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Roger Brown
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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