NASA has powered the American space program with liquid hydrogen since the 1970s. Boosters have been predicting breakthroughs with earthbound hydrogen energy for nearly as long. It faces a lot of problems. Green hydrogen energy faces even more hurdles.

For one thing, pure hydrogen doesn’t exist in nature. The ordinary way of making it uses fossil fuels and emits significant greenhouse gases. The cleaner way costs a lot more.  Also, transporting and using hydrogen needs extensive infrastructure.

Market forces have already started to drive costs down. Many companies and research teams are exploring new technologies. Green hydrogen promises to help decarbonize energy.

Manufacturing hydrogen, or what color is hydrogen?

Hydrogen is a colorless, odorless gas. And yet it goes by a bewildering number of color names.

Most pure hydrogen comes from fossil fuels by a process called steam methane reforming. It releases greenhouse gases into the atmosphere. Therefore, it produces what’s called brown or black hydrogen if made from coal and gray hydrogen if made from methane or natural gas.

It is possible, though, to capture and store about 90% of the greenhouse gases. Steam reforming of fossil fuels plus carbon capture and storage is called blue hydrogen. Making it emits a tenth of the carbon of the dirtier hydrogens.

Splitting water molecules into hydrogen and oxygen uses a process known as electrolysis. It is cleaner but requires a lot of electricity. It can cost six times as much as steam methane reforming.

Green hydrogen means hydrogen produced by electrolysis using excess clean, renewable energy. Making it produces no greenhouse gases. Oddly enough, I can’t find a color assigned to hydrogen from electrolysis powered by electricity generated from coal or gas. Maybe it’s a dingier green.

I won’t try to describe white, yellow, pink, or turquoise hydrogen.

How a hydrogen fuel cell works

A hydrogen fuel cell works sort of like a battery. It has positive and negative electrodes separated by an electrolyte.

The primary difference is that a battery converts certain chemicals into electricity. After it has used up the chemicals, the battery is dead. It’s necessary to recharge it or discard it. In a hydrogen fuel cell, a tank provides hydrogen. The cell works as long as the hydrogen flows.

Turn off the hydrogen, the fuel cell stops. When the tank is empty, it needs to be refilled, but the fuel cell itself works as before.

Hydrogen is the smallest and simplest of all atoms. It most commonly comprises a single electron and a single proton. (We need not consider so-called heavy hydrogen.”

A catalyst at the positive electrode splits the hydrogen atom. The proton travels through the electrolyte to the negative electrode. The electrons flow through an external circuit to the negative electrode, creating electricity. In the presence of air at the negative electrode, the two particles reunite to reform hydrogen. And since pure hydrogen doesn’t exist in nature, it combines with the oxygen in the air to form water, which flows out of the cell.

So the whole process of using green hydrogen starts with water and ends with water as its only end result. No greenhouse gas emissions.

Advantages and disadvantages of green hydrogen energy

Green hydrogen is by definition a clean energy source. It’s scalable from small operations such as a family car to grid-scale operations.

It takes no longer to fill a car with hydrogen than it does with gasoline. Contrast that with how long it takes to charge an electric vehicle. Plus the fact that manufacturing lithium-ion batteries and disposing of them have significant environmental downsides.

Despite the claims of its boosters over the past several decades, green hydrogen has as many disadvantages as advantages. It has yet to become a big part of the world’s energy mix. After all, it’s only truly green if the electricity to perform electrolysis comes from renewable sources. And that will require a huge expansion of wind and solar production.

According to BloombergNEF, it would take more electricity than the world now generates from all sources to provide a quarter of the world’s energy needs from hydrogen to. It would also cost about $11 trillion to pay for manufacturing and storage infrastructure. It seems safe to say that such a massive project will never happen.

What’s more, once generated, hydrogen is hard to store and transport. Storing it requires compressing it to 700 times atmospheric pressure at super-cold temperatures. Under those conditions, it can embrittle metal. It will find its way out of the tiniest leaks. And it’s highly explosive.

The best way to move hydrogen from one place to another is dedicated pipelines. Building any new ones will attract vigorous opposition. And after all that, it only has a quarter of the energy of the same volume of natural gas. (It does, however, have an energy density triple that of jet fuel.) In the US, anyway, hydrogen remains much more expensive than natural gas.

Some hopeful signs for green hydrogen

Even so, only green hydrogen appears suitable for certain energy needs. Solar and wind can’t effectively address about 15% of the economy. This portion includes aviation, shipping, long-distance trucking, and manufacturing of energy-intensive products such as concrete or steel. Green hydrogen can also decarbonize fertilizer production.

