Hybrid vehicle and environment impact

A hybrid electric vehicle (HEV) combines an internal combustion engine (ICE) with one or more electric motors and a battery, so that each works where it is most efficient.

Working principle

• At low speed or start, the electric motor drives the car (the engine is off, no idle emission).
• At normal and high speed, the engine drives the wheels and also charges the battery through a generator.
• During hard acceleration, both engine and motor work together.
• During braking and coasting, regenerative braking converts kinetic energy into electricity and stores it in the battery.
• An electronic controller decides the best mix, and the engine is shut off at stops (start-stop).

Types

1. Series hybrid: the engine only drives a generator; the motor drives the wheels.
2. Parallel hybrid: both engine and motor can drive the wheels directly.
3. Series-parallel (power-split) hybrid: combination (Toyota Prius).
4. Plug-in hybrid (PHEV): larger battery that can be charged from the grid, with an electric-only range.

 Fuel tank -> [Engine] --+--> [Transmission] -> Wheels
                         |         ^
              [Generator]-> [Battery]<->[Motor]

Environmental impacts

Positive

• Higher fuel economy (30–50% better than a conventional car) and lower CO₂, NOₓ, CO and PM per km.
• Quieter in the city and lower dependence on imported petroleum (relevant for Nepal).
• PHEVs charged with hydroelectricity have very low emissions.

Negative

• Battery production uses lithium, cobalt and nickel, with mining impacts and energy use.
• Battery disposal and recycling issues; heavier vehicle and higher cost.
• Still burns fossil fuel and emits pollutants, unlike a pure battery EV; emissions depend on how electricity is made. Overall, the life-cycle emissions of hybrids are lower than those of petrol or diesel cars.