Blog: Long-Haul Lorries Powered by Hydrogen or Electricity?


There is an increasingly vociferous debate between those who think that future long-haul heavy goods vehicles should be powered by Hydrogen and those who favour direct electrification.

Most Hydrogen-powered vehicles use fuel cells to convert Hydrogen and Oxygen into electricity and water. The electricity drives electric motors to propel the vehicle – for example, the Nikola fuel cell lorry.  Direct electrification involves either: (i) carrying the electricity in large batteries (eg as proposed by Tesla); or (ii) using an ‘Electric Road System’ (ERS) to transmit the electricity to the vehicle in motion (eg the eHighway by Siemens).

The major benefit of Hydrogen over electrification is its flexibility.  A Hydrogen truck can be refuelled in approximately the same time as a diesel truck and the operating range and operating patterns are similar.  So Hydrogen-powered trucks could fit into the existing logistics system without too much change.  However Hydrogen is much more energy intensive than electricity and consequently is inherently more expensive for the economy, the environment and probably for the vehicle operator.  Conversely, electrification of road freight transport would require some modifications to logistics practice [1], but would be significantly lower cost and lower environmental impact to operate.  Both would require infrastructure investments at large scale. Given the urgent need to limit Carbon emissions in the short term to avoid the 1.5 deg C global temperature rise, there is a further imperative to deploy solutions quickly.

The decision about which ‘energy vector’ to use for lorries is very important.  Proponents of both electricity and hydrogen recognise that the choice of energy systems for freight transport interacts with the overall energy economy: including electric power, all modes of transport and heat.  Consequently, system-level considerations are needed.  So ‘electricity vs hydrogen’ is a milestone decision, with major long-term ramifications at national and international levels.

1  Hydrogen

There are two main ways that Hydrogen can be manufactured to power future heavy lorries:  (i) ‘Green’ Hydrogen, manufactured by electrolysis – using electricity to split water into Hydrogen and Oxygen; and (ii) ‘Blue’ Hydrogen, manufactured by Steam Methane Reforming (SMR) – using high temperature steam to convert Methane into Hydrogen.  (Click here for definitions of ‘Green’, ‘Blue’ and ‘Grey’ Hydrogen.)

‘Green’ Hydrogen Generated by Electrolysis

Figure 1 shows three option for powering long-haul vehicles.  It follows the same methodology as used in my previous blog on hydrogen-powered vehicles.  The left hand pathway illustrates use of 100 kWh of renewable electricity to generate ‘Green’ Hydrogen by electrolysis and use of the resulting Hydrogen to power fuel-cell electric vehicles.  Each step in the process introduces energy losses and the overall energy performance is the product of the individual efficiencies.  The ‘round-trip’ process of using renewable electricity to make Hydrogen by electrolysis, storing and transporting it on a vehicle, then converting it back to electricity in a fuel-cell and powering the electric motors – is only about 23% efficient overall.  That is, for every 100 kWh of ‘renewable electricity’ purchased from the grid, only 23 kWh will reach the road wheels of the lorry.

The middle pathway shows that  69kWh (of the original 100 kWh) reach the wheels of a battery electric vehicle and the right hand pathway shows that 77 kWh reach the wheels of a lorry travelling on an Electric Road System (ERS). The ERS is the most efficient pathway because the motors are powered directly from the electricity supply (via an inverter), avoiding energy loss through charging and discharging a battery.

Options for long-haul vehicles: (i) Fuel cell Electric Vehicle running on 'Green' Hydrogen; (ii) Battery Electric Vehicle; (iii) Electric Road System vehicle.

Fig. 1.  Efficiencies of long-haul vehicle energy pathways: (i) Fuel cell Electric Vehicle running on ‘Green’ Hydrogen; (ii) Battery Electric Vehicle; (iii) Electric Road System vehicle.

The very low efficiency of the ‘green’ Hydrogen (electrolysis) pathway means that the process uses a lot of renewable electricity to make the necessary quantity of Hydrogen.  The (unsubsidised) cost of Hydrogen created by electrolysis is therefore high and the amount of power required is very large.  This latter point can be illustrated by estimating the land area of renewable energy generation systems (assumed here to be land-based wind turbines) needed to supply the power used by the UK’s lorries – either by direct electrification (ERS) or via the Green Hydrogen (electrolysis) route.

