Submitted by Diana Powers - A Florida voter living in France.

Hydrogen has inspired and excited proponents of the Energy Transition as the missing link, the connective tissue that provides coherence to the disparate pieces of the future energy puzzle. Hydrogen is versatile. It carries energy. It is a feedstock for chemicals. It can link the electricity grid to the gas grid. It can power transportation from scooters to cars to trains and rockets and, in the future, ships and airplanes. It is envisaged as the successor to petroleum as the maker of nations and the remaker of geopolitics.

This tiniest of atoms links up by twos to create H2, the tiniest of molecules.

But not all hydrogen molecules are created equal. And the whimsical hydrogen community has color-coded the many and varied sources of hydrogen.

Grey Hydrogen

Over 99% of the current 70 million tons of pure hydrogen produced worldwide every year is grey hydrogen, made from fossil fuels. According to the International Energy Agency’s report, The Future of Hydrogen, this uses 6% of global natural gas and 2% of global coal production, resulting in 830 million tons of carbon dioxide (CO2) emissions every year. The key process to transform natural gas to hydrogen is called Steam Methane Reforming (SMR), wherein steam and a catalyst are used to break the natural gas molecules, and after a couple more processes, very pure hydrogen is achieved.

This flourishing industry has been largely invisible to the public, feeding in as a factor of production to key industries. A large part goes to the refining of crude oil. Hydrogen is used to clean sulfur dioxide (SO2) from oil, thus reducing the harmful SO2 tailpipe emissions further down the line, as well as supplying elemental sulfur as a byproduct, eliminating much of the need to mine it.

Hydrogen is a major input in the production of fertilizers. Using the Haber-Bosch process, developed about a century ago, the hydrogen is mixed with nitrogen from the air under pressure and at fairly high temperatures to produce the fertilizer ammonia. Hydrogen is also an ingredient in many other chemicals, including methane, methanol, and synthetic hydrocarbons.

Blue Hydrogen

The concern with carbon dioxide emissions has led to the development of blue hydrogen, which essentially entails retrofitting carbon capture technology onto existing grey hydrogen plants and storing the CO2 in salt caverns or depleted oil fields. The advantage of this technology is that it avoids the premature retirement of existing hydrogen-producing assets, avoiding stranding them. The key disadvantage is that it places further hopes and pressures on carbon capture and storage (CCS) technologies and sites. These remain underdeveloped and certainly not nearly able to deal with the excess carbon emissions of the entire industrial age. Another disadvantage of blue hydrogen is its susceptibility to the price volatility of the natural gas that feeds it.

Green Hydrogen

And now for something completely different! Green hydrogen is created by subjecting the water molecule to electrolysis, wherein a stream of electricity splits the molecules into a stream of pure oxygen and a stream of pure hydrogen. If the electricity used is renewable, then no carbon enters the process at all. Green hydrogen fits the high standards of a true energy transition. Fuel cells can reverse the process and turn the hydrogen back into electricity. Herein lies the crux of hydrogen’s versatility. Electricity is terribly difficult to store. Batteries require a lot of material to store them, and mainly for short periods of time (although battery research continues to open new frontiers). Other large storage technologies, hydroelectricity, and pumped storage are not available everywhere. But green electrolysis takes green electricity and transforms it into a gas, green hydrogen, that can be transported and stored indefinitely. Excess wind and solar power can be stored for weeks, months, or seasons and then turned back into electricity as needed. Renewable energy is often criticized for being “non-dispatchable,” that is, not necessarily available when needed. Alternatively, excess renewable energy is “curtailed” or disconnected, wasting valuable power. Green hydrogen provides a solution to both problems of undersupply and oversupply. It balances supply and demand for renewable energy, increasing its efficiency and making it more user-friendly.

Because electrolytic hydrogen can be transformed into so many other molecules, we call this overall process power-to-x (PtX), where X can be hydrogen or any of its derivatives: power-to-methane, power-to-methanol, power-to-ammonia, power-to-synthetic fuels. When the hydrogen makes the full return to electricity, it is called power-to-X-to­-power (PtXtP).

Green hydrogen has captivated the imaginations of policy-makers and corporate leaders in recent years leading to the broad global consensus that it will play a key role in a renewable energy world. Many countries have developed “hydrogen strategies” to stake out their claim in this new world, backed by multiple billions of dollars. Countries with excellent renewable energy sources plan to export their sunshine and wind in the form of hydrogen by pipeline or ship to ports and industrial hubs in importing countries.

There is no how-to manual for an industrial revolution, but the hydrogen community and energy experts have sketched out some themes and priorities that organize the movement. And some controversies have yet to be resolved.

One organizing principle is to avoid unnecessary energy conversions since some energy is lost with each conversion. If renewable energy can be used directly, that is preferable to converting it to hydrogen. The massive deployment of renewable energy that is needed for hydrogen, therefore, is just a part of the more massive deployment that is needed to produce direct electricity. Don’t put the cart before the horse, and renewable energy is the horse.

If practically everything in the energy world can be accomplished with hydrogen, what should be prioritized? One no-brainer is to replace current applications of grey hydrogen with blue or green hydrogen. Given the existing infrastructure, blue hydrogen could be the cheapest option here and the path of least resistance ahead of a longer-term replacement of infrastructure for green hydrogen.

Another priority is to employ green hydrogen in the so-called “hard-to-abate” (HTA) sectors that have proven difficult to decarbonize. New technologies and processes are finally able to decarbonize iron and steel-making, cement, chemicals, building materials, and heavy-duty transport using green hydrogen.

Some applications should not be prioritized for hydrogen because very efficient solutions already exist, such as heat pumps for heating buildings. Electric vehicles for city driving are already an efficient solution using direct electricity as well. Most think that a mix of electric and hydrogen fuel cell vehicles will share our roads in the future.

Green hydrogen technologies, such as electrolyzers and fuel cells, are on a rapid research and learning curve. Together with increased manufacturing, these breakthroughs will make green hydrogen cheaper than blue or grey hydrogen in years to come. Recent oil price spikes have led some to claim that, at least for now, green hydrogen is cheaper than blue or even grey.

New industries often face the classic chicken and egg problem of which comes first, supply or demand? The concept of a hydrogen cluster, often located at hydrogen ports, will bring together demanders and suppliers of green hydrogen, reinforcing fragile supply chains.

There are other colors of hydrogen: pink for nuclear-powered electrolysis, turquoise for pyrolysis of methane resulting in hydrogen and solid black carbon, or white for naturally-occurring hydrogen, for a few examples. But it is green that is the keystone of our renewable energy future.