Green hydrogen has been in the news often lately. Leon Musk reckons hydrogen powered vehicles are “bullshit” whilst Hyundai has launched its NEXO hydrogen fuel-cell electric vehicle (FCEV) in Australia and Toyota has announced its upgraded Mirai FCEV will arrive in Australia this year.
In Australia, the $70 million Renewable Hydrogen Deployment Fund is on-foot. Meanwhile, the European Union will invest $430 billion in green hydrogen by 2030 to help achieve the goals of its Green Deal. And USA, Chile, Japan, Germany and Saudi Arabia are all making major investments into green hydrogen.
So, what is green hydrogen? Simply put, it is hydrogen fuel that is created using renewable energy instead of fossil fuels. It has the potential to provide clean power for manufacturing, transportation, and more — and its only byproduct is water.
Where does green hydrogen come from?
Hydrogen energy is very versatile, as it can be used in gas or liquid form, be converted into electricity or fuel, and there are many ways of producing it. Approximately 70 million metric tons of hydrogen are already produced globally every year for use in oil refining, ammonia production, steel manufacturing, chemical and fertilizer production, food processing, metallurgy, and more.
There is more hydrogen in the universe than any other element—it’s been estimated that approximately 90 percent of all atoms are hydrogen. But hydrogen atoms do not exist in nature by themselves. To produce hydrogen, its atoms need to be decoupled from other elements with which they occur— in water, plants or fossil fuels. How this decoupling is done determines hydrogen energy’s sustainability.
Most of the hydrogen currently in use is produced through a process called steam methane reforming, which uses a catalyst to react methane and high temperature steam, resulting in hydrogen, carbon monoxide and a small amount of carbon dioxide. In a subsequent process, the carbon monoxide, steam and a catalyst react to produce more hydrogen and carbon dioxide. Finally the carbon dioxide and impurities are removed, leaving pure hydrogen. Other fossil fuels, such as propane, gasoline, and coal can also be used in steam reforming to produce hydrogen. This method of production—powered by fossil fuels—results in grey hydrogen as well as 830 million metric tons of CO2 emissions each year, equal to the emissions of the United Kingdom and Indonesia combined.
When the CO2 produced from the steam methane reforming process is captured and stored elsewhere, the hydrogen produced is called blue hydrogen.
Hydrogen can also be produced through the electrolysis of water, leaving nothing but oxygen as a byproduct. Electrolysis employs an electric current to split water into hydrogen and oxygen in an electrolyzer. If the electricity is produced by renewable power, such as solar or wind, the resulting pollutant-free hydrogen is called green hydrogen. The rapidly declining cost of renewable energy is one reason for the growing interest in green hydrogen.
Why green hydrogen is needed
Most experts agree that green hydrogen will be essential to meeting the goals of the Paris Agreement, since there are certain portions of the economy whose emissions are difficult to eliminate. The top three sources of climate-warming emissions come from transportation, electricity generation and industry.
Energy efficiency, renewable power, and direct electrification can reduce emissions from electricity production and a portion of transportation; but the last 15 percent or so comprising aviation, shipping, long-distance trucking and concrete and steel manufacturing, is difficult to decarbonize because these sectors require high energy density fuel or intense heat. Green hydrogen could meet these needs.
Advantages of green hydrogen
Hydrogen is abundant and its supply is virtually limitless. It can be used where it is produced or transported elsewhere. Unlike batteries that are unable to store large quantities of electricity for extended periods of time, hydrogen can be produced from excess renewable energy and stored in large amounts for a long time. Pound for pound, hydrogen contains almost three times as much energy as fossil fuels, so less of it is needed to do any work. And a particular advantage of green hydrogen is that it can be produced wherever there is water and electricity to generate more electricity or heat.
Hydrogen has many uses. Green hydrogen can be used in industry and can be stored in existing gas pipelines to power household appliances. It can transport renewable energy when converted into a carrier such as zero-carbon fuel for shipping, for example.
