Electrification of road freight using overhead cables

The government recently announced plans for the electrification of road freight, with installation of overhead cables on major roads in the UK. In this article, Gautam Kalghatgi, an engineer and a member of GWPF’s Academic Advisory Council, looks at some of the practicalities.

Putting overhead cables on just motorways and dual carriageways could cost around £58 billion (the basis of this figure is set out below). It will be practically impossible to install overhead cables on most of the rest of the 31,800 miles of the major road network. If the freight fleet is to be fully electric, lorries would therefore have to rely on on-board batteries in places where they cannot be charged by the overhead cable.

Electrifying the freight fleet would require a major expansion of electrical generation capacity. Assuming this comes from from wind power, 22 GW of new windfarms would be needed (assuming an improved capacity factor of 0.4) supported by sufficient storage capacity. Detailed calculations are set out below. This new capacity is likely to cost over £88 billion and there would be significant ongoing operating costs. For comparison, total wind capacity in 2019 in the UK was 24.1 GW.

Energy supply to the trucks would have to be guaranteed at all times. This will mean that electricity generation from natural gas has to be retained for when the wind was not blowing. The alternatives – electricity or nuclear power – are both prohibitively expensive.

The total capital cost could therefore be £130–150 billion, and there would be significant ongoing operating costs.

Honest life-cycle analysis is needed for all the alternative approaches. This should include greenhouse gas (GHG) contributions from the electricity used for running the lorries, manufacturing and the end- of -life disposal/recycling of batteries and installing the infrastructure. Running long-haul transport on electricity alone will certainly not be a zero-GHG solution even with increasing decarbonisation of the electricity supply. If the battery capacity needed is large, even after some of the electricity is taken from overhead cables, such an approach could have minimal or even negative impact on GHG emissions compared to using advanced diesel engines.

Detailed calculations and considerations

Infrastructure

There are 31,800 miles of major roads (2,300 miles of motorway and 29,500 miles of ‘A’ roads) in Great Britain.1 Dual carriageways account for about 17% of A roads2 so there are around 7,315 miles of dual carriageways and motorways.

Electrification of the rail network has taken decades and offers some guidance about the costs. However, there are great practical difficulties in installing overhead cables on roads compared to railway tracks:

  1. Normal A-road verges are not secure, unlike railway lines, and so a different and more expensive electrical supply cabling will be required.
  2. Bridges on the road network limit the overhead clearance.
  3. Managing the power supply to the overhead cables will be challenging. For instance, unlike on the railways, there could be several lorries on a steep hill drawing electricity. This draw would need to be limited to avoid overloading or burning the overhead cable.

Complex electrification projects on the railways have cost up to £2.5 million per km of single track.3 So, installing cables on both sides of the road should cost up to £5 million per km. Hence, installing overhead cables just on the motorways and dual carriageways would cost £58 billion.

Additional electricity generation

The UK HGV fleet’s fuel consumption is around 12 million tonnes pa (140 million MWh).4 Assuming an average brake thermal efficiency of 0.42 for modern diesel powertrains,5 59 million MWh actually gets to the wheels and this has to be supplied by electricity, some of it from overhead cables. However, up to 10% of electricity is lost in transmission and distribution in the UK.6 A further 5% of the energy is lost in converting the overhead AC power to DC and typically another 10% in the DC motors. The result is that only around 77% of the electricity produced is available at the wheels. So, to supply 59 million MWh, 77 million MWh of electricity needs to be produced on average. This is equivalent to 8.8 GW of continuous power generation on average, equivalent to three Hinckley Point C nuclear reactors at around £25 billion each.

The capacity factor for wind in the UK, averaged over 2019 was 0.3 – the installed wind capacity of 24.1 GW, if it had worked continuously at rated capacity, should have supplied 0.76 exajoules, but actually supplied only 0.231 exajoules7 on average. Assuming a much-improved capacity factor of 0.4, new wind capacity of 22 GW has to be built to supply 8.8 GW needed on average. Assuming a capital cost of £4000 per MW, the capital cost of this new wind installation alone would be around £88 billion and the operating costs also would be extremely high.8 The excess electricity that will be produced from time to time can be used to produce hydrogen or electro fuels or stored in batteries. Providing this “storage” capacity will add further to the costs.

In any case, the power supply to the HGV fleet has to be guaranteed at all times and hence has to come from baseload electricity, and needs to be dispatchable, so as to quickly adapt to any changes in demand. Baseload electricity is usually produced from fossil fuels, so taking this path to power long-haul transport will not get rid of electricity generation from natural gas. The actual CO2 benefit will be less than assumed with zero-CO2 electricity. The only alternatives are:

  • electricity storage, such as batteries, but this would add significantly to the costs
  • new nuclear capacity, but this could cost £75 billion.

Honest life-cycle analysis is needed for all the alternative approaches. This should include greenhouse gas contributions from the electricity used for running the lorries, manufacturing and the end- of -life disposal/recycling of batteries and installing the infrastructure. Running long-haul transport on electricity alone will certainly not be a zero-CO2 solution. If the battery capacity needed is large, even after some of the electricity is taken from overhead cables, such an approach could have minimal or even a negative impact on greenhouse gas emissions compared to using advanced diesel engines.

References

  1. https://ift.tt/2Tv6D3e
  2. https://ift.tt/3znWRix
  3. Railway Industry Association, 2019 https://ift.tt/34SGldo
  4. https://ift.tt/3wV5e3G
  5. Ch.8: SuperTruck program in “Review of the 21st century truck partnership: third report (2015). National Academic Press. ttps://www.nap.edu/read/21784/ chapter/10
  6. BP Statistical Review of World Energy 2020. https://ift.tt/3eM2u2b
  7. Hughes, G., Wind Power Economics – Rhetoric and Reality, 2020 https://ift.tt/3zowVn3
  8. Mike Travers, Hidden Cost of Net-Zero: Rewiring the U.K., 2020, https://ift.tt/2V6eLHD

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July 22, 2021 at 04:37AM

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