Electric Vehicle University - 201a Range
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THE CENTRAL QUESTION ... Just how far can an EV go before the battery runs out and what factors affect how far I can go? COURSE ABSTRACT A 2-part discussion of EV range including the parameters that affect range, the impact of speed and acceleration, battery technology, and aerodynamic drag. The effect of driving conditions and methods for maximizing range are also considered. To obtain a copy of the EVU study guide for this and other available EVU courses, please complete the form on this page. Course level: Intermediate
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Electric Vehicle University - 201a Range
- 1. 1
- 2. 2 EV Range, part 1 EV-201a This course is presented as part of Evannex University—a free, open learning environment that presents concise, video-based mini-courses for those who have interest in electric vehicles (EVs) …
- 3. 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 0 75 150 225 300 Category 1 PHEV-1 PHEV-2 CityCar EV Model S/60 Model S/85
- 4. Vehicle Parameters Vehicle parameters—specific characteristics of the vehicle and the way you drive it Vehicle speedincreases “drag”more force required to move the EV through the air Vehicle design”drag”force required to move the EV through the air The batteryhigher the capacitymore energy is storedthe greater the range 4
- 5. Speed vs. Acceleration For EVs, steady-state speed matters … acceleration doesn’t For ICE: ICE is notoriously inefficient labor to produce torque at low end For EVs high efficient motor instantaneous torque “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” Nick Howe, Owning Model S
- 6. Speed and Range The faster you drive, the shorter your range The force required to propel the car forward increases as the square of the velocity For techies: http://www.ev- propulsion.com/EV- calculations.html Source: http://www.hypermiler.co.uk/green-car-news/teslas-model-s-ev-could-top-350-miles-from-a-charge
- 7. Design and Range Anything design characteristic that reduces drag, increases range Consider: the drag area external attachments side mirrors air turbulence fabrication details 7
- 8. The Battery and Range Capacity is measured in kWh small: 4 - 15 kWh moderate: 16 - 35 kWh large: >35 kWh 8 Chevy Volt battery: 17kWh
- 9. Building a better battery Why can’t we build a higher capacity EV battery What’s the challenge? geometric constraints technological constraints specific energy cost life span performance safety specific power 9 Source: http://batteryuniversity.com/learn/article /batteries_for_electric_cars
- 10. 10 … 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
Editor's Notes
- 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, there’s no worry for ICE owners when the fuel gage approaches E. Unless of course, you’re on a lonely, desolated road far from civilization. The emotion you feel in situations like that is called “range anxiety,” and as we’ll 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 vehicle’s surroundings
- 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. Let’s 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 vehicle’s 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 vehicle’s range We’ll talk more about vehicle design issues and range a bit later, but first, let’s consider speed
- >> It’s important to make a distinction between speed and acceleration. In general, speed has a significant impact on EV range, acceleration doesn’t. That may come as a bit of surprise. Over the years, you’ve heard that hard driving—that is, rocketing away from a stop light—will kill the mileage in an ICE vehicle. It’s 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. That’s why hard driving kills mileage for an ICE car. >> But that’s 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 …
- >> The faster you drive, the shorter your range. That’s true for every car, or truck, or SUV, or motorcycle. To descend into the technical weeds for a moment— >> that’s 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 S’s range is an astonishing 450 miles at 20 mph. But driving 20 mph is … well … it’s 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.
- 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 we’ll 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.
- 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.
- >> The natural question is, why can’t 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, what’s 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 energy—also known as the capacity of the battery >> cost—the overall cost per kWh >> life span—the number of charging cycles that the battery can accommodate >> performance—the ability to operate effectively in various climates >> safety and >> specific power—the ability of the battery to deliver on-demand current when needed The 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 Ion—the current ‘go-to’ battery for EVs. In the next part of this mini-course, we’ll explore EV range in more detail.