How Clean is Hydrogen, Actually? With Prof. David Cebon | The PLUS Podcast

Green hydrogen electrolysis is approximately 75% efficient in energy conversion, but when that electricity (work) is converted to hydrogen (heat) and then back to electricity via a fuel cell (~50% efficient), and accounting for compression and transportation losses, the round-trip efficiency from electricity to hydrogen to electricity in a fuel cell vehicle is approximately 30%, meaning 70% of input energy is wasted.

“Electrolysis process itself is about 75% efficient... But heat is not nearly as good as work... the round trip from electricity to hydrogen and back to electricity again, which is what you have to do if you want to run in a fuel cell vehicle, that is at best about 30% efficient. You've lost 70% of the energy”

Using a heat pump to heat homes is 6 times more efficient than using green hydrogen: a heat pump delivers ~300 kilowatts of heat per 100 kilowatts of renewable electricity input (via 3-4x coefficient of performance from work-to-heat conversion), while green hydrogen delivers only ~50 kilowatts of heat (due to 75% electrolysis efficiency, 50% fuel cell efficiency, and transport/compression losses), requiring 6 times more offshore wind turbines for equivalent heating via hydrogen.

“if you take you could take your your your um renewable electricity. If you go via a heat pump route... you generate three times what you started with. So, that's brilliant. If you go the hydrogen route... by the time you get to all of that, you've got about uh the amount of heat that you come that comes out is about half of the amount of electricity. So, if you started with 100 kilowatt hours of renewable electricity, the heat pump gives you 300. Right. The hydrogen route gives you 50... you need six times more offshore wind turbines if you want to heat countries' homes with green hydrogen than if you just use electricity in a heat pump.”

Burning hydrogen in home boilers or cookers produces significantly higher nitrous oxide (NOx) emissions than burning natural gas (methane) because hydrogen burns at higher flame temperatures, exacerbating indoor air quality problems and asthma risk.

“it's highly explosive. It's much higher much more explosive than gas. Uh generates higher NOx emissions... we've got these problems of nitrous oxides generated when you burn gas in the home in a boiler or a in Right. on a gas cooker, much much worse, higher flame temperature, much much worse NOx emissions from burning hydrogen... the problems of asthma and air air quality in the home is much worse.”

Blue hydrogen production from natural gas requires 40% more feedstock than would be needed if the same energy were delivered as natural gas directly, because carbon carries most of the chemical energy in methane (CH4), and when carbon is stripped off and stored, the remaining hydrogen is a much lower-energy fuel.

“when you take that methane, the CH4, the natural gas, when you strip the carbon off it, it's actually the carbon that carries most of the energy. It's not the hydrogen that carries the energy... when you strip the carbon off, you end up in a much lower energy fuel... you need a lot more if you want to deliver the same amount of energy at the end, you need a lot more methane if you're going to deliver it by hydrogen... it's something like 40% more.”

Delivering hydrogen to filling stations requires 18 tube trailers at 700 bar pressure to carry the energy equivalent of one standard 44-ton diesel fuel tanker, making daily refueling of filling stations economically impossible (1 diesel tanker per day becomes 18 hydrogen trailers per day) and demonstrating why hydrogen infrastructure is fundamentally non-viable.

“if you want to carry the same amount of energy in hydrogen... at 700 bar... How many how many tube trailers do you reckon you need... I'm going to say three... Well three would be a good number but actually it would be wrong by a factor of six. So the true number is 18... If you've got 18 tankers a day... That isn't going to work.”

On-site hydrogen electrolysis at every filling station would require 3 times more electricity grid connection capacity compared to battery charging infrastructure at the same location, making grid investment for hydrogen even more expensive than for battery electric vehicles.

“every vehicle you need three times more electricity to do that than to just charge the batteries in the first place. So now you need three times the size of grid connection at every one of those points if you're going to electrolyze water to make hydrogen compared to if you're going to just charge batteries, right?”

All hydrogen produced globally today is made on-site at the point of use (ammonia factories, petrochemical plants, refineries) because engineers have learned over decades that moving hydrogen is 'next to impossible,' making industrial hydrogen transport a solved negative—the technology avoids it by design.

“All hydrogen today is made right at the point of use because it's so difficult to transport it. It's made right at the ammonia factory fertilizer factory. It's made right at the petrochemical plant. And that's because engineers over decades and decades have learned that moving hydrogen is next to impossible.”

Blending hydrogen into the gas grid at typical 20% maximum concentration only dilutes the energy content (like adding water to petrol) and yields only a 6% reduction in carbon emissions, while simply operating existing boilers at proper condensing temperatures achieves far better than 6% emissions reductions—making hydrogen blending a complete waste of effort.

