Select Committee on Environmental Audit Written Evidence




    —  Most hybrids simply use electricity as a means to store and transfer energy within the vehicle—all 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.

Fuel Cells

    —  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:

February 2006

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