While researching a previous story about hydrogen trucks, I came across several references to the work of Dr. David Cebon. He’s a professor of mechanical engineering at Cambridge University in England and a fellow of the Royal Academy of Engineering. What further attracted me to David was his trucking background.
He is director of the Cambridge Vehicle Dynamics Consortium and the Centre for Sustainable Road Freight. He leads Cambridge University Engineering Department’s Transport Research Group.
Further, he has authored or co-authored more than 150 peer-reviewed papers on dynamic loads of heavy vehicles, road and bridge response and damage, advanced suspension design for heavy vehicles, heavy vehicle safety and mobility, heavy vehicle fuel consumption and the micromechanics of asphalt deformation and fracture.
He earned his PhD in the early 1980s looking at road damage caused by trucks. He has studied many different aspects of heavy vehicle dynamics and performance, and for the past 15 years or so, he has been focused on fuel consumption, emissions, and productivity.
“I was always interested in productivity,” he told HDT. “One of the things that I've worked on heavily over the years is long combination vehicles and high-capacity vehicles, which is one of the greatest ways to improve fuel consumption.”
In short, unlike a lot of academics and researchers, he knows trucks like he knows the back of his hand.
He also has very strong opinions on the use of hydrogen as a heavy-truck energy source: he doesn’t like the idea, and he’s got strong and well-reasoned arguments against it. We are presenting only his side of the story here. We welcome opposing points of view. Please contact the author, or chime in the comments, if you’d like to share your thoughts on the matter.
Hydrogen: Not the Perfect Fuel for Trucks
There are several inherent problems with hydrogen, Cebon says. Each one could technically be a deal breaker without willfully ignoring the fundamental questions surrounding its use.
The first is efficiency. Cebon says the process of electrolyzing water to produce hydrogen, compressing and transporting it, running it through a fuel cell to produce electricity to drive to motors is only about 25% efficient.
He says, for example, if you start with 100 kWh of electricity for electrolysis, the energy contained in the hydrogen you have produced is only 75% of what you started with. When you combine that with the roughly 50% efficiency of a fuel cell, you’re now down to about 37.5% of the energy you started with. When you factor in the losses from compression, transportation, and the motors themselves, Cebon says the energy yield to the wheels is about 25% of the initial 100 kWh.
“You throw away 75% of the energy you start with as heat into the into the environment,” he says. “From the 100 kilowatt hours you started with, you have only 25 kWh left to drive your truck.”
That’s physics. There’s no arguing with that. Though you might gain few percentage points here or there allowing for advances in technology, you’re still looking at huge losses in the conversion process.
It’s one thing to talk about efficiency, but at the end of the day, somebody still has to pay for that 100 kWh of energy, even though you’re only using 25% of what you’re paying for.
“This means that your 25 kWh of electricity is actually costing you about four times more than it would have otherwise,” he says.
In comparison, the energy conversion losses in a battery electric chain are much less. It’s on the order of 70-75% efficient, wire-to-wheel, so to speak. The efficiency ratio between a battery powered truck and a hydrogen powered truck is about three to one (3:1).
“That means you’ll need three times more electricity to start with for a hydrogen vehicle than an electric vehicle,” Cebon claims. “So, the arithmetic is, to power your hydrogen truck per mile will cost you three times more than it will cost you to power an electric vehicle.”
And that’s just factoring the cost. The upstream implication is, by extension, we will need three times as much renewable generating capacity to make up for all the conversion losses. That’s three times as many windmills or solar panels or hydroelectric generating capacity. You’ll also need three times as much land for all those windmills and solar panels, three times the capital cost for all those turbines, three times the maintenance cost, etc.
“A factor of three is a lot,” he notes. “Hydrogen trucks will cost up to three times as much to power as a battery truck.”
Capital Costs of Fuel-Cell Trucks
The next significant barrier to fuel-cell trucks is the capital cost. He notes that BEVs and FCEVs are fundamentally the same: they both have electric motors, invertors, batteries (though the FCEV battery is considerably smaller), controllers, and such. With the FCEV, you also have the fuel cell, the hydrogen storage tanks, and a bunch of what he calls delicate and expensive equipment.
