Green hydrogen may be the solution to a cleaner carbon-free future, or it may just be another bit of greenwashing from the fossil fuel industry that will make no real difference but let them carry on as normal. My initial hunch is that it's not a solution. Rough calculations and careful research also suggest that it's only a good idea if you want to keep selling gas and pumping oil out of the ground. Who on earth would want to do that?
In theory it sounds great. Hydrogen is literally floating around in the ocean and all we need to do is snip off those oxygen atoms. Then we can burn the hydrogen and it will just give off clean water.
Getting hydrogen out of water is simple: you just need to pass electricity through it. The molecules will break up, oxygen will bubble up from the anode and hydrogen will bubble up from the cathode. I tried that when I was a school kid, after hearing the squeaky pop in a science classroom. In practice it's not as easy as just taking the Os off the H2 atoms. Not everything that is simple is easy. To get electricity to pass through the water you have to add a bit of salt, otherwise it doesn't really conduct. This means you have sodium and chlorine in the mix and start getting some build up of chemicals and noxious gases coming off the electrodes. This was Ok for a little after-school science experiment but to do this on a larger scale there are more complications.
 |
| Picture from I mean Penn State University |
Actually it probably wasn't that good an idea for a child to do since you're also going to get some chlorine gas coming off the anode, which is deadly poisonous. The sodium ends up as sodium hydroxide which is highly corrosive, or can act as an insulating coating on the electrode. In fact electrolysis does not split the H2O into H2 and O; it actually splits it into H and OH, but I don't want to get into too much chemistry. My own experiment stopped working after a while, and I had to replace the electrodes. A large-scale application needs an electrolyte that will let the electrodes keep working without regular replacement or cleaning.
The most critical difference with the real world is that I wasn't worried about how much electricity I was using in my experiments. This was only a small fraction of our household use and my parents were paying the bill anyway—it would be at least ten years before I took an electricity bill seriously. And only a small fraction of that electrical energy was going into the splitting of those chemical bonds with most of it probably just warming up the water. I was really only interested in the squeaky pop when I burnt a small collection of hydrogen and not the amount of energy it would release when burning.
Energy is the biggest consideration if we're talking about Hydrogen for energy use in a real-world application. Chemical energy is all in the electrons and the energy required or released when a chemical reaction happens. So energy is required to split two hydrogen atoms from the oxygen atom. You get energy back when the two hydrogen atoms combine with an oxygen atom, but you will never get back all the energy you put in. Are you keeping track of all these inefficiencies?
Also, you need to collect and store the hydrogen, then transport it. It would be lovely to put the hydrogen into bags and send them floating to where they are needed. There was some experience with floating bags of hydrogen up to the 1930s which I will come back to later. More likely you'll need a compressor, which will use more energy but will make it easier to store in terms of space and perhaps easier to transport in gas bottles.
Quick reality check: the energy in the hydrogen is just in the electrons, and if you're thinking of transporting that hydrogen it may be a lot less efficient than just using electricity, which sends the electrons only. It's the difference between sending an email and printing out the email and sending it as a letter. When people say that hydrogen is the future of energy, you have to wonder whether letters are the future of communication.
Until now commercial hydrogen has not been made from electrolysis, it is produced by steam cracking fossil fuel gas, which is some combination of carbon and hydrogen atoms, and then throwing the carbon away, usually in the form of CO2. This is called "Grey Hydrogen" and produces more global warming gases than just burning the fossil fuel gas.
"Blue Hydrogen" is split from fossil fuels, but the carbon is captured, which in theory means there is no carbon. However, some of the carbon escapes rather than being captured, and since carbon-capture also uses energy, this still ends up being worse than just burning the fossil fuels in the first place. It's not as bad as grey carbon, but it's still worse than burning coal.
Some companies are also making electrolysers so renewable energy can be turned into "Green Hydrogen". This is probably going to produce less carbon than Blue Hydrogen, but it depends on the electricity being low carbon to start with, and I'm really not sure if it's better than sending the electricity over the existing grid, or putting it into batteries.
We haven't even talked about using the hydrogen yet. To be honest I can already see enough problems above to write off hydrogen as an energy source because it's going to use so much energy to make.
