EPA Test Data released

[DucRider]

The Fuel economy data for the Bolt is in the latest EPA datafile.

Fuel economy data are the result of vehicle testing done at the Environmental Protection Agency's National Vehicle and Fuel Emissions Laboratory in Ann Arbor, Michigan, and by vehicle manufacturers with oversight by EPA.

http://www.fueleconomy.gov/feg/epadata/17data.zip
Of note:
City Range: 255.1
Hwy Range: 217.4
(tested in the Drive mode without using the "Regen-On-Demand" steering wheel paddle)

Chevy used the 2 cycle test (not the 5 cycle test as reported in some articles relates to the 238 announcement)
Annual Fuel Savings: $4250

Battery:
Pack voltage 350
Amp hours 171.4
Watt Hours per kg 140

Car Class: Small Station Wagon

Unadjusted test numbers
City: 182.2 MPGe, 18.4999 kWh/100 miles
Hwy: 157.4 MPGe, 21.4109 kWh/100 miles
Combined: 170.1369 MPGe, 19.8098 kWh/100 miles

Since they used the 2-cycle test, these numbers are "derated" by 30% to better simulate real world conditions.
Adjusted results:
City: 127.54 MPGe, 26.427 kWh/100 miles
Hwy: 110.18 MPGe, 30.5909 kWh/100 miles
Combined: 119.0958 MPGe, 28.3007 kWh/100 miles


Here is where the disconnect comes that I don't understand:
Combined rating of 28.3007 kWh/100 miles = 3.533481504 miles per kWh (100/28.3007) * 60 kWh = 212 miles range
238 miles range/60 kWh = 3.966666667 miles/kWh. 100/3.966666667 = 25.210084 kWh/100 miles

 

[wwhitney]

Here is where the disconnect comes that I don't understand:

I'm also unclear on the discrepancy.

For the seven cars listed on the EV page of the spreadsheet you linked to, the EPA range never agrees with the computation Battery V * Battery A-h / (Combined, adjusted kWh/100 miles) / 10. The ratio of the EPA range to the computed range varies from 1.12 (Bolt) to 0.79 (Mercedes B250e).

So we are missing something in the computation used.

Cheers, Wayne

 

[boeselhack]

Here is where the disconnect comes that I don't understand:
Combined rating of 28.3007 kWh/100 miles = 3.533481504 miles per kWh (100/28.3007) * 60 kWh = 212 miles range
238 miles range/60 kWh = 3.966666667 miles/kWh. 100/3.966666667 = 25.210084 kWh/100 miles

Maybe it has to be multiplied by the full kWh number of the battery?
Combined rating of 28.3007 kWh/100 miles = 3.533481504 miles per kWh (100/28.3007) * 67,5 kWh = 238.5 miles range

 

[Geo]

Doesn't the EPA test include efficiency of the charging system? In other words, they measure the power put into the plug, then test the car, then measure at the plug again? This would include the charging hardware in the calculation.

If that is the case, then perhaps losses incurred during charging account for the discrepancy.

 

[GetOffYourGas]

Doesn't the EPA test include efficiency of the charging system? In other words, they measure the power put into the plug, then test the car, then measure at the plug again? This would include the charging hardware in the calculation.

If that is the case, then perhaps losses incurred during charging account for the discrepancy.

Yes, it absolutely does. EPA counts kWh coming from the wall socket, not the battery.

 

[boeselhack]

So they put more than 60 kWh into the Chevy Bolt?

 

[Zoomit]

Here is where the disconnect comes that I don't understand:
Combined rating of 28.3007 kWh/100 miles = 3.533481504 miles per kWh (100/28.3007) * 60 kWh = 212 miles range
238 miles range/60 kWh = 3.966666667 miles/kWh. 100/3.966666667 = 25.210084 kWh/100 miles

Gary,

You didn't account for charging losses. The 28.3 kWh/100mi number is based on the EPA fuel economy data (119 MPGe) and so it includes charging losses. The real over-the-road efficiency of 25.2 kWh/100 mi is calculated from the usable battery capacity divided by EPA range, 60/2.38= 25.2 kWh/100 mi.

So when considering efficiency in terms of real miles of range, and not how much energy goes into the car, you need to use EPA range based efficiency data, not EPA fuel economy data. (I know you know this but am being pedantic.)

Right now, I'm assuming the car has 60 kWh usable battery capacity. The EPA fuel economy is therefore 3.5 mi/kWh (or 283 Wh/mi) which includes charging losses and so is needed for energy cost calculations, time to charge, etc.

The driving efficiency is 4.0 mi/kWh (or 252 Wh/mi) which is just from the battery to the ground. This number is needed for realtime range prediction and vehicle performance calculations.

Edit: looks like others beat me to the punch.

