# Dissecting my Zoe – energy consumption

**Posted:**2013/07/21

**Filed under:**Zoe 4 Comments

This morning I thought it would be a perfect opportunity to do some EV science. The weather prediction said there would be very little wind, and Sunday mornings the traffic is light, almost non-existent. So I headed out at 6:30 to a straight, dead flat, five lane section of the A4.

When I got there, the wind turned out to be a bit stronger than I had hoped, but the direction was almost parallel to the road. Cross-winds increase your energy consumption in both directions and would spoil a good measurement. Of course I made two runs in opposite directions at each speed to cancel out the effect of wind as best as possible.

The stretch of motorway that I had selected is about 5 km long. I used the trip computer to record energy consumption. The energy consumption settled to a stable value after 2 km, so a 5 km stretch looks to be enough to make accurate measurements. I don’t know how accurate my Zoe is measuring her consumption, so my results may not be comparable to those from other Zoe’s.

My Zoe has now rolled 300 km, maybe she still needs some breaking in. I don’t know if EV’s need that. Tire pressure front and rear was 2.6 bar. The speedometer has a +4 deviation from real speed. I have corrected for that, the table shows the real speed. The calculated range is based on the official figure provided by Renault: 22 kWh usable capacity. I completely switched of the air conditioning and fan. When I got home at 8:00, the energy consumption screen still showed 0.5 kWh used for ancillary systems. 500 Wh in 1.5 hours suggests a ~350 W drain that I can not account for at the moment.

The meteorological conditions were: temp 17°C, relative humidity 80%, wind speed 3 m/s, pressure 1020 hP.

I had planned to do tests at 10 km/h intervals from 70 up to top speed, but I had to skip the last ones because the battery was not fully charged.

These are the results:

Real speed (km/h) | Run 1 (kWh/100 km) | Run 2 (kWh/100 km) | Average (kWh/100 km) | Calculated range (km) |
---|---|---|---|---|

70 | 14.2 | 12.2 | 13.2 | 167 |

80 | 15.2 | 13.2 | 14.3 | 154 |

90 | 17.6 | 15.2 | 16.4 | 134 |

100 | 19.4 | 17.2 | 18.3 | 120 |

110 | 21.3 | 19.4 | 20.4 | 108 |

The line graph looks a bit surprising. I would have expected more of a parabole, as air resistance (the dominant force at those speeds) increases with the square of the speed, but from 80 km/h upwards it looks like a straight line.

Air resistance (aerodynamic drag) increases with the square of speed (at the Reynolds numbers applicable to a car on the highway). Power required increases with the cube since power is force*speed. I’ll be interested in following your blog.

Hi Rob,

You are of course 100% correct, thanks for pointing that out. I corrected the post accordingly.

Arne

Driving at 80 km/h, a 7 kw genset in the trunk will double your range to more than 300 km.

And when the battery is depleted you can still limp home with the 7 kw, but at what speed, maybe 40 km/h ?

The manual states that the Zoe may not be charged with a generator. But I was never interested in generators, and never will be. The point of my Zoe is getting rid of the ICE. For good.

Arne