Hydrogen is going to be a big player in the zero-carbon economy the world needs. But we need to understand what it does and how it will be used.

"Green" hydrogen can be produced from water by electrolysis using renewable electricity. It can then be stored - in tanks or chemical compounds. It can be transported through pipelines, or else it can be liquefied and carried by road and sea in trucks and tankers.

When energy is needed, hydrogen can be burnt, or reacted in fuel cells, to provide electricity. The only by-product is the water we started with.

Effectively, hydrogen is a means to store renewable energy. When you use it, you get back the electricity you put in - but, of course, you lose some energy in the process.

Electrolysis is 80 percent efficient, but oxidizing the hydrogen in a fuel cell may only give back less than 46 percent of the energy put into the electrolysis.

If you are just putting energy in and getting it back out later, with a rather inefficient round trip, why bother with hydrogen? There are two reasons.

Firstly, most renewable energy is intermittent. The sun doesn't shine at night, and the wind doesn't blow all the time. If electricity demand is low, a solar farm will have to be switched off, even if the sun is shining.

In developed markets, more than 1.5 percent of the possible output of renewable sources is "curtailed" in this manner. Unless there's a way of storing that energy, the amount curtailed will get larger as more renewable sources come onstream, and go off the scale when they replace fossil sources.

California has a lot of solar and wind installations, and in 2020, it curtailed around five percent of its renewable energy output, amounting to 1.5 million MWh. For context, that is equivalent to around 170MW of power.

So you need storage. And if you are going to store energy, then hydrogen has some important advantages over batteries.

It has an energy density of around 33 kWh per kg, which is more than a hundred times that of Lithium-ion batteries (which hold around 0.26 kWh/kg). It's also three times as much as gasoline or natural gas.

The efficiency is expected to increase as processes are improved, with some operators claiming to approach efficiency in the 90 percent region.

That's why hydrogen is often considered a replacement for various hydrocarbon applications, including transport.

First users

Because it's portable and has a high energy density, hydrogen will first be used in transportation, driving vehicles too large to be powered by batteries.

A truck might have a 50,000kg payload, and carrying 20,000kg of battery would reduce that substantially. And charging times for the battery would make it less effective as part of a logistics network.

"If it takes a day and a half to recharge that battery pack," says Mark Monroe, of Energetic Consulting. "Instead, you can just add a few high-pressure hydrogen fuel tanks, run a hydrogen truck over that same route, and carry more payload, rather than carrying batteries."

Hydrogen companies are already providing systems for this application. Hydrogen specialist Plug Power has produced a green hydrogen facility for commercial trucking in Southern California, which uses two 5MW electrolyzers to provide two tons of hydrogen per day, which can be fed to trucks.

Monroe was formerly at Microsoft, working on hydrogen applications for data center power, but he admits that vehicles will use hydrogen first: "Transportation is going to be much, much larger than the footprint of data center usage for a long, long time," says Monroe.

Even for smaller vehicles powered by batteries, hydrogen could have a support role: "One of the most important applications for hydrogen could be in electric vehicle fast charging stations."

Fast charging stations in remote areas have to store energy to charge cars up fast. Companies including General Motors and Plug Power have developed container-sized energy storage units, which contain hydrogen fuel cells.

Plug's system has an 18,000-gallon liquid hydrogen tank and a megawatt-scale fuel cell system that can provide over 60 megawatt hours (MWh) of energy quickly - enough to fast charge more than 600 electric vehicles.

"They can get the DC power that's needed, they can get the high voltage, they can get the high currents that they need - with no connection to the grid," says Monroe.

"Putting a fast charging station at a convenience store or a truckstop becomes much easier. You just drop a container down in the parking lot, and cars can get an 80 percent charge in 15 or 20 minutes and pay in the store. And once a week or every few days, a hydrogen tanker comes by and refuels the container."

For the minority of hydrogen vehicles, the same system could have a tap to take hydrogen directly: "That might be a way to start expanding the hydrogen vehicle fleet as well. Electric vehicle chargers will come first, and then the hydrogen cars will take their place where they're needed, for people who do long trips.

Alongside transportation, he thinks hydrogen power in data centers will eventually expand quickly: "As soon as products are available, and as soon as hydrogen is available, people are chomping at the bit to try and get things going."

Several data center operators are looking into hydrogen very seriously, although the switch over from diesel is not completely straightforward.

Gas storage takes a lot more room than liquid diesel tanks - and hydrogen can be a tricky gas to handle. It is the smallest atom in the universe, and H2 molecules are tiny. This means that pipes and tanks must have a high specification to prevent leaks.

And hydrogen gas distribution, as we shall see, is in its infancy.

Despite this, Microsoft is leading the way, testing a variety of ways to consume hydrogen at its facilities.

Data centers could be pushed to take up hydrogen faster, if diesel power becomes a risk factor for new data centers. For instance, Maryland recently denied exemptions for 504MW of diesel generators that Aligned had applied to place on a plot within Quantum Loophole's giant data center park.

Monroe thinks that this sort of decision means a lot of businesses may be "forced" into some kind of clean solution.

