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Roger Brown
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David Levesque Thanks for the links. The NEL press release talks about 1.5$/kg costs in certain markets by 2025 but does not specify which markets. For solar electricity dedicated generation for hydrogen production in high insolation locations might approach 40% capacity factor but in order to deliver such hydrogen across the globe either a supergrid or liquid carriers would be required thus reducing effective capacity factor due to energy losses associated with transportation.
Dave Mart, Could you post some links about the costs of electrolyzers? The last I checked PEM had not caught up to alkaline, and I do not have the impression that alkaline costs are dropping rapidly.
Recyling CO2 from coal fired power plants is not much use if you believe that we need to head towards a net zero carbon economy relatively rapidly. On the other hand recycling the CO2 from gas fired turbines into CH4 could provide a path to net zero electricity production. I suspect, however that, ignoring the energy storage aspect, direct electricity production by conventional solar panels will much cheaper than this method. However, if some amount of long term energy storage (e.g. Summer to Winter) is needed then such a CO2 recycling scheme is a potential candidate. I have read a similar proposal in the past with CH3OH (methanol) as the energy carrier rather than methane.
I believe that the high end of the quoted efficiency range requires waste heat. If you are hoping for an energy system powered primarily by renewables then a question arises as to where the waste heat will come from.
If you go to the Fraunhofer IFAM web site ( it is clear that they already have developed a process for casting copper coils. Presumably these coils have higher performance than the aluminum ones, but there may be economic reasons for preferring the aluminum variety.
EP: NGK insulators has been manufacturing and selling sodium sulfur batteries with solid ceramic electrolytes for a long time. The operating temperature is around 300C. Na and S react to form polysulfides not Na2S, thus the lower operating temperature. The batteries above have higher energy density by a factor of 2 and 4 respectively. This energy density advantage is not as critical for stationary storage applications as for mobile applications, although a smaller footprint will still have some advantages. The real key to the economics is the lifetime cost per kWh delivered which cannot be evaluated from the information given
If one is hoping for an all renewables energy future one has to ask where the "waste heat" is going to come from in such a future. Heat from solar or wind will be more expensive than waste heat from fossil sources.
I guess that "exceptional efficiency" is simply referring to high temperature electrolysis as opposed to low temperature electrolysis. However, I do not think this higher efficiency is of much benefit unless you happen to have a source of high temperature "waste heat"
I was struck by the opening phrase of the abstract: "High-temperature CO2 electrolysers offer exceptionally efficient storage of renewable electricity in the form of CO and other chemical fuels" My question is exceptionally efficient relative to what? Is the implication that electrolytic reduction of CO2 to CO is potentially more efficient that electrolytic reduction of H2O to H2? A brief internet search does not reveal any indication of such a belief among electrochemists.
The possibility of two stage alkaline electrolysis has been discussed previously ( Alkaline electrolyzers are cheaper than PEM electrolyzers because they do not require platinum group metals for catalysts, and they use porous separators between the two half cells rather than expensive and relatively short-lived PEM membranes. However, the use of porous separators requires that the half cell pressure should be equalized at all times to prevent gas crossover between the half cells. This pressure equalization requirement means that alkaline electrolyzers cannot be ramped up and down quickly, thus making it difficult to couple them to variable electrical input from renewable energy sources. I believe that this new two stage electrolysis scheme without a separator frees alkaline electrolyzers from this limitation. Of course there is any performance degradation in terms of efficiency or current density then these changes would effect the overall economic evaluation of the new design scheme.
Let us consider this scheme from the viewpoint of total CO2 emissions. I will consider concrete and aluminum only. I would have included steel in this analysis but some of the numbers I need are behind a pay wall. From the figure included with this article we can conclude CNT reinforcement will reduce CO2 emission from concrete and aluminum by 31% and 27% respectively simply by virtue of the fact that less material needs to be produced to carry out a given mechanical function. In addition some amount of CO2 will be sequestered by production of CNT from CO2. From a global emissions standpoint one might as well assume that this CO2 comes directly from the production of the associated material. That is we can assume that the CO2 for CNT reinforcement of concrete comes from concrete production and the CO2 for aluminum reinforcement comes from aluminum production. Making this assumption the CO2 reductions for concrete and aluminum production become 31.1% and 27.03% respectively. If we wish to achieve a net zero carbon economy the remaining emissions (more than 2/3 in each case) must be eliminated by carbon capture and storage. As for the CO2 emissions from other fossil sources (e.g. electricity generation, passenger and freight transportation, space and water heating, industrial process heating, etc.) nothing whatsoever has been accomplished.
