Halifax’s Misguided Hydrogen Bus Effort: The Data Tells the Story – CleanTechnica

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Halifax’s just announced hydrogen-diesel hybrid bus trial is intended to be an ambitious stride forward in the city’s climate action plan and a trial that transit operators globally will gain insights from. Yet, scratching just below the surface reveals a problematic disconnect between optimistic projections and operational realities. The trial, designed to showcase significant diesel fuel reductions by injecting hydrogen into existing diesel engines, fundamentally misrepresents the well-documented constraints of the technology when applied to urban bus operation. This approach, rather than pioneering new territory, simply reaffirms limitations already clearly demonstrated in previous trials.

Hydrogen-diesel dual-fuel technology involves adding hydrogen to a conventional diesel engine, theoretically substituting a substantial fraction of diesel fuel. Under ideal circumstances — steady-state highway driving, commonly experienced by heavy-duty trucks — hydrogen substitution rates of 30-40% are indeed achievable, as shown in trials in Alberta, another province where the misguided technology is being tested.

Halifax’s own projections, however, assert even higher possible diesel displacement, claiming reductions between 40-60%. Such optimism conveniently ignores critical operational dynamics characteristic of urban buses, which spend considerable portions of their operational hours idling, coasting, or moving at low speeds. Under these conditions, engine control systems routinely shut down hydrogen injection to maintain engine stability and safety, significantly constraining the actual hydrogen substitution rate.

The real-world outcomes from other global trials serve as stark warnings against overly enthusiastic predictions. Notably, the hydrogen-diesel hybrid bus trial conducted in Wellington, New Zealand, offers a critical counterpoint grounded in reality. Operating under precisely the type of stop-and-go urban conditions Halifax buses face, Wellington’s trial demonstrated hydrogen substitution rates averaging only 10%. This figure sharply contradicts Halifax’s optimistic forecasts, and decisively illustrates that urban transit environments fundamentally limit hydrogen’s potential to meaningfully displace diesel fuel. The reason for this limitation is clear: frequent idle periods and low-load conditions drastically curtail hydrogen injection to avoid combustion instabilities and other mechanical issues. Consequently, the maximum achievable diesel displacement in urban transit buses consistently remains far lower than hypothetical or laboratory-based scenarios suggest, and far lower than the already not great 30% to 40% seen with heavy trucks traveling at consistent speeds on highways.

Applying Wellington’s realistic 10% substitution rate significantly alters Halifax’s emission reduction claims. Consider baseline emissions for a fleet of four conventional diesel buses, estimated at approximately 270 tons of CO₂ annually. With only a modest 10% diesel reduction achieved through hydrogen substitution, the total reduction in emissions from diesel combustion becomes negligible in the broader context. Far worse, however, is the dramatic increase in upstream emissions associated with grey hydrogen production, the likely hydrogen source for Halifax’s buses.

Nova Scotia currently lacks any meaningful capacity for green hydrogen production, primarily because its electricity grid remains heavily reliant on fossil fuels, notably coal and natural gas. With a grid emission factor averaging between 600 and 700 grams of CO₂ per kilowatt-hour, producing hydrogen via electrolysis using this electricity would result in hydrogen that is even more emissions-intensive than conventional grey hydrogen made from natural gas. Without significant increases in renewable electricity generation, particularly from wind or hydroelectric resources, Nova Scotia’s pathway toward genuinely green hydrogen remains blocked. Unsurprisingly, all of the proposed green hydrogen initiatives have been failing to launch, just like most in the rest of the world.

Grey hydrogen, produced via steam methane reforming without carbon capture, emits roughly 10 kg of CO₂ per kilogram of hydrogen generated. There is no blue hydrogen in Halifax or eastern Canada either. Halifax’s modest hydrogen consumption would directly cause an additional 32 tons of upstream CO₂ emissions per year, overshadowing the minor diesel savings at the tailpipe.

