Electrification and the Other “E” – E-Fuels
PACCAR executive Phil Stephenson discussed at SAE COMVEC 2021 the why, how and when of commercial-vehicle electrification, but also put in a plug for e-fuels.
While “Electrification and Commercial Vehicles” was the ostensible topic of Dr. Philip Stephenson’s keynote at the recent SAE COMVEC 2021 conference, the efficacy of e-fuels – or renewable synthetic fuels – to reduce heavy-vehicle emissions was brought up more than once.
“E-fuels are an often-overlooked topic,” said Stephenson, the general manager of the PACCAR Technical Center. He explained e-fuels are hydrocarbons created by combining “sequestered carbon” with “green hydrogen” formed by electrolysis. “Put in the back of your minds, there’s a lot of talk about electric vehicles but there’s this other [technology], if the regulations went a little bit different way, where our customers could continue to operate like they are, without some of the challenges [of electrification].”
PACCAR’s praise of e-fuels was coordinated. In a separate COMVEC session on electric propulsion, another of the company’s experts asserted that combining hybrid powertrains with e-fuels is a promising short- to mid-term solution that further reduces emissions.
Stephenson emphasized the importance of well-to-wheels emissions analysis. “Certainly, locally the emissions from an electric vehicle are zero,” he said. “One needs to factor though the whole ecosystem; there are emissions in manufacturing battery systems, there are emissions in producing energy in many cases. Much of our energy in North America comes from nonrenewable sources like coal and natural gas.”
Hydrogen is another option gaining steam, particularly for long-haul trucking applications. Kenworth collaborates with Toyota Motor North America to develop zero-emissions Kenworth T680 trucks powered by Toyota hydrogen fuel-cell electric powertrains. Burning hydrogen in combustion engines also is possible, but Stephenson points out that “burning it does create some oxides of nitrogen.” Following his keynote address, Stephenson took a few questions from the audience and expanded on these topics.
If e-fuels are so clean and easy to transport, store and use, why are they overlooked?
What’s really driving us towards not going the e-fuel route is that most regulatory pressure right now is focused on local tailpipe emissions, so zero local emissions. If we take a broader well-to-wheels approach, if our regulators do that, we have some more flexibility and transport mechanisms for energy like liquid fuels could play a part going forward.
When you think about the charging rate – the fastest charger we have right now being 350 kW – the energy going through your hand when pumping gasoline into your car, if you take the energy content and the flow rate, you’re ‘charging’ your gas tank at 5 MW – 15 times the fastest electric charger. Of course, a diesel pump at a truck stop is another order of magnitude faster than that. So, there’s a lot of potential [for e-fuels] if the regulations allow that as an energy transport mechanism in the future.
[Stephenson did not discuss it, but prohibitive pricing for at least the next decade and a dearth of green-hydrogen production have been cited as potential barriers to widespread e-fuel adoption.]
Battery swapping could be an option to avoid long charge times. Why not do this with medium- and heavy-duty vehicles?
This is my personal opinion: there are a couple challenges with swapping. These battery packs have high-voltage connection between the pack and the chassis. They have a communication interface and very often they have a cooling interface. These interfaces typically are not designed to be made and broken once per day for 5,000 cycles, so there’s a durability risk that would need to be overcome.
The other issue is what I like to call the ‘propane-bottle exchange program.’ If you have a propane bottle on your grill at home and it runs out, typically you don’t go and get it refilled, you swap it. That’s fine, because you pay $25 and you don’t care. If you’re driving your truck in, swapping out your $12,000 or $20,000 battery pack for one whose lineage you’re not familiar with, you may find the next day you go to drive your truck your range has been reduced by 30%. So, that limits it to maybe fleets having their own [dedicated] swapping systems.
Swapping systems also take a lot of space. You need robotic systems to move these battery packs, which are probably the footprint of a ping-pong table and a foot thick or more, in and out of trucks. It turns out to be a lot of infrastructure, and there are alternatives like fast-charging or hydrogen.
We’ve heard a lot about hydrogen fuel cells here at COMVEC. What do you feel are barriers to hydrogen fuel-cell use in the next decade?
First of all, infrastructure. Distribution of hydrogen will continue to be an issue. Storage density of hydrogen on trucks isn’t great. If you look at the back of that Kenworth/Toyota fuel-cell truck, to store 60 kg of hydrogen [six tanks capable of operating at 700 bar], we have a closet on the back that is 3 or 4 feet deep and the full height of the tractor. That’s not very good energy density, so that’s a concern as well.
And there’s relatively high costs that go into a fuel-cell stack. They contain precious metals, very expensive to make, and that will need to improve probably by an order of magnitude for them to get competitive with battery systems.