Is bio-methane the greenest?

In the ongoing debate about the suitability and sustainability of biofuels for vehicle transport in the UK, the potential of bio-methane is often forgotten

The UK’s natural gas vehicle (NGV) infrastructure is negligible compared with that of other countries. The recently announced King review listed technologies that are available to reduce carbon emissions from vehicles over a 25-year time frame. And this offers a chance to re-examine the economic and environmental case for bio-methane-fuelled NGVs.

Biogas is the gaseous product of the anaerobic digestion of wet organic waste materials, consisting of about 55-75% methane and 25-45% CO2.

Bio-methane is biogas purified to above 95% methane and cleaned. Methane, as compressed natural gas or liquefied natural gas, is a widely used vehicle fuel around the world. According to the UK Natural Gas Vehicle Association, there are more than 400,000 NGVs in Italy.

Natural gas offers numerous attractions as a green fuel:

  • Methane, as the simplest hydrocarbon, contains a high proportion of hydrogen to carbon, so it burns more cleanly than petrol or diesel
  • Exhaust pipe emissions of NGVs are low in particulates and nitric oxides (NOx)
  • Natural gas engines are often much quieter than their diesel counterparts

Turning to bio-methane – a renewable non-fossil fuel – in terms of greenhouse gas reduction, it is potentially the most effective biofuel, according to the 2007 EUCAR/CONCAWE/JRC Well-To-Wheels report. This is because biogas produced from liquid manure has the potential for negative greenhouse gas emissions, as the process captures methane that would otherwise be released into the atmosphere, thereby acting as a methane sequestration technique.

One of the principal arguments in favour of promoting the capture and use of biogas from organic waste digestion is that it would alleviate the growing problem of finding sustainable waste disposal solutions.

The UK is one of the largest generators of methane from the controlled digestion of waste from landfill in Europe (most of which is used to generate electricity). But the 1999 EC Landfill Directive set challenging targets for the diversion of bio-degradable municipal waste from landfill. By 2020, each local council will be have to cut disposal of bio-degradable waste to landfill by 65%.

In the UK, the Landfill Allowance Trading (Lats) Scheme permits local authorities to trade allowances. Therefore, the development of a biogas capability for local authorities will enable them to:

  • Satisfy EU and UK legislative requirements on waste
  • Gain credits from other local authorities via allowance trading
  • Provide a sustainable fuel for their fleets

But what are the barriers to using bio-methane as a transport fuel?

  • Infrastructure

    The principal barrier to the wider adoption of bio-methane, and indeed all NGV technologies in the UK, is the lack of a distribution infrastructure. Case studies in Europe show that investment in this infrastructure will promote the wider adoption of bio-methane as a road transport fuel.
  • Lack of vehicles

    Figures presented recently by the NGVA at the recent Cenex Naturally Gas conference in Loughborough showed that there are around 400 NGVs in the UK, and the refuelling infrastructure is actually shrinking. Worldwide, however, there are 20,000 refuelling stations and more than six million NGVs, with the number of new vehicles being introduced rising by 20% annually. There is a dearth of domestically manufactured passenger and light goods vehicles. But there are some innovative heavy goods vehicles being manufactured in the UK, such as those provided by Hardstaff and Clean Air Power.
  • Electricity and gas generation

    It is inevitable that there has been, and in many cases will continue to be, a preference to generate electricity from bio-methane. In addition, many existing biogas plants, and those under consideration in the UK, pump the purified methane produced back into the national gas grid. But, within the current UK legislative framework, renewable obligation credits are not issued for bio-methane entering the national gas grid – so biogas producers receive no green credit for its production.

According to a recent analysis (Biogas as a Road Transport Fuel, NSCA, 2006), there are around 30.5Mt of waste that could be made available for anaerobic digestion to biogas every year. If this were all converted to bio-methane, this could yield 6.3Mt of oil equivalent, or around 16% of the UK’s total usage of 38Mt of oil equivalent. As much of this waste will continue to have other uses, a more realistic conversion estimate still suggests that bio-methane could still supply 8-10% of road fuel.

Figures presented at the Naturally Gas conference claimed that bio-methane vehicles are around 40% cheaper to run than diesel, and 55% cheaper than petrol equivalents. But these fuel savings are offset by higher capital costs – around £20,000 for a dual-fuel heavy goods vehicle conversion and £5,000 for a light goods vehicle – and possible higher maintenance costs. Hardstaff chairman Trevor Fletcher said, in driving 80,000 miles in a year, a Hardstaff dual-fuelled heavy goods vehicle averaged 21 pence per mile, with a fuel consumption equivalent to that of pure diesel, equivalent to savings of £16,000 over a pure diesel heavy goods vehicle, which more than offset the capital cost of the vehicle.

Cenex was created by the UK government as a public-private partnership to ensure the competitiveness of the UK automotive supply chain in low-carbon technology. Its core strategy is to broker technology demonstration, and to promote knowledge transfer in key technology areas via the Low Carbon and Fuel Cell Knowledge Transfer Network (LCFC KTN), Bio-methane provides a logical focus for the activities of Cenex. It develops showcase projects in turning waste into bio-methane for transport. And it works with the knowledge transfer networks and other stakeholders in engaging the supply- and demand-side communities who wish to use bio-methane.

To bring together the activities of the bio-methane community – spanning digestion technology, waste disposal, vehicle operators and vehicle manufacturers – Cenex and the LCFC KTN have joined with other stakeholders to form Biomethane for Transport. This is a forum to promote bio-methane in the UK.

The King review aims to answer the question as to whether decarbonisation of vehicles can be achieved cost-effectively in a 25-year time frame by incremental evolution of existing technologies or more radical approaches. Responding to the review allows the bio-methane and NGV community to promote the case for NGVs as a mature technology that is widely used around the world. It is clear that a wider take-up of NGV technology would be a starting point towards the wider rollout of bio-methane as a vehicle fuel.

Consistent long-term support and policy making from government will further speed bio-methane adoption. This includes carrying through the stated intention to increase the Renewable Transport Vehicle Obligation level above 5% as soon as is practical; opening the Bus Service Operators Grant to other fuels; and fuel duty incentives on a par with other biofuels. Although the UK does not have a positive track record with NGV technology, the case for natural gas and bio-methane in captive vehicle fleets – particularly local authority fleets where bio-methane offers an integrated waste disposal solution – is strong. Cenex, the LCFC KTN and Bio-methane for Transport aim to promote the case of bio-methane as a credible and sustainable biofuel whose time has come.

Further Information

Much of the information in this article was abstracted from the report Biogas as a Road Transport Fuel, published in August 2006 by NSCA and co-sponsored by Cenex on behalf of the LCFC KTN. The report can be downloaded from

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