A plug-in hybrid electric vehicle (PHEV) is a full hybrid, able to run in electric-only mode, with larger batteries and the ability to recharge from the electric power grid. They are also called gas-optional, or griddable hybrids. Their main benefit is that they can be gasoline-independent for daily commuting, but also have the extended range of a hybrid for long trips. They can also be multi-fuel, with the electric power supplemented by diesel, biodiesel, or hydrogen. The Electric Power Research Institute's research indicates a lower total cost of ownership for PHEVs due to reduced service costs and gradually improving batteries. The "well-to-wheel" efficiency and emissions of PHEVs compared to gasoline hybrids depends on the energy sources of the grid (the US grid is 50% coal; California's grid is primarily natural gas, hydroelectric power, and wind power). Particular interest in PHEVs is in California where a "million solar homes" initiative is under way, and global warming legislation has been enacted
A gas-electric hybrid engine is a combination of a gasoline/petrol or diesel internal combustion engine with an electric motor to power a vehicle. Various designs exist for how the motor and engine interact with the drive train. Because the engine recharges the battery smaller batteries are required than in an electric vehicle.
A standard combustion engine is required to operate over a range of speed and power, yet its highest efficiency is in a narrow range of operation. Also, an engine designed for a reduced operating range can be more efficient than a standard engine. The battery storage and electric motor allows the engine to operate at its point of maximum efficiency, to be of a higher efficiency design, and to be smaller than non-hybrid applications.
The gas-electric hybrid uses less gasoline than conventional internal combustion engines and does not have the limitations in range that have been a problem for traditional electric vehicles. This type of piston engine is used in hybrid electric vehicles which have begun to enter the market as of 2002.
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