Government support

Hydrogen could become cheaper thanks to public-sector support. The US government has included hydrogen in the more than $500-billion investment package known as the Infrastructure, Investment and Jobs Act. "Billions of dollars are being put towards hydrogen hubs, hydrogen transport systems, storage research, generation of hydrogen, and subsidies on hydrogen," says Monroe..

The US Department of Energy (DOE) has a "Hydrogen Shot" aimed at reducing the price of green hydrogen from its current level of around $10 to $15 per kg, down to $1 per kg..

"At $1 per kilogram, you start to compete with hydrocarbons in terms of energy per dollar," says Monroe. He's optimistic the DOE will achieve its goal. Its previous "Sun Shot" in the 2010s aimed to get solar electricity down from $6 per Watt to a target of $1 per Watt by 2020 - and met the goal by 2016..

"I see the exact same kind of things going on in the hydrogen industry, in terms of the projects that are being announced, the companies that are involved, the governments that are subsidizing and funding and encouraging projects.".

The US currently has a $3 per kilogram subsidy for green hydrogen, he says: "So you just need to get the cost down to four bucks a kilogram and you'll see that hydrogen economy start to develop.".

Transporting hydrogen

But if the industry is going to use hydrogen, it must be available where it makes sense. Electricity is provided by a grid, while water and gas are piped where they are needed.

Hydrogen will be produced where there is a surplus of green electricity that can be used to run electrolysis plants. For instance, in Denmark, H2 Energy has ordered 1GW of electrolyzers from Plug Power to produce hydrogen from electricity generated in a giant offshore wind farm.

Getting that to industries wanting to use hydrogen will require a new infrastructure. Monroe says this will have to start from basics: "In the beginning, hydrogen will mostly be transported by truck."

That's not a surprise, he says, because hydrogen's physical profile, and its early applications, is so similar to those of oil.

"Where I live near Denver, we have a lot of scattered oil drilling developments, and I have this picture of the hydrogen transport system developing the way the oil transport system has developed over the last 30 or 40 years," he says.

"They start with a promising well site, they make it a producing site, and then they begin to pull product out by trucks," he explains. "When there gets to be enough traffic, and the profits are high enough, they may have a rail spur line that goes to a central area, and then they transport by rail as much as they can, because that's cheaper."

Finally, he says, "over decades, they decide this is an area where we need a pipeline to a broader area. That can make the transport of the oil much, much cheaper. I think we'll see a progression like that in the hydrogen industry. But for now, almost all the transport plans I've seen for hydrogen hubs are truck based."

Eventually the hydrogen industry will have to get its product shipped where it is needed, just like other industries: "If you remember when Tesla first started manufacturing in the US, they knew that one of the biggest problems was there weren't enough charging stations. So, along with rolling out the vehicles, they paid for charging stations. They knew that they needed to get the distribution network widespread enough that you could travel from California to New York in the US using an electric car."

He says: "I think you'll see the same thing in hydrogen. These hubs will be center points for the creation of green hydrogen and transport of green hydrogen. And then, as more demand builds around those hubs, the plans will expand out.

And eventually, it will go into pipelines.

The reliability of pipes

If hydrogen is available on a network of pipes, then it could become a very serious contender for reliable backup, or even primary power for data centers. Some data centers are already looking at natural gas that way despite its carbon intensity. Hydrogen from a pipe could potentially be a reliable green power source,

"The natural gas network is 10 times more available than the electrical grid," says Monroe. This may be counter-intuitive, but it's based on the fact that gas is physically pumped into the system under pressure, and the pipe system effectively act as an energy storage system in itself.

"In the event of a failure on the natural gas grid, you have pressure in the system still, and systems will continue running for some time, until the pressure gets too low," he explains.

But there's a problem: when hydrogen starts to get into pipelines, things can get political.

Pipeline politics

There is already a widespread network of pipes distributing natural gas. Sadly, these can't be switched over completely to hydrogen because, as we noted earlier, hydrogen has different properties.

Hydrogen's tiny molecules can permeate the metal of pipes and containers. This can potentially create leaks, but there's a more serious concern. Hydrogen atoms can penetrate the metal structure and affect the steel pipes' fatigue- and fracture-resistance properties, making them more susceptible to cracking.

Hydrogen also has a lower energy per unit volume than natural gas (note to alert readers: as we said earlier, hydrogen has more energy density by weight than natural gas, but it is much lighter).

This means that if it is put into a pipe system currently used for natural gas, the users on that system will get less energy from the gas they get - unless the pressure is increased to give a faster flow, which creates other problems for the pipeline operator.

Tests such as the US Hyblend initiative suggest that it is possible to blend hydrogen with natural gas in existing pipelines, in concentrations up to 20 percent.

The EU's policy seems to be suggesting the percentage should be kept between five and 10 percent, with an increase to 15 to 20 percent "towards the end of the decade."

In the UK, the Energy Networks Association (ENA) has said it can put 20 percent hydrogen into the gas grid from 2023.

