Do you understand range and efficiency?
I’m the first to admit that my fitness leaves much to be desired. I can lift things, go for walks or even run for short distances at reasonable speed…just don’t ask me to do any of these things for any sustained period of time.
That’s about all I know. I can only assume the body has finite resources, between oxygen, hydration and nutrients that will be consumed during physical activity, and I probably don’t have enough of them (or know how to use them effectively).
That said, I do know that there’s a difference between a 5 kilometre marathon and the 100 metre dash. As a kid, I remember giving the dash my maximum effort in hopes of being first (admittedly, a rare occurrence). The marathon was trickier, as I had to regulate my speed, breathing, water intake and my stride to make sure I didn’t run out of energy and be forced to give up half-way through.
I’m doubtful I could complete a 5k at any considerable speed now, yet I regularly walk the same distance with no issue. I reckon at walking speed, my range is probably 10-15 kilometres before I need a break (largely because I’ve yet to acquire decent walking shoes).
What impacts efficiency?
Based on this, I must be reasonably efficient at consuming my resources at walking speed. I know if I walk at 5 km/h, I can go 15 km. I also know if I run at 10 km/h (double the speed), I cannot endure even half that distance. Presumably this is because my efficiency drops as the required speed (and therefore power) increases. My cardio sucks, so this likely means my body can’t get the oxygen I’m breathing in to the muscles efficiently enough to sustain forward motion for that distance.
In many ways, a car is similar. It truly has finite resources, whether it be electrons in a battery or petroleum in a fuel tank. If the car is sprinting as fast as it can move (i.e. using all the power available), it will deplete these resources at the fastest rate. If the car is trying to cover a long distance, it needs to be as efficient as possible with its resources, whilst maintaining an acceptable speed. What is deemed “acceptable” is a bit subjective…more on that later.
Aero
Formula 1 cars use efficient aerodynamic design to prolong range and increase downforce (grip).
Like someone running, there are many factors that can reduce the efficiency of converting energy to forward motion. These are broken up into fixed and variable factors. Let’s consider some variable ones first:
Aerodynamic drag: Do you hear air rushing by your ears when you’re running? That’s evidence of aerodynamic drag. Your car, much like your body, has to push air out of the way to move forward in space. In some cases, wind is blowing against you, making this more difficult. That means some energy is lost moving air, rather than propelling you forward. It is worse if you aren’t aerodynamically efficient, making it harder for the air to get past you. Remember, the faster you go, the more air you have to move and thus the more energy is lost due to drag.
Rolling resistance: Ever notice that your bike gradually slows down when you are coasting, and that this differs whether you are on a mountain bike or road bike? That’s due in part to the tires’ resistance to roll. You might not realize this, but the tire actually deforms when it contacts the surface, dissipating some energy to the ground. Tire pressures, tread pattern, compounds and all sorts of other characteristics affect the rolling resistance. As it is a coefficient, the amount of energy lost increases with speed.
Mechanical drag: Similar to rolling resistance, there are other rotating mechanical components in the vehicle. The motor isn’t connected directly to the wheels…a series of shafts, gears, clutches, bearings, and other rotating devices transmit power to move you forward. Each one of these things take a little bit of energy to overcome their own inertia and frictional losses (like those caused by the viscosity of oil). Similar to tire rolling resistance, it usually increases with speed.
Temperature: This is a big one. If it’s hot outside, you sweat more, a symptom of your body using some resources to keep you cool. Conversely, you will shiver when it’s cold outside, using some energy to keep you warm. Cars are no different. There’s sophisticated thermal management systems in both ICE (internal combustion engine vehicles) and EVs (arguably more complex in EVs) that work to keep certain components in the temperature range where they are most efficient, despite the outside temperature. Keep in mind, there are heat sources throughout the car that are variables as well, including the inverters, motors, computers and anything else dissipating heat (remember, most energy lost mechanically or electrically is converted to heat!). The more power you demand, the more energy is lost to heat, requiring even more energy to remove it.
Gravity: This one really gets me down (pun intended). It gets cars down, too. That’s why you have to push harder to go up a hill and less going down one. As a result, the grade and overall stack up of elevation changes during a trip will have an enormous impact on overall efficiency.
