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HIGHLIGHTS
􀂄 PROCESS AND TECHNOLOGY STATUS – A hybrid electrical vehicle (HEV) is a vehicle equipped with either an
internal combustion engine (ICE) and an electrical motor powered by electrical batteries. In 1997, Toyota sold in
Japan the first modern hybrid electric car, the Toyota Prius. Today’s HEVs are an emerging technology in the
automotive market, with manufacturers designing and producing hybrid systems for passenger cars, light-duty
vehicles, heavy duty vehicles, and even locomotives. The improved efficiency of HEVs over conventional (i.e. nonhybrid)
vehicle is achieved by operating a smaller (more efficient) ICE within a narrower, more efficient operational
speed/power band and using an electric engine and electrical storage (i.e. the battery) to balance the performance
energy requirements. In general, in the current-generation HEVs, the combustion engine provides the main power
during long-distance drive while the electrical motor can either complement the ICE or power the vehicle in electriconly
mode (as long as energy is available from the battery) during the urban service, where the ICE is less efficient.
The battery charge is provided by regenerative braking and excess energy from the ICE (stored when the vehicle
has lower power requirements). There are however different grades of hybridization and many configurations of
hybrid vehicles, including micro, mild, full hybrids, with different role for the electric motor. Currently, only hybrids
combining a petrol or diesel combustion engine with an electric motor are commercially available. Improving battery
capacity and technology may enable longer electric drive range and reduce the need for the ICE contribution. Newgeneration
HEVs include batteries rechargeable from the grid (known as plug-in hybrid electrical vehicles, PHEVs,
see also ETSAP TB05).
􀂄 PERFORMANCE AND COSTS – The hybrid vehicles can benefit from the best features of both conventional ICE
vehicles and electric vehicles. Hybrids offer drive range and rapid refuelling the same as conventional vehicles, and
provide high efficiency at low loads, potentially better acceleration, environmental benefits and 25-40% CO2
emissions saving as compared to conventional vehicles [1]. The HEVs cost however is higher. This is largely due to
the high price of the battery. Currently most hybrids use NiMH battery packs, although Lithium-ion is the most
promising battery technology for the future. Li-ion offers better performance and much greater power density
(gravimetric 120+ Wh/kg, volumetric 300 Wh/litre), compared to NiMH (~70 Wh/kg and 150+ Wh/litre respectively).
Smaller and lighter battery packs are therefore possible with Li-ion (around half the size/weight of NiMH). However,
further developments are needed to improve capacity and lifetime, reduce volume and costs (currently around
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