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Hydrogen: Does Earth hold vast stores of a renewable, carbon-free fuel?

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Re: Hydrogen: Does Earth hold vast stores of a renewable, carbon-free fuel?

#21

Post by Teknoman117 »

bloppe wrote: post #9

Is hydrogen really more renewable though? It releases energy when combined with Oxygen to make water, and it requires energy to split it from water (electrolysis). In this sense, it's not fundamentally different from fuel, which releases energy and carbon when burned, but requires energy (sunlight) and carbon (CO2) to re-create via photosynthesis. The involvement of carbon is a difference, but either way it's a 2-way…

I imagine so. The main trouble with the biofuels is that you'd have to get everything else right for it to truly be neutral impact. (i.e. not depleting the soil, making the chemical fertilizer, reactions to convert biomass into ethanol, etc.)

Electrolyzing water with wind/solar/nuclear would seem to result in far fewer steps that could go wrong.

Re: Hydrogen: Does Earth hold vast stores of a renewable, carbon-free fuel?

#25

Post by jojobas »

barathr wrote: post #18

I was hoping to see in the article -- but didn't -- an analysis of the CO2e per KJ produced from natural hydrogen. Water vapor is a greenhouse gas and it'd be important to do the math to see how much better it is vs. other alternative fuels. (I expect it to be better, but how much is the question.)

You don't have to release it as vapor. Otherwise energy is energy and depositing it into the atmosphere raises the equilibrium liquid/vapor point.

Re: Hydrogen: Does Earth hold vast stores of a renewable, carbon-free fuel?

#26

Post by sp332 »

barathr wrote: post #18

I was hoping to see in the article -- but didn't -- an analysis of the CO2e per KJ produced from natural hydrogen. Water vapor is a greenhouse gas and it'd be important to do the math to see how much better it is vs. other alternative fuels. (I expect it to be better, but how much is the question.)

Putting water into the air at low altitudes doesn't do much for global warming. The best way to reduce the effects of water vapor at high altitudes is... to reduce warming. https://en.wikipedia.org/wiki/Greenhouse_gas#Role_of_water_v...

Re: Hydrogen: Does Earth hold vast stores of a renewable, carbon-free fuel?

#27

Post by Rimintil »

I think this is important to note about hydrogen as a 'clean' fuel source:

> Today’s hydrogen is “gray,” made by reacting methane with steam at high pressures or using fossil fuels in other ways. Those processes emit some 900 million tons of carbon dioxide every year, almost as much as global aviation. In principle, that carbon could be captured and sequestered underground, yielding “blue” hydrogen. But most hopes rest on “green” hydrogen—using renewable solar or wind power to split water molecules into oxygen and hydrogen with electrolyzers.

_Today_, it is not a clean source of energy for vehicles.

Re: Hydrogen: Does Earth hold vast stores of a renewable, carbon-free fuel?

#28

Post by diggernet »

starbase wrote: post #22

In what sense is fossil hydrogen renewable?

"Critically, natural hydrogen may be not only clean, but also renewable. It takes millions of years for buried and compressed organic deposits to turn into oil and gas. By contrast, natural hydrogen is always being made afresh, when underground water reacts with iron minerals at elevated temperatures and pressures. In the decade since boreholes began to tap hydrogen in Mali, flows have not diminished, says Prinzhofer, who has consulted on the project. “Hydrogen appears, almost everywhere, as a renewable source of energy, not a fossil one,” he says. "

Re: Hydrogen: Does Earth hold vast stores of a renewable, carbon-free fuel?

#29

Post by DennisP »

barathr wrote: post #18

I was hoping to see in the article -- but didn't -- an analysis of the CO2e per KJ produced from natural hydrogen. Water vapor is a greenhouse gas and it'd be important to do the math to see how much better it is vs. other alternative fuels. (I expect it to be better, but how much is the question.)

Water vapor is a greenhouse gas but it's not a driver of global warming, because of rain. Total water vapor is a function of global temperature, not the other way around. Put extra water vapor in the air, and it will just rain out.

Re: Hydrogen: Does Earth hold vast stores of a renewable, carbon-free fuel?

#30

Post by phkahler »

sp332 wrote: post #20
bloppe wrote: post #9

Is hydrogen really more renewable though? It releases energy when combined with Oxygen to make water, and it requires energy to split it from water (electrolysis). In this sense, it's not fundamentally different from fuel, which releases energy and carbon when burned, but requires energy (sunlight) and carbon (CO2) to re-create via photosynthesis. The involvement of carbon is a difference, but either way it's a 2-way…

The main engine of natural hydrogen production is now thought to be a set of high-temperature reactions between water and iron-rich minerals such as olivine, which dominate Earth’s mantle. One common reaction is called serpentinization, because it converts olivine into another kind of mineral called serpentinite. In the process, the iron oxidizes, grabbing oxygen atoms from water molecules and releasing hydrogen. So…

But then we burn all that hydrogen and use up all our oxygen. CO2 may be a greenhouse gas, but plants pull the oxygen back off and return it to the air.
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