Tires
More aggressive tread, lower pressures and softer compounds all increase rolling resistance as a trade-off for increased grip.
As you can imagine, these aren’t the only things impacting a vehicle’s overall efficiency. I could probably go on and on, but the key point is that these are major factors that will vary depending on the driving situation and the vehicle.
There are a few more that are less tied to speed, but are factors nonetheless. Examples include the computer systems, lighting, HVAC, etc. Optimizing the efficiency of these systems is important, as they will take energy regardless of whether the car is moving or not.
Cold = Lower Efficiency
Batteries don’t lose charge in the cold, but they do discharge more slowly. Winter tends to increase the current demand to:
Heat the cabin
Defrost the windows
Run the wipers and headlights
Overcome the cold, thicker gearbox oil
Overcome the resistance from winter tires
Precondition the battery for charging
How do I quantify resources?
I won’t pretend to understand or quantify a human’s resources (or HR, but that’s a different matter). But I will switch to a different analogy that most can understand: money. Consider the following scenario:
You have a bank account. It’s got some money in it, perhaps $100 Canadian dollars. Let’s say you are traveling in the US, and want to take a taxi 16 miles across town. You ask the driver, he says he will need $40 US, factoring in his costs, taxes and the profit that makes it worth his while. You go to the ATM and withdraw $50 in US cash from your bank account, which actually costs you $60.50 Canadian dollars, factoring in the 1.2:1 exchange rate and 50 cents the bank gets for their trouble. You enjoy the ride and at the end of the trip you give the driver an extra $5 US as a gesture of goodwill. The remaining $5 you spent on a bottle of water as the taxi’s A/C was particularly weak.
In summary, $60.50 Canadian got you 16 miles of transportation, or roughly $3.78/mi. Based on the fact you only have $39.50 left in your account, you will only afford about 10.5 miles.
Driving a car is not much different. I’ll outline a similar scenario with an ICE vehicle:
You are in a car with 50 litres of gasoline in the tank, traveling down the freeway. You want to travel 100 kilometres across town. About 20 horsepower (15 kW) is needed (continuously at the wheels) to maintain 100 km/h, factoring in drivetrain losses, rolling resistance and drag. Your car withdraws 8 litres of gasoline, factoring in the 10 kWh/L exchange rate and the engine’s 60 kWh heat fee for its trouble. You enjoy the ride and spent the remaining 5 kWh to keep the A/C running, charge your phone and keep the engine cool.
What’s a kW?
Watt is a unit of power, quantifying the rate of energy transfer. A kilowatt (kW) is simply 1,000 watts or 1.34 horsepower.
In summary, 8 litres of fuel got you 100 kilometres of transportation at highway speeds. This is why you often see ICE fuel consumption denoted in L/100 km (or the inverse “MPG”, miles per gallon for the Americans). Based on this efficiency (8 L/100 km), if you continued on the freeway at the same speed you could drive another 525 kilometres until your tank is dry.
Driving an EV is very similar, just different exchange rate:
You have the same car but with an EV powertrain and battery charged with 50 kWh of energy. The same 15 kW is necessary to maintain 100 km/h. Your car’s inverter withdraws 22kWh, factoring in the 1:1 exchange rate to convert from DC to AC power and the inverter’s 1 kWh heat fee for its trouble. The motor wants a 1 kWh heat fee as well and you spent the same 5 kW for comforts and cooling.
What’s a kWh?
Kilowatt-hour is a unit of energy, equal to 1 kW of power sustained for 1 hr. It’s used to measure battery capacity.
In this scenario, 22 kWh of energy got the same 100 kilometres at 100 km/h. Occasionally, you’ll see an ICE-like consumption denoted in kWh/100 km (Americans use MPGe, more on that later). Based on this efficiency (22 kWh/100 km), if you continued on the freeway at the same speed you could drive another 127 kilometres until your battery is dead.
Now for the engineers reading this, I’ve oversimplified these calculations and used conversion rates and efficiencies in pretty round numbers that may not reflect reality. For the rest of you, the point you need to understand is that your range is dependent on your remaining resources (in litres of gasoline or kWh of energy) and how quickly you are consuming them (L or kWh per 100 km). How quickly you consume them depends on the car, the environment and how fast you want to get there.
Why does everyone focus on range?