Hydrogen is a gas. Natural gas is a gas. So we can just use it the same way. Right?
Again there are a few problems to work out. Hydrogen has much smaller molecules than natural gas, so it has more chance of leaking. Also it's much more reactive, and will react with most kinds of steel so you need to make sure the pipes and cookers or boilers are free of steel.
Of course hydrogen does not produce Carbon oxides when burnt, which is great, but it can produce six times more nitrous oxides as it burns more of the nitrogen in the air. At a local level NOx are already much more dangerous pollutants than Carbon dioxide.
To summarise, conventional "grey" hydrogen is a carbon disaster. "Blue Hydrogen" produces more carbon than just burning the fossil fuels. "Green" hydrogen may be possible from renewable energy but is not likely to be very efficient. Different infrastructure and units will be needed to use hydrogen domestically or commercially instead of natural gas. For transport it will make most sense with fuel cells and electric motors. So why not just use batteries?
As for transporting hydrogen around the world, bags of hydrogen were floating around in the 1920s and 1930s. Airships may seem like a ridiculous way to travel, but the first round-the-world flight was in an airship, as was the first aircraft to clock up a million miles and the first scheduled transatlantic air crossings, which knocked days off the alternative ocean liners. Until the 1940s travelling a long distance by fixed wing plane would have seemed as realistic as travelling by space shuttle did in the 1990s.
A few high-profile airship accidents helped bring down the airship as the future of long-distance transport, but in the end it was probably the second world war that brought their era to an end. Switching from hydrogen to helium would have made the airships much safer, but the airship technology was mostly in Germany and trade became difficult with the United States which had all the helium. More critically, the war came and a fight between a fixed-wing plane and an airship is something like a fight between Mike Tyson and a piece of damp tissue paper, so technical development went into aircraft of increasing speed and size. The passenger jets that arrived after the war resulted from developments that were driven by the need to fight and flee more quickly and to carry more and larger bombs.
Back in the 1920s when the R100 was being designed, they considered using an engine that could switch between diesel and hydrogen. Airships usually got their lift from hydrogen and their thrust from diesel engines. As a journey went on the diesel would burn away and the airship would get lighter. In order to descend they would need to release some hydrogen. Rather than throwing it away, it would make more sense to burn the hydrogen in one of the engines.
They did not develop hydrogen engines even when they were literally carrying around bags of hydrogen that they were going to throw away. There is some evidence that we are much cleverer now and could easily come up with hydrogen engines, but I don't think the evidence is very strong.
Energy is the biggest consideration if we're talking about Hydrogen for energy use in a real-world application. Chemical energy is all in the electrons and the energy required or released when a chemical reaction happens. So energy is required to split two hydrogen atoms from the oxygen atom. You get energy back when the two hydrogen atoms combine with an oxygen atom, but you will never get back all the energy you put in. Are you keeping track of all these inefficiencies?
Also, you need to collect and store the hydrogen, then transport it. It would be lovely to put the hydrogen into bags and send them floating to where they are needed. There was some experience with floating bags of hydrogen up to the 1930s which I will come back to later. More likely you'll need a compressor, which will use more energy but will make it easier to store in terms of space and perhaps easier to transport in gas bottles.
Quick reality check: the energy in the hydrogen is just in the electrons, and if you're thinking of transporting that hydrogen it may be a lot less efficient than just using electricity, which sends the electrons only. It's the difference between sending an email and printing out the email and sending it as a letter. When people say that hydrogen is the future of energy, you have to wonder whether letters are the future of communication.
Until now commercial hydrogen has not been made from electrolysis, it is produced by steam cracking fossil fuel gas, which is some combination of carbon and hydrogen atoms, and then throwing the carbon away, usually in the form of CO2. This is called "Grey Hydrogen" and produces more global warming gases than just burning the fossil fuel gas.
"Blue Hydrogen" is split from fossil fuels, but the carbon is captured, which in theory means there is no carbon. However, some of the carbon escapes rather than being captured, and since carbon-capture also uses energy, this still ends up being worse than just burning the fossil fuels in the first place. It's not as bad as grey carbon, but it's still worse than burning coal.