Those in favor, including the UK's government-appointed "hydrogen champion" Jane Toogood, say this will help build critical mass for hydrogen use, and cut the carbon intensity of the nation's gas.

"Blending must be available by 2025 to unlock investment in hydrogen production," said Toogood, who is chief executive of catalyst technologies at chemical company Johnson Matthey. "Blending potentially aids investment, reduces emissions, enables supply and demand to be balanced, and facilitates early experience with hydrogen, including in the gas National Transmission System (NTS), subject to satisfactory demonstration of the safety case."

But the idea has faced significant opposition. A group including utility Octopus Energy, thinktank E3G, Greenpeace and Friends of the Earth said in a letter to the government, that the scheme would "greenwash" the fossil gas industry, and raise bills for consumers for a negligible level of decarbonization.

'Raising energy bills during a cost of living crisis is the wrong way to develop industrial demand for H2," said the group. The hydrogen available at the start will be a mix, including green hydrogen, but also a lot of "grey" hydrogen produced from natural gas and oil, so it won't decarbonize as much as is hoped.

Similar arguments have taken place in the European Parliament, but hydrogen advocates say we have to take up an option that improves what we have, rather than holding out for perfection.

Don't wait for perfection

"I have a problem with people that throw out a good solution because it's not perfect, right?" says Monroe. "I wouldn't disparage a 10 or 20 percent saving of carbon based on blended hydrogen, if it was available."

Part of this argument is about the uses of hydrogen. If it goes into consumer networks, it will be used for home and office heating, applications that are better served by electric heat pumps.

By contrast, heavy industries such as steelmaking have a huge need for heat that can't be delivered electrically, and their carbon intensity will be lowered by hydrogen at any percentage:

"Consumption in the heat generation industries is so large that even if we only knock off five or 10 percent of emissions through blended hydrogen, that's a huge amount of carbon that won't be generated," says Monroe.

"A steel mill could knock 10 or 20 percent off their carbon footprint by having a blended natural gas hydrogen solution for creating the heat that they need for their processes," says Monroe.

The use of hydrogen in the natural gas pipeline can become more sophisticated, however, because filters exist that can remove pure hydrogen from a blend of gases - because, as we observed earlier, hydrogen molecules are much smaller than the other gases involved.

"There's demand on both sides," says Monroe. "Some people want pure hydrogen for fuel cells, but there are also people that want pure natural gas, because they need the higher heat content. I think you'll have benefit on both sides if you get to separating the hydrogen at scale"

Blended hydrogen also benefits from the storage function of gas networks, "Research at UCI has shown that we cannot achieve high renewable power use without the features of hydrogen," says Jack Brouwer, University of California Irvine's professor of mechanical and aerospace engineering and director of the UCI-based National Fuel Cell Research Center.

Brouwer is leading a project to inject hydrogen into pipelines, and says: "The massive storage and resilient underground transmission and distribution of renewable energy that will be enabled by transformation of the gas system to renewable and clean hydrogen use will be investigated and advanced in this important effort."

Monroe agrees: "If you take 100 miles of natural gas pipeline with five percent hydrogen blended, that's a lot of hydrogen. And if you use it that way, the natural gas system has storage and transport. That'll advance hydrogen quite fast!"

Digging for hydrogen

Naturally occurring hydrogen, known as "white hydrogen" could boost the availability. "The optimistic view is that it's there in quantities that may be large. No one has ever really looked for it before, because we're always looking for oil," says Monroe.

The oil and gas industry tends to ridicule the idea, saying that if people are digging hydrogen from the ground, that's "just like we get oil, so why don't we just focus on oil from the ground?"

In Monroe's view, this is progress - "if they've raised the hackles of the oil and gas industry enough that they're paying attention even to just ridicule it, maybe there is something real to the hydrogen mining industry."

If it's there, it might be cheap to extract using existing techniques for natural gas: "It seems like a technology transfer would happen pretty quickly.

"It may be even cheaper than generating hydrogen by electrolysis, because I don't think you'll have the amount of capital equipment that you have with a wind farm or a large solar factory. "But like every other piece of the hydrogen industry, it will take some time to get to scale - and then we'll have the same transport problems."

Geopolitical hydrogen

Once the world can create and distribute hydrogen easily, it could shift the balance of power as new nations become energy rich.

"With the availability of wind and solar, and the ability to produce hydrogen as an energy storage medium, there could be a significant shift in who the real energy producers in the world are over the next 50 years or so," says Monroe. Australia's Woodside Energy has formed a plan with Singapore's Keppel to ship liquefied hydrogen from its H2Perth plant to power Keppel's data centers, because Singapore has very little green power of its own.

Other countries could do similar things: "Maybe this would be an opportunity for Sub-Saharan Africa to become dominant in an energy space. The equatorial countries will have an advantage because they have more sunshine hit them than any other spot on Earth, more reliably and more consistently throughout the year."

There have been experiments with floating PV panels: "Even the island nations could get into hydrogen production.

"It's going to be very interesting over the next 50 years. If hydrogen becomes a dominant fuel, then who are the energy providers around the world? It could be a significant shift from where it is today."