Re:The Electric-Vehicle Cheating Scandal
by Animats on Sunday January 28, 2024 @03:21AM
(#39163531)
I'm trying to figure out where this figure comes from. The immediate source is the Institute for Energy Research, which seems to be a lobbying organization for the oil and gas industry.
Not clear what "efficient" means in this context. All heat engines have a second law of thermodynamics efficiency limit. Cars run 20%-40% efficient, measured by dynamometer output at wheels / energy content of fuel.[1] (Motor Trend says 20%. [2]) Electric cars aren't limited in that way, and reach 63%-80%. Of course, if fuel was burned to create electricity, there was a thermodynamic efficiency loss upstream. Those values have objective engineering measurements.
There's something called "Miles Per Gallon Equivalent".[3] This is more of a marketing/regulatory term. It appears on car window stickers. It's just miles per kilowatt hour multiplied by kWh per gallon of gasoline, which is 33.7 kWh / gallon. Motor Trend says that the Tesla Model 3 is rated at 142 MPGe, which is a reasonable number.
This probably has to do with pollution credits, not energy efficiency. It's may be related to the Corporate Average Fuel Economy rules. Those have a big loophole on the gasoline-powered side - there are different limits for "cars" and "light trucks".[4] US vehicle production is currently over 50% "light trucks", which includes many SUVs.
Not clear what "efficient" means in this context. All heat engines have a second law of thermodynamics efficiency limit. Cars run 20%-40% efficient, measured by dynamometer output at wheels / energy content of fuel.[1] (Motor Trend says 20%. [2]) Electric cars aren't limited in that way, and reach 63%-80%. Of course, if fuel was burned to create electricity, there was a thermodynamic efficiency loss upstream. Those values have objective engineering measurements.
There's something called "Miles Per Gallon Equivalent".[3] This is more of a marketing/regulatory term. It appears on car window stickers. It's just miles per kilowatt hour multiplied by kWh per gallon of gasoline, which is 33.7 kWh / gallon. Motor Trend says that the Tesla Model 3 is rated at 142 MPGe, which is a reasonable number.
This probably has to do with pollution credits, not energy efficiency. It's may be related to the Corporate Average Fuel Economy rules. Those have a big loophole on the gasoline-powered side - there are different limits for "cars" and "light trucks".[4] US vehicle production is currently over 50% "light trucks", which includes many SUVs.
[1] https://en.wikipedia.org/wiki/Engine_efficiency
[2] https://www.motortrend.com/news/evs-more-efficient-than-inte...
[3] https://www.motortrend.com/features/what-is-mpge-meaning
[3] https://www.kbb.com/car-advice/what-is-mpge/
[4] https://en.wikipedia.org/wiki/Corporate_average_fuel_economy