Neither hydrogen nor nuclear power are silver bullets to make the world’s energy supply sufficiently non-emitting of greenhouse gases, but both are widely seen as essential components to combat planetary warming.
Electricity from sources with low greenhouse-gas emissions are rapidly eroding the dominance of carbon-based energy. But matching the supply of electricity to demand is often challenging. The two big groups of low-emitting electricity are wind/solar and nuclear. Nuclear operation favours continuous supply; wind and solar are hugely variable over all time intervals, in most non-tropical regions including large seasonal averages. Neither of these sources easily match supply to demand. Enter hydrogen, with two advantages: converting electricity to hydrogen by water electrolysis allows for energy storage, and hydrogen can power vehicles where battery volume and weight preclude the unconverted use of electricity.
For light vehicles with relatively low usage, battery power is adequate and getting better. For heavier duties — trucks, trains, buses, ships, and ultimately planes, batteries falter on weight and volume, and take too long to recharge. In weight terms, hydrogen packs about three times the energy of hydrocarbons. But in volume terms, it is at a decided disadvantage even when compressed to 700 atmospheres or cooled to -253°C as a liquid. However, even where available space is a constraint, displacing large internal combustion engines with extremely compact PEM fuel cells – to convert hydrogen to electricity – satisfactorily constrains overall volumes. This was demonstrated in an extensive study for the Canadian transport utility Metrolinx, which showed that hydrogen storage and fuel cells could be fitted into the existing shells of diesel-electric locomotives. “Hydrail” is seen as an early adopter of hydrogen fueling and Alstom’s Coradia iLint hydrogen fuel cell trains are operating in commercial service in Germany, winning the prestigious 2022 German Sustainability Design Award. While PEM fuel-cell-powered vehicles are still unusual, more than 1300 buses powered by fuel cells already operate, notably in China. This focus on heavy-duty applications also greatly curtails the scale of a hydrogen-supply network. Building supply networks is also simplified by accessing existing electricity grids for local electrolytic production.
In jurisdictions like Ontario, the expansion of wind-generated electricity has created a rising proportion of time where the value of generated electricity is negative. Some mitigation will come from balancing electricity supply to energy demand through battery storage (with increasing numbers of light vehicles being recharged overnight). While this will help, it does nothing to address the 2:1 ratio of average monthly wind generation between winter and summer that is experienced in mid-latitudes. Hydrogen, however, can be stored in vast quantities in underground salt caverns — just as natural gas is currently stored seasonally.
Hydrogen is already a bulk commodity, supplying oil-upgrading and ammonia-fertilizer production. It is made very efficiently and cheaply from natural gas by steam reforming of methane, however, this co-produces CO2. Today, hydrogen produced by electrolysis of water at average electricity prices is two or three times more expensive than hydrogen from steam reforming. But hydrogen’s economics are steadily closing that gap with falling costs of both electrolysis cells and wind/solar electricity. Already electrolytic hydrogen is competitive when absorbing surplus grid electricity. Provided that the electricity used for water electrolysis comes from sources with low CO2 emissions, putting a price on CO2 emissions can help enhance electrolytic hydrogen’s price competitiveness: Canada’s tax on CO2 emission at 170 $/tonne in 2030 will add about 50% to the price of hydrogen from steam reformers.
Apart from water electrolysis, hydrogen has two other low-emitting (colour-coded) pathways for production:
1. CO2 from reforming (“grey”) can be captured and sent to secure underground storage (leaving hydrogen dubbed “blue”).
2. Methane can be pyrolyzed—with modest electricity input—to produce only half the (“turquoise”) hydrogen quantity from steam reforming but co-producing only solid carbon, which is extremely stable, easily disposed of, and has some industrial uses.
Both blue and turquoise hydrogen could be significant adjuncts to the electrolytic route since they can transform the existing production of natural gas (methane) to a non-emitting source — with the essential proviso of requiring negligible emission of methane in its production. (Molecule-for-molecule, methane has a far larger impact than CO2 as a greenhouse gas.)
In summary, while hydrogen is not a primary energy source, it offers two key functions. It can smooth mismatches in electricity supply and it can power the needs of heavy-duty transport far beyond the foreseeable capability of batteries.