[This is the second post in our Hydrogen Blog Series. Read the first post here.]
In the first post, I alluded to the technical issues hydrogen developers are considering. Here we’ll look at how hydrogen is produced and what it will be used for.
How is hydrogen produced today?
We make hydrogen mainly using steam methane reforming (“SMR”). SMR requires steam, heat, and pressure to convert methane (in natural gas) to hydrogen and carbon monoxide. SMR is a high-carbon process that uses fossil fuels for process heat. Stakeholders have assigned colors to hydrogen depending on how it is produced. They typically refer to fossil SMR hydrogen as “grey” hydrogen.
How is clean hydrogen produced?
Clean hydrogen, by contrast, is produced through zero-carbon or low-carbon processes. The gold standard—so-called “green” hydrogen—is hydrogen produced via electrolysis using renewable electricity from wind or solar. The types of electrolyzers vary, but they consist of three key components: an anode on one end, a cathode on the other, and an electrolyte in between. When water and electricity are introduced to the electrolyzer, water splits at the anode into oxygen and positively charged hydrogen ions. As electricity flows through an external circuit, the hydrogen ions migrate through the electrolyte to the cathode, where hydrogen gas is formed and collected.
The two main types of electrolyzers are Alkaline and Polymer Electolyte Membrane (“PEM”). Alkaline electrolyzers have existed for more than 100 years and use a liquid electrolyte solution. Many, however, are focusing on PEM electrolyzers, which use a specialty plastic material instead of a liquid electrolyte. According to the Department of Energy (“DOE”), PEM electrolyzers can operate “effectively at a range of loads with sub-second response times,” making them “particularly compatible with variable energy sources, such as sun and wind power.” A third type of electrolyzer—solid oxide electrolyzer cells (“SOECs”)—use as an electrolyte a solid ceramic material. SOECs are the least commercialized type of electrolyzer and require high temperatures, up to 700°-800°C, to operate.
What’s with the colors?
I’ve mentioned green and grey hydrogen. There’s also “pink” hydrogen—produced via electrolysis with electricity from nuclear power—and “blue” hydrogen—produced via SMR but with carbon capture and sequestration, among other colors.
While the colors are helpful because they signal whether a low-carbon energy source is used to produce hydrogen, many have suggested that the focus of regulatory programs should instead be on hydrogen’s carbon intensity. If a producer can show that its hydrogen is produced using zero- or sufficiently low-carbon means, it should receive benefits in clean hydrogen programs.
What is hydrogen used for?
According to DOE, the United States produces about 10 million metric tons of hydrogen per year. Total global production is around 90 million metric tons per year. Most of the hydrogen that’s consumed in the United States is used for petroleum refining and ammonia (for ammonium nitrate fertilizer) and methanol production. DOE’s draft Hydrogen Roadmap provides this helpful graph:
Apart from petroleum refining and fertilizer manufacturing, DOE reports, hydrogen is used for 50,000 fuel cell forklifts, 50 open retail hydrogen fueling stations, 70 fuel cell buses, over 13,000 fuel cell vehicles, and 500 MW of fuel cells for stationary/backup power.
What could hydrogen be used for?
This is the exciting part. We’ve previewed some of hydrogen’s potential uses in a previous post. Here’s a longer list based on DOE’s draft Hydrogen Roadmap:
Ammonia. Hydrogen is an essential ingredient in ammonia (NH3) production, and ammonia is an essential ingredient in chemicals like ammonium nitrate fertilizer. Ammonia could also be an important carbon-less fuel.
Steelmaking. We’re going to need a lot of steel to build structures, including those supporting clean energy, such as wind turbines, solar facilities, and associated transmission and other infrastructure. As we mentioned previously, steelmakers burn coal to make steel, but they could replace coal with hydrogen or cleaner hydrogen/natural gas blends.
Medium- and heavy-duty vehicles, marine shipping, and aviation. Clean hydrogen could replace fossil fuels for large vehicles and vessels that make long trips. It could also be used to make cleaner liquid fuels, such as “electrofuels,” (subscription required) fuels that combine hydrogen and biogenic carbon dioxide from biomass sources, such as ethanol plants.
Energy Storage. Hydrogen can also store energy, particularly when it’s converted into ammonia.
DOE has estimated the potential demand for most of these sectors. Here’s a breakdown of estimated demand by sector based on data from DOE’s draft Hydrogen Roadmap:
- Ammonia – 4 to 5 million metric tons (MMT)/year
- Steel and chemicals manufacturing – 1 to 3 MMT/year
- Medium- and heavy-duty vehicles – 5 to 8 MMT/year
- Aviation – 2 to 6 MMT/year
- Energy Storage – 4 to 8 MMT/year
- Total – 16 to 30 MMT/year
The International Energy Agency recently published some promising figures: “If all [hydrogen] projects currently in the pipeline were realised, by 2030 the production of low-emission hydrogen could reach 16-24 [MMT] per year.”
But while clean hydrogen has immense potential, its success hinges on significantly reducing its costs. We take up costs in our next post, as well as the many federal programs meant to cut the cost of clean hydrogen.