options can be demonstrated without first dismantling our nuclear infrastructure, thus given the urgency of reducing emissions from fossil fuel use, any environmental policy which places anti-nuclear actions ahead of anti-fossil fuel action should be strongly rejected.

Nathan Wilson's picture
Nathan Wilson on July 4, 2016

Jim, yes, all energy production systems can be thought of as self-replicating. But to make the concept useful, you have to assess the Energy Return on Energy Invested (EROI). Obviously, this is easier to do for sources such as nuclear fission and windpower which are deployed at scale, than for fusion and OTEC which work in theory, but currently contribution nothing to our grids.

To include secondary benefits in the comparison, I would think it best to convert them to equivalent energy. Since that doesn’t make sense for CO2 sequestration (it might in a fossil fuel dominated world if CC&S were prevalent), I think you have to justify your energy source on an EROI basis first, then on a cost basis. If your secondary benefit can’t be assigned a cost either, then I don’t think it should bear much weight in the choice.

Roger Arnold's picture
Roger Arnold on July 4, 2016

What you say is certainly correct if you’re looking only at the process energy.

The problem with direct air capture, however, is the sheer volume of air that must contact the CO2 absorber. You need a really large, spread out surface area to make it work. Porous materials that pack a large surface area into a small volume don’t really help, because you need to pass a huge volume of air through that (relatively) small volume of porous material. The energy expended in pumping air can easily dwarf the process energy. But if the absorber surface is spread out enough to take the pumping energy, then the facility ends up with a very large footprint and (probably) a high cost for materials and construction.

Not saying it can’t work. I’m actually a fan of air capture, and guardedly hopeful about the humidity swing methods. But if there are easy solutions out there, I haven’t discovered them.

Roger Arnold's picture
Roger Arnold on July 4, 2016

All good points, Nathan.

I think it’s particularly important for people to understand the fundamental difference between baseload + intermittents + DR, on the one hand, vs. just intermittents + DR on the other. DR can never generate real power for other loads. It can only make power from elsewhere available by reducing their own draw. But the power from elsewhere has to be there. And with the statistical nature of intermittent renewables, there will always be times when it isn’t.

That means that intermittents + DR cannot be a full solution. If you’ve done away with baseload (in order to reduce the need for curtailment of intermittents), then you’re obliged to make up for its absence with dispatchable capacity. That means either discharge from energy stores, or dispatch of low CF fossil fueled resources. The former is currently too expensive at the storage capacity levels needed, and the latter is dirty. The low CF at which such backing capacity is utilized makes it uneconomic to use high efficiency combined cycle plants. Carbon emissions end up higher, not lower, as Germany’s experience has shown.

The idea that “baseload capacity is unnecessary”, which morphs to “baseload is bad”, has got to be the craziest meme that has managed to infect the European green community. Somebody has been borrowing from Carl Robe’s playbook: “attack your opponent’s greatest strengths; portray them as weaknesses”.

Engineer- Poet's picture
Engineer- Poet on July 4, 2016

The problem with direct air capture, however, is the sheer volume of air that must contact the CO2 absorber. You need a really large, spread out surface area to make it work.

If the absorber is cheap enough, you can hang it out in the breeze over an extended area and just store it up until you have the process heat to regenerate it.  The processing is not time-critical.

At 50% capture efficiency and 3 m/sec air speed, 1 m² of absorber sweeps up the CO2 from 15 kW of primary energy.  At a more reasonable 1 m/sec air speed, it sweeps up the CO2 from 5 kW.  If you had an absorber system near a plant like Diablo Canyon spanning 3 km of perimeter by 10 meters high, an average 1 m/s wind speed would sweep up the CO2 from 150 MW of fossil-fired energy.  I’m sure a concerted effort could install 30 km of absorbers and offset 1500 MW.  The nature of these absorbers is TBD, but people are creative.  If they were combined with e.g. freeway noise walls they might be very popular.

DC generates on the order of 6.8 GW of primary energy; if it also offset emissions from 1.5 GW of other energy in its “spare time”, it would be quite the climate-remediation king.

Roger Arnold's picture
Roger Arnold on July 4, 2016

The link you gave above is to a paper at NREL whose lead author is Klaus Lackner. I like Dr. Lackner, and I strongly recommend his 2010 Provost’s Lecture at Stony Brook University [q.v.]. But I’m not yet completely sold on his air capture story.

The full statement from that report that you’ paraphrased is:

If one could maintain a flow of 3 m/s
through some filter system, and collect half the CO2 that passes through it, then the system would
collect per square meter the CO2 output from 15 kW of primary energy.

“If one could..” A rather large conditional. I don’t question that 50% of the CO2 from 3 cubic meters per second covers the CO2 output from 15 kW of primary energy, but what’s missing there is any estimate of the power that would be needed to push air at 3 mps through a one square meter filter capable of absorbing half its CO2. If the pressure drop across the filter were as large as one bar, we’d be looking at 300 kW of pumping energy to collect the CO2 from 15 kW of primary energy.

Of course, one bar — a full atmosphere of pressure — is an outrageous projection for the pressure drop across the filter. The pressure drop can be made arbitrarily small by increasing the area and depth of the filter, and reducing the velocity of air flow. As you say, if the absorber is cheap enough, you can hang it out in the breeze over an extended area. Of course you still have to collect it, release the CO2, and then deploy it again. What does than take, in capital and energy? I don’t know. It’s hard to imagine that nobody has run rigorous calculations, but I haven’t seen them.

Nor have I run them myself, even though I theoretically could. If I hadn’t gotten lazy and partially senile over the years.

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