My foray into electric vehicles

Over the course of the 16 years that I've maintained this blog (sporadically at best in recent years), there have been a wide variety of cars that I've driven. Some have been very stingy with respect to fuel consumption (my Lexus CT200H is the best example) to fuel hogs (I just ended the lease on a Jeep Trackhawk). My early blogging was almost exclusively related to fuel consumption, both personally and generally. As the years have gone by, my topic space expanded well beyond vehicle fuel consumption and into energy in general and even into politics.

But, for this post, it's back to basics. I turned in the Trackhawk that I'd leased and purchased a battery electric vehicle, the Genesis GV60. The performance model I purchased features all-wheel drive, with 160kW (215 horsepower) to the front wheels and the same to the rear wheels for a total of 320 kW. It delivers 350 Nm (258 ft lbs) of torque to the front wheels and the same to the rear for a total of 700 Nm. Its 77.4 kWh battery pack makes it a heavy car for its size, with a curb weight of 4,890 pounds but in "sport' mode with the "boost" on, it will go from 0 to 60 mph in about 3.8 seconds, very similar to the 710 horsepower Trackhawk I turned in.

With a full charge, it's good for about 250 miles but, unlike an internal combustion engine, there's no fuel economy vs. speed curve with a peak. There's no "engine map." The vehicle "fuel economy," as far as I've been able to determine, is strictly a function of tire rolling resistance and aerodynamic drag. Thus, freeway travel at, say, 75 m.p.h. is far less efficient than lower speeds in city driving.

I'm not getting what I expected, my most recent charge was 67.5404 kWh to drive 181 miles, or 2.68 miles/kWh. I expected something more on the order of 3.5 miles/kWh but the bulk of my driving has been on the freeway at around 80 m.p.h. Still though, I'm paying something like $0.17/kWh at the moment, so I'm spending around 6.34 cents per mile.

In comparing that to an internal combustion engine, it's probably unfair to compare it to my Trackhawk, which is a 710 horsepower beast in which I averaged something like 14.5 m.p.g. and which required 91 octane fuel. But if I consider a vehicle averaging 30 m.p.g. and 87 octane fuel with California 87 octane fuel around $4.49/gallon at the moment, the owner of that vehicle is spending 14.97 cents per mile, over twice what I'm paying. Further, I can utilize a perquisite to get free charges for three years!

I will say that I encounter the "range anxiety" often described for purchasers of battery EVs, and I approach trips that are outside of my commute with more forethought than previously, given that there's not a charging station on every corner. For example, I have a relative that lives in Ramona, CA. The round trip from my home to hers is about 202 miles. To make that trip with no concerns, I need to be close to fully charged and, without locating a charging station, I'd need to avoid side trips. And, as recommended, I generally limit my charging to 80% of full capacity. This limits me to 200 miles at best!

The car is heavy, the battery pack consists of 384 Lithium Ion Polymer cells with a nominal capacity of 77.4 kWh and a usable capacity of 74.0 kWh. As mentioned above, the curb weight of the car is 4,890 pounds. 

In an unusual move, parent Hyundai Motor Group opted to use an electronic architecture for the E-GMP platform that can operate at either 400 or 800 volts (but see below). That allows for “ultra-speed charging” when the latest, 350 kilowatt charger is plugged in — the battery pack going from 10 to 80% of capacity in 18 minutes.

In any case, I'm over 11,000 miles in the GV60 as I type this. When asked if I'm happy with the purchase, my answer is that I would not purchase this particular EV again. There are several reasons, but most are related to ergonomics and systems engineering, not the actual EV platform. However, even with respect to that, my suggestion would be to wait. Range seemingly goes up with each passing month, and many game-changing energy density developments are being touted. There will likely be no retrofit for current EVs!

And now Ford, GM, and Rivian are adopting (and adapting) their EVs to use the Tesla Superchargers, which pretty much assures that the Superchargers will become the national standard. My GV60 would need an adapter, and Hyundai is considering it.

All that said, I believe that the GV60 provides good value for its price and it's pretty clear that EVs are the coming thing. But I'll look elsewhere for my next EV a few years from now.

Inserted because it's a fantastic cover of a Dylan song and it's from Hendrix' album "Electric Ladyland."