“when you put hydrogen into the gas grid you're actually diluting the energy content. It's like putting water in your petrol tank. Right. It gives you something which is much lower quality... even if you put 20% hydrogen into the gas grid it only gives you 6% reduction in carbon emissions. Right. We get much better than 6% reduction in carbon emissions just by running our boilers at a at at a proper condensing temperature.”

Steel production via hydrogen reduction (replacing coking coal as the reducing agent to convert iron oxide back to iron) represents a major industrial hydrogen application because steel production is ~7% of global carbon emissions and is currently dependent on fossil fuels.

“in the steel industry, um you have to uh when if you take a piece of steel and you put leave it out in the out in the rain, it it goes rusty... To turn rust back into iron, you have to do the opposite of oxidation, which is called reduction. And that reduction process uh is typically done with coking coal. Now, it can be done using It can be done electrically. Possibly. So-called uh uh But most likely it it it will be done with hydrogen... the iron industry the steel industry is about something like 7% of global carbon emissions. That's as big as the total trucking industry.”

Electrification is the one clear solution that works across sectors (transport, heating, industrial processes where feasible) and should be prioritized absolutely, with hydrogen reserved only for specific chemical applications where no electrification alternative exists.

“We absolutely shouldn't delay electrification. Electrification is the one thing that we can really do to help this energy transition. Right.”

The only legitimate uses of hydrogen in the energy transition are as a chemical (not fuel) in ammonia production (~1% of global emissions), steel production (via reduction of iron oxide, ~7% of global emissions), and petrochemical processes, where fossil hydrogen must be replaced with green hydrogen but hydrogen serves chemical functions, not energy delivery.

“the very first one is fertilizer as we mentioned, and it's you know, it's 1% of the world's carbon emissions... Fertilizer is going to be made from ammonia. There is no choice... Another interesting one is the steel industry... the steel industry is about something like 7% of global carbon emissions... cleaning up the existing hydrogen and and and chemical processing physics for example for steel. Some other industrial processes. There's no shortage of business. Uh but when you As soon as you start to use it as a fuel for heating or for driving trucks, it becomes it suffers from all those terrible inefficiencies.”

Hydrogen blending into gas infrastructure is marketed as a bridge solution but is actually a stalling tactic: even at maximum feasible 20% concentration, it only yields 6% emissions reductions, whereas simpler efficiency measures (operating boilers at condensing temperature) achieve greater reductions without capital expense.

“it doesn't make sense for um the population. And particular the particular problem is First of all, first of all, you get you got to get it to homes... even if you put 20% hydrogen into the gas grid it only gives you 6% reduction in carbon emissions. Right. We get much better than 6% reduction in carbon emissions just by running our boilers at a at at a proper condensing temperature than you know if we just all set our boilers properly you get way better than 6% reduction in emissions.”

Hydrogen is used in petrochemical refining to treat oil products via hydrogenation (adding hydrogen to fuel molecules) and is typically made on-site in the refinery, not transported, and as refinery demand for hydrogen decreases (due to fewer petrol and diesel cars), the existing hydrogen infrastructure becomes stranded capacity.

“hydrogen is actually used in the refining of crude oil into diesel and petrol... hydrogen is typically made on site in the refinery. Uh it's not taken anywhere. It's It's made there and then, and it's used to process the uh the petrochemical products... hydrogenation. It's exactly mixing hydrogen with uh with the fuel.”

Hydrogen is colorless and odorless, so hydrogen leaks in homes are invisible and undetectable by smell, making hydrogen gas grid lines and boilers a safety hazard because leaks cannot be easily identified before they cause hydrogen explosions.

“It it's uh it's colorless and odorless and uh uh you can't see it burning. Uh it's highly explosive.”

Hydrogen molecules are extremely small and readily permeate steel and cast iron pipes, causing hydrogen embrittlement (making metal brittle as hydrogen enters cracks), so existing gas infrastructure cannot be reused for hydrogen and would require complete replacement with specialized materials.

“the hydrogen molecules are the smallest. They're you know, very very small molecules and they get through everything. They do uh steel uh gets what's called hydrogen embrittlement. It becomes very brittle as a result of hydrogen uh getting into the cracks... Most cast iron and steel pipes can't be used. So, they have to be replaced.”

Using green hydrogen instead of direct electrification requires 3 to 5 times more renewable electricity generation capacity because the 70% energy loss must be compensated by building additional wind turbines or solar panels, making hydrogen economically uncompetitive when renewable capacity is limited.

“you have a situation where if you want another kilowatt hour of electricity, you have to have another kilowatt hour of of offshore wind turbine or or solar panel... if you waste electricity, if you waste energy, you have to build a lot more of that renewable capacity, right? So, um in uh you know, the hydrogen process is a very inefficient. It means that you need three, four, five times more renewable electricity if you're going to do green hydrogen than if you just electrify in the first place.”

