Electric vehicles 101

Electric vehicles 101

Get to know electric vehicles better.

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What is an EV?

An electric vehicle (EV) is a vehicle that runs on an electric current. There are three main types of vehicle commonly called "electric", and it's worth knowing the difference:

  1. Battery electric vehicles (BEVs) run only on electricity. With a BEV, you charge the car's battery with electricity. That battery then powers the electric motor, which propels the car forward. Since the car itself is not burning a fuel to generate movement, there are no tail-pipe emissions. Instead, the carbon footprint of a BEV depends on how the electricity that runs it is produced. Some common BEVs in our program are the Chevrolet Bolt, Nissan LEAF, and BMW i3.
  2. Plug-in hybrids (PHEVs) combine a battery-powered electric motor with an internal combustion engine. You charge your vehicle with electricity and use it much like an all-electric vehicle. However, if and when you run out of charge, the internal combustion engine serves as a back-up. While running only on electricity, a PHEV's carbon footprint again depends on the fuel mix that generated the electricity. As soon as the internal combustion engine switches on, the engine's tail-pipe emissions add to the vehicle's carbon footprint. Some common PHEVs in our program are the Chevrolet Volt, Honda Clarity, Toyota Prius Prime, and BMW i3 with Range Extender.
  3. Hybrid electric vehicles (HEVs) also combine an internal combustion engine and an electric propulsion system. However, HEVs are “charged” with gasoline; you cannot plug them in to charge them with electricity, so they are not strictly speaking “EVs”. However, HEVs are more efficient than traditional internal combustion engines because they take advantage of technologies such as regenerative braking. The best known HEV is the Toyota Prius.

When we talk about “EVs”, we’re talking about battery-electric vehicles (BEVs) and plug-in hybrids (PHEVs). The Drive Green program does not include HEVs.

EVs contrast with conventional vehicles, which run on an internal combustion engine: you add a fuel (gasoline, diesel fuel, or ethanol), it ignites and releases energy that is translated into motion. In the process, however, the vehicle releases carbon dioxide, one of the greenhouse gases contributing to climate change.

EVs are more efficient than gasoline-powered cars

EVs are better for the environment than gas-powered cars, not just because gas-powered cars rely on fossil fuels, but because EVs are more efficient.

A little background: cars can move because they convert energy from fuel (diesel, gasoline, or electricity) into kinetic energy, or the energy of motion. Efficiency measures how much of the energy in fuel is converted into kinetic energy to get the tires rolling.

It is impossible for any machine to be 100% efficient because some energy is always lost to generating heat in the process. Due to physical limitations of cars, some energy will be lost to wind resistance and rolling resistance from tires. But in general, the higher the efficiency, the less energy we need to power our car. In other words, efficiency means achieving the same performance without consuming as much energy.

(This has big implications for moving towards a low-carbon future. For every unit of energy we don't have to use because of improved efficiency, we are reducing our demand for energy and making it more feasible for renewables to dominate our electrical grid. It means we're doing more with less, or creating what environmentalist Amory Lovins would call a "negawatt.")

Gas- and diesel-powered vehicles are not very efficient because they rely on internal combustion engines, which generate a lot of waste heat. There are also a lot more moving parts in thermal engines, like fuel pumps, and they use some of the gasoline's energy but don't contribute to the car's motion. As a result, gas-powered cars can convert only about 17% - 21% of the available energy in gasoline to kinetic energy. You can see a breakdown of where all that lost energy goes here.

 

energy losses in gasoline-powered cars

Regenerative braking, which recovers the energy that is otherwise wasted when we use brakes, has been instrumental in improving vehicle efficiency. Hybrid cars have this feature. Regenerative braking can improve the efficiency of a fossil-fuel-powered car up to between 21% and 40%. That means that even the most efficient gas-powered cars can use only about 40% of the available energy stored in gasoline.

By comparison, the effciency of an electric car typically hovers around 60%, jumping up to about 77% if you include the effects of regenerative braking – which you should, since all electric cars use it – some better than others. EV efficiency is then four times better than the average gas-powered vehicle and two times better than the most efficient hybrid. So by driving an electric car, you're not only reducing demand for oil specifically, but you're consuming less overall energy to travel the same number of miles.

This difference in efficiency has two big implications. First, it costs less to run a car on electricity than petroleum. Second, it adds to the environmental benefits of EVs.

Eventually, when EVs are the norm, instead of asking how many miles per gallon a car gets, people will ask how many miles per kilowatt-hour. 

Car shopping & EV basics

Hybrid/EV Buying Guide

Buying Guide from Consumer Reports
Last updated January 2018

A concise guide to buying and owning a plug-in vehicle.

Read the guide

The Car Book's Snapshot Guide to Electric Vehicles

Buying Guide from the Consumer Federation of America
Posted on May 14, 2018

A snapshot guide to the next generation of vehicle power and how they rate.

Read the guide

Best Electric Cars

Buying Guide from Edmunds.com

Browse electric cars and see Edmund's top picks.

Read the guide

More Useful Links

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Range & Charging

The Battery & Range

The Battery & Range

EV battery size is measured in kilowatt-hours (kWh). The more kWh capacity your car’s battery has, the farther you can go between charges. This kWh capacity, along with your car's efficiency, determines your car’s range.

The Onboard Charger

The Onboard Charger

Your car will have an onboard charger. Its capacity, measured in kilowatts (kW), affects your charging speed. The more kW, the faster the charge!

Emissions & Climate Change

A vehicle running only on electricity has zero tail-pipe emissions. Even if you account for the emissions associated with producing the electricity to charge them, electric vehicles charged with electricity in New England produce far fewer greenhouse gas emissions than vehicles powered by internal combustion engines.

On top of that, our electric grid is getting greener with each passing year, thanks to laws like the Renewable Energy Portfolio Standard in Massachusetts and the Renewable Energy Standard in Rhode Island, which require electricity suppliers to increase their renewable energy content each year. This means the environmental benefits of EV will increase each year.

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