COMPARING THE ENVIRONMENTAL BENEFITS OF HYBRID,
FUEL CELL AND BATTERY VEHICLES
Most hybrids simply use electricity
as a means to store and transfer energy within the vehicleall
the energy used by the vehicle ultimately comes from petrol or
diesel in the fuel tank. The practical effect is simply to enable
petrol vehicles to compete in terms of fuel economy with diesels.
In urban situations, the stop/start
ability of the hybrid saves fuel (up to 50%) but on motorway journeys
the energy storage system becomes largely irrelevant, which is
why practical fuel savings from hybrids are generally reported
as being around 15-20% compared to conventional equivalents.
Plug-in hybrids act as a pure electric
vehicle to the extent that they use electricity from the mains
to supplement the energy from petrol or diesel. This configuration
of vehicle typically has a pure electric range of 10-20 miles
and offers some of the advantages of a pure electric vehicle.
There are currently no plug-in hybrid vehicles in production.
Before the development of more advanced
and efficient fuel cell technology, using methanol from renewable
sources, hydrogen fuel cells have been proposed as an intermediate
step, along with the concept of a "hydrogen economy".
Hydrogen fuel cell vehicles have been demonstrated and small scale
hydrogen distribution systems built.
The key point is that hydrogen is
an energy storage mechanism, rather than a primary fuel. To make
hydrogen from natural gas produces more CO2 than to
burn petrol or diesel. To make hydrogen from water using electricity
generated from renewable resources is the ideal. However, to convert
electrical energy into hydrogen, transfer, store it and convert
it back into electricity to drive a car is less efficient than
to simply transmit the electricity via the existing grid and store
it in a battery.
Battery electric vehicles
Battery or `pure' electric vehicles
are charged up from the mains and as such they generate zero local
emissions. Although mains electricity is not inherently zero carbon,
it is extremely easy to connect to a renewable energy tariff and
incentives such as the climate change levy (0.43p per KWh for
non renewable electricity supplied to businesses) are in place
to encourage the use of renewable energy.
Indicative environmental performance of vehicles
can be thought of along two key axes: