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Roger Arnold's picture
Director Silverthorn Institute

Roger Arnold is a former software engineer and systems architect. He studied physics, math, and chemistry at Michigan State University's Honors College. After graduation, he worked in...

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  • Jul 14, 2021
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Many companies have been exploring SOECs (Solid Oxide Electrolyzer Cells). There's good reason: operating at high temperatures, they obtain much of the energy needed to split water molecules from heat rather than electricity. They can get close to 100% electrolytic efficiency simply with good thermal insulation. Waste heat from the electrical over-potentials needed to drive the hydrogen and oxygen evolution reactions can be retained as heat within the cell. The thermal energy replaces a corresponding amount of electrical energy, reducing the cell operating voltage. If an external source of high grade heat that can be tapped, the electrical energy is reduced even more.

All that has been known for a long time. High temperature SOECs have proven difficult to commercialize, however. I believe it's been mostly due to issues of cost and durability of the ceramic membranes involved. Bloom may have been able to leverage its considerable experience with high temperature SOFCs (solid oxide fuel cells) to become "first out of the gate" with this announcement of commercial SOECs. Other companies are likely to follow. It's all very good news for the prospects of green hydrogen for cheap long-term energy storage. This development alone promises to raise round-trip energy storage efficiency from its miserable current value of ca. 40% to northward of 50%. I'll speculate that within 3 years, we'll be looking at better than 60%.

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Matt Chester's picture
Matt Chester on Jul 14, 2021

This development alone promises to raise round-trip energy storage efficiency from its miserable current value of ca. 40% to northward of 50%. I'll speculate that within 3 years, we'll be looking at better than 60%.

That would be a really immense development. Hoping you're right-- maybe we set a calendar reminder for 2024 to see if we came close or maybe even breezed past this prediction!

Charles Botsford, PE's picture
Charles Botsford, PE on Jul 19, 2021

Hi Roger,

The hydrogen roundtrip efficiency includes: (1) electricity to electrolyzer to hydrogen (water to H2), which is about 40% for PEM (Proton Exchange Membrane) based on higher heating value, and maybe 45% for SOFC (Solid Oxide Fuel Cell); (2) H2 compression, which is a 30% loss, (3) H2 to fuel cell to electricity, which is maybe 40% efficiency. If you want to operate a fuel cell powered vehicle, the overall roundtrip efficiency turns out to be ~20% (includes the drivetrain losses of maybe 10%), which is slightly higher than gasoline at 17% and diesel at 19%. The references are out there that document these numbers and their ranges, in detail. On the other hand, electricity used to directly power EVs has a very high overall roundtrip efficiency (I've seen 60-70% from ICCT) that results in a factor of three less kWh used versus hydrogen per EV mile driven. The CEO of Enel recently commented (July 16, 2021, Recharge Magazine) on the "Nonsensical" pushing of hydrogen for transportation by the oil industry. He dived into a nice point by point analysis.

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