Hydrogen is 11 times worse than CO2 for climate

(ORDO NEWS) — Hydrogen will be one of humanity’s key weapons in the war against carbon emissions, but it must be handled with care. New reports show that fugitive hydrogen emissions could contribute 11 times more indirectly to warming than CO2 emissions.

Hydrogen can be used as a clean energy carrier, and when it passes through a fuel cell to generate electricity, only water is produced as a by-product.

It carries much more energy for a given weight than lithium batteries, and refilling a tank is faster than recharging a battery, so hydrogen is seen as a very promising “green” option in several hard-to-decarbonize applications where batteries can’t do the job – for example, in aviation, shipping and long-distance cargo transportation.

But when released directly into the atmosphere, hydrogen can interact with other gases and vapors in the air, causing a powerful warming effect.

Indeed, a new UK government study has put these interactions under the microscope and determined that the global warming potential (GWP) of hydrogen is about twice as bad as previously thought; over a 100-year time period, a ton of hydrogen in the atmosphere will heat the Earth about 11 times more than a ton of CO2, with an error of ± 5.

How does hydrogen act as a greenhouse gas?

One way is to extend the lifetime of atmospheric methane. Hydrogen reacts with the same tropospheric oxidizers that “clean up” methane emissions.

Methane is an incredibly powerful greenhouse gas, causing about 80 times more warming than the equivalent weight of CO2 in the first 20 years. But hydroxyl radicals in the atmosphere clean it up relatively quickly, while CO2 stays in the air for thousands of years, so CO2 is worse in the long run.

However, in the presence of hydrogen, hydroxyl radicals react with hydrogen. There are fewer cleaning agents, so there is a direct increase in the concentration of methane, and it stays in the atmosphere longer.

Moreover, the presence of hydrogen increases the concentration of tropospheric ozone and stratospheric water vapor, enhancing the effect of “radiative forcing”, which also contributes to temperature increase.

How does hydrogen get into the atmosphere?

According to a second report from Frazer-Nash Consultancy, most of it enters the atmosphere as a result of leakage. Store hydrogen in a compressed gas tank and you can estimate that you will lose between 0.12 and 0.24 percent hydrogen every day.

It will leak out of pipes and valves if you distribute it this way, wasting about 20 percent more volume than the methane gas that now flows through municipal pipelines, although since hydrogen is much lighter than methane, this more volume is only 15 percent weight.

When transporting hydrogen as a cryogenic liquid, boil-off is unavoidable, and an average loss of about 1 percent of hydrogen per day can be expected. Currently, these losses are emitted into the atmosphere.

Indeed, venting and purging operations are now common throughout the life cycle of hydrogen. They occur during electrolysis, during compression, during refueling and during the process of converting back to electricity through a fuel cell.

Where ventilation or purge is present, percentages tend to exceed losses from simple leakage—for example, current electrolysis procedures using ventilation and purge lose between 3.3 and 9.2 percent of all hydrogen produced, depending on how often the process starts and stops is of some concern in situations where hydrogen production is seen as a way to store excess renewable energy that is not in immediate demand.

Purge and vent emissions can be significantly reduced by adding systems to recombine the escaping or purged hydrogen back into the water and feed it back into the process – but it will be some time before such operations are economically viable.

Overall, the Fraser-Nash report expects 1 to 1.5 percent of all hydrogen in the central modeling scenario to be emitted to the atmosphere, with transport emissions accounting for about half of that amount and production and consumption emissions accounting for about quarters.

Meanwhile, in the first report, based on other assumptions, 1 to 10 percent of all hydrogen is expected to be released into the atmosphere under the global scenario,

Does this mean that “green hydrogen” should be avoided in the race to zero emissions?

No. A UK government report explains that “an increase in CO2 equivalent emissions based on 1% and 10% H2 leakage offsets about 0.4% and 4% of the total CO2 equivalent reduction, respectively”, so even assuming a worst-case leakage scenario, this is still huge improvement.

“While the benefits of equivalent CO2 emission reductions far outweigh the disadvantages of H2 leakage,” it goes on to say, “they clearly demonstrate the importance of controlling H2 leakage in a hydrogen economy.”

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