Green Hydrogen – “Escapey, Explodey Expanded Polystyrene”

Tom Powell and Tim Jones – Coal Action Network Aotearoa

​This is how technology advisor Michael Liebreich recently described hydrogen in Threadreader.  

In some renewable energy circles, green hydrogen is all the rage.  It can be made from ordinary water and electricity. It can be burned like fossil gas but without the greenhouse gas emissions.  And, it can be used in fuel cells to make electricity again.  What is there not to like?  Quite a lot, it turns out.

The usual argument against using green hydrogen for energy is the abysmally poor efficiency of turning electricity into hydrogen and then turning it back into useful energy.  Presently, a hydrogen fuel cell vehicle gets back only about 30% of the electrical energy used to make the green hydrogen in powering the vehicle. A typical battery electric vehicle gets back around 80% of the electrical energy used to charge its batteries.

The Parliamentary Commissioner for the Environment, in a December letter to Megan Woods, criticised proposals to use wind power to make green hydrogen at Taranaki, store it underground until needed then burn it to make electricity again, due to the lifecycle efficiency of only 20%.  By comparison, pumped hydro storage has a lifecycle efficiency of about 75%.  There are better ways to store energy than converting electricity to green hydrogen.

Like the petroleum fuels we have grown to know and love, hydrogen’s best attribute is that it is a flammable fuel that can be moved around and stored.  But, what about the other properties of this weird and wonderful new fuel? 

Let’s first talk about “escapey”.  Hydrogen is a very small molecule and being small, it can squeeze through most materials.  It leaks through ordinary carbon steel, which is what most fossil gas pipelines are made of.  Along the way, it can cause “hydrogen embrittlement” which further weakens the steel.  So, here we have a flammable gas that needs careful containment in special materials.

Now, let’s talk about “explodey”.  Hydrogen is flammable in air with a wide range of concentration, 4% to 74% by volume.  By comparison, fossil gas is flammable in air with a concentration range of 4.4% to 17%.  Hydrogen burns with a flame invisible in daylight – when it is burning, you can’t see it. 

It also has a very low ignition energy – a spark of static electricity is reportedly enough to set it off.  And, it is known to ignite for unknown reasons when suddenly decompressed, as with the rupture of a high pressure fuel tank.

Add to this the fact that when it leaks, you won’t be able to smell it, like you can fossil gas.  Hydrogen has to be very pure in order to work in automobile fuel cells, so perfume can’t be added.  Sophisticated sensors are needed to detect leaking hydrogen.

There have been a number of recent accidents due to hydrogen explosions: one in South Korea in 2019 and one in Norway, also in 2019.

And, what’s this about “expanded polystyrene”? Hydrogen is much lighter than air, which is why it was used to lift early dirigible air ships, at least until the 1937 Hindenburg disaster.  Being so light, it is still pretty light when compressed or liquefied.  Hydrogen compressed to the NZ standard storage pressure of 350 bar (5,000 psi –14 times the pressure in an LPG tank and 2 times the pressure in a SCUBA tank) has a density of only 23 kg per cubic metre – about the same as expanded polystyrene used for home insulation.  So, although it holds about 3 times more energy per kilogram than gasoline, the same amount of energy requires roughly 12 times the volume. Fuel tanks for trucks or aeroplanes would need to be many times larger, and many times stronger, than petrol tanks, in order to drive or fly the same distance. 

The upshot of all this is that hydrogen is not an easy or efficient fuel to work with.  We will need special materials to store and transport it – materials that keep it from leaking out, as well as hold it at very high pressure.  We’ll also need lots of sensors to make sure it doesn’t leak and explode. 

Green hydrogen is not all bad, however.  It has a role in reducing emissions in the manufacture of steel and fertiliser, for instance, but that is very different than using it as a transport fuel.
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When you add to this the poor round trip efficiency of turning electricity to green hydrogen and back to useful energy again, requiring abundant renewable electricity that Aotearoa New Zealand doesn’t have at the moment, we can only hope that somebody comes up with a better renewable fuel than hydrogen.  Otherwise, I am afraid we are in for an “escapey, explodey, expanded polystyrene” future.