Thomas Pedersen: The CO2 from cement production and steel production is fossil carbon. You are making the carbon double duty, but the carbon is still flowing from fossil reservoirs into the atmosphere.
"Even if the MeOH was made from natural gas, you can expect 2/3 or more of the energy to be delivered as electric power from the grid rather than liquid fuel. EP: The CO2 reduction from natural gas usage would not be has high as the above sentence suggests since CO2 is also produced when MeOH is synthesized from natural gas.
Methanol is made from synthesis gas (a mixture of CO and H2) which is in turn made from fossil hydrocarbons. Natural gas and coal can be used for this purpose. Widening the range of hydrocarbons that can be used in the transportation industry seem like a negative development from the point of view of GHG emissions. It is true of course that chemists George A. Olah, Alain Goeppert, and G. K. Surya Prakash in their book The Methanol Economy suggest that in the future methanol could be economically be produced from atmopheric CO2 and H2 produced via electrolysis (high temperature electrolysis using waste heat from advanced nuclear reactors is their preferred production method). However, I am not holding my breath waiting for this future to arrive.
HarveyD: The article mentions renewable H2 not H2 from fossil fuels. The article I found on the tar sands process claims that O2 is injected and H2 is extracted. I do not believe that this process does not produce CO2. Perhaps the claim is that the CO2 remains underground so that this process is a form of CCS. If so I would need to see a lot of operational data in order to be convinced that the CO2 is permanently sequestered. Furthermore hydrogen pipelines are considerably more expensive than natural gas pipelines because of the tendency of H2 to embrittle steel and other metals. This cost would have to be factored into the cost of the delivered H2.
I am surprised at the claim that fuel cell planes will have lower operating costs than planes powered turbine engines. As far as I know hydrogen produced from electrolysis is still substantially more expensive per unit of store energy than conventional aviation fuel produced from petroleum. I know that significant progress is being made in lowering the costs and improving the durability of fuel cells, but I don't think that the costs of fuel cell/electric motor power trains have yet dropped below those of combustion engines. Conceivably the overall efficiency of the fuel cell/electric motor power train is higher than that of the combustion engine, but I would be surprised if this advantage were sufficient to lower the overall operating costs. Certainly no one is making this claim in the more advanced technology of fuel cell buses.
In order to achieve 34% efficiency these solar cells have to be triple junction III/V type cells which means that they are a lot more expensive than silicon cells. There is a good reason people use concentration ratios of 500 when they are trying to use this type of cell for commercial power generation.
The attractiveness of synthetic hydrocarbons vis a vis battery storage of renewable energy is easy transportability within the existing infrastructure. For example if you locate solar energy production in equatorial deserts with 12 to 18 hour of storage then the electrolyzers and chemical processing facilities could be used with high capacity factors, and the resulting hydrocarbons could be moved around the world using existing transport infrastructure. Of course ubiquitous nuclear power would obviate the need for such a scheme, but such a power infrastructure does not appear imminent. Even in China where the government does not have to worry about an anti-nuclear lobby I do not detect any sign of convergence on a predominantly nuclear future.
In order for this technology to contribute significantly to decarbonization the CO2 must be directly extracted from the atmosphere. Making carbon do double duty (e.g. using CO2 captured from fossil fuel generators or from cement making) would decrease CO2 emissions per unit of economic output but would not stop the flow of fossil carbon into the atmosphere.
Donald Trump geenwashing? Give me a break. This is just an attempt to lower gasoline prices and garner some farm state votes.
In order for CO2 reduction to be of any use in preventing fossil carbon from getting into the atmosphere we need an economical method of extracting CO2 from the atmosphere. Using CO2 captured from cement production or fossil fuel burning might increase economic output per tonne of CO2 released to the atmosphere but would not stop the flow of fossil carbon into the atmosphere. We still have a long way to go before synthetic hydrocarbon fuels can become a significant contributor to a zero net emissions economy.
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Sep 22, 2018