 

[Zoomit]

So they put more than 60 kWh into the Chevy Bolt?

No, you can kind of think of it as they need a 67.5 kWh battery IN THE WALL to fully recharge a 60 kWh battery in the car. Charging losses from the wall to the battery account for the difference.

 

[Aidan]

I think I might be confused but does the Chevy Bolt get better City mileage than it does highway mileage and if this is the case is that standard for most electric vehicles? Gas powered vehicles usually get better mileage on the highway versus the city this is why I'm asking

 

[SparkE]

Most EVs get better City mileage than highway mileage, yes. This is due to the increased air resistance at higher speeds. (IIFC, the drag coefficient goes up by a power of 2 for every doubling of the speed - but I could be remembering wrong).

 

[user 387]

Most EVs get better City mileage than highway mileage, yes. This is due to the increased air resistance at higher speeds. (IIFC, the drag coefficient goes up by a power of 2 for every doubling of the mileage - but I could be remembering wrong).

Yes, this is a factor, but probably even more of a factor is that regen is used more in the city - slowing the car charges the battery. On the highway, presumably, there is a lot less slowing, more of a constant speed.

 

[GetOffYourGas]

Most EVs get better City mileage than highway mileage, yes. This is due to the increased air resistance at higher speeds. (IIFC, the drag coefficient goes up by a power of 2 for every doubling of the mileage - but I could be remembering wrong).

Yes, this is a factor, but probably even more of a factor is that regen is used more in the city - slowing the car charges the battery. On the highway, presumably, there is a lot less slowing, more of a constant speed.

Regen is less than 100% efficient. Slowing the car and using the recaptured energy to get back up to speed will always be less efficient than driving at a constant speed.

 

[SparkE]

Most EVs get better City mileage than highway mileage, yes. This is due to the increased air resistance at higher speeds. (IIFC, the drag coefficient goes up by a power of 2 for every doubling of the mileage - but I could be remembering wrong).

Yes, this is a factor, but probably even more of a factor is that regen is used more in the city - slowing the car charges the battery. On the highway, presumably, there is a lot less slowing, more of a constant speed.

Regen is less than 100% efficient. Slowing the car and using the recaptured energy to get back up to speed will always be less efficient than driving at a constant speed.

AND, since the OP stated (tested in the Drive mode without using the "Regen-On-Demand" steering wheel paddle), regen was pretty minimal during the test cycle.

 

[SeanNelson]

Most EVs get better City mileage than highway mileage, yes. This is due to the increased air resistance at higher speeds.

...and due to the fact that EVs waste far less energy than ICE vehicles in start/stop traffic (because of regenerative braking) and when "idling".

 

[SparkE]

Most EVs get better City mileage than highway mileage, yes. This is due to the increased air resistance at higher speeds.

...and due to the fact that EVs waste far less energy than ICE vehicles in start/stop traffic (because of regenerative braking) and when "idling".

The fact that EVs waste far less energy than ICE vehicles in start/stop traffic in no way explains why EVs get better mileage in town than EVs get on the highway. EVs generally get better mileage in town than on the freeway due to the greatly increased air resistance travelling at 65 mph compared to travelling at 30mph.

 

[DucRider]

Most EVs get better City mileage than highway mileage, yes. This is due to the increased air resistance at higher speeds.

...and due to the fact that EVs waste far less energy than ICE vehicles in start/stop traffic (because of regenerative braking) and when "idling".

The fact that EVs waste far less energy than ICE vehicles in start/stop traffic in no way explains why EVs get better mileage in town than EVs get on the highway. EVs generally get better mileage in town than on the freeway due to the greatly increased air resistance travelling at 65 mph compared to travelling at 30mph.

SparkE is right on the money. Air resistance is inverse squared. Doubling your speed requires four times the energy. Traveling at 30 mph takes 4x what it takes at 15 mph. Traveling at 60 mph take 4x what it takes at 30 mph, or 16 times a 15 mph. speed. This is wind resistance only, Tire rolling resistance and other mechanical drag variables also play into the equation.
The EV's that are the exception to the city/hwy rule are the Tesla S and X.
They pay a penalty in town due to their heavy weight, and reap rewards on the freeway with their superior aero. Every Tesla has a greater (EPA) range on the highway test than the city.

 

[SeanNelson]

Most EVs get better City mileage than highway mileage, yes. This is due to the increased air resistance at higher speeds.

...and due to the fact that EVs waste far less energy than ICE vehicles in start/stop traffic (because of regenerative braking) and when "idling".

The fact that EVs waste far less energy than ICE vehicles in start/stop traffic in no way explains why EVs get better mileage in town than EVs get on the highway.

Fair enough, especially considering what I quoted of your post. But it does help to explain the lopsidedness between how EVs and ICE vehicles score on the city vs. highway tests, which was the original question I was trying to address.