I love innovation, love technology, and love efforts to decarbonise transport, so what’s not to love about hydrogen? The simplest atom is about to show it’s far from simple when powering transport.

We all know why we’re on the alternative fuel journey: diesel and petrol are brilliant fuels except for those damned emissions putting everything we value under threat. And the $10 billion health costs they land on New Zealand every year. And the environmental devastation their extraction causes. Oh yes, and those oil wars …

There are lots of compelling reasons to quit fossil fuels, but the heavy transport sector knows that’s easier said than done, so where might hydrogen fit in?

Hiringa Energy is behind an embryonic “green hydrogen” (hydrogen extracted by electrolysis using renewable electricity) refuelling network in the upper North Island, and Transport Minister Simeon Brown has been on RNZ, extolling the potential of “white hydrogen”. But most of the world uses grey, brown or black hydrogen made – with massive emissions – from fossil fuels.

Obviously, there’s hydrogen and hydrogen and, even though it’s a clear gas, its kaleidoscopic names reveal how it’s made.

Notwithstanding Brown’s enthusiasm for white hydrogen, it’s unlikely to boost New Zealand’s energy prospects: the world’s biggest known deposit, under France, would only keep the US going for six weeks. Which makes green hydrogen of particular interest.

So, what’s to love about green hydrogen? There is heaps around (think “water”); it can be low emissions (but not zero, as a GNS scientist claimed on The Detail podcast); it’s portable, with high energy density (but occupies many times the volume of equivalent diesel); and hydrogen trucks fill quicker than batteries, albeit slower than diesel.

Plus, transitioning off diesel can be easier with hydrogen than with battery trucks.

And what’s not to love? Well, spectacular energy inefficiency is centre stage: a battery truck returns say 80% of the energy the grid generated, while hydrogen struggles to reach 30%. “The rate at which battery electric vehicles outstrip both hydrogen fuel cell electric vehicles and hydrogen combustion engines on efficiency is astronomical,” Cummins’ GM for hydrogen, Jim Nebergall, wrote in Hydrogen Insight. (Nebergall, instead, pitches that hydrogen makes it easier to transition off diesel.)

But Hiringa’s CEO Andrew Clennett considers hydrogen’s feeble energy efficiency has been overplayed and “is only telling part of the story”. He highlights hydrogen’s potential benefit to “enable system efficiency for the electricity and heavy vehicle sector,” partly by levelling out electricity peaks by generating hydrogen when the grid has surplus, and shutting down their electrolysers during times of high demand.

Retired professor of power engineering Pat Bodger isn’t convinced. He notes that the existing grid is already “highly efficient” at over 90% and that, with increasing electrification of society, “the troughs and peaks of generation have evened out”.

Maybe storing energy as green hydrogen can help ease challenges for a decarbonised grid, but it’s a big “maybe”. The claims seem short on facts to back them, and the best report I found concluded, “There is a paucity of studies that integrate hydrogen supply chains with the functioning of electrical power grids.”

So, the jury is still a long way out on how much sense hydrogen makes for transport.

Next time, I’ll unpick what this means for reducing emissions. It’s no surprise that that’s what I’m really chasing.