We are extremely unlikely to be able to achieve our net zero targets without building out the hydrogen economy

Hydrogen will play a critical part in our journey to net zero. This is because we do not yet have ways to heat all homes - including less well-insulated, older houses - or power high heat intensity industrial processes with renewables. We also need to find good ways to store renewable energy for long periods of time.

Hydrogen does not occur in its pure state anywhere in nature. It therefore has to be made from another energy source: either electricity or methane. The chemical potential energy in hydrogen power is then turned back into electrical energy by combining it with (ambient) oxygen in a fuel cell. The only waste product is water.

There are two main ways to produce hydrogen without emitting GHGs:

  • through steam reformation of methane with carbon capture – “blue hydrogen”
  • through electrolysis using renewable electricity - “green” or renewable hydrogen.

A further possible route to green hydrogen is reformation of bio-methane coupled with CCS which could – in principle – be a negative carbon sink.

Steam reformation looks as though it can be quite cost-effective, even when we add in CCS, but there are two residual problems: not all the carbon is captured and the hydrogen produced is not pure so cannot be used directly in certain applications. Green hydrogen is much higher quality – it can go directly into a fuel cell without further processing – but because of the large requirement for (renewable) energy, the cost of production is currently about double the steam reformation approach. Because the cost of electricity makes up about 80% of the cost of green hydrogen, the cost of renewable energy has a critical impact on the economic viability of electrolysis.

Hydrogen can be stored as a compressed gas, in a solid state or it can be converted into ammonia (which has the advantage of becoming liquid at the relatively mild temperature of -33C, making this a promising technology for transporting hydrogen power - for example for export). Energy stored as ammonia would have to be converted back to hydrogen before entering a fuel cell, but the losses during tis process are thought to be relatively moderate (only around 10%).

Around 90% of ammonia production is currently used as a source of nitrogen in agricultural fertiliser. Most of this ammonia is produced using natural gas which is reacted with nitrogen to form liquid ammonia, emitting carbon in the process (ammonia is estimated to be responsible for about 1% of global emission). Research is currently being conducted into various ways of creating green ammonia which could then be used for industrial energy and - importantly - for zero carbon maritime transport.