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U.S. Department of Energy Energy Efficiency and Renewable Energy

Hybrid and Plug-In Electric Vehicle Conversions

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A conventional vehicle can be converted to a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), an all-electric vehicle (EV), or a hydraulic hybrid. Such conversions provide options beyond what is available from original equipment manufacturers (OEMs). Certified installers can economically and reliably convert many light-duty and heavy-duty vehicles to operate on electricity alone or to improve the efficiency of conventional vehicle designs.

Hybrid Electric Vehicle Conversions

HEV conversions are becoming attractive options for fleets seeking to increase fuel efficiency and lower emissions. Light-duty HEV conversions require certification from the U.S. Environmental Protection Agency (EPA) and/or the California Air Resources Board (CARB), as do hybrid systems installed in heavy-duty vehicles that modify the OEM engine.

Some companies perform conversions on vehicles purchased by a fleet, while others only install hybrid systems in new vehicles prior to delivery. If a hybrid system will be installed on an existing vehicle, that vehicle must have enough payload capacity to allow for the added weight and space requirements of the hybrid system components.

Hydraulic Hybrid Vehicle Conversions

Hydraulic hybrid systems can increase fuel economy and improve vehicle performance. These systems are well suited for vehicles like refuse trucks, which make frequent stops.

There are two main types of hydraulic hybrid systems: series and parallel. A series hydraulic hybrid vehicle uses hydraulic pumps or motors and storage tanks to recover and store energy, similar to the way HEVs use electric motors and batteries. In parallel hydraulic hybrid systems, when the vehicle slows or stops, the system uses the vehicle's momentum to compress hydraulic fluid. The stored energy then helps the vehicle accelerate on takeoff.

Hydraulic hybrid systems that modify the engine in any way require EPA certification to ensure emissions standards are met.

Plug-In Hybrid Electric Vehicle Conversions

Conventional vehicles and HEVs can be converted to PHEVs by adding additional battery capacity and on-board charging equipment. Some converted vehicles can achieve up to 100 miles per gallon until the auxiliary battery is exhausted, and the vehicle then acts like an HEV.

In some cases, conversions can affect the vehicle's factory warranty. PHEV conversions require certification from EPA and/or CARB.

Several manufacturers offer PHEV conversion systems:

All-Electric Vehicle Conversions

A vehicle with an internal combustion engine can be converted to an EV by completely removing the engine and adding a battery pack, one or more electric motors, high-voltage cables, and instrumentation. To maximize EV driving range, such conversions are often performed on smaller, lighter-weight vehicles.

Neither EPA nor CARB require that EV conversions be certified, as long as the conversion does not add a device that produces fuel combustion emissions. Vehicles that have a gross vehicle weight rating of less than 10,000 pounds, use more than 48 volts of electricity, and have a maximum speed greater than 25 miles per hour must meet Federal Motor Vehicle Safety Standard 305, Electric Powered Vehicles: Electrolyte Spillage and Electrical Shock Prevention.