“Fuel cells are full of platinum,” he points out. “And because hydrogen is such a difficult material to work with [owing to the tiny size of the molecule], the seals and the materials in the system have to be good enough to prevent leakage at extremely high pressures.”
We all know these advanced trucks will be more expensive, but nobody is sure exactly how much more because much of the actual cost is hidden by subsidies at this point. And to be fair, we don’t have really accurate predictions on how far the cost will come down once manufacturing scale is achieved. That said, Cebon and his research team at Cambridge University’s Engineering Department recently put out tenders to buy a small fleet of BEV and FCEV trucks for field tests.
“That forced the OEMs to actually give us quotes for the price of vehicles,” he says. “And that's important, because up till now, it's just been speculation what the price would be at the point where you say, we're actually going to buy it, you have to deliver it on a certain date. That's a different deal. Now we have to have a real price.”
The price he was quoted by several European truck makers for a 600 kWh battery electric truck delivered in the UK was £250,000 to £300,000 (US $310,000 to $375,000). The quoted price of the fuel cell trucks was £600,000 (US $745,000).
“If you wanted to buy a hydrogen truck today in the UK, it will cost you double what the battery electric truck would cost, and three times the energy costs to run it,” he says.
Clearly, based solely on price, most fleets wouldn’t opt for a fuel cell truck if a battery truck will do the job.
Cebon and his team have concluded, based on analysis of “tens of thousands” of truck journeys around the UK, “there's really no logistics in the UK that you can't do with a battery electric vehicle charging when the opportunities present themselves during the day.”
As he sees it, trucks will have charging opportunities during statutory driver rest stops (45 minutes off following 4.5 hours of driving), and at depots and warehouses when picking up or delivering loads.
“If you can fast charge on the dock while loading and unloading, you can get at least a half-way to a full charge in that period,” he estimates. “So, if you use those opportunities in the logistics day to fast-charge, you can run all UK logistics on a battery electric vehicle.”
Here’s where Cebon’s calculus gets a bit murky.
He readily acknowledges logistics in the UK is significantly different from the way we do trucking here in the United States. For one thing, at about 50,000 square miles England has roughly the same land mass as the state of Alabama — but 10 times the population density. That means more, but shorter trips are required to satisfy the logistics needs of that population.
Here, short-haul and regional service is a significant percentage of our trucking operations, but long-haul is a factor and it’s not going away. Hydrogen trucks are often positioned as the long-haul alternative to diesel.
That’s a whole other conversation. Sticking with the hydrogen theme for the time being, Cebon says there are still more concerns about hydrogen that make is a less than attractive option.
Hydrogen’s Carbon Footprint
Yes, you read that right. Certain sources of hydrogen production produce enormous quantities of CO2 — the greenhouse gas we’re trying to eliminate by decarbonizing transportation. Hydrogen’s dirty little secret is that most of the hydrogen produced today comes from fossil sources.
According to the U.S. Department of energy, most hydrogen produced today in the United States is made via steam-methane reforming, a production process in which high-temperature steam (700 degrees Celsius to 1,000 degrees Celsius) is used to produce hydrogen from a methane source, such as natural gas. We refer to this as “gray hydrogen.”
SMR is a relatively inexpensive method of producing hydrogen, and per unit of energy input to the process, it’s among the most efficient we have at the moment. However, SMR yields almost 10 kg of CO2 per 1 kg of pure hydrogen.
Writing in Forbes in June 2020, author and chemical engineer, Robert Rapier, references a study conducted by Praxair that breaks down the carbon intensity of SMR hydrogen production. “... the carbon dioxide produced from the natural gas reactions becomes 19.3 metric tons of carbon dioxide produced per million SCF of hydrogen." However, the Praxair paper noted that this is the theoretical minimum. Due to heat losses and inefficiencies, the actual number in practice in a large hydrogen plant is 21.9 metric tons.
“This converts to 9.3 kilograms (kg) of CO2 produced per kg of hydrogen production. One kilogram of hydrogen is the energy equivalent of one gallon of gasoline, which produces 9.1 kg of CO2 when combusted.”
According to Cebon, “Every kilogram of hydrogen you make, you get 10 kilograms of CO2, or more.”