What’s more, wind and solar power require storage to make up for their fluctuating availability. Hydrogen storage is more easily scalable than lithium batteries. To increase the time batteries can provide reliable electricity requires adding more and more batteries. Multiplying batteries multiplies the cost of energy storage.  Multiplying hydrogen storage, on the other hand, simply requires building a larger tank or underground cavern for it.

For hydrogen to replace carbon-emitting fuels requires hydrogen fuel cells onboard vehicles or ships. Plus building infrastructure for distributing and storing it for use. Or, for that matter, retrofitting power plants to use hydrogen fuel cells to make electricity for the grid. Creating this infrastructure will require a lot of money and time.

So when will costs come down?

Electricity accounts for about 60% of the cost of electrolysis. The machinery itself is also expensive. The cost of renewable energy from solar and wind power is declining steeply. The cost of the electrolyzers is also projected to fall rapidly. But the International Energy expects the cost of green hydrogen to decline 30% by 2030. If market trends continue, it could become a competitive technology by then.

In some places, it could come faster. renewable energy is already producing excess electricity at times. This excess drives the price of the electricity to nearly zero. It could cheaply perform electrolysis. According to an analysis by Morgan Stanley, locating green hydrogen near major wind farms in Texas or the Midwest could make it competitive there within two years.

Some promising alternative technologies

Converting hydrogen to something else

But there are alternative ways to use hydrogen during development of this infrastructure. A century-old process can combine hydrogen with carbon monoxide to make synthetic versions of various fossil fuels.

It is also possible to capture carbon dioxide from the air and combine it with hydrogen to make synthetic fuel. If the hydrogen is carbon-free, burning these fuels will be carbon neutral. It will emit no more carbon dioxide than was taken from the air in the first place.

Falling solar and wind prices should make it possible to bring these fuels to market for about $1 per liter (or about $4 per gallon) by the middle of the 2020s. It might be competitive with gasoline. In any case, prices will fall from there. This use of hydrogen will provide yet another way to convert intermittent renewable energy to storable, carbon neutral liquid fuels.

Developers of the Neom project described below plan to convert pure hydrogen to ammonia, a compound of hydrogen and nitrogen. In that form, it’s easier to store and ship. At its destination, another process will split the two gases apart again, releasing pure hydrogen. No one knows yet whether it will really be practical.

Finding cheaper ways to make green hydrogen

A company called SGH2 claims to have developed a new technology for producing green hydrogen. Instead of electrolysis, the plant it’s planning in southern California will use waste gasification. Heating various kinds of waste to high temperatures reduces them to molecular compounds, including a hydrogen-rich biogas. Further processing splits the hydrogen apart.

Similarly, SunHydrogen is about to start on a pilot project to use sunlight instead of electricity to derive hydrogen from water. That is, instead of electrolysis, it claims its approach mimics photosynthesis.

Joi Scientific claims that its process will produce hydrogen inexpensively at the point of need. So instead of supplying a hydrogen filling station through a pipeline or other method of transportation, the station can make its own from water.

Researchers at the University of Calgary have developed an emissionless technique for extracting hydrogen from spent oil fields.

Many companies in all industries come up with attractive innovations. Sometimes what works in the lab doesn’t work at industrial scale.  Sometimes a company goes bankrupt before it can market its process. But sometimes, successful development creates a game changer.

Some company is bound to find a scalable way to reduce the cost of making and distributing green hydrogen energy. Most likely, more than one.

Some largescale hydrogen energy projects

About a hundred large-scale hydrogen projects worldwide are in the planning stages. Not all of them use green hydrogen. The European Commission is co-funding some blue hydrogen projects, a controversial decision.

Technology to make it already exists and is well understood.  It gets major oil companies involved in hydrogen production, which is a good thing or a bad thing depending on what anyone thinks of oil companies. It diverts investment from green hydrogen and could make it non-competitive.

Here is but one of many largescale green hydrogen projects:

Saudi Arabia is building a city, called Neom, that will be a technologically advanced home to a million people. Although Saudi Arabia is the world’s top oil producer, Neom won’t use oil. It will derive its power from green hydrogen. The Saudis want to use it as a demonstration project, with an eye toward selling green hydrogen to the world.

Already, an American company called Air Products & Chemicals has been working on a green hydrogen plant for Neom powered by 4 gigawatts of electricity from wind and solar farms in the surrounding desert. And the Saudis have other similar projects in the works.

 

Related articles on Sustaining Our World

Can hydrogen fuel cells provide green electricity and storage?
Hydrogen as an alternative fuel

Sources:

Green hydrogen: could it be key to a carbon-free economy? / Jim Robbins, Yale Environment 360. November 5, 2020
How falling solar costs have renewed clean hydrogen hopes / James Temple, MIT Technology Review. August 7. 2020
Tension arises as clean hydrogen projects spread / Alex Scott, Chemical & Engineering News. July 9, 2020