Hydrogen has long been a mainstay in industry and is an important component in refining, ammonia production, and methanol production. Of the 10 million metric tonnes (MMT) produced in the US in 2020, about 70% was used by refineries and 22% for ammonia production. For the same year, the world produced 90 MMT, with 44% going to refineries and 38% for ammonia production. The remaining amounts were used in methanol production, steel production, feed processing, and treating metals.
Hydrogen is becoming a more versatile fuel, however, and is receiving interest in energy storage, as a transportation fuel, as a fuel for electricity generation, and as a fuel for heating. Renewables such as solar photovoltaics (PV) and wind have variable output, so hydrogen is one option for storing electrical energy from renewables to better match production and demand. In addition, the hydrogen made from renewables could be transported from regions with abundant solar PV and wind to large cities for subsequent use. Such means of transportation include sending it as a gas via pipeline or converting it to liquid form and transporting by truck or ship.
The transportation market
The US government started the Freedom Car Fuel Partnership in 2006 to study the use of hydrogen as a transportation fuel. The goal was to transform the transportation market to one using hydrogen fuel cell vehicles (FCVs). If the hydrogen is produced from renewable energy, the overall CO2 emissions will be quite small. An FCV is as much as three times more efficient than a gasoline vehicle, so a higher percentage of the energy in hydrogen is used relative to gasoline. Compared to battery electric vehicles (BEVs), hydrogen FCVs allow a refueling time similar to gasoline, thus avoiding the long charging times common with BEVs.
“Hydrogen made from renewables could be transported from regions with abundant solar photovoltaics and wind to large cities.”
The US program has not rapidly advanced, however, as there are less than 50 hydrogen fueling stations in the US (mostly in California) which, along vehicle costs, have limited the transition to a hydrogen transportation economy. At the end of 2021, the US had less than 13,000 hydrogen FCVs in service. In spite of the slow development in the US, Denmark has an energy plan to establish a nationwide hydrogen infrastructure with a goal of being independent of fossil fuels by 2050. The plan is to produce hydrogen using wind energy, both onshore and offshore, and solar PV. Time will tell whether Europe is more committed to hydrogen FCVs than the US, and how BEVs and FCVs will compete in a transition from fossil fuels.
Electricity and heating
As a fuel for electricity generation, hydrogen can be used with oxygen in a fuel cell to produce electricity and water. Hydrogen can also be blended with natural gas, thereby using a blended fuel mixture in a natural gas turbine, with an overall a reduction of CO2 emissions. Hydrogen can also be used for heating. While the use of pure hydrogen would require considerable alteration or replacement of existing home and industrial heating infrastructure that uses natural gas, hydrogen can be blended with natural gas up to concentrations around 20% without changes to the infrastructure.
Demand for hydrogen, which has grown more than threefold since 1975, is still mostly produced from fossil fuels. Of the 10 MMT produced in the US, 95% is from natural gas (methane), 4% from coal gasification, and 1% from electrolysis. For worldwide production of hydrogen, 76% is from natural gas, 22% from coal gasification, and 2% from electrolysis.
“A hydrogen fuel cell vehicle is as much as three times more efficient than a gasoline vehicle.”
Significant amounts of hydrogen do not exist in pure form but there are great quantities available in different chemical compounds, especially natural gas, coal, biomass, and water. Therefore, hydrogen, unlike fossil fuels, is not an energy source but rather an energy carrier. It can be produced in a variety of ways and it is now common to assign a color code based on the source of the hydrogen and the relative amount of CO2 made during production. For example, the majority of hydrogen in the US is produced via natural gas reforming, a reaction of natural gas and steam to make synthesis gas, a mixture of hydrogen, carbon monoxide (CO), and CO2. In this case the hydrogen is referred to as “grey” hydrogen. If the hydrogen is produced from coal or biomass via gasification, such that oxygen is used to convert the fossil fuel into CO, hydrogen, and CO2, it is referred to as “black” hydrogen. Reforming and gasification produce large amounts of CO2 and if these processes are coupled with carbon capture and sequestration (CCS), such that the CO2 is captured and transported to a geological formation for permanent storage, it is referred to as “blue” hydrogen. “Green” hydrogen is produced from electrolysis of water using electricity from only renewable energy types, such as wind, solar, and hydroelectric. If, instead, nuclear energy is used to provide energy for the electrolysis it is referred to as “pink” hydrogen.
In conclusion, the use of hydrogen for storing energy, as a transportation fuel, to generate electricity, and for heating could greatly expand hydrogen demand, adding to the existing industrial uses in refining and ammonia production, as well as a variety of other applications.