Who's telling the truth -Tesla or Lightyear?

I guess they both are, but a recent article by Lightyear got me thinking:

Lightyear has recently set a new standard for EV efficiency: 710 kilometers on a single 60kWh battery charge! That means just 8.45 kWh per 100 km.

By comparison, Tesla's most efficient car, the standard range Model 3, claims a consumption of 14.9 kWh/100 km. That's 76% more than the Lightyear One! That sounded really weird, as their claimed Cd values are just 15% apart:

• Lightyear One: "sub 0.20"
• Tesla Model 3: 0.23

So what can explain the massive difference in efficiency between these two vehicles? Well, here are some theories:

Theory 1 - constant speed versus WLTP

The Lightyear One test was performed on a track at a constant speed of 85 km/h. That is quite a different scenario from the WLTP (Worldwide Harmonised Light Vehicle Test Procedure), which takes into account acceleration/deceleration, various speeds, etc (see image - credit: Wikipedia). Nevertheless, that's exactly the scenario where EVs can shine (energy recuperation, low speed driving, ...) compared to ICE cars (which suffer more losses at low speeds and lots of acceleration & deceleration). The WLTC test cycle does feature speeds above 85 km/h, which will penalize effiency for EVs, but also features much lower speeds. And to conclude this discussion, Lightyear actually claims a 8.3kW/100 km WLTP consumption. So this theory is a dead end...

Theory 2 - Battery usage

It's pretty bad for a battery to be completely charged or discharged, as this can degrade its performance over time. So very often, the BMS (battery management software) will prevent you from using the top and bottom 5-10% of a battery's capacity. It's likely that the Tesla tests take this into account (thus not using the full battery) while the Lightyear One perhaps used more or all of its capacity. Assuming Tesla reserves the top 5% and bottom 5%, this could represent a 10% difference. (Image below: Tesla battery - credit: HSR Motors)

Theory 3 - The sun

The Lightyear One features 5m2 of solar panels that help charge the battery. We didn't really find any information on whether this assistance was used during the long distance test and/or the official WLTP figures. Lightyear claims a 12km per hour solar charge, which would account for 108 of the 725km they travelled during their 9 hour run - that's a 15% contribution!

Theory 4 - It's not all about aerodynamics

At highway speeds, aerodynamics are by far (75% and up) the biggest source of energy drain. The other main drain is the mechanical resistance, like the rolling resistance of the tires. EVs are typically very heavy, which directly increases the rolling resistance. At 1.750kg, the Tesla model 3 weighs 35% more than the 1.300kg Lightyear One. Assuming rolling losses to be 25% of total losses (a very crude approxmation) and assuming a linear correlation to weight, this alone would lower total energy consumption by almost 9%.

Theory 5 - It actually IS all about aerodynamics

I know, we're biased at AirShaper. But after having simulated several production cars (including comparison to wind tunnel results), like the Tesla model Y, we've learned that a Cd number isn't as clean & simple as it sounds. This number depends heavily on ride height, definition of frontal area, environmental conditions (temperature, density, pressure, ...), wind tunnel setup (no/partial/full moving ground, blockage ratio, ...), velocity and many other parameters. And very often, we come to the conclusion that officially stated Cd coefficients are optimistic. So it could very well be that the "sub 0.20" Lightyear Cd value is perhaps a bit more honest than the average Cd claim, and perhaps substantially lower than 0.20.

Conclusion

In the past, we've already been impressed by the Lightyear One, especially after learning more about the design process behind the car. But seeing these tests results, we're completely convinced of this concept. It's not just a bit more efficient - it's massively more efficient! We've tried to provide a number of theories on why its energy consumption is barely 57% of that of a Tesla model 3 - we're curious for your comments!