Range Confidence: Charge Fast, Drive Far, with your Electric Car

By David Herron

Range Extension & total driving range

The hundred or so years humanity has driven cars, society has adapted to taking road trips. Hop in the car, stopping for quick gas stops, and racking up hundreds of miles a day of driving. With current electric cars and charging infrastructure, that mode of road trip is difficult, which has folks urgently looking for ways to implement road trips with electric cars. Some car makers taught us the phrase "extended range electric vehicle" to satisfy the road trip urge.

What does the phrase Extended Range or Range Extension mean? Doesn't it just mean quickly recharging the energy stored in the car?

The "Extended Range Electric Vehicle" phrase the car makers taught us refers to Plug-in Hybrids. In that case gasoline is used to quickly recharge the energy stored in the car. But doesn't recharging the car at a charging station also extend the range? Why can't EREV or EVER refer to other kinds of electric vehicles?

The key to a road trip isn't the size of the battery pack or the gas tank. The key is how quickly stored energy can be added to the car. The best measurement is the total driving range in a day. This is how far you can drive accounting for recharging sessions throughout the day.

Total Driving Range: Let's try to define this a little better. One definition is "The theoretical maximum distance drivable in 24 hours with optimal driving and recharging."

Is this theoretical maximum driving range useful for you in your life? A healthy road trip covers 12 hours of driving a day, not 24 hours of driving per day. But the theoretical range in 24 hours is a great way to compare vehicles.

What you need to know which electric car handles your long trips, your weekend trips to the mountains, or to Grandma's house, or wherever.

Marketing phrases

"Extended Range EV" is the phrase GM invented for the Chevy Volt. The Volt is billed as being more than an EV, because it has "extended range". Meaning, the gasoline engine extends the vehicle range.

There's a semantic thing to quibble about. The Volt is an electric car in the sense that it can be plugged in to recharge the battery pack. For a long time the quip was "it’s not electric if you can’t plug it in", and by that measure the Volt is an EV. But there is also a well defined phrase, "plug-in hybrid", describing a hybrid vehicle (two power sources working together to drive the car) which can be plugged in to recharge the battery pack. The Volt is a Plug-in Hybrid EV (PHEV), and it even says so on the EPA sticker. To the extent the "Extended Range Electric Vehicle" has any meaning, the Volt is also an EREV.

Let's not get lost in this semantic thing. The Volt, and other PHEV's, are fine cars and the gasoline engine is a pragmatic solution to driving road trips. The gasoline engine range extender means it's not as "pure" an electric vehicle as one that only runs on battery power. But, it also demonstrates the value of quickly replenishing the on-board energy storage for longer total driving range.

Range Extension

There's two general ways to extend total driving range with an electric car

  • Extending the range while driving - somehow the battery pack recharges while driving
  • Extending the range by stopping to recharge - plugging in and charging

Some say that stopping to charge does not qualify as a "range extender" system. That a range extender system must add range while the car is driving. That's another semantic quibble that could detour us into a verbal swamp. Isn't the "Total Driving Range" the measurement we need to focus on?

Extending the range while driving

Portable towable battery packs: This is a design idea some have floated, to have a battery pack on a small trailer towed behind a car. One could easily rent the trailer for long trips, connecting it to a special charging port that allows the car to drive while the addon pack is plugged in. Battery trailer exchange stations could be located at stops along highways, similar to the propane tank kiosks seen at gasoline stations today.

Portable towable gasoline generators: A similar idea is to, instead of a towed battery pack, to have a towed gasoline generator. A big issue is this arrangement stops being a battery EV, and starts being a Plug-in Hybrid, and legally it stops being a ZEV. There are government emissions rules with ZEV meaning a vehicle that has zero tailpipe emissions. But if the vehicle has a part-time gasoline engine, it would fall into a classification that does not yet exist.

A problem with the towable battery pack or gasoline generator is that electric cars are explicitly designed to not charge through the charging port while the car is driving. That was a safety feature to prevent drive-off's. The impact is needing to bypass that design feature when using a towed recharging gadget.

Fuel Cell: Fuel cell vehicles do have an all electric drive train, and a small battery pack to hold electricity. Hence, it’s not that much of a stretch of terminology to call the fuel cell a range extender. There’s even some work to design fuel cell vehicles with larger battery packs where the fuel cell is used as a portable range supplement.

Gasoline Engine range extender: These vehicles are what we normally use the phrase “range extender” to describe. The Chevy Volt, Fisker Karma, Via Motors VTRUX line all have explicitly used the phrase “extended range electric vehicle.” BMW does not use this phrase to describe the BMW i3 REX, instead REX is an acronym Range EXtension.

Solar panels on the roof: Many time this is asked, why don't "they" put solar panels on the roof? The problem with that is there's simply not enough space on a car roof to carry enough solar panels to generate enough electricity to make any significant impact. See (greentransportation.info) The number of solar panels required to power an electric car for a deeper discussion.

Extending range by stopping to charge

DC Fast Charging: CHAdeMO or Combo Charging System or Supercharger can all quickly add range to an electric car. DC Fast Charging adds between 150-300 miles of range per hour of charging. That means about an hour of recharging after 4-5 hours of driving. It is rather healthy to stretch your legs for awhile after that much driving. See When will electric cars charge faster than it takes to fill-up an equivalent gasoline car?

The car makers are starting to talk about 250 kiloWatt and 350 kiloWatt electric car charging systems. At that rate a 15-20 minute recharging time is possible. That's pretty fast even if it's not the same as the 5 minutes to refill the gas tank on a gas car.

Battery swapping range extender: This concept is way older than Better Place and Tesla Motors, both of whom have implemented modern roboticized battery swapping systems. A manual battery swap system was used for electric taxicabs in New York City around 1900. With a well designed station the battery exchange can add range at a rate similar to refilling a gasoline tank. However, modern battery swapping schemes have all failed to gain traction in the marketplace. See Wouldn't battery swapping be preferable over waiting to recharge?


Range Confidence is Copyright © 2016-17 by David Herron

Range Extension & total driving range

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