On Cleaning Up this week, Michael Liebreich is joined by David Cebon, Professor of Mechanical Engineering at the University of Cambridge. Professor Cebon has spent more than a decade researching sustainable solutions for the transportation industry. Cebon is a systems-thinker, however, and offers Michael a breadth of insight beyond the confines of the industry, especially on the UK’s likely path to net zero. Chiefly though, Professor Cebon is a vital voice in divining the role, small or large, of hydrogen in a green future.
Below are edited highlights of the discussion, condensed for brevity.
Michael Liebreich One of the things I enjoy about your work is that you take a whole system approach.
David Cebon I think that when you look at decarbonisation, and the energy transition in general, it's essential to take a system view. It's very easy to say, here's a really fabulously clean solution when we look at it through this sort of window, and then if you look at it in the wider sense, you discover that it's actually terrible. That's definitely the case with hydrogen; just from the point of view of an individual vehicle, it looks like a pretty good decarbonisation solution. But the carbon footprint of hydrogen manufacture is what kills it from my point of view.
ML Let's take that system thinking as a starting point. What does the UK energy system look like in a net zero future?
DC To decarbonize the UK's economy, we really need to electrify everything that can possibly be electrified. Certainly, the big elephants: transportation - ground transportation - and heating. If you don't electrify those, you end up with really dramatically increased energy demand. The challenge with a renewable energy mix is getting electricity supply and demand to match. To do that, I think we'll do a few different things. The first is that we'll over-build some renewables, and we will curtail. The second is increase demand management. There's some great examples of that like Octopus, where the electricity industry can manage demand and manage pricing. The third thing is we will have to have some storage; to solve this particular problem of day-to-day fluctuation of supply and demand, the amount of storage needed is not that high, and can be achieved using a combination of technologies. One approach that's been proposed is to build salt caverns and fill them up with hydrogen. My calculation is that would take something like 160, 500,000 cubic metres salt caverns, running at 200 bar. I think it's a ridiculous concept.
ML So now you're going to tell us what we should do instead?
DC I am going to tell you what we should do instead. What I've said so far doesn't account for the fact that our electricity demand is going to increase dramatically. And we will need a lot more electricity in the summer to power heat pumps. The answer is to import the energy using high voltage DC interconnects. If you do that, at the current electricity consumption rate, eight or ten gigawatts is perfectly doable. From an energy security perspective, it’s not perfect, but it would be a way better solution than what we've currently got. For doldrum days of low wind and solar, you keep your combined cycle gas turbines, in a form where you can spin them up, if necessary. My opinion is that that's a far better thing to do than spinning up a whole big hydrogen economy. If the perfect solution is to completely switch off all fossils as quick as we possibly can, and to fire up this hydrogen economy in order make that work, it will make things much worse. Decarbonizing everything is important, but the problem now is not the last few percent. The argument that we have to focus on hard to abate sectors is ridiculous – let's get the easy to abate sectors done! And that means heating and transport get electrified. Let's deal with the dunkelflaute by just keeping those CCGT's available if we need them, and do everything else by electricity as quickly as we can.
ML Let's stay at the system level and talk about hydrogen. What is hydrogen going to be doing?
DC If politicians want to do something, right now what I would say is make that grey hydrogen that's being used for fertiliser green, because there is no alternative to that. While there's controversy about heat pumps and transport, there can be no controversy about green hydrogen for fertiliser. One of the possibilities for steel reduction is hydrogen; it's not the only one, but it seems to be a front runner at the moment. I don't believe in hydrogen for aviation, I believe in drop-in replacement fuels, so sustainable aviation fuel or biofuel are the two possibilities. If I was king of the world, I would say I would reserve the biofuels for shipping, which is much more cost constrained. If you've got a choice of where you use a biofuel, it would be better off in shipping.
ML I want to move on to hydrogen production. Is it all green?
DC It’s nice to talk about green, but then you're talking about dedicated, new renewable assets. When you build those, if you use it for making hydrogen, the opportunity cost is decarbonizing the rest of the electricity grid. It's important to consider the average carbon intensity of the grid when you're thinking about the future. At the scale that people are talking about, for hydrogen, it's a really massive amount of green electricity needed... you can't build that massive amount of electricity and also do all the other stuff we've been talking about decarbonizing. If you wanted green hydrogen for heating in the UK, you would need an installed capacity of 385 gigawatts. Now, that's about 10 times the current average electricity demand of the country. That's just to heat homes using green hydrogen boilers, because of all of the losses in that chain. Now, the heat pump, on the other hand, is a miracle of modern engineering, so you just need enough electricity to run those heat pumps; I think that the total installed capacity is about 60 gigawatts of offshore wind turbines. It's a sixth of what you need for the hydrogen route.
ML David, we have to talk about transport and trucks. There are a lot of people saying the heavy goods vehicle is the absolute natural use case for hydrogen. What do you say to that?
DC. The first thing is the hydrogen truck costs twice as much as an electric truck. Why is that? They're both actually battery electric trucks. The difference between them is that the electric truck has a bigger battery; the hydrogen truck has a hydrogen fuel cell, hydrogen tanks, hydrogen delivery equipment - all expensive and actually rather heavy. So just at current prices, you can go and buy a 44 tonne truck and it'll cost you £300,000 - the battery electric version - £600,000, in a hydrogen fuel cell version. So, on capital cost, you're at about double, on energy costs, you're at about three times, because of the inefficiencies of using hydrogen. When you look at the simple thermodynamics of converting renewable electricity to hydrogen and running it in a fuel cell vehicle, you end up with about a quarter of the energy you started with. You go through electrolysis, compression, transportation, fuel cell, drivetrain.... With an electric vehicle, you end up with about 70%. The question is, can you do UK current logistics without time penalties with electric vehicles? We've concluded that it is perfectly possible to do all current UK logistics using battery electric vehicles by charging at rest stops and warehouses. Given that, there's no incentive to buy hydrogen powered vehicles, which have much higher capital costs and much higher running costs.
ML I would love to have you talk about the catenaries - so this is charging on some of the major motorways of the UK, and they're going to look like tramways. Your calculations are that it makes a whole lot of economic sense?
DC The basic kind of technology that we're talking about is the sort of system that is used to power trams and trolleybuses in cities. It's the most efficient way that you can power a vehicle; nearly 80% of the electricity ends up at the wheels, which is fabulous. So, the carbon emissions are the smallest, the battery sizes are the smallest, and that's highly beneficial because of constraints on the battery supply chain, and it's the cheapest thing you can do to the truck. You take this battery electric platform with a small battery, and you put a £10,000 pantograph on the roof. That's a very low cost addition. Because of its energy efficiency, the Treasury can raise revenue through electricity sales, to account for some of the diesel tax that they won't be getting. So, rather than subsidising hydrogen, they're generating revenue from electricity sales from the same vehicles. The total cost of installing such a system on the UK's motorways would be about £20 billion. £20 billion pounds sounds like a huge amount of money. But you can compare it with £28 billion, which is the Department of Transport's budget for roads for the period 2020 to 2025. It's well within the realms of a practical project.