Some companies are also making electrolysers so renewable energy can be turned into "Green Hydrogen". This is probably going to produce less carbon than Blue Hydrogen, but it depends on the electricity being low carbon to start with, and I'm really not sure if it's better than sending the electricity over the existing grid, or putting it into batteries.
We haven't even talked about using the hydrogen yet. To be honest I can already see enough problems above to write off hydrogen as an energy source because it's going to use so much energy to make.
Hydrogen is a gas. Natural gas is a gas. So we can just use it the same way. Right?
Again there are a few problems to work out. Hydrogen has much smaller molecules than natural gas, so it has more chance of leaking. Also it's much more reactive, and will react with most kinds of steel so you need to make sure the pipes and cookers or boilers are free of steel.
Of course hydrogen does not produce Carbon oxides when burnt, which is great, but it can produce six times more nitrous oxides as it burns more of the nitrogen in the air. At a local level NOx are already much more dangerous pollutants than Carbon dioxide.
What about vehicles?
Using hydrogen in an internal combustion engine is also not impossible, as long as you first get over those issues of leakage, reaction and pollution. Since internal combustion engines are not very efficient it turns out to be much better to use a fuel cell to turn hydrogen and oxygen back into water and release electricity, then use an electric motor. If you have an electric motor, please remind me why we're not just using a battery? We have battery technology, and there is already a grid to get it around wherever people go, and connect it to sources of renewable energy. And you would probably want a small battery at least in your vehicle to handle some energy recovery braking with the electric motors.To summarise, conventional "grey" hydrogen is a carbon disaster. "Blue Hydrogen" produces more carbon than just burning the fossil fuels. "Green" hydrogen may be possible from renewable energy but is not likely to be very efficient. Different infrastructure and units will be needed to use hydrogen domestically or commercially instead of natural gas. For transport it will make most sense with fuel cells and electric motors. So why not just use batteries?
A few high-profile airship accidents helped bring down the airship as the future of long-distance transport, but in the end it was probably the second world war that brought their era to an end. Switching from hydrogen to helium would have made the airships much safer, but the airship technology was mostly in Germany and trade became difficult with the United States which had all the helium. More critically, the war came and a fight between a fixed-wing plane and an airship is something like a fight between Mike Tyson and a piece of damp tissue paper, so technical development went into aircraft of increasing speed and size. The passenger jets that arrived after the war resulted from developments that were driven by the need to fight and flee more quickly and to carry more and larger bombs.
Back in the 1920s when the R100 was being designed, they considered using an engine that could switch between diesel and hydrogen. Airships usually got their lift from hydrogen and their thrust from diesel engines. As a journey went on the diesel would burn away and the airship would get lighter. In order to descend they would need to release some hydrogen. Rather than throwing it away, it would make more sense to burn the hydrogen in one of the engines.
They did not develop hydrogen engines even when they were literally carrying around bags of hydrogen that they were going to throw away. There is some evidence that we are much cleverer now and could easily come up with hydrogen engines, but I don't think the evidence is very strong.
References
Hydrogen: Get-out-of-Jail-free card for the building industry?https://energymonitor.ai/tech/built-environment/building-insulation-is-hydrogen-our-get-out-of-jail-free-card?s=03
"the greenhouse gas footprint of blue hydrogen is more than 20 percent greater than burning natural gas or coal for heat and some 60 percent greater than burning diesel oil for heat,"
https://onlinelibrary.wiley.com/doi/full/10.1002/ese3.956
"Two European studies have found that burning hydrogen-enriched natural gas in an industrial setting can lead to NOx emissions up to six times that of methane"
https://www.cleanegroup.org/hydrogen-hype-in-the-air
ITM power is set to leave blue hydrogen in the dust by producing electrolyers as cheap as £500,000 per Mega Watt. (This compares to the cost of solar panels at around £700,000-£1.3 million per Mega Watt
https://www.rechargenews.com/energy-transition/green-hydrogen-itm-power-s-new-gigafactory-will-cut-costs-of-electrolysers-by-almost-40-/2-1-948190
