In the last issue, exploring hydrogen for transport revealed lousy energy efficiency but two potential redeeming features: easing the clean energy transition for transport operators and, perhaps, helping “peak shaving” for the electricity grid. So, might a gas that burns to water be a godsend for transport decarbonisation?

Let’s revisit the energy efficiency of electrolytic hydrogen. Passing an electric current through water separates the water’s hydrogen and oxygen at about 75% efficiency. Then comes a series of downstream processes, like compression, cooling and actual application.

For heavy transport, the combined effect is that 20% to 30% of the energy propels the truck, and the rest is wasted. The comparison of H2 and fossil-fuel trucks is clear in EECA’s image alongside.

This gives electricity huge running-cost advantages, but operators must factor in capex as well as opex, and Cummins’ Jim Nebergall (whom we quoted last month) pitches in on that at hydrogeninsight.com.

But back to emissions. It’s now 2pm on 6 June, clear of daily peaks. The electricity market’s real-time website EM6 shows the grid running at 79% renewables and emissions at 149g C02/kWh.

If hydrogen trucks are 25% energy- efficient (using 4kWh of electricity for 1kWh of propulsion), on today’s grid, that would cause emissions of virtually 600g CO2/kWh of output (compared with battery trucks at 80% efficiency, which cause 187g CO2/kWh).

Some 600g CO2/kWh is greater than straight fossil-gas generation (455g CO2/ kWh), and over half of arch-villain coal (1073g CO2/kWh). EV trucks might have other issues, but they win hands down on cutting emissions.

So let’s think hard about the problem we’re trying to solve: slashing emissions by getting off fossil fuels.

Accepting the above is a simplification, how might hydrogen make sense?

Short term, there’s help from lower ‘embodied carbon’ in making the truck. That gives an edge for a year or two.

Electrolysers can optimise off-peak power use and avoid grid peaks, and theoretically generate electricity with hydrogen to help ease peaks. But the figures above show that would struggle to be lower emissions than fossil-gas generation.

Maybe the likes of Hiringa can erect its own wind turbines and work exclusively off them. That might reduce their emissions, but would come with consequences, such as needing turbines that generate about four times the energy the hydrogen will deliver.

This broadly aligns with Concept Consulting’s research for MBIE and several energy companies, which concluded: “Larger-scale hydrogen production would drive the need for new renewable power stations to be built.”

But the dilemma doesn’t end there. To maximise our electrification with renewables, New Zealand must build the equivalent of a 3MW wind turbine roughly every three days forever, escalating to one every two days if New Zealand follows what Concept termed “the green hydrogen route”.

Add in the real possibility that supplies of minerals for renewable electricity hardware will fall far short of global demand, and we must obviously tread cautiously.

Retired professor of power engineering Pat Bodger offers wise guidance on that: “In any application, the alternatives need to be compared in an unsubsidised manner. Otherwise, an inferior option can wrongly be supported.”