The UK’s HGV fleet transports about 189 billion t.km of freight per year.  A 44t lorry at 75% load factor uses about 0.19 kWh/t.km.  Spreading this over 12 hours per day, 365 days per year, the power requirement is approximately 8.2 GW.  If the ‘wind turbine to road wheel’ efficiency is 77% (as for the ERS solution), powering the vehicles would require 10.6 GW, ie approximately 3,500 x 3MW wind turbines.  These would require a land area of about 5,300km2, as shown to scale by the smaller circular area on the map in Figure 2.

If the ‘wind to wheel’ efficiency is 23%, as for the Green Hydrogen pathway, powering the vehicles would require 35.6 GW, ie approximately 12,000 x 3MW wind turbines.  These 12,000 wind turbines would require a land area of 18,000 km2 as shown by the larger circular area on the map.  (For reference, the average electricity demand of GB in 2019 was 31 GW.  So an additional 35.6 GW would approximately double the average electricity demand of the country.)

Estimated land areas of wind turbines needed for powering the UK’s heavy goods vehicles by electric road system or via 'Green' Hydrogen (electrolysis)

Fig. 2 Estimated land areas of wind turbines needed for powering the UK’s heavy goods vehicles by electric road system or via ‘Green’ Hydrogen (electrolysis)

The world’s largest electrolysis plant is currently being built by Hydrogenics in Canada.  It has a capacity of 20 MW, which is about 1/1800 of 35.6 GW needed to run the UK’s truck fleet.  Given the amount of scaling-up to be done, it is questionable whether a Green Hydrogen economy could be deployed in time (by 2030) to avoid the 1.5 deg C global temperature rise.

Conclusions: The Green Hydrogen route would require approximately 3.3 times more power (from whatever renewable source), 3.3 times more land area and 3.3 times more money to power the same vehicles as an ERS solution.  It is unlikely that Green Hydrogen could be scaled to power UK road freight before 2050.

Green Hydrogen for Energy Storage?

A key issue in the low carbon future is energy storage. Because of the variability of sustainable electricity (wind, solar) and its lack of synchronicity with the peaks of electricity demand, there is a need to store electricity at times of excess supply for use at times of high demand.

Proponents of a Green Hydrogen Economy propose to solve the electricity demand problem by using excess electricity to make Hydrogen by electrolysis; storing it in underground salt caverns; and converting it back to electricity at peak times.  However the low round-trip efficiency of approx 32% (electricity-Hydrogen-electricity) makes the Green Hydrogen route very expensive per stored kWh.  A hydrogen-based electricity storage scheme would only break even financially with large subsidies, because 68% of the energy would be wasted through the low conversion efficiencies and only the remaining 32% would available to be sold back to the electricity grid by the storage company.

There are much more efficient electricity storage technologies – such as pumped-storage hydroelectricity (efficiency 70-85%), lead acid batteries (80-90%), Li-ion batteries (85-95%); flywheels (70-95%); compressed air (40-70%), liquid air (cryogenic) (70%), and others. (See Appendix A of [2] for an excellent summary.) All of these would be much lower cost per kWh of storage than Hydrogen and all could be implemented at scale, without significant subsidies, given an appropriate market structure for electricity storage.

Conclusion:  Storage of electricity using Green Hydrogen would not be competitive with readily-available alternatives. So electricity storage is not a reason for selecting Hydrogen to power the economy.

‘Blue’ Hydrogen generated by SMR

Steam Methane Reformation (SMR) strips the Carbon atoms from Methane (CH4), creating CO2 and Hydrogen (H2).  See Figure 3. It has been argued that ‘Blue’ Hydrogen generated by SMR could replace natural gas for heating and transport in a Hydrogen Economy.  For example, ‘H21’ project in the North of England [3] proposes to extract natural gas from the North Sea oil fields, convert it to Hydrogen by SMR at facilities on the UK coast, inject the Hydrogen into the National Transmission System (NTS = the ‘gas grid’) and pump the CO2 back into empty oil/gas wells, to be sequestered under the sea (‘Carbon Capture and Storage’ – CCS).

Summary of the SMR Process

Fig. 3  Summary of the SMR Process

In a ‘net zero’ Carbon scenario, all natural gas used by the nation would have to be replaced by Blue (or Green) Hydrogen and 100% of the CO2 generated by SMR would have to be captured and stored.  It is questionable whether CCS technology can achieve the necessary level of storage fidelity, with many predictions that significant leakage of CO2 is likely in large-scale CCS schemes [4].  Since there are no existing large scale carbon capture facilities in the UK, there is also an important question of whether this technology could be rolled-out in-time for full-scale deployment for the entire UK energy system, by 2030, 2040 or even 2050.

