Between a Rock and a Hard Place

HGVs – Henceforth Gas Vehicles?

This post was inspired by my recent attendance at the ADBA UK Biomethane & Gas Vehicle conference.

You may not own or drive a car, but it is almost inevitable that part of your day-to-day your is delivered by heavy goods vehicle (HGV). That Amazon parcel, the food you bought in the supermarket, the pint of beer you drunk in the pub…it all came on a lorry. This transport sector comprises a mere 2% of UK road traffic, yet is responsible for 20% of greenhouse gas emissions (GHG).

The majority of HGVs run on diesel, rather than petrol, due to its ability to generate greater horsepower per volume unit.

HGV traffic on the M25. Credit: N Chadwick

Heavy traffic on the M25. Spot the lorries! Photo credit: N Chadwick

Thanks to global warming infamy, CO2 is firmly lodged in most people’s minds as public enemy numero uno; however, other two components of diesel emissions present an even more immediate risk to human health and the environment:

Particulate matter (PM) is the name given to microscopic solids or liquids suspended in air. When dealing with human health, the two most commonly considered parameters are PM10 (mass per cubic metre of air of particles with diameter <10 microns) and PM2.5 (as before, but diameter <2.5 microns).

Human exposure to particulate matter is pretty bad news; the small size of the particles means they can pass unfettered from the lungs to the bloodstream. This leads to all manner of health problems, ranging from asthma to heart attacks and lung disease. Research from Public Health England shows that in UK urban centres, PM2.5 is responsible for 1 in 20 of the population suffering an early death. Moreover, according to DEFRA, there is no safe threshold below which no adverse effects would be anticipated.

Nasty stuff.

Nitrogen oxides (NOx) are a family of reactive gases produced during diesel combustion. As well as having a detrimental effect on human health, high concentrations of NOx can Inhibit vegetation growth and contribute to the formation of acid rain and ‘city smog’.

Credit: Eriw Preston

City smog is formed when NOx and volatile organic compounds (VOCs) react in the presence of heat and sunlight. London is no stranger to this phenomenon. Photo credit: Eriw Preston

The economic cost from the impacts of air pollution in the UK is estimated at £9-19 billion every year, comparable to the annual economic cost of obesity (over £10 billion). Furthermore, major urban centres in the UK currently exceed EU set targets for NOx emissions, leading to fines of over €400 million per annum to the UK government. Under delocalisation laws, these are set to be passed on to under-performing local authorities.

So, what can be done? Vehicle manufacturers have, in the past, turned to mechanical engineering for inspiration. The European Commission regulates the amount of pollutants that can be emitted by a diesel enginel. In turn, this has led to increasingly complex incarnations of engines which smother and capture the nasties before they are emitted. But there’s a limit to how low we can go using diesel engines, and this approach doesn’t even touch on the carbon footprint associated with the manufacture of petrochemical fuels. Electric vehicles, touted by some as the green transport panacea, have a limited range and the technology is not yet at the level where it can be used on HGVs.

Instead, gas-fuelled vehicles are emerging as a truly credible diesel alternative.

The gas in question is natural gas, a methane-rich fossil fuel which is extracted from geological reservoirs. As a vehicle fuel it can either be compressed (CNG) or supplied in liquid form (LNG); when combusted in engines, both types offer an astonishing 97% and 80% reduction in emissions of PM and NOx, respectively.

If the words ‘fossil fuel’ make you shudder, then fear not – gas with the same composition can also be manufactured using the methane produced by anaerobic digestion of sewage, manure, food waste and agricultural feedstock. Termed biomethane, it offers the same air emissions benefits as natural gas, but in comparison to diesel offers a ‘well-to-wheel‘ CO2 saving of 95%, a ‘tank-to-wheel’ CO2 saving of 20 – 30%. An added bonus is that the solid remnants of the anaerobic digestion process can be used as a fertiliser or soil conditioner, recycling bio-essential nutrients back to soil.

Food waste. Photo credit: Nick Saltmarsh

In the absence of oxygen, organic matter decomposes anaerobically to produce methane. Photo credit: Nick Saltmarsh

Importantly for the commercial fleet market, gas-fuelled vehicles are becoming economically viable. The ‘forecourt’ price of gas is around half that of diesel (ADBA figures estimate an average of 78p/litre), and the differential in fuel duty between diesel and gas has been fixed until 2024. Gas-powered vehicles have half the operating cost of diesel and operate using similar mechanisms to diesel or petrol engines, so can be retrofitted to standard model vehicles.

And it is happening. Although the UK has been slow to catch on, there are currently 85 biomethane-fuelled buses in the UK (though we have a long way to catch up with Sweden, where the number is over 1,500!) and major hauliers are starting to shift away from diesel. For example, 180 of Sainsbury’s HGV fleet now run on dual-fuel engines1.

Photo credit: Jon Law

Reading Buses operate a fleet of 20 CNG-fuelled buses. Photo credit: John Law

For the UK gas vehicle market, there are still many challenges ahead. Improvements are needed in infrastructure: there are currently around only natural gas 14 fillings stations in the UK. We need to ensure long term supply of biomethane, most easily achieved by banning the disposal organic waste to landfill or incineration. Government subsidies must be balanced to incentivise gas use transport fuel rather than for heating.

These issues notwithstanding, natural gas, supplemented by increasing volumes of biomethane, really does have the potential to revolutionise the way we fuel HGVs. Small scale farming operations could use tractors fuelled by biomethane from their own agri-waste feedstock; supermarkets could potentially run trucks being powered by biomethane from inedible food waste; buses may one day be powered from crop residues. Add in the intrinsic energy security benefit of being able to locally generate HGV fuel and you really start to see why people are beginning to get so excited.

In environmental terms, it’s a no brainer; in human health terms, this transition really will save lives.

[Footnote 1] Dual-fuel engines are designed to use diesel at speeds <50mph so are unlikely to contribute to improving air quality in urban areas; the carbon savings still hold.



Charly completed a PhD in experimental petrology. She used to make pretend volcanoes; now she works in renewable energy. Charly tweets at @C_Stamper.