A new study by the UK-based Zemo Partnership recommends that UK Government policy should increase its focus on the well-to-wheel (WTW) greenhouse gas (GHG) emissions and overall energy efficiency performance of new fuels for transport. While hydrogen, electric and renewable fuels (produced from waste-based feedstocks) can all radically cut emissions compared with their diesel-powered counterparts, there are major variations in their effectiveness and efficiency in terms of cutting emissions depending on choices made over the full well- to-wheel life cycle.
The study warns that a focus solely on mitigating tailpipe emissions can risk neglecting the full impacts and the overall energy consumption of the system.
With limited biogenic resources and renewable electricity supplies, it is critical to adopt energy efficient solutions to maximise full system benefits wherever possible.
The new study looks specifically at hydrogen, extending analysis provided in the recently published (also by Zemo) Low Carbon Hydrogen Well-to-Tank Pathways Study.
The work comes shortly after the publication of the Government’s UK hydrogen strategy, a potentially important component of the overall decarbonization plan for transport. Key building blocks of the hydrogen strategy are currently under consultation and the Zemo Partnership work is intended to help inform these.
The Zemo analysis combines GHG and energy consumption data for four vehicle applications: D-segment passenger car, small van, single decker bus and a fully laden 18t GVW heavy goods vehicle. It presents well-to-wheel results for the most promising hydrogen vehicle powertrain architectures using battery-electric, diesel and renewable fuels for comparison.
Trends in WTW GHG emissions and energy consumption for different vehicles. The trends between scenarios with different powertrains and hydrogen supply pathways are similar for each of the vehicle categories modeled. Source: Zemo
The study looks at hydrogen produced for transport use through electrolysis; biomass gasification with carbon capture and storage (CCS); and methane reformation with CCS (all potentially very low carbon and GHG solutions)—as well as from fossil fuels without CCS mitigation. The work explores the sensitivity of GHG emissions and energy consumption to a range of inputs and options, with more than 250 well-to-wheel scenarios being modeled in the 2020-2035 timeframe.
Among the main findings:
Each of the hydrogen vehicle architectures analyzed can deliver low carbon, and in some cases negative, WTW GHG emissions solutions over the next decade. This outcome is identical across light and heavy-duty vehicle segments and is predicated on the use of low-carbon hydrogen.
When comparing the WTW GHG emissions performance of BEV, ICEV using renewable fuels (produced from waste-based feedstocks), and hydrogen HGVs using low-carbon hydrogen, all technology options perform better than incumbent fossil-fueled diesel vehicles.
The WTW energy efficiency of hydrogen vehicles is lower than diesel ICEV, BEV and ICEV using renewable fuels. The difference is most pronounced for heavy-duty vehicles. In the case of HGVs, FCEV trucks are in the order of four to six times less energy efficient than BEV on a WTW basis. Irrespective of the low-carbon hydrogen supply pathway, the hydrogen production process is energy-intensive thereby influencing WTW energy efficiency. This finding highlights the importance of accounting for energy consumption along with WTW GHG emissions and ensuring an energy efficient transition to net zero GHG emissions.
There are a variety of powertrains and fuels that can potentially achieve net zero WTW GHG emissions, but with limited biogenic resources and renewable electricity supplies, it is critical to adopt energy efficient solutions to maximise the benefits wherever possible. For example, hydrogen vehicles would need to demonstrate other benefits beyond WTW (e.g. superior payload, vehicle range, lower operational costs) to compensate for the increased energy consumption compared to alternative powertrain solutions such as BEV.
WTW GHG emissions are dominated by the hydrogen supply chain production method, with distribution and dispensing having less impact. Green hydrogen supply chains deliver the lowest WTW GHG emissions for hydrogen vehicles. Vehicles using hydrogen produced from steam methane reformation and electrolysis using current grid electricity do not perform better than diesel ICEV; grey hydrogen is to be avoided.
WTW GHG emissions are highly sensitive to the electricity grid carbon intensity; this is relevant for both hydrogen and battery electric vehicles. As a result, it is critical that consistent WTT GHG emissions factors for electricity are adopted by Government and industry when comparing different zero, and low carbon, vehicle technologies. This is especially important for hydrogen produced by electrolysis and in comparison to BEV.
Care needs to be exercised with carbon accounting for low carbon hydrogen supply chains that achieve negative GHG emissions, notably BECCS (BioEnergy with Carbon Capture and Storage). These pathways could inadvertently result in the promotion of energy inefficient technology.
When we look at the energy efficiency of potential pathways for hydrogen to be used in transport we see challenges. These vehicles will need to demonstrate considerable complementary benefits such as longer range, superior payload or lower operating costs to compensate for the increase in energy consumption compared with other zero emission powertrain solutions such as battery electric vehicles.
Emissions from the hydrogen supply chain are dominated by the fuel production method, with distribution and dispensing having less impact.
So called ‘green’ hydrogen (produced through electrolysis powered by renewable electricity) currently delivers the lowest WTW GHG emissions for a hydrogen vehicle. However, vehicles using ‘grey’ hydrogen made from current steam methane reformation perform worse than conventional fossil-fueled diesel vehicles on a well-to-wheel GHG basis.
The study recommends that further feasibility work including energy analysis, should be done to assess the suitability of different vehicles for different use cases to inform the potential role of hydrogen in the HGV sector. Relevant factors would include vehicle payload and capacity, range, refueling/charging time and infrastructure. The work could potentially be integrated into the Government’s ongoing Zero Emission Freight Trials (ZERFT) which Zemo is also supporting.
The choice of carbon intensity factors for grid electricity, both now and in the future, is a critical sensitivity within the analysis and an area needing much more consistent data.
Zemo Partnership, formerly LowCVP, was established in 2003 as a public-private partnership working to accelerate a sustainable shift to lower carbon vehicles and fuels and create opportunities for UK businesses. More than 220 organizations are engaged from diverse backgrounds, including automotive and fuel supply chains, government, vehicle users, academics, environment groups and others. In February 2021 the organization changed its name to reflect heightened ambition as the UK embarks on a trajectory to achieve net-zero greenhouse gas emissions by 2050.