 |
 |
 |
 |
|
 |
 |
biomass could be used either directly in the form of liquid fuels or indirectly in the form of electricity
production for charging BEVs which are discussed in section 5.3.
5.2
Using an hydrogen based fuel
Hydrogen is often touted as the fuel of the future since it contains no carbon and can be used directly in fuel
cells to generate electricity relatively efficiently and cleanly. Therefore, superficially at least, the hydrogen fuel
cell route appears attractive as a transport option. However, hydrogen is best seen as an energy carrier, since it
must be generated from another energy source and all the economic methods of producing hydrogen use fossil
fuels as a feedstock. Moreover, the entire hydrogen fuelling process is inefficient, since it involves many
processes each with its own inherent energy losses. It is generally easier, more energy efficient and more
economically viable to use the electricity from power stations either directly using a grid connection and electric
motor or via electrochemical batteries for storage.
There are many other practical disadvantages with hydrogen, particularly the cost. This was clearly
demonstrated during the CUTE project which trialled hydrogen fuel cell buses in various cities using a variety
of energy sources.
31
These buses used more than three times the primary energy and two and a half times the
carbon than the equivalent Diesel bus. Moreover these vehicles typically cost £1 million each and frequently
broke down. The extensive disadvantages and problems with hydrogen generation and storage are discussed in
more detail in this critique
32
Critics of hydrogen also charge that the time frame for overcoming the technical and economic challenges to
implementing wide-scale use of hydrogen vehicles is likely to be at least several decades, and hydrogen vehicles
may never become broadly available. They believe that the focus on the use of the hydrogen car is a dangerous
detour from more readily available solutions to reducing the use of fossil fuels in vehicles
33
Probably the most viable route for hydrogen as a transport fuel lies in generating it through steam reforming
processes from natural gas, although the CO2 generated would still have to be sequestered to qualify as a low
carbon energy source. Some CCS power station concepts already include this process; therefore hydrogen
cannot be entirely discounted as a transport fuel, although it must be viewed only as a long-term possibility.
5.3
Using Battery Electric Vehicles (BEVs)
34
True BEVs are powered from on board batteries that are charged from mains electricity. These should not be
confused with so called ‘hybrid electric’ vehicles, which merely use an intermediate electric drive for
transferring the IC engine power to the wheels more efficiently, and therefore use petrol or Diesel fuel as the
sole source of energy. Plugs-in hybrids represent a cross between an electric hybrid and genuine BEV since
some of the energy used to power them originates from the mains electricity supply.
5.3.1
Environmental benefits of BEVs
BEVs exhibit a major local environmental advantage over IC engined vehicles in that there are no direct
emissions from the vehicles themselves, this provides a substantial benefit in urban areas with air quality
problems. However, emissions can be generated at the power stations that produce the electricity to charge their
batteries, and the overall greenhouse gases emitted are heavily dependent upon the energy generating sources
used.
Most studies suggest that switching to BEVs from equivalent IC engined vehicles would substantially reduce
carbon emissions. In the case of the UK it is estimated that carbon emissions could be reduced by more than
31 CUTE, Urban Transport for Europe, A Hydrogen Fuel Cell Bus Project in Europe 2001 – 2006 Vision, Teamwork and Technology (p.77
fig 4.1.2)
34 A BEV in this section refers to a 4 to 5 person battery electric car or small van which obtains it’s power from an external electricity
supply
|
 |
|