Modec electric vehicles - factory tour and regenerative-braking data

Modec very kindly gave me a factory tour and let me drive one of their delivery vehicles for 60 minutes, instrumented so as to gather detailed data on engine power and regenerative braking (and lots of other stuff). This was exciting for me because I had tried hard to get real data on regenerative-braking performance when writing my chapter about electric vehicles, and the best I had managed to get was informal estimates from experts.

This page contains some of the data and some photos from the factory tour.

the test vehicle

Test drive data

The test drive included a wide range of conditions - urban roads, dual carriageways, country lanes, speed-bumpy streets, and slow-speed manoeuvers. The instrumentation logged battery current and voltage and the vehicle's speed. From these data we can estimate three interesting things:
  1. The overall energy consumption in kWh per 100 km.
  2. The efficiency of energy-recovery by the regenerative braking - by looking at a single rapid braking event from top speed down to zero.
  3. The overall contribution of regenerative braking to the vehicle's average performance.
The energy used, measured at the battery, was 60.6 MJ during a 46.6 km trip. That's 36.1 kWh per 100 km. At the socket, the electricity required would be bigger, because battery-charging systems lose some energy. The Modec folks said their measurements showed that with best practice, the overhead at the socket was about 5%; but if the charger was left switched on unnecessarily long, the overhead was bigger, about 54%. Taking the best of these two figures, the truck I drove was using at least 38 kWh per 100 km at the socket.

Whole Trip power and speed
Power and speed for the whole test drive

Single deceleration

The maximum power that can be delivered from the battery is 80 kW. The maximum power to the battery from the wheels is 20 kW. The kinetic energy of the vehicle (m=3500 kg) at top speed (v=77.5 km/h, 21.5 m/s) is estimated to be 0.226 kWh (0.81 MJ). During the single braking episode shown, the energy recovered to the battery was about 0.11 kWh. The recovered power clipped -20 kW during the deceleration, therefore the friction brakes were partly used - this was not a perfect regenerative deceleration! We can conclude that during typical regenerative braking, at least half of the kinetic energy gets recovered. Modec's engineers told me that their energy conversion chain, in the current design, is estimated to be roughly 70% efficient in both directions (battery to wheel and wheel to battery). They are planning a redesign that will significantly improve this efficiency. Taking 70% efficiency in both directions, the round-trip efficiency of regnerative braking (from kinetic energy to battery energy and back to kinetic energy again) is 70% x 70% which is roughly 50%. Happily, this matches the rough estimate I used in my book.
Was the road flat, uphill, or down-hill? I don't recall. So the above numbers should certainly not be taken as gospel truth on regeneration efficiency.

One Deceleration
Power and speed during a piece of top-speed driving followed by a single deceleration

Overall contribution of regenerative braking

The above image shows the scatterplot of power versus speed during the drive.

The top left image shows a histogram of the power, with positive values (red) counting times at which power went from the battery, and negative (green) counting times of regeneration. (I've removed values close to zero from this histogram.)

The lower-left image shows the same histogram with all the frequencies multiplied by the power, so that the area under the graph is a visualization of the total power leaving or entering the battery. The green area shows the total amount of regenerated energy; the red area shows the total energy taken from the battery. You can see by eye roughly how much energy-saving is obtained from having regeneration (for this test drive's mix of driving styles) - it's roughly 15%.

Factory tour

Modec factory
First view of the factory

Charger Charger Plug
Charger and charger plug
Lithium-ion battery in its cassette
Lithium-ion battery in its cassette
The hole in the chassis where the battery cassette goes
The hole in the chassis where the battery cassette goes
One 80kW motor
One 80kW motor
80 kW motor
80 kW motor in situ
motor, with one side revealing motor brain
motor, with one side open revealing motor brain