Interestingly, you rarely hear people talk about range in the context of ICE vehicles. The last time I remember someone advertise range was VW and how their Golf TDI could travel 800 km on a tank of diesel—of course, this was before we learned VW sometimes fibs a little. Nonetheless, the industry’s focus has been to improve L/100 km and MPG metrics. You wouldn’t believe the amount of engineering dollars automakers have invested in the last decade to eke out an extra 1 MPG for the window sticker.
It makes sense that they don’t talk about range. A Cadillac Escalade can theoretically travel a whopping 1,150 kilometres, whereas a Honda Civic can only manage 660. Obviously, the Escalade is less efficient than the Civic (10.2 vs 7.1 L/100 km, respectively), but it can carry over 70 litres more gasoline. Despite the Escalade burning more fuel for every kilometre it moves, it can go further simply because it has more of it.
In the ICE world, everyone is focused on improving efficiency because reducing the amount of fuel burned is more important than going a longer distance (who really travels 1000+ km non-stop?). It certainly helps that finding a petrol station is pretty easy in most areas of the world.
In the EV world, the fascination with range is rooted in history. Firstly, when automakers began flirting with EVs, the amount of energy they could stuff into a battery pack was relatively small. To get range comparable to ICE vehicles, they would need to dramatically increase the size of the battery, adding significant cost and weight (which hurts efficiency, thereby diminishing returns). Thus, we got EVs with small batteries and not many places to charge them. If you had an ICE car with a gas tank from a lawn mower, with only one petrol station in a 50 km radius, you’d be pretty concerned about range too.
Then in 2012, Tesla happened. They decided to start from scratch, using the entire floor to pack battery cells from laptop computers tightly together, dramatically increasing capacity to 85 kWh. They wrapped it in the shell of an aerodynamic luxury sedan to improve efficiency and justify the higher price of the big battery. Most importantly, it could theoretically achieve 400 km of range on the highway, a seemingly magic number that was comparable to ICE cars of similar performance.
Tesla knew that the widespread focus on range was preventing EV adoption. They also knew that the easiest solution was to get a commercially-viable vehicle out there with a bigger battery. Not to diminish their work, but they essentially played the Escalade card…put out an attractive, luxury vehicle with a big tank.
Why is consumption important?
The reality is though, most people don’t really need the range. The average Canadian drives 16,000 km/year. Assuming they only drive on working days, that’s an average of about 63.5 km/day. Yes, there will be the occasional weekend road trip, but charging infrastructure is dramatically better than it was in 2012.
Efficiency by situation
The cars are dramatically better, too. Even a tiny Smart EQ gets 95 km of range. More importantly, the average advertised range of all EVs available on the market is over 300 km. I don’t know about you, but I usually need a bathroom break and a snack by then.
But if you’ve learned anything from this article, you’ve realized by now that range is a bit of a bullshit metric. In that Smart EQ, I’m sure if I was driving light-footed, with all the windows up on a spring morning along a perfectly flat road, I could probably get over 100 km of before it died. Conversely, I doubt a hustling Uber Eats driver in the winter would manage much over 60 km.
If you’re driving 60 km ±20% every day, the range will only influence how often you stop to charge. Since the charging speed is capped by the current limits (similar to a gasoline pump’s flow rate), the time it takes to add electricity is usually the same between cars. The only time it won’t be is if you’re lucky enough to have a 350 kW charger nearby, where the car may become the limiting factor. Don’t be fooled by the “charge to 80% in 10 minutes” advertising, that number is mostly influenced by the size of battery (a small battery would get to 80% faster than a big one) and the car’s DC-DC converter current limitations. Of course, all of this is really a moot point if you charge at home every night.
But if you only drive 60 km every day and rely on public chargers, the consumption is arguably more important than range. A more efficient EV will ultimately mean less time spent charging, as you’re getting more distance out of every kilowatt. In some jurisdictions, this also means less coal or natural gas burned to generate the electricity necessary for your daily driving habits.
kWh/100 km or Wh/km?
1 kWh = 1,000 Wh
For most consumers coming from an ICE vehicle, L/100 km is a familiar fuel consumption metric. The EV equivalent is kWh/100 km (or kWh/100 mi in the US).
For ICE cars, calculating consumption over a long distance allowed a metric in litres (rather than millilitres), which is familiar to how fuel is measured at the pump.
