[dredmorbius]

We have a cheap, stable, infrastructure-friendly, high-density storage formula for hydrogen. Or better, since the application here isn't hydrogen-specific but is simply looking to find a fuel-storage solution: energy storage.

It's hydrocarbons.

In this case, synfuel hydrocarbons as direct analogues of fossil-fuel based compounds of chain-lengths 1 (methane) to around a dozen or so (kerosene / aviation fuel, at a stretch, diesel fuel).

It stores forever (proved to 300 million years), it is drop-in compatible with extant infrastructure and equipment, it's infinitely miscable with present fuels, it doesn't leak out of storage, it doesn't embrittle metals (and in fact generally lubricates and protects them).

Yes, the round-trip storage efficiencies are low (as low as ~15--20% recovery based on thermal electrical generation, roughly the same as the solution named here), but that's in exchange for something that can readily provide weeks to months of storage capacity in a stable, low-risk form. Where you need storage that's long-term stable, dense, safe, and instantly dispatchable, your options are few.

The technology has been demonstrated in numerous experimental trials, and is similar to processes run at national scale for decades in Germany and South Africa. US-based research has been conducted at Brookhaven National Laboratory, M.I.T., and the US Naval Research Lab, amongst others. The stumbling block to date has been that fossil fuel prices are sufficiently low[1] that synfuels simply are not competitive presuming market-based mechanisms which fail to account for externalities and other market failures.

I've be aware of this for about a decade and have written about the technology, Fischer-Tropsch fuel synthesis, multiple times on HN:

<https://hn.algolia.com/?dateRange=all&page=0&prefix=true&que...>

________________________________

Notes:

1. A market failure of staggering proportions, as the under-pricing is on the order of a million-fold. See: Jeffrey S. Dukes, "Burning Buried Sunshine", <https://core.ac.uk/download/pdf/5212176.pdf> (PDF)

[kragen]

agreed. there are a fairly wide range of possible hydrogen storage forms like this (ammonia, carbohydrate, hydrazine, metal hydrides) but paraffin has many practical advantages. possibly aluminum (without any actual hydrogen, similar to the iron in the article) is superior, due to lower weight and higher round-trip efficiency, but possibly not. i think we can take widespread fischer-tropsch fuels for granted as part of the transition to renewable energy

[mglz]

How much incoming solar power ends up in the methane? And how do you get the energy back out?

[wffurr]

>> How much incoming solar power ends up in the methane?

As in how many power to gas plants are operating currently? I would guess not many due to the price vs fossil methane, but as the GP notes this is a major market failure due pricing the externalities of fossil methane.

>> And how do you get the energy back out?

Easy, burn it. For heat, or with a turbine, electricity. Zero carbon impact because it started out as atmospheric CO2.

[dredmorbius]

This.

Synthesis efficiency is on the order of 60%. Combustion efficiency, driven by Carnot's Law, ~30--50%, possibly a bit higher for combined and/or power-to-thermal. But the overall round-trip efficiency, based on both synthesis and generating losses will be low, 15--25%, perhaps as high as 30%.

The goal of such a system isn't efficient storage so much as it is persistent and dispatchable. It's possible to store large quantities of liquid fuels for long periods of time and tap into them within seconds or minutes as generating, or other fuel-based energy applications, are required. Other storage/release options either don't have the long-term storage capability, or cannot be ramped up as quickly.

Other storage options range from the exceedingly short-lived but responsive (supercapacitors, kinetic flywheels) which can respond on a sub-second to second basis, but aren't viable for long-term storage at all, to options which work over a few hours, daily supply-demand inconsistencies, etc., such as pumped hydro and high-termperature thermal storage (e.g., molten salt), to seasonal thermal storage (hot water, ground geothermal where geology supports this).

Fuel synthesis makes sense where there's exceedingly high seasonality in energy generating capacity (e.g., summer vs. winter for PV / solar), or where there are longer-term highly-variable generating trends (e.g., wind, with higher and lower output over the course of days or weeks). Or where communities are highly isolated and cannot readily be connected to a grid to balance consumption and generation over time (remote islands, arctic communities), or where a region has a very high generating potential but low domestic demand (say, northwest Australia, with sun-drenched deserts and low electrical demand from sheep and roos).

Banking summer-time / high-production capacity as fuel, and drawing down those fuel reserves or shipping them to areas of high demand could be the shape of a future energy economy. It should dramatically rewrite energy geopolitics.

[dotancohen]

  > Zero carbon impact because it started out as atmospheric CO2.

How about leaks? Isn't methane a far more potent greenhouse gas than CO2?

[dredmorbius]

A principle source of methane leakage is from gas wells themselves, as well as the extensive infrastructure involved in processing and transporting gas from its point of extraction to usage.

<https://www.epa.gov/natural-gas-star-program/primary-sources...>

In situ / on-prem methane production, storage, and usage would tend to minimise much of that.

Further, I don't see methane synthesis as a likely option for synfuel storage applications as described here, as heavier fuels (~C-12 -- C-15 chain-length kerosene) is liquid (far easier to handle than a gas), nonvolatile (as contrasted with petroleum or lighter hydrocarbon distillates), and can be stored in simple, unpressurised, unrefrigerated tanks virtually indefinitely. You're creating a problem which needn't exist.

[User23]

The usual way—boiling water.

[dredmorbius]

More generally: combustion, though there might be other options.

Boiling water, internal combustion (turbines or reciprocating engines), or external combustion (heating a boiler, and using the steam to drive turbines), would cover most of it. There might be some more exotic options of fuel cells, but those tend to be cost-prohibitive.

All combustion processes follow Carnot's laws, which limit fundamental efficiency.