Hybrid car: Uses a mixture of power sources; at present, petrol engine and electric motor in parallel if not qualified. Example: Toyota Prius.
Parallel hybrid: Both engine and electric motor are connected to a conventional gearbox. Various modes of operation are available, including electrical power alone, though most systems only allow this for short journeys. The electric motor usually assists the engine. Example: Honda Insight.
Series hybrid: This is what we now call a "range extender", where drive to the wheels comes from an electric motor – even if a conventional internal combustion engine is used to drive an electric generator that charges batteries, from which the motor takes its power. Example: 2012 Opel Ampera.
Series-parallel hybrid: The main difference between this and a regular parallel hybrid is that both power sources can be decoupled or connected to the wheels independently. Example: Lexus RX 450h.
Range extender: See series hybrid.
Plug-in hybrid: A plug-in hybrid has a battery pack that can be recharged by plugging it into an external electricity source – either a domestic supply or special quick charger. The hybrid type could theoretically be any of the above, although it is likely to be a feature used in a car that has a substantial electric-only range. Example: 2011 Toyota Prius.
Start-stop: To save fuel while stopped in traffic or at the lights, some cars have a start-stop system that automatically turns off the engine and quickly restarts it when pulling away. Most cars so equipped have uprated starter motors and batteries, along with other modifications. Example: Mazda3 with i-Stop.
Brake energy regeneration: Cars fitted with generators (usually combined in unit with a motor) can recover energy usually lost as heat to a car's brakes. The generator slows the car while charging the battery. (Some makers claim to feature brake energy regeneration when their system attempts only to charge the battery with the alternator during deceleration.) Example: Lexus LS 600h.
Mild hybrid: Despite the title, this refers only to cars that use start-stop and some form of brake energy regeneration – even just smart alternator use. Example: Mini Cooper.
Fuel cell: An electrochemical cell that produces electricity from a chemical reaction. In terms of cars, this means a hydrogen fuel cell, where the chemical reaction is between hydrogen and oxygen and the only output is water. A fuel cell could be used instead of an internal combustion engine in a range extender. Example: Honda FCX Clarity.
Biofuel: Liquid fuel derived from plant origins, including bio-ethanol and bio-diesel. Bio-ethanol is sold as E85 – 85 per cent ethanol and 15 per cent petrol, the latter to assist with cold starting.
FFV: Flexible Fuel Vehicle. Can run on a variety of fuel types, typically regular petrol and either ethanol or methanol (usually a biofuel). Engines and their control systems require modification, but many cars have the capability to run on small percentages of alcohol-based fuel as standard. Example: Volvo S40 Flexifuel.
CNG: Compressed Natural Gas. Used as an alternative to petrol or diesel in suitably converted FFVs. Burning CNG releases greenhouse gases, but is cleaner than other fossil fuels.
LPG: Liquefied Petroleum Gas – usually a mixture of propane and butane, and used in converted bi-fuel vehicles. Significantly less CO2 is emitted than when running on petrol. Also referred to as "Autogas".
– Shane O’Donoghue
