Decades will pass before diesel disappears from our vocabulary, but transportation sectors now using diesel will migrate toward other energy sources in the coming years.

No single alternative energy source will dominate the energy landscape the way diesel fuel has for generations. In terms of cost, portability and energy density, diesel is the perfect fuel for heavy trucks.

Public and regulatory disdain for diesel might be driving the shift toward alternatives, but factors such as geography and climate, the availability of alternatives, and the practicality of any alternate in a given application should decide the winners and losers, not public opinion or activists’ favorites. Trucking needs not just one alternative fuel, but a little bit of everything to keep all its wheels turning as greenly as possible.

“When we have those discussions about electrification, there seems to be an assumption that there are no emissions, that all electrons are clean and created with 100% renewable energy. And this is just truly not the case,” says Allen Schaeffer, executive director of the Diesel Technology Forum. “There are some parts in the U.S. where most of those electrons are created from coal or natural-gas-fired power plants. We’re just trading tailpipe emissions for smokestack emissions. There are always some impacts associated with whatever it is that’s powering whatever vehicle you have.”

Schaeffer acknowledges that places like California, with its aggressive stance on renewable energy, and the Northwest and Southwest, with high solar, wind and hydro-electric capacity, are ideal locations to foster near-zero energy strategies. He worries, though, about imposing those solutions in the Midwest and the Northeast, where renewable capacity is limited.

“Electricity there comes from conventional fossil-fuel-fired power generators or nuclear,” he said in an interview with the HDT Talks Trucking podcast. “So, we need to have a lot more honesty and transparency in these discussions.”

Cost and ROI Questions

In addition to battery-electric vehicles (which come with their own baggage, including charging infrastructure, upstream emissions from electricity fossil-fuel generation, and battery component mining manufacturing), hydrogen fuel cells and renewable natural gas show promise. In the absence of cold fusion or the flux capacitor popularized in the film Back to the Future, any alternative to diesel has to be practical. At this point in time, fuel cells have proven capable of powering heavier vehicles such as transit buses, but the (assumed) current cost of such systems stretches the definition of practical. 

It has proven impossible to get any fuel-cell manufacturer to even hint at pricing for a fuel-cell-powered truck. We did learn recently from Hyundai, when it revealed in early October that it would soon begin U.S. trials of its fuel-cell-powered Class 8 Xcient tractor, that California would make subsidies available to support the purchase of such trucks.

“Several states, including California, are already moving quickly with new [incentive] programs,” said Sae hoon Kim, senior vice president, Hyundai Motor Group’s Fuel Cell Center. “The Low Carbon Standard program provides credits to set up hydrogen charging stations. The HVIP program [Hybrid and Zero-Emission Truck and Bus Voucher Incentive Project] supports clean-large-truck buyers with up to $300,000 per vehicle in subsidies.”

While that startling figure can’t be taken as a firm indication of the eventual cost of a fuel-cell vehicle, compare that figure with the subsidies of $150,000 per vehicle offered through HVIP for Class 8 BEVs such as Freightliner’s eCascadia or Peterbilt’s 579EV. As of Oct. 1, the California HVIP website includes no reference to hydrogen fuel cell vehicles.

Pricing has to be a consideration, as does the total lifecycle cost. The latter is difficult to estimate, because residual values cannot yet be determined, even though they are a vital component of the total cost of ownership. Duty cycles and life cycles are equally difficult to pin down. A typical diesel highway tractor has a first-term life of three to five years, whereas a concrete mixer or refuse truck will serve its first and likely only owner 10-12 years, making the ROI much easier to work into the business case than a 5-year life cycle for a BEV that currently costs more than a conventionally fueled vehicle.

Trucking will need to adjust to this new business model.

Everyone seems to look toward California when talking about alternative fuels, but it’s fairly unique among the 48 contiguous states. Its climate and terrain are well suited to BEVs, compared to the Northeast where winters are considerably colder and much less opportunity exists for solar charging. California is also offering very aggressive incentives, which won’t be easily matched by smaller jurisdictions.

However, that hasn’t stopped several northeastern states, including New York and Rhode Island, from signing on to a compact among 15 states and the District of Columbia pledging to develop a plan to eliminate diesel emissions by 2050.

The other question is whether these alternative-fueled vehicles can achieve something close to cost parity with diesel. The cost of diesel trucks will continue to rise as new emissions technologies are incorporated. At the same time, manufacturing supply-chain efficiencies will bring down the cost of the newer technologies. By how much and when remains unknown, but hopefully that will happen before the government subsidies become unsustainable.

Meet a New Old Friend

Slipping up the middle between lithium-ion batteries and hydrogen fuel cells is renewable natural gas. To some, natural gas has become a four-letter word, but renewable natural gas really could be a game-changer.

We already have the technology needed to take advantage of the fuel, and the fuel itself is often, depending on the source, net sub-zero in carbon emissions. Renewable natural gas is derived from the methane produced by the decomposition of organic matter from a variety of sources, such as landfill operations, manure lagoons at cattle farms and even waste-water treatment plants. The nearly pure methane gas emitted by such sites can be 40 times more potent as a greenhouse gas than the carbon dioxide targeted by many emissions initiatives, says Hugh Donnell, the business growth and development manager at Cummins Westport.

“That methane, or the renewable natural gas coming up from landfills, would normally be discharged to atmosphere or simply burned off,” he explains. “But when you capture and consume that methane to do work such as powering a truck or a bus, you get a double benefit. You’re not only taking a very harmful emission out of the waste stream; you’re also replacing an equivalent volume of fossil fuel previously used to power that equipment.”

According to data from the California Air Resources Board, renewable natural gas, or bio-CNG, has the lowest carbon intensity value (grams of CO2e per megajoule) of any of the alternatives currently under active consideration, using diesel as a baseline.

• diesel fuel: +100 (grCO2e/MJ)

• bio CNG: -400 to +100

• hydrogen: -10 to +70

• electric: -200 to +30

The data for both hydrogen fuel cells and batteries involves the conversion of one source of energy to another and storing and transporting that energy before it can be put to use. The costs associated with the harvesting and storage, as well as the energy lost to the processes, can be considerable. Renewable natural gas, on the other hand, needs only to be harvested and cleaned of impurities, which also comes at a cost, though it’s considerably less than most of the alternatives.  

Each of these options – battery-electric, hydrogen fuel-cell electric, or renewable natural gas – may fit better into certain applications, and certain regions of the country, than others. There’s no real winner or loser here – just a better fit for some than others.