Hydrogen has a significantly lower energy content per unit volume (10.8 MJ/m) than Methane (35.8 MJ/m) [5], see Fig. 3.  The factor of 35.8/10.8 = 3.3 means that transferring the same amount of energy to consumers through the NTS using Blue Hydrogen instead of Methane, at the same transmission pressure, would require most gas pipes in the system to carry 3.3 times higher volume flow rate of gas.  To do this they would need 3.3 times larger flow area or 1.8 times larger internal diameter. It is not simply a matter of using the existing gas grid and pumping Hydrogen instead of Methane. The entire gas grid would have to be replaced by pipes with 3.3 times the capacity.  This problem is recognised by the H21 project, which plans to install an extensive network of new Hydrogen gas mains across the North of England [3].

It is difficult to compare the energy efficiency of Blue Hydrogen with electricity because of the fundamental inefficiencies of converting chemical into mechanical/electrical energy in a power station.  One fair comparison is shown in figure 4 below.  On the right is the pathway for creating Blue Hydrogen from 100 kWh of Methane by SMR; compressing and transporting it in a lorry, and converting it to electricity to propel the vehicle.  Accounting for all the energy losses in the process chain, 29kWh would be available at the wheels of the vehicle.  On the left of figure 4 is the pathway for using the same 100kWh of methane to generate ‘clean electricity’ in a Combined Cycle Gas Turbine, CCGT, (as used in modern gas-fired power stations), then transmitting the electricity via the grid and using it to power a battery electric vehicle.  In this case 44kWh would be available at the wheels of the vehicle.  Both processes would require capturing and sequestering the CO2  to make them ‘clean’ (zero carbon).

Alternate pathways for fuelling electric vehicles using Methane

Fig. 4  Two pathways for fuelling electric vehicles using Methane: (i) Using a Combined Cycle Gas Turbine with CCS to create clean electricity; (ii) Using an SMR plant plus CCS to create ‘Blue’ Hydrogen.

The amount of methane (natural gas) needed to power the UK’s heavy vehicle fleet for a year by these two pathways can be calculated using some of the assumptions in Figure 2.  The answer is 82 billion kWh of Methane (295 PetaJoules) for the electrification route and 124 billion kWh of Methane (446 PJ) for the Blue Hydrogen route.  So 51% more natural gas would be needed to fuel Blue Hydrogen vehicles than to generate clean electricity and power electric vehicles.  That inevitably means 51% higher energy costs, plus the knock-on effects on energy security and the national trade deficit, caused by the much higher demand for natural gas imports.  (Note that this calculation assumes that the CCS processes in both pathways have the same level of inefficiency. This is probably not correct, but will cause a relatively small error in the numbers.)

Why is the Blue Hydrogen route so much less efficient than the CCGT route?  Because every time you convert energy from one form to another (change colour in figure 4) you waste energy.  The electrification route involves one conversion (Methane-electricity). The Blue Hydrogen route involves two conversions (Methane-Hydrogen-electricity).  The Blue Hydrogen route is therefore fundamentally less efficient.

Conclusions: Use of Blue Hydrogen (SMR + CCS) to provide heating for UK homes would require replacing the entire gas grid with higher capacity pipes.   Use of Blue Hydrogen to power UK freight would cost about 50% more in ongoing energy costs than using the natural gas to fuel the conventional electricity generation system, using CCS to capture the Carbon dioxide.  It is unlikely that the necessary SMR + CCS facilities could be built in time for 2030, 2040 or 2050.

Of course there are other issues associated with the lower energy storage capacity of battery electric vehicles.  These are covered in the next section.

2  Direct Electrification

Electrification with large batteries and fast chargers

As described in a previous blog about the Tesla electric truck, electrification of long haul lorries using large batteries and fast chargers requires the vehicles to carry batteries with capacities of 300 kWh-600 kWh or more. Typical power consumption levels for articulated HGVs are 2-3 kWh/km, so these battery sizes correspond to ranges of 100-300km.  Such batteries are expensive, heavy and contain large amounts of scarce Cobalt.  For example, the stated capabilities of the Tesla Semi would require batteries of mass at least 7 t (with a corresponding reduction in payload) and would cost $100k-$200k.

