[Lasidar]

The Volt's calculation of MPGe or Le/100km, which should be based on a fairly standard calculation, comes up with a value that does not make sense to me. For instance, it routinely gives me around 100MPGe (2.3Le/100km) for my daily commute, which is about 87km (54 miles) on a full charge (14.6kWh). By most calculations, this should land closer to 1.9Le/100km or 125MPGe.

I'm wondering why there seems to be such a discrepancy. The industry accepted conversion is around 1-gallon to 33.70 kWh, so for my commute, 14.6kWh=0.43gal, 54 miles/0.43gal = 125MPGe.

Any thoughts?

 

[Sheldon]

The Volt's calculation of MPGe or Le/100km, which should be based on a fairly standard calculation, comes up with a value that does not make sense to me. For instance, it routinely gives me around 100MPGe (2.3Le/100km) for my daily commute, which is about 87km (54 miles) on a full charge (14.6kWh). By most calculations, this should land closer to 1.9Le/100km or 125MPGe.

I'm wondering why there seems to be such a discrepancy. The industry accepted conversion is around 1-gallon to 33.70 kWh, so for my commute, 14.6kWh=0.43gal, 54 miles/0.43gal = 125MPGe.

Any thoughts?

I'm not familiar with Le/100km, but MPGe is based on power from the plug, not power from the battery. There is a 12%-20% charging overhead. I'm averaging 15.8kwh to fully charge the battery which uses 14.0kwh (13% overhead), but I think GM's mpge calculation uses a value closer to 16.8 kwh to fully charge the battery (20% overhead). The actual charging overhead may also be a few percent higher (closer to 20%) with L1 charging than with L2 charging, and would also be higher in the heat of the summer with more kwh required for the battery thermal management system (TMS) for cooling during charging. I think the car's estimate uses the pessimistic 20% charging overhead value in the MPGe calculation, instead of the more realistic 13% value for charging overhead.

So the calculation would use 33.7 kwh/gallon equivalent. Let's assume 20% overhead to fully charge the battery
miles / gallon_equiv = miles * (1/kwh)*(1/charging overhead * (kwh/gal) = miles * (1/1.2) * 33.7 / kwh

For the Op's case: 54 miles * (1/14.6kwh) * (1/1.2 overhead) * 33.7 kwh/gallon = 104 mpge
If the Op is charging with L2, the "correct" mpge number might be (54 / 16.0kwh) * 33.7 kwh/gallon = 114 mpge

 

[Lasidar]

That's definitely something I did not consider! Has anyone done real-world measurements of wall-to-wheel efficiency? I am running a 240V Schneider EV230WS if that matters.

 

[Arcanox]

That could vary wildly with environmental and other factors. Depending on the ambient temperature of the charging site, the A/C or heater may have to run occasionally. If the cells become unusually unbalanced somehow, it may take more power to balance them. Even a difference of 220v versus 240v (actual line voltage) could make a difference. I'm not sure if it also counts any preconditioning draw from the outlet in the MGPe; I wouldn't be surprised if it did.

 

[wordptom]

Seems to me the price you pay for each kWh of grid power stored in the battery depends on the efficiency of the refueling methodology (L1, L2, or plugless recharging). Your fuel mileage, i.e., how the Volt performs using the available fuel, shouldn’t be affected by how you filled your fuel tank.

The distance you drive on each kWh of grid power doesn’t depend on how you charged that battery. Should your MPGe go down only because you started using a plugless recharging system?