Haven't researched this , just wondering if anything official on economy rating format for PHV's, REEV's. Without too much thought into it, seems a reasonable format might be, for example - 11 to 14 miles electric range, 50 city/48 hwy in hybrid mode What do you think? And geez shouldn't the Volt's numbers be out by now? News already blabbing it is Motor Trend COTY.
I believe that the EPA has not yet come out with a final rating format. I believe that there is an effort to come up with a rating that would "look" the same as today's City/Highway/Average (though the average does not always appear in the same big numbers) by somehow figuring out a conversion of electric energy from the plug to gas milage. The problem is massive. You could, for example, try to equate the cost of a mile's worth of plugged in electricity to a that much gas (so if the mile's worth of electricity was cheaper than the mile's worth of gas, the overall "mileage" would go up. That would sort of make sense, but there are a lot of other things you could try to equate. Of course, the idea of the "cost of a mile's worth of electricity" is as dependent on driving conditions as the cost of a mile's worth of gas. So, one natural way to do it might be to see how far the car goes on a charge when you put it through the various gas driving cycles. And there are lots of other complexities. Anyway, tell me if I'm wrong gang, but: I think the reason the Volt numbers are not out is that the EPA has not finalized its protocol for determining "mileage" for Plug in Hybrids or pure EVs.
Check the US EPA site. They are already trying to figure this one out: Fuel Economy Label | Fuel Economy | US EPA
It is funny that they are switching to kWh/100 miles instead of going for MPkWh (Miles per Kilowatt-hour) which would be more MPG-like. Or worse, MPBTU to stick to the imperial system.
There's nothing funny about the shortcomings of MPG. It's a very misleading way of representing efficiency. The other is what most of the rest of the world has been using all along. It's nice to see us moving toward that measurement approach too. .
Mathematically, they are just inverses--except for translation of units. What's interesting is that some of the proposed l;abels use both methods-- one method is so-called MPG equivalent, the other is kWh/100 miles. That means the units of energy are different (energy contained in a gallon of gas vs. kilowatt-hours}, and the distances are different, miles vs. 100 mile units. Whether people will know enough about this even to be confused not clear to me. Maybe it's good to have both.
I agree that distance per volume is the wrong way to do it. When I drive, I don't do so with the intent of burning a gallon, I drive to go a distance, and want to know how much gas it takes. Consumption is more logical, but it's also a less-is-better concept which confuses people. For a dual-energy-source vehicle, miles per kWh (on battery) and MPG (on the engine) makes more sense. You'd