Real-world hydrogen systems typically experience leakage rates of 5-10% over the full supply chain from manufacturing to compression to trucking to refueling. Given hydrogen’s high Global Warming Potential (GWP20) of 37, these leakage rates substantially amplify greenhouse gas impacts. At the lower leakage estimate (5%), the emissions associated with leaked hydrogen contribute an additional 6 tons of CO₂-equivalent per year; at the higher end (10%), leakage amounts to approximately 12 tons annually.

Hydrogen slippage in diesel-hydrogen dual-fuel engines closely parallels the methane slippage phenomenon widely documented in LNG-fueled internal combustion engines. The International Council on Clean Transportation’s (ICCT) landmark FUMES study clearly demonstrated that methane slippage — unburned methane escaping during combustion and through crankcase ventilation — significantly undermines the climate benefits of LNG engines, due to methane’s powerful global warming potential.

Similarly, hydrogen slippage in diesel-hydrogen hybrids is caused by incomplete combustion. Although hydrogen itself does not contain carbon, its indirect warming potential (GWP20 of around 37) mirrors the significant climate impact concerns raised by ICCT regarding methane (GWP20 of approximately 82). Both slippage types reflect inherent operational drawbacks that dramatically diminish or negate the environmental benefits initially claimed by proponents. Real-world experience with hydrogen-diesel engines shows slippage of up to 5%, although some after market providers of the technology claim much better of course. The hydrogen tanks and lines are likely to leak as well. Testing in South Korea found that 15% of all hydrogen buses and cars were leaking.

When combined with diesel combustion, grey hydrogen production, and transportation emissions, Halifax’s supposedly climate-friendly hydrogen-diesel buses ultimately result in an annual emission increase of 5-10% over traditional diesel-only operations.

Additionally troubling is the lack of original equipment manufacturer (OEM) support for hydrogen-diesel dual-fuel configurations in transit buses. OEMs neither offer nor endorse these conversions, which are typically done using aftermarket equipment and retrofits. Such modifications inevitably void the buses’ original warranties. For transit agencies, warranties are crucial to managing operational risks and costs, and the absence of OEM endorsement means Halifax is assuming substantial technical and operational risks without any safety net. Should mechanical issues arise, the financial consequences would be solely borne by the transit authority, posing significant additional financial and operational vulnerabilities.

Ultimately, Halifax’s hydrogen-diesel bus trial fails to break any new ground, merely reiterating constraints that have already been demonstrated and understood from previous global experiences. Wellington’s detailed real-world data alone provides sufficient confirmation of the inherent limitations of hydrogen substitution under stop-start urban bus operations. Halifax’s project, despite well-intentioned environmental goals, inadvertently becomes a redundant exercise in reaffirming established technological boundaries and operational constraints.

Rather than advancing the transit industry’s understanding or reducing emissions, the project serves primarily as a cautionary tale, underscoring the critical necessity of aligning ambitious climate strategies with established operational realities.

Battery technology continues to advance rapidly, characterized by consistent improvements in energy density and simultaneous, significant reductions in cost. Over the past decade, battery prices have fallen by roughly 90%, while energy density has steadily increased, enabling longer driving ranges and improved operational flexibility for battery-electric vehicles, including transit buses.

Halifax’s recent strides toward electrifying its transit fleet clearly show a practical and scalable path forward. With over 200 battery-electric buses planned and initial buses already operating successfully, the city is demonstrating both operational readiness and commitment to proven zero-emission technology. This approach leverages rapidly advancing battery technology, benefiting from ongoing increases in energy density and decreasing battery costs, making it increasingly feasible to electrify even the longest transit routes.

Given this trajectory, Halifax’s experimentation with hydrogen-diesel hybrids — an approach burdened by operational complexities, questionable emissions outcomes, and limited real-world effectiveness — appears unnecessary and counterproductive. Halifax would be far better served by doubling down on its current battery-electric bus plans, progressively expanding their deployment as higher-capacity, longer-range electric buses inevitably enter the market.