How much further ahead are we really when you consider the CO2 produced by industrial hydrogen production is nearly the same as gasoline or diesel?
Some believe the answer to that problem is carbon capture and sequestration (CCS), where CO2 is captured from industrial processes and stored underground. Only about a third to half of the CO2 is currently captured using today’s best practices.
“For practical purposes, the amount of carbon dioxide that can be captured is limited. It's very hard to capture all of it,” he says. “For example, the Quest CCS venture in Canada, one of the better ones around, has a capture rate of only about 25% of the carbon that's emitted.
“It may be theoretically possible to capture 70% of the carbon dioxide, but it's very difficult and it's never been done,” he adds. And it's very expensive, which is one of the reasons we have never achieved 70% capture rate.”
The operators of the Quest project in Alberta, claim they currently capture around 45% of CO2 emissions. You have to be wary of the sources of those capture rate claims as the numbers tend to float up and down depending on their position on CCS. While various reports often show gross tons of CO2 captured over time, they usually don’t say what percentage of the total output that represents.
Fugitive methane is the other problem.
Without muddying the waters even further, methane that escapes from the extraction and transportation of natural gas is a problem, and it will continue to be problematic as long as we consume natural gas. It’s not a problem confined only to the industrial production of hydrogen. But for the record, Cebon says fugitive methane is a very significant problem.
“The fugitive emissions from the European oil and gas industry [the problem exists in the U.S. as well] is equivalent to something between one and two times the entire carbon emissions of Europe,” he says. “That’s all the airplanes and trucks and cars and industry and heating and everything. Take that number and double it and you get the fugitive emissions. And that's just the methane that the gas industry doesn't care about. They are just happy to let it go.”
Is H2 The Fuel of the Future?
None of this is news to the proponents and advocates of hydrogen. Cebon says he’s quite sure they have all done the same math as he has, and could not have come to different conclusions, knowing what we know about hydrogen production and the renewable alternatives.
“I think they do understand because the likes of Exxon and Shell and BP are full of smart engineers. I think they've done the calculations and I think they know,” he says. “To me, it’s worse if they know and they’re not telling us.
“The factor of three isn’t rocket science. Anyone can work that out. I think they also know that green hydrogen can't work because the amount of electricity required is so massive,” Cebon says. “I think Shell, Exxon, and others are pushing hydrogen because it is a lifeline for the fossil fuel industry.”
Even with all that to consider, don’t discount the utility of renewable sources of hydrogen. In an academic paper published last fall in the International Journal of Hydrogen Energy, researchers at Aalborg University in northern Denmark attempted to model a fossil-free energy system across the EU and in Britain circa 2050.
The paper presented some mind-boggling numbers around the amount of energy required and the hydrogen production the EU would need to run about half of the cars, light trucks, buses, and heavy trucks. Researchers estimated the supply needed to keep up with European transport and industry demands would exceed 3,000 terawatt/hours (tWh) of hydrogen.
“Such large demands also mean that over 4,000 tWh of electricity are needed solely for this purpose, clearly discarding the idea that hydrogen can be produced on excess electricity at a low cost.”
On the vehicle-only front, researchers estimated that overall system costs would be $290 billion higher than if those vehicles were all [battery] electric.
We are somewhat sorry for all the European references in this story. We haven’t been able to find much in the way of reliable research (that is, research not funded by some entity with a dog in the fight) on hydrogen use for transportation in North America. Much has been written about industrial consumption of hydrogen, but not so much on hydrogen’s use in heavy trucks.
The costs we talk about today here in the U.S. are largely forecasts and estimates, as we have no large-scale experience with green-hydrogen production and distribution, nor the manufacture and operation of heavy fuel-cell trucks. If Cebon is correct, it seems hydrogen as an energy source for long-haul trucks might be a fantasy — even with the subsidies.
“With hydrogen, you can have a bit of a subsidy for now. But as soon as the subsidy goes away, it will be three times more expensive again,” he says.
Editor's Note: This article stems from a wide-ranging interview conducted for a forthcomming HDT Talks Trucking video and podcast episode. It captures the essence of a discussion we had on the use of hydrogen as an energy source for heavy trucks. The full interview also went deep into battery-electric and natural gas, but we’re saving those topics for another day.
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