Hydrogen can also be used with fuel cells to power anything that uses electricity, such as electric vehicles and electronic devices. And unlike batteries, hydrogen fuel cells don’t need to be recharged and won’t run down, so long as they have hydrogen fuel.
Fuel cells work like batteries: hydrogen is fed to the anode, oxygen is fed to the cathode; they are separated by a catalyst and an electrolyte membrane that only allows positively charged protons through to the cathode. The catalyst splits off the hydrogen’s negatively charged electrons, allowing the positively charged protons to pass through the electrolyte to the cathode. The electrons, meanwhile, travel via an external circuit—creating electricity that can be put to work—to meet the protons at the cathode, where they react with the oxygen to form water.
Hydrogen is used to power hydrogen fuel cell vehicles. Because of its energy efficiency, a hydrogen fuel cell is two to three times more efficient than an internal combustion engine fuelled by gas. And a fuel cell electric vehicle’s refuelling time averages less than four minutes.
Because they can function independently from the grid, fuel cells can be used in the military field or in disaster zones and work as independent generators of electricity or heat. When fixed in place they can be connected to the grid to generate consistent reliable power.
Importantly, green hydrogen has the potential to be a huge industry, employing thousands of people.
The challenges of green hydrogen
Its flammability and its lightness mean that hydrogen, like other fuels, needs to be properly handled. Many fuels are flammable. Compared to gasoline, natural gas, and propane, hydrogen is more flammable in the air. However, low concentrations of hydrogen have similar flammability potential as other fuels. Since hydrogen is so light—about 57 times lighter than gasoline fumes—it can quickly disperse into the atmosphere, which is a positive safety feature.
Because hydrogen is so much less dense than gasoline, it is difficult to transport. It either needs to be cooled to -253˚C to liquefy it, or it needs to be compressed to 700 times atmospheric pressure so it can be delivered as a compressed gas. Currently, hydrogen is transported through dedicated pipelines, in low-temperature liquid tanker trucks, in tube trailers that carry gaseous hydrogen, or by rail or barge.
Natural gas pipelines are sometimes used to transport only a limited amount of hydrogen because hydrogen can make steel pipes and welds brittle, causing cracks. When less than 5 to 10 percent of it is blended with the natural gas, hydrogen can be safely distributed via the natural gas infrastructure. To distribute pure hydrogen, natural gas pipelines would require major alterations to avoid potential embrittlement of the metal pipes, or completely separate hydrogen pipelines would need to be constructed.
Fuel cell technology has been constrained by the high cost of fuel cells because platinum, which is expensive, is used at the anode and cathode as a catalyst to split hydrogen. Research is ongoing to improve the performance of fuel cells and to find more efficient and less costly materials.
A challenge for fuel cell electric vehicles has been how to store enough hydrogen—five to 13 kilograms of compressed hydrogen gas—in the vehicle to achieve the conventional driving range of 500 kilometres.
The fuel cell electric vehicle market has also been hampered by the scarcity of refuelling stations.
It all comes down to cost
The various obstacles green hydrogen faces can actually be reduced to just one: cost. Julio Friedmann, senior research scholar at Columbia University’s Center on Global Energy Policy, believes the only real challenge of green hydrogen is its price. The fact that 70 million tons of hydrogen are produced every year and that it is shipped in pipelines around the U.S. shows that the technical issues of distributing and using hydrogen are “straightforward, and reasonably well understood,” he said.
The problem is that green hydrogen currently costs three times as much as natural gas and producing green hydrogen is much more expensive than producing grey or blue hydrogen because electrolysis is expensive, although prices of electrolyzers are coming down as manufacturing scales up. Currently, grey hydrogen costs about €1.50 euros ($1.84 USD) per kilogram, blue costs €2 to €3 per kilogram, and green costs €3.50 to €6 per kilogram, according to a recent study. However, it is noted that Infinite Blue Energy is looking to produce at AU$2 per kilogram.