Why ‘green’ hydrogen is a VERY bad idea

2022-05-08

Hydrogen is a valuable industrial raw material for making products like fertilizer and is used for all kinds of refinery processes. So I think it is safe to say that we really need hydrogen, even when not using it for energy storage.

The question is, what is the most sensible way to produce hydrogen when the intend is to reduce CO2 emissions?

Hydrogen production

Currently most hydrogen is made from natural gas (= methane = CH4) through a process called steam reforming. Hydrogen made this way is called ‘gray’ hydrogen because of its natural gas origin:

Hydrogen can also be made from water and electric energy using a process called electrolysis in a device called an electrolyzer. This is called ‘green’ hydrogen when the electricity used for the electrolysis is from renewable resources such as solar and wind:

Release of CO2 into the atmosphere

For every kg gray hydrogen 9.3 kilogram CO2 is released in the atmosphere.

The production of green hydrogen releases no CO2. This sounds fantastic but it is only half of the story: green hydrogen is mainly made during times without green energy surplus, so the green electricity used for the production of green hydrogen must be replenished by gray electricity to accomplish total electricity demand. The full green hydrogen picture then looks more like this:

This way, the production of 1 kg green hydrogen results in releasing at least 23kg CO2 into the atmosphere. This is 2.5 more CO2 then with the production of gray hydrogen!

Let's crunch some numbers to support this:

100% Efficient electrolysis requires about 32kWh per kg H2. The most efficient electrolyzers today have an efficiency of 75%, but the overall efficiency (including water treatment, compression, etc) is below 60%. So, in reality the energy requirement per kg hydrogen is at least:

32kWh / 60% = 53 kWh per kg H2.

Natural gas (CH4) is the least CO2 producing way to generate gray electricity: about 0.43kg CO2 / kWh. So generating 53kWh required for making 1kg H2 results in 53*0.43 = 23 kg CO2 using the most optimistic and efficient conditions to produce green hydrogen with current technology. This results in a factor 23/9.3 = 2.5.

Using the green electricity surplus

Of course, proponents of green hydrogen will argue overproduction of green electricity already exists, and they are right! Currently this happens (in The Netherlands) about 5% of the time, and this number will increase in the future. This is mainly caused by the daily discrepancy between production and demand of green electricity - the so called duck curve - combined with the fact that there is almost no grid-level battery storage.

Battery storage can be used to compensate the short term discrepancy between green electricity production and demand. Current battery technologies can already be applied efficiently and economically for up to about a day (e.g. using proven sodium-sulfur battery technology, or the newer iron-air or liquid metal batteries). This has a second advantage: the very expensive peek-power and electricity generators can become obsolete.

With battery technology progressing fast, using grid level battery storage will become even more viable in the near future. When extending the storage up to a few days than also most calm weather and cloudy days can be compensated leaving no prolonged green energy surplus for hydrogen generation. Of course, this might change when more solar and wind is installed.

Concluding

As shown, for the most part green hydrogen only adds to the CO2 problem. Therefor current investments in large scale green hydrogen production facilities are a very bad idea. However, investing in research for long term energy storage must be done to overcome the seasonal green energy discrepancies. For that, green hydrogen might be a solution.

I hope I am wrong, but I do not expect prolonged green electricity overproduction to happen within the coming 10 to 20 years in moderate climate and/or dense populated areas. It would be very hard to operate an expensive hydrogen generator that can only be active for a small percentage of the time, and still make a profit.

That said, the “green energy surplus” condition is a local condition, so it might already make sense to generate green hydrogen at remote locations with a large green energy potential but without an economic viable way to connect to a power grid. E.g. large scale solar power in the north of Africa, or ocean based wind power.

2022-09-26 edit:

A while ago it has come to my attention there is another reason to avoid hydrogen: hydrogen in itself, even when called completely 'green', might also be a problem. This is because hydrogen is an indirect greenhouse gas.

Because the hydrogen molecule is so small, it is extremely difficult to not leak hydrogen.

2022-10-21 edit:

I came across this article and this one as well showing that reality is even worse for the short term (20 years) greenhous potential of hydrogen: somewhere between 20 and 40. It also shows estimated fuel leaks in various stages for the hydrogen fuel cycle, from production to end use: somewhere between 10 and 20%. While this leakage adds up to the inefficiency of the hydrogen fuel cycle, it also immediately discredits hydrogen as a measure to counteract global warming!