The Hydrogen Question

AHydrogen enjoys an unusual privilege in energy policy: it tends to be judged entirely by what emerges at the far end of the pipe. Burned in a turbine or passed through a fuel cell, it yields water and nothing else, and a fuel carrying no carbon in its molecule seems to settle the argument before the argument has properly begun. The accounting, however, stops at the flame. It takes no account of the energy spent making the gas, which has to be manufactured rather than dug up, and until very recently it took no account whatever of the portion that never reaches the flame because it has escaped along the way. Hydrogen is the smallest molecule there is, and it slips through seals, valves and welds that would hold methane comfortably. The gas is also colourless and odourless, and it burns in air across an unusually wide range of concentrations, so any escape is harder to notice than a comparable leak of natural gas would be. Whether such losses matter has become, over the past five years, the most consequential question in the field, and the answer depends on chemistry that has nothing to do with burning anything.

BHydrogen is not a greenhouse gas in the ordinary sense, since it absorbs almost no infrared radiation. Its influence is indirect. Once aloft it reacts with hydroxyl radicals, the compounds that scavenge methane, and every radical consumed in that way is one no longer available to break methane down, so the methane already present lingers for longer than it otherwise would. The gas also raises the concentration of water vapour in the stratosphere and disturbs the balance of ozone at lower altitudes. Ines Ekstrand, of the Grenland Institute for Atmospheric Chemistry, has assembled these effects into a single figure and estimates that a tonne of hydrogen released to the air warms the climate across a century roughly eleven times as much as a tonne of carbon dioxide. Her group sampled the air around 26 production and storage sites between 2020 and 2023 and calculated an average loss of 2.7 per cent of throughput. Above about 3 per cent, she maintains, the advantage of replacing natural gas with hydrogen made from renewable electricity vanishes entirely for the first two decades.

CThat figure has not gone unquestioned. Peter Nakagawa, of the Koriyama Centre for Energy Systems, observes that nearly every site in her sample was experimental, assembled at speed with temporary fittings and run by teams whose priority was demonstration rather than containment. His own measurements, taken at two long-established ammonia works over eighteen months, put losses at 0.4 per cent. Mature engineering, he contends, does not leak in the way that pilot plants leak, and policy built on early numbers will misprice the technology for a generation. Nakagawa readily concedes the weaknesses of his own evidence: ammonia works are enclosed sites that make and consume the gas in one place, they operate no distribution network at all, and eighteen months is a thin basis for any claim about a system that would eventually take in pipelines, road tankers and millions of domestic fittings. Measurement is itself awkward, since instruments that detect the gas reliably at low concentrations were not sold commercially before 2019 and even now perform well only in still air.

DRunning alongside this dispute is an older objection that has nothing to do with escaping gas. Splitting water consumes about a third more energy than the hydrogen subsequently delivers, and compressing, chilling and moving it costs more again; by the time current has been turned into gas and the gas back into current, roughly 30 units survive out of every 100 that entered, against 80 or more where the electricity is simply used as it is. That arithmetic is decisive for anything a wire can already reach. Batteries, moreover, have improved faster than most forecasts allowed, which has steadily narrowed the range of tasks for which a stored chemical fuel is the obvious answer. A car, a domestic boiler and a suburban train are all better served by electricity itself, and the case for the gas is confined to the places no wire will serve: the reduction of iron ore, the manufacture of fertiliser, and possibly the largest ships afloat. In those applications the fuel is consumed where it is made, or delivered in bulk to only a handful of industrial customers.

EThe two objections, although they are usually voiced by different people, point the same way. Escape becomes serious in proportion to the length and complexity of the network the gas must travel through, so the heaviest losses belong to precisely the vision of hydrogen that the efficiency argument has already rejected: gas piped into houses and pumped into private cars. Keep the molecule inside steelworks and fertiliser plants and Nakagawa's low figure is probably the relevant one; send it down every street and Ekstrand's threshold becomes the one that counts. What looks like a dispute about a percentage is in truth a dispute about the shape of the system, and it is not obvious that either party has settled it. Governments that have written the gas into their industrial plans have, for the most part, left that question of shape unanswered, promising volumes without naming destinations. The prudent reading is that hydrogen deserves a narrow and well-sealed role, and that the case for a broad one carries a burden of proof it has not yet discharged.