Comment by pdovy | Hacker News Reader

Comment by pdovy | Hacker News Reader

You've elsewhere quoted 60 kWh per gallon of renewable gasoline. The US consumed 391.40 million gallons per day on average in 2018 [1], and concurrently had generation capacity for 1.153 billion kWh per day from non-hydroelectric renewable sources [2]. That suggests that full replacement of current gasoline usage would require ~23.48 billion kWh per day, which far outpaces what is currently available.

Of course any replacement of fossil fuels is a great goal, but just curious where you see this going at scale, if it were wildly successful? It seems like if you or others were able to scale this up massively, you'd run into unit economics issues as demand for the required renewable electricity outpaced supply, raising the price.

[1] https://www.eia.gov/tools/faqs/faq.php?id=23&t=10 [2] https://www.eia.gov/outlooks/steo/report/electricity.php

To replace all gasoline in the US, it will require a substantial increase in renewable power plants. We estimate it will cost approx. $1T to build that capacity, although the cost could go down as it is done. To put that in context, the amount invested in shale fracking in an 8 year period between 2010 and 2018 was approx. $0.7 T, so not as crazy as it sounds. https://www.iea.org/newsroom/news/2018/july/investment-analy...

Thanks - that makes a lot of sense. I suppose the same issue exists with a large scale up of electric vehicles, so your interests would dovetail with other parties there and hopefully collectively spur grown in renewable generation capacity.

The real question should be: How much improvement over time in the efficiency of this process could be expected? 1.1x? 2x? 10x? 100x?

Every new technology goes through a refinement cycle where costs & resources are reduced, and I would assume the same is possible here.

We will likely make improvements primarily in capex, power costs, and transportation to lower our cost of producing fuel. Fundamental thermodynamics and overpotential limits will hold our efficiency to some cap, likely 75% or lower. We could try to push higher than 60%, but there will be an optimum for capex vs opex that will probably not favor the highest possible efficiencies.

Presumably they would make gains in efficiency, but only to a point - if a gallon of gasoline contains 34 kWh of energy you'll always need at least that much to create one, and at 60 kWh/gal now they aren't that far off.

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