Green hydrogen is promoted as a 'smoke screen' because the renewable electricity required for large-scale green hydrogen production is economically and practically not viable, and every unit of renewable electricity used for hydrogen is electricity not available for direct electrification, making green hydrogen marketing primarily a delay tactic.

“Green hydrogen is a little bit of a smoke street scheme smoke screen in my view because it requires so much energy that um Yeah. it's not really practical... if you build a new wind turbine for the purpose of making hydrogen, then it's It's being used for decarbonizing the electricity grid. It is not being used for decarbonizing industry or for running electric vehicles or for running homes and whatever. So, there's a kind of an opportunity cost.”

Making hydrogen currently generates about 2% of the world's carbon emissions, which is roughly equivalent to the total emissions from all aviation combined.

“2% of the world's uh carbon emissions comes from making hydrogen, mostly Right. from from gray from this sort of hydrogen... So, making hydrogen currently generates about the same emissions as making aviation. As as as flight as all flights.”

Hydrogen fuel cell cars do not solve air pollution—they emit only water vapor while driving—but the infrastructure paradox and market failure make them commercially non-viable, whereas battery electric vehicles have solved the market competition decisively.

“if I'm cycling along a road in a city and a hydrogen fuel cell car overtakes me, I'm very happy. Because what's coming out of it is some water and or an electric car. But I'm very unhappy when a diesel car overtakes me because then I've got to breathe in the fumes... They were all great. There was nowhere to refuel them. They're incredibly expensive, but they as cars, they were fantastic.”

Carbon capture and storage (CCS) technology has been promoted for decades with claims of imminent deployment ('it will be rolled out in the next 5 years') but has never achieved significant real-world scale or economic viability, and without economic incentives to operators, CCS adoption remains negligible despite decades of policy discussion.

“I did a We did an episode about carbon capture and storage... in 2012... they were talking about this will be rolled out in the next 5 years... it hasn't ever worked... hasn't happened for decades. People have been talking about this for decades.”

The Zappi charger enables solar-powered electric vehicle charging by capturing excess solar energy that would otherwise feed into the grid and directing it into the vehicle, allowing solar-powered miles without grid electricity and eliminating most electricity costs for vehicle charging when solar is available.

“Zappi charger is a really simple charger. You stick it on your wall and you plug it in and if you're if you've got solar panels, you can take just the solar panel solar power that would have gone into the grid and you put it in your car. It's as simple as that. I reckon I've done about 12,000 miles of charging. So 12,000 miles worth of electricity just from solar just this year that I put into our electric cars.”

The fossil fuel industry actively lobbies for hydrogen (both green and blue) to maintain future markets, with blue hydrogen being particularly attractive because it requires 40% more natural gas feedstock than would be used if the same energy were delivered as gas directly, making hydrogen a rescue lifeline for an industry facing declining demand from electrification of transport and heating.

“when you hear people talk about hydrogen, unfortunately, you have to say, 'Well, this is the fossil fuel industry talking.' because it is. Uh the fossil fuel industry is lobbying very hard for hydrogen... They really want blue hydrogen... the fossil fuel industry's got a problem, right? Because we're no longer going to be powering cars with fossil fuels... all that's we think going to go electric. And so, the fossil fuel industry has got no market. But now, of course, if you can have hydrogen and you sell 40% more gas, that is like a that's a a real blessing for a fossil fuel industry that that is has got problems on the horizon.”

Hydrogen production via reforming of natural gas (gray and blue hydrogen) requires applying very hot steam to methane (CH4), causing hydrogen molecules to separate from the carbon, which is then oxidized to CO2—a process that generates 2% of the world's carbon emissions when CO2 is vented (gray hydrogen).

“if you take uh natural gas and you treat it with very hot steam, then hydrogen comes out of that and carbon dioxide comes out. So, what you're doing is natural gas is methane, which is uh uh its chemical s- chemical name it is its chemical symbol is CH4, which means it's got one carbon atom and four hydrogen atoms in a molecule of methane. So, when you treat it with hot steam, the hydrogen goes off one way and the carbon gets bonded to oxygen and goes off as carbon dioxide.”

A heat pump is thermodynamically superior to hydrogen heating because it uses electricity (work) to move heat, achieving a coefficient of performance of 3-4x (delivering 3-4 kilowatts of heat per kilowatt of electricity input), exploiting refrigeration cycle advantages that hydrogen-based heating cannot match.

“the thing about heat pump is that it's um it it can pump about three or four times more heat than the energy it uses. So, if you put in 1 kilowatt 1 kilowatt into a heat pump, you get three or four kilowatts of heat into your house. Right. That's fabulous, right?... You're putting in 1 kilowatt of work, that electricity, which is work... and you're getting three kilowatt hours three kilowatts of heat.”