Concerns over environmental impacts and long term availability of liquid fossil fuels means that sourcing alternative, renewable transport fuels has increased in importance. To date, implemented approaches have concentrated on the production of liquid biofuels biodiesel and bioethanol from crops. Even though technology for implementation is readily available in the form of biogas production and upgrading, gaseous fuels have been largely overlooked in the UK. Research completed showed that if produced from indigenous crops using currently viable technology, it is energetically more favourable to produce gaseous fuels rather than biodiesel or bioethanol with gaseous fuels also delivering some emission benefits at end use. To date, the subsidy system supporting biofuel production has not functioned well. Research showed that if the subsidies approached the maximum allowable value, and when produced from waste materials, the production of gaseous fuels can be economic compared to liquid biofuels. Life cycle assessment has showed that utilising biomethane as a vehicle fuel could be an environmentally appropriate approach if the conventional use for biogas of combusting in a combined heat and power plant cannot utilise the majority of the excess heat produced. A two stage process to produce a hydrogen / methane blend was shown to be energetically favourable when utilising wheat feed, although hydrogen production was low. The process was not energetically favourable when food waste was utilised, indicating the importance of optimising process according to feedstock characteristics. Life cycle assessment of electrolytic hydrogen production using a range of energy sources found that electrolysis driven by renewable energy was a valid option for future deployment. However, given current feedstock availability, indigenous biofuel production, regardless of the fuel produced, could only make minor contributions to overall fuel requirements. As such, a range of fuel vectors, or a significantly greater commitment of land resources to fuel production, will be required in the future.

Drastic reductions of greenhouse gas emissions are required to limit the severe risks associated with a changing climate. One measure is to disrupt the fossil-fuel dependency in the transport sector, but it appears difficult and costly in comparison to other measures. Vehicles and fuels are available, but no single alternative can replace petrol and diesel in all parts of the transport system. None of them are ideal regarding all of the following aspects: vehicle performance, fuel production potential, sustainability, infrastructure, technology development and economy. Instead, several fuels are needed. In this thesis, the aim is to investigate the role of methane and hydrogen in a fossil- free vehicle fleet in Sweden, and compare them with other fuels in terms of well-to-wheel energy efficiency and economy. Processes for producing methane from biomass, waste streams from pulp mills and electricity are studied with techno-economic methods. Furthermore, well-to-wheel studies and scenarios are used to investigate the fuel chains and the interaction with the energy and transport systems. Effects of policy instruments on the development of biogas in the Swedish transport sector are also analysed and policy instruments are suggested to increase the use of methane and to introduce hydrogen and fuel cell electric vehicles. The results reveal that tax exemptions and investment support have been and will continue to be important policy instruments, but that effective policy instruments are needed to develop fuelling infrastructure and to support alternative vehicles. Electricity will be an important transport fuel for several reasons; the electric powertrain enables high energy efficiency and electricity can be produced from various renewable energy sources. Nevertheless, other fuels will be needed as complements to electricity. The results reveal that methane and hydrogen and associated vehicles may be necessary to reach a fossil-free vehicle fleet in Sweden. These fuels have several advantages: -        The function of the vehicles resembles conventional vehicles but with lower local and global emissions. -        Methane is a well proven as a transport fuel and hydrogen infrastructure and FCEVs, are commercial or close to commercialisation. -        They enable high well-to-wheel energy efficiency. -        They can be produced from renewable electricity and act as energy storage. / <p>QC 20150929</p>