Question of the Month: What are the key terms to know when discussing electric drive vehicles and their fueling infrastructure?
Answer: It is important to know how to “talk the talk” when it comes to electric drive vehicles. Becoming familiar with the terms below will help you better understand these vehicles and the associated fueling (charging) infrastructure, so that you can ask the right questions and make informed decisions:
There are two main categories of electric drive vehicles:
1. Hybrid electric vehicles (HEV) are powered by an internal combustion engine or other propulsion source that runs on conventional or alternative fuel, as well as an electric motor that uses energy stored in a battery. The battery is charged through regenerative braking and by the internal combustion engine, and is not plugged in to charge. Regenerative breaking is a technology by which energy normally lost during braking is captured by the electric motor and stored in the battery for extra power during acceleration. There are two different types of HEVs:
Mild hybrid: This type of HEV uses a battery and electric motor to help power the vehicle and can allow the engine to shut off when the vehicle stops (such as at traffic lights or in stop-and-go traffic). Mild hybrid systems cannot power the vehicle using electricity alone. Example: Chevrolet Malibu Eco
Full hybrid: This type of HEV generally has more powerful electric motors and larger batteries, which can drive the vehicle on just electric power for short distances and at low speeds. Example: Toyota Prius
HEVs can be designed in two different configurations:
Parallel: This configuration connects the engine and the electric motor to the wheels through mechanical coupling and allows both the electric motor and the engine to drive the wheels directly, either simultaneously or independently.
Series: In this configuration, only the electric motor drives the wheels. The internal combustion engine is used to generate electricity for the motor.
2. Plug-in electric vehicles (PEV) refer to any on-road vehicle that can be charged through an external source of electricity. There are two different types of PEVs available:
Plug-in hybrid electric vehicle (PHEV): Like HEVs, these vehicles are powered by an internal combustion engine that can run on conventional or alternative fuel, as well as an electric motor that uses energy stored in a battery. The difference is that these vehicles can be plugged into an electric power source to charge the battery. PHEVs can have a parallel or series design as well. Example: Chevy Volt
Electric vehicle, or all-electric vehicle (EV): These vehicles use a battery to store the electric energy that powers the motor. EV batteries are charged by plugging the vehicle into an electric power source. EVs are sometimes referred to as battery electric vehicles (BEVs). Example: Nissan Leaf
Neighborhood electric vehicle (NEV): These vehicles are smaller and have less battery power than traditional EVs, and are often referred to as low-speed vehicles. NEVs are confined to roads with lower speed limits and states set specific regulations regarding their use.
Charging equipment for PEVs is known as electric vehicle supply equipment (EVSE). Charging times vary based on how depleted the battery is, how much energy it holds, the type of battery, and the type of EVSE. Before exploring types of EVSE, it’s important to first understand the basics of electricity through the following terminology:
Alternating current (AC): Movement of electric current that reverses or alternates direction. AC is the form of current normally generated and delivered by an electric utility to homes and businesses.
Direct current (DC): Movement of electric current that continuously flows in the same direction. DC is the form of current normally delivered through batteries and is essential to charging vehicle batteries. As certain types of EVSE only provide AC (Level 1 and Level 2 described below), all PEVs are equipped with onboard equipment to convert the current to DC.
Amperage: The amount of electrical current, which can be thought of as the rate of flow. Amperage is measured in amperes, commonly referred to as amps.
Voltage: The electric potential energy per unit charge, which can be thought of as the force or pressure that drives the electric current. Voltage is measured in volts (V).
By multiplying amperage by voltage, you can find the unit of power, otherwise known as watts (W). There are 1000 watts in a kilowatt (kW). A typical residential three-prong outlet can supply 12 amps at 120V, or 1.44 kW based on the following equation:
12 amps x 120V = 1440 W / 1000 = 1.44 kW
PEV battery pack energy capacity is measured in kilowatt-hours (kWh). A kWh is a unit of energy that indicates the ability to provide a given amount of power for one hour. In theory, a 24 kWh battery pack would take 16.7 hours to charge using a standard 3-prong outlet based on the following equation:
24 kWh / 1.44 kW = 16.7 hours
There are five different types of EVSE outlined in the table below.
Additional information on electric drive vehicles, infrastructure, and batteries can be found on the Alternative Fuels Data Center Electricity website (http://www.afdc.energy.gov/fuels/electricity.html).