The Fisker Ocean

I've published previously on the seeming futility of solar panels on the roofs of vehicles. But Fisker has announced the "Ocean" in various configurations. It's an SUV style vehicle with the "Fisker Ocean Extreme" boasting solar panels for the full length of the passenger cabin. The claim is that solar charging will produce 1,500 miles worth of charge, or even up to 2,000 miles. Let's investigate!

First, how much energy is needed to travel 1,500 miles in the Fisker? Unlike internal combustion engine powered vehicles, there's no curve with a peak in terms of energy mileage as a function of speed. For the IC vehicle going very slowly uses a lot of the energy from burning fuel to keep the engine turning over, and going very fast has a high drag penalty. The sweet spot differs for various models but might be in the range of 50 m.p.h.

For a battery electric vehicle, there's no such function. The faster you go, the worse your energy economy since it's only a matter of overcoming drag. So, in earlier data collection of my own driving, my overall block speed was on the order of 30 m.p.h. with a blend of city driving, freeway driving, and freeway driving in traffic. I'll use that number, but convert it to 13.41 meters/second.

We'll go to the naive drag equation, ~D=1/2 \rho C_dAv^2~ where D is drag force, ~\rho~ is air density (I'm using sea level, at altitude density would be lower and insolation would be slightly higher), ~C_d~ is the vehicle's drag coefficient, ~A~ is flat plate area, and ~v~ is speed. All are in SI base units. I can't find a drag coefficient spec for the Ocean, I'll go with 0.3. The vehicle's height is 1.631 meters, its width is 1.995 meters. Sea level atmospheric density is about ~1.225 kg/m^s~. Multiplying, we get ~D=0.595 (kg/m) v^2 Nt.~

The other drag factor is rolling resistance. This is, to first order, linearly dependent only on the vehicle's weight (NOT mass!). The curb weight is 2,250 kg force or 22,065 Nt. Add, say, 250 kg of people and luggage for a traveling weight of 2,500 kg force or 24,516 Nt. We'll use 0.014 as the coefficient of rolling resistance, resulting in a rolling resistance of 343 Nt. The result is a total drag of ~D=0.595 (kg/m) v^2+343 Nt~.

Next, power (work/time) is force times speed, so, at 13.41 meters/second, we need ~((0.595*13.41^2)+343)*13.41~ or 6,034 Watts or 8.09 horsepower. This is surprisingly small but, to first order, I'm confident that it's close. Call it 7 kW for our purposes.

Then, we'll assume the electric motor operates at 95% efficiency and that the drivetrain is 85% efficient, so we need 6,352 watts from whatever energy source we're utilizing. Now, 1,500 miles at 30 m.p.h. will take 50 hours or 180,000 seconds. And power times time is energy so the Ocean's solar panel will need to deliver 6,352 watts * 180,000 seconds, 1.14*10^9 joules, or 317 kWh. OK, can the panel on the Ocean's roof deliver 317 kWh in a year?

I'll estimate that the dimensions of the panel are 1.5 meters X 3 meters, or 4.5 m^2. In my Southern California area, the average solar insolation is about 5 kWh/(day*meter^2). This has to be reduced because the panel on the Ocean sits horizontally rather than following the sun. We'll use 50%, so if the Ocean sits outside in the sun all day, we might average 11.25 kWh delivered to the panels. Next, we'll estimate that the panels are 18% efficient, so about 739 kWh ~(11.25*0.18*365)~ are delivered to either the motor or the battery pack over the course of a year. And here, we're assuming that either the car is in motion and the panels are delivering energy to the motor or that there is capacity in the battery pack to accept the energy.

Now, speeds above 30 m.p.h. will hurt more than those below will help due to the dependence of drag on the square of speed (refer to plot at right). And this doesn't account for use of accessories, losses due to climbing hills (not all the gravitational potential energy is regained on the downhill), and stopping and starting (even regenerative braking doesn't recapture all of the kinetic energy). It doesn't include being blocked by buildings and trees, and many other factors. And Minnesota, New York, and other Northern states don't receive the insolation of Southern California. That said, I can't say that the claim is irresponsibly exaggerated so, using the Mythbusters' scale, I'll call it plausible.