Comment by energ8 | Hacker News Reader

Comment by energ8 | Hacker News Reader

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A previous comment on HN went something along the lines of "what is going to happen in the summer when we've built solar/wind/etc to fulfill this winter months needs?"

I started researching energy storage. Creating liquid fuels from electricity would be handy for storage. There are processes, but getting CO2 and H2 to create hydrocarbons is currently very energy intensive. On the CO2 side, I think biogas can help this out. biogas is 25-50% CO2. In biogas upgrading, CO2 is considered a waste product (with purer methane the desired output). CO2 from this source looks noticeably less energy intensive than direct air capture.

I know biogas can be done on the small scale (e.g. homebiogas.com). My research focused especially on liquid fuel creation that could work in someone's backyard. I haven't found it. "High‐Selectivity Electrochemical Conversion of CO2 to Ethanol using a Copper Nanoparticle/N‐Doped Graphene Electrode" [0] was an exciting find, dampened after reading how well ethanol stores.

I mostly became convinced that existing oil, gas, and chemical companies will maintain dominance producing many of the same outputs, from a different (renewable) set of inputs.

[0]: https://onlinelibrary.wiley.com/doi/full/10.1002/slct.201601...

Looks like you've been going down a similar path as me. Unfortunately, liquid fuels from pure electricity is extremely energy inefficient. For example, the fischer tropsch process will consume the hydrogen that you've split with precious electricity, and only half of that will make its way into the fuel, the other half of ends up converting back into water. And that is before you figure out how to get CO2 in concentrations high enough to be cost effective.

You might want to check out plasma reforming. It's the path I'm currently on, although targeted for a different end product.

https://drexel.edu/nyheiminstitute/researchlabs/plasma-energ...

Yeah, FT looked insane, which is one of the reasons the linked paper was so attractive. Ethanol from CO2, electricity, and water at ambient temperature and pressure.

I mostly think I have to be doing some chemistry/math wrong, based on how not terrible the energy efficiency is. I'd love corrections or reading material, as this is not a knowledgeable area for me. - 2 CO2 + 9 H20 + 12e- -> C2H5OH + 12 OH- = 0.084 V - over voltage of 1.2 V is best - 1kWh @ 1.2V yields 30 moles electrons - 30 moles electrons has theoretical yield 2.5 moles ethanol = 0.146 L ethanol - reduced to appx 116ml ethanol due to selectivity - 116ml ethanol has raw energy of 778 Wh, probably 550 Wh recoverable with Combined Heat and Power

I think 55% round trip efficiency for energy-dense long term storage would be big. Of course, this isn't that (math is partially based on theoretical bests, ethanol isn't long term, CO2 capture and material movement not accounted for).

Thanks for the plasma reforming tip!

Pumping water uphill is another one. A lot of farms ditch water off the property in wet months and then irritate with precious well water during dry spells. If you’re on a slope, or build a tower, you could use excess electricity to pump water from a pond to a higher point. The receiving tank becomes a battery, and the energy can be released with gravity to irrigate during droughts.

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