EV Range, part 1

EV-201a

This course is presented as part of Evannex Universitya free, open learning environment that presents concise, video-based mini-courses for those who have interest in electric vehicles (EVs)

What is Range?Range is the distance you can travel in an EV with a battery that is fully charged.Range is a function of:A specific set of vehicle parameters A specific set of driving conditions

Of all issues that have retarded the grow of EVs, there is little doubt that range tops the list.In fact, for those of us who own an EV, there is no more common question than how far can the car go before the battery runs out?

Of course, every car has a finite supply of onboard fuel, and therefore, every car has limited range.But because gas stations are everywhere, theres no worry for ICE owners when the fuel gage approaches E.

Unless of course, youre on a lonely, desolated road far from civilization. The emotion you feel in situations like that is called range anxiety, and as well see in the next EVU mini-course in this sequence, range anxiety is a big, big issue in the EV world.

But back to range

>> Range is the distance you can travel in an EV with a battery that is fully charged.>> More specifically, range is a function of:>> A specific set of vehicle parameters that include the manner in which the vehicle is driven and it exterior design >> A specific set of driving conditions that include external factors associated with the vehicles surroundings

Vehicle ParametersVehicle parametersspecific characteristics of the vehicle and the way you drive itVehicle speedincreases dragmore force required to move the EV through the airVehicle designdragforce required to move the EV through the airThe batteryhigher the capacitymore energy is storedthe greater the range

The vehicle parameters that affect range are not exclusive to EVs. In fact, they affect the mileage of every ICE vehicle and therefore, the range of every car. Lets take a look.

>> Vehicle parameters are the specific characteristics of the vehicle and the way you drive it.>> Vehicle speed increases drag and that results in more force required to move the EV through the air.The more force required, the lower your fuel economy, and therefore, the shorter your range.

>> Vehicle design dictates the external shape of the car, which in turn affects the way the air flows over the vehicles surfaces, which affects drag which affects the force required to move the EV through the air.

>> Finally, the battery the higher its capacity the more energy can be stored and the greater the vehicles range

Well talk more about vehicle design issues and range a bit later, but first, lets consider speed

Speed vs. AccelerationFor EVs, steady-state speed matters acceleration doesntFor ICE:ICE is notoriously inefficientlabor to produce torque at low endFor EVshigh efficient motorinstantaneous torqueThe Amazing efficiency of the electric motor means that driving 70 vs. 50 has a MUCH bigger impact on range than accelerating from 0 60 in 4 seconds vs. 8 seconds Nick Howe, Owning Model S

>> Its important to make a distinction between speed and acceleration. In general, speed has a significant impact on EV range, acceleration doesnt. That may come as a bit of surprise.

Over the years, youve heard that hard drivingthat is, rocketing away from a stop lightwill kill the mileage in an ICE vehicle. Its only natural to assume the same holds true for EVs. Part of the reason is that>> ICE motors are inefficient and because of that and other design factors,>> they labor to produce torque once you floor the gas pedal. Thats why hard driving kills mileage for an ICE car.

>> But thats not the case for EVs,. The reason is that>> the high efficiency of an electric motor produces>> instantaneous torque from a dead stop.Nick Howe discusses this in the context of the Tesla Model S, when he writes:>> The Amazing efficiency of the electric motor means that driving 70 vs. 50 has a MUCH bigger impact on range than accelerating from 0 60 in 4 seconds vs. 8 seconds

But back to speed

Speed and RangeThe faster you drive, the shorter your rangeThe force required to propel the car forward increases as the square of the velocityFor techies: http://www.ev-propulsion.com/EV-calculations.htmlSource: http://www.hypermiler.co.uk/green-car-news/teslas-model-s-ev-could-top-350-miles-from-a-charge

>> The faster you drive, the shorter your range. Thats true for every car, or truck, or SUV, or motorcycle.

To descend into the technical weeds for a moment>> thats because the force required to propel the vehicle forward increases as the square of the velocity.

Like most things in life, speed vs. range is a trade-off. If you want to get there fast, you will reduce your range.

If you have to go a long, long way, reducing your speed helps.

>> The graph on your screen illustrates this for the Tesla Model S BEV.

The Model Ss range is an astonishing 450 miles at 20 mph.But driving 20 mph is well its not an option, at least not for me.

But if I drive 70 on an interstate, the Model S range drops to 225 miles, at 80, 200 miles. Based on my experience, the actual numbers may be slightly lower.

Design and RangeAnything design characteristic that reduces drag, increases rangeConsider:the drag areaexternal attachmentsside mirrorsair turbulencefabrication details

Earlier, I mentioned that design is a vehicle parameter that has a significant impact on range.

>> Anything in the vehicle design that reduces drag increases range>>So, a good EV designer works hard to:>> reduce something called the drag area that well talk about in part 2 of this mini-course >> minimize external attachments, such as roof racks, an antenna, a large spoiler and the like>> improve the profile of side mirrors, which surprisingly, can reduce drag by as much as 2 to 7 percent >> reduce the air turbulence around the vehicle>> In addition, fabrication details (like the design wheels) for an EV matter have an impact on range.

The Battery and RangeCapacity is measured in kWhsmall: 4 - 15 kWhmoderate: 16 - 35 kWhlarge: >35 kWh

Chevy Volt battery: 17kWh

But the most important single EV component that effects range is the battery itself. The energy required for an EV is derived from it's battery. Therefore, it should come as no surprise that's the size of an EV battery will have a direct influence on the range of the car.

>> As you already learned, battery capacity is measured in kilowatt hours.

>> Small batteries are typically used in PHEVs and have a capacity in the neighborhood of 4 - 15 kWh. For example, the Prius plug-in PHEV has a 4.5kWh battery.

>> Moderately sized batteries are found in both PHEVs and some small BEV's and typically have a capacity between 16 and 35 kWh. For example, the Nissan Leaf BEV has a battery capacity of 24 kWh.

>> Large EV batteries are rare today. Only the Tesla Model S offers battery sizes of 60 and 85 kWh.

It should come as no surprise that the Model S is the clear range leader, offering vehicle range of 208 and 265 miles, depending on the battery chosen.

Building a better batteryWhy cant we build a higher capacity EV batteryWhats the challenge?geometric constraintstechnological constraintsspecific energycostlife spanperformancesafetyspecific power

Source: http://batteryuniversity.com/learn/article/batteries_for_electric_cars

>> The natural question is, why cant we build higher capacity, cheaper EV batteries?It can be argued that battery capacity and battery cost are the two things that have retarded the growth of the EV market

>>So, whats the battery capacity and cost challenge>> Inside an EV, there is a limited space and a limited geometry in which we can place a battery.Therefore, we need to build batteries with higher energy density per cubic cm to overcome these constraints.>> But that leads us to other technological constraints. There are six battery characteristics that must be evaluated for every new battery technology that is proposed:>> specific energyalso known as the capacity of the battery>> costthe overall cost per kWh>> life spanthe number of charging cycles that the battery can accommodate>> performancethe ability to operate effectively in various climates>> safety and>> specific powerthe ability of the battery to deliver on-demand current when neededThe radar diagram on the right of your screen can be developed for every new battery technology to determine whether its footprint is more compelling than li Ionthe current go-to battery for EVs.

In the next part of this mini-course, well explore EV range in more detail.

a free study guide for all EVU mini-courses is available for download from our website For a complete list of mini-courses and the study guide, visit: www.evannex.com

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