Charging the batteries quickly would require high local electric power capacity at depots, etc.  For example, the Tesla Semi would need a 2 MW charger to meet the stated 30 minute fast charge [6].  This implies very large and expensive substations at depots, distribution centres and motorway services.

Electric Road Systems (ERS)

ERS technology, particularly the ‘eHighway’ version which uses overhead catenary cables, contacted by pantographs carried on the vehicles is well developed and has been tested in 5 major trials in the past few years.  The trials have demonstrated that eHighway technology could be deployed reasonably quickly around the UK’s Strategic Road Network (‘SRN’ = 7000 km of motorways and major A-roads), within the next 10-15 years, or possibly sooner.  The cost of deployment over the entire SRN is estimated to be about £25b, which is comparable with £28.8b announced in the UK Government’s 2018 Budget for the ‘National Roads Fund‘ for spending on roads in 2020-2025; and about ¼ of the projected cost of the HS2 railway project.  Since 2/3 of all HGV kms occur on the SRN, this single measure would go much of the way to decarbonising the entire road freight system in the UK.  The series hybrid and battery electric vehicles could all have batteries with capacities of 100kWh or less [1] and would carry relatively inexpensive pantograph mechanisms on their roofs.

eHighway - Electric Road System (ERS)

Fig. 5 eHighway – Electric Road System.  (Image courtesy of Siemens)

ERS technology would provide deep decarbonisation (approximately 90% from 2016 levels by 2040) [1].  Such a system would distribute charging electricity requirements around the UK land area, with consistent power requirements through the day, instead of major electricity hot-spots in depots at night.

The remaining 1/3 of journeys mainly occur in urban environments. Current indications are that, in the relatively near future, these journeys will be performed by battery electric lorries with modest ranges and battery sizes and possibly some opportunity charging at delivery points.

3  Overall Conclusions

  1. The available evidence indicates that Hydrogen by electrolysis or by SMR are poor choices for energy vectors to power heavy goods vehicles and to power the economy as a whole.  Both systems are fundamentally wasteful in energy terms.  Consequently they would have high economic costs and would require major government subsidies to be economically viable.
  2. An economy based on ‘Green’ Hydrogen would require very large amounts of renewable electricity to account for the energy losses in electricity-Hydrogen-electricity conversions.  An economy based on ‘Blue’ hydrogen would cost about 50% more than an equivalently clean system that used the Methane to generate electricity.
  3. In an electrical economy, buildings can be heated using heat pumps and electricity demand can be managed using efficient, modern storage systems to store electricity.  Using Blue (or Green) Hydrogen to meet these needs would be wasteful and very expensive.
  4. A better solution for long-haul HGVs is direct electrification, particularly using an electric road system – ERS.  This could be implemented in the UK within 10-15 years, for a cost comparable with the UK Government’s planned expenditure on roads for 2020-2025.  The combination of a national ERS and battery electric urban delivery vehicles would decarbonise almost all of the UK’s road freight operations.

So the ultimate question for politicians is whether the future road freight system should be more flexible for operators but have high energy consumption and carbon emissions in the medium term, or be a bit less flexible but much lower energy and carbon in the shorter term.  The jury is out at the moment.  But with the climate change imperative becoming much more urgent, I know which one I would choose…

David Cebon
19 February, 2020

References

  1. Nicolaides, D., Cebon, D., & Miles, J. (2018). “Prospects for Electrification of Road Freight.” IEEE Systems Journal, 12, 1838-1849. https://doi.org/10.1109/JSYST.2017.2691408
  2. Delloite, ‘Energy storage: Tracking the technologies that will transform the power sector’, 2015, https://www2.deloitte.com/content/dam/Deloitte/no/Documents/energy-resources/energy-storage-tracking-technologies-transform-power-sector.pdf
  3. ‘H21 North of England’ project https://www.northerngasnetworks.co.uk/event/h21-launches-national/
  4. Vinca, a. Emmerling, J, Tavoni, M. ‘Bearing the cost of stored carbon leakage’, Front. Energy Res., 15 May 2018 https://doi.org/10.3389/fenrg.2018.00040
  5. ‘Fuels – Higher and Lower Calorific Values’, The Engineering Toolbox, https://www.engineeringtoolbox.com/fuels-higher-calorific-values-d_169.html 
  6. Nicolaides, D. (2018). “Power infrastructure requirements for road transport electrification.” PhD dissertation, University of Cambridge.  https://doi.org/10.17863/CAM.28055