For EVs, you may also see Wh/km (watt-hour per kilometre). Simply multiply/divide by 10 to convert to/from kWh/100 km from Wh/km: (i.e. 18.5 kWh/100 km = 185 Wh/km).
How is all this calculated?
Porsche Taycan Turbo
Suspiciously more efficient in the real-world than EPA ratings suggest.
With 83.7 kWh usable capacity, EPA suggests a range of 323 km (25.9 kWh/100 km).
One journalist drove the car 340 km at 113 km/h. Their average consumption was 18 kWh/100 km, 30% more efficient than the EPA rating.
That translates to 142 km more range!
Remember how I mentioned that a car needs to be as efficient as possible at an acceptable speed? Yeah, there’s differing opinions on what is “acceptable”. As you now know, the speed heavily influences the consumption rate and therefore the range of the vehicle.
You will often see consumption and range metrics based on EPA (American) or WLTP (European) tests. Broadly speaking, the tests are supposed to reflect the driving cycles of the average American or European, respectively. Without going into much detail, the tests are completely different, with WLTP favouring higher average speeds than the EPA (as high as 131 km/h on the highway, versus 88 km/h, respectively).
Do these tests reflect how you actually drive? Most definitely not. In fact, they can be quite misleading, with reports of the Porsche Taycan going a significantly longer distance on the highway than its EPA rating, or the Tesla Model Y falling short. ICE vehicles suffered from this problem, but no one cared. The disparity is far worse for EVs and as mentioned, range practically determines the commercial success of a new EV.
As you can imagine, automakers do optimize their design and programming for the target market. Porsche knows their drivers will have higher average speeds (especially the German buyers who enjoy the benefits of the Autobahn), so they optimize the aerodynamics, powertrain, thermal systems and software to maximize efficiency in higher speed situations. Tesla knows the EPA range matters most to their market, so it’s no surprise that most Teslas I’ve been in seem mysteriously more efficient around 88 km/h.
Gasoline gallon equivalent
GGE is the amount of energy that would be equal to burning a gallon of gasoline. For electricity, 33.4 kWh is the GGE.
To put it another way, 1 litre of gasoline theoretically contains the same amount of energy as 8.8 kWh of electricity.
To further complicate matters, the EPA has this funny MPGe metric, which compares the fuel economy of an electric vehicle to the theoretical equivalent of a gallon of gasoline being burned. They did this because a focus group told them that the American public couldn’t understand mi/kWh in the same way as mi/gal…perhaps they should’ve tried “KPG”.
The good news is that if you look closely, the EPA publishes consumption figures for both city and highway cycles separately. Depending on whether your driving habits are more in the city or on the highway, you can at least ballpark the kind of electricity use and range to expect by considering some proportion of the two figures. For example, a Tesla Model 3 Long Range consumes 1.12x more electricity per mile on the highway than it does in the city, according to the EPA.
You need to go for a drive.
Once you factor in test procedure, correction factors, weather conditions and software optimizations, you probably will realize that the range on the window sticker has little to do with the reality of your driving habits. For most Canadians, the number is further misleading, as it doesn’t factor in cold weather conditions, which will have a significant and varying effect on range depending on the vehicle (10% to 40% reduction is not unrealistic).
However, the consumption figure during a test drive may give you a clue. If you drive as you normally would and take note of what the trip computer’s consumption figure is, you can do some quick math: Usable Capacity / Consumption = Expected Range.
Last time I drove a Model 3, the computer suggested 20 kWh/100 km. No one really knows the usable capacity of a Model 3, but assume 50 kWh on a Standard Range Plus. 50 kWh / 0.2 kWh/km = 250 km. A far cry from the 423 km that Tesla advertises, but given a 100 km/h cruising speed in 0 degree weather, the estimate is probably realistic.
If you’re buying an EV hoping to commute from your new home in Belleville to downtown Toronto next winter, you might want to take a closer look at how efficient the EV will be in those conditions rather than the range figure you are told. A mixture of the design decisions of the automaker, the weather, the road and how you drive ultimately determines how far you will go.
“Range is dependent on your remaining resources and how quickly you are consuming them. How quickly you consume them depends on the car, the environment and how fast you want to get there.”
