HEVs

Hybrid electric vehicles (HEVs) are light-duty vehicles that combine an internal combustion engine with one or more electric motors and a battery. The battery is charged through regenerative braking and from the engine, and typically cannot be charged from an external power source. In operation, the electric motor provides assistance to the engine, or can propel the vehicle at low speeds, while the engine develops power at higher speeds or heavy load. HEVs use various configurations, including series hybrids, where the engine only powers a generator for the electric drive; parallel hybrids, where both engine and motor can drive the wheels; and complex power-split or series-parallel designs that blend both modes. Mild hybrids use a small electric motor primarily for start-stop and torque assist, while full hybrids offer electric-only operation for short distances and higher efficiency.

The primary goal of HEVs is to improve fuel economy and reduce emissions relative to conventional internal combustion engines. Regenerative braking recovers kinetic energy to recharge the battery, enabling smoother starts and better efficiency during city driving. Limitations include a higher initial cost, added weight and electrical system complexity, and a battery with finite life. Real-world gains depend on driving patterns, with urban, stop-and-go cycles typically yielding the largest benefits. Battery performance is a concern in extreme temperatures.

Since their introduction in the late 1990s with models such as the Prius, HEVs have become common in many markets, offered by most major manufacturers. They complement fully electric vehicles by providing efficient operation without requiring large-scale charging infrastructure. Policymakers often view HEVs as a transitional technology toward lower-emission transportation, alongside plug-in hybrids and battery electric vehicles.