Three Ways Out of Diesel: The Depot-Level Case for HVO, Batteries and Hydrogen

Ask a dozen UK transport managers what should replace diesel and you will get a dozen confident answers, most of them shaped by whichever supplier visited last. That confidence is not yet justified. In 2026 the three credible options \u2014 hydrotreated vegetable oil, battery-electric traction and hydrogen fuel cells \u2014 occupy genuinely different territories, and the useful work for an operator lies not in picking a winner in the abstract but in mapping each option onto a specific duty cycle, depot and customer contract.

The duty cycle decides before the fuel does

A 44-tonne tractor unit running overnight trunking between Daventry and Motherwell faces a different set of constraints from an 18-tonne curtainsider doing eighty miles of multi-drop around Leeds. Payload sensitivity, daily mileage, the availability of a long overnight dwell, the local electricity connection, ambient temperature, and the willingness of a customer to share a higher standing charge \u2014 these variables eliminate options faster than any technology comparison.

Operators who start with the fuel tend to buy a narrative. Operators who start with the route tend to buy a vehicle that works.

HVO: the drop-in that is not a free lunch

Hydrotreated vegetable oil remains the least disruptive lever available. It meets EN 15940, can be used neat in the overwhelming majority of modern heavy-duty engines without modification, and requires no new tanks, no new nozzles and no new training regime beyond the usual housekeeping. For a fleet that needs to cut reported emissions in the current financial year without renegotiating its maintenance contracts, nothing else comes close on speed of deployment.

It is not, however, a destination. The UK's supply of waste-derived HVO \u2014 principally from used cooking oil and tallow \u2014 is finite, and it is now contested by the sustainable aviation fuel mandate, which draws on the same hydroprocessing capacity and many of the same feedstocks. Crop-based HVO sits beneath the Renewable Transport Fuel Obligation's crop cap and carries a weaker sustainability story that few corporate customers will accept in a tender response. Prices have been volatile, and the premium over diesel \u2014 historically in the high teens to mid twenties pence per litre before the value of renewable transport fuel certificates is passed back \u2014 tracks feedstock markets rather than the oil price.

There is also an accounting trap. A haulier cannot claim RTFCs directly; the certificates accrue to the fuel supplier, and any benefit reaches the operator only to the extent that the supplier chooses to share it. Ask for the proof of sustainability documentation, the feedstock classification and the greenhouse gas saving figure, and put the answer into the contract rather than the brochure.

Electricity: cheap per mile, expensive per site

Battery-electric trucks have crossed the threshold from pilot curiosity to commercial proposition for a defined slice of the market. Energy cost per mile is substantially lower than diesel \u2014 the gap narrows once high-capacity public charging and network charges are included, but it remains real. Driveline maintenance is lighter. Drivers, past the novelty, generally like them.

The capital arithmetic is more awkward. A 44-tonne electric tractor unit still costs appreciably more than its diesel equivalent, and the Plug-in Truck Grant, worth up to £25,000 on the largest vehicles, narrows rather than closes the gap. Then there is the depot: upgraded supply, switchgear, charge points and, in too many cases, a distribution network operator connection date measured in years rather than months. A site that cannot secure capacity cannot run the fleet, and no amount of grant funding alters that.

Where battery-electric works well in 2026 is where it always worked well: return-to-base operations with predictable daily mileages, overnight dwell and a depot with electrical headroom. Where it struggles is tramping, unpredictable subcontracted work, and any duty cycle that depends on public HGV charging infrastructure which remains thin outside a handful of corridors.

Hydrogen: the promise that keeps moving

Hydrogen fuel-cell trucks remain, for most UK operators, a demonstration rather than a procurement option. The vehicle market is narrow, the heavy-duty refuelling network amounts to a handful of sites, and the delivered cost of hydrogen at the pump is high enough that a compelling whole-life case is difficult to construct without support.

That is not a dismissal. Fuel-cell drivetrains suit high-utilisation, long-distance work with heavy payloads, and the plausible early market is a cluster model: captive fleets running between a depot and an industrial hydrogen supply in places such as Teesside, Merseyside, Grangemouth or the south Wales corridor, where the fuel is produced close to the route. The HyHAUL initiative in Wales has shown what a demonstration looks like. It has not yet shown what a commercial fleet looks like at scale.

Carbon accounting is where the three genuinely diverge

The RTFO obliges fuel suppliers, not operators, and that distinction is routinely blurred in tender documents. What matters for a haulier is the well-to-wheel carbon intensity it can evidence to a customer, and here the three options behave very differently.

Waste-derived HVO typically delivers lifecycle savings in the region of 80 to 90 per cent against fossil diesel. Bio-CNG and bio-LNG, where they are available, sit in a similar band. Battery-electric vehicles approach zero at the tailpipe, but their reported footprint depends heavily on when and where the electricity is generated; a fleet charging overnight on a standard tariff is not the same as one charging on a renewable-backed supply. Hydrogen's figure swings widely with production route: electrolysis using grid electricity in a high-carbon hour is not a decarbonisation story, while hydrogen derived from biomethane or dedicated renewables is a different proposition altogether.

A defensible position for the current year is to report well-to-wheel, keep the fuel's chain-of-custody documentation on file, and resist the temptation to compare a tank-to-wheel figure for one technology against a well-to-wheel figure for another. Those numbers are not interchangeable, and procurement teams increasingly know it.

A short framework

Five questions will settle most decisions:

• How many miles does the vehicle cover on its busiest day, and can it reliably return to base?
• How much payload can the operation afford to lose?
• When will the depot's electricity supply be adequate, and at what capital cost?
• What contract length is the customer offering, and will they share the capital burden?
• What residual value risk sits with the operator over a five-to-seven-year hold?

If the answer to the first question is a long, unpredictable day, HVO is the pragmatic bridge and will remain so for as long as feedstock allows. If the vehicle returns home every night to a site with capacity, battery-electric is already the cheaper answer on a whole-life basis for many duty cycles. If it runs high mileage on a fixed corridor near a hydrogen cluster and a partner will carry the fuel risk, a fuel-cell trial is defensible.

Three fuels, three different problems. The error in 2026 would be to solve for the option that looks best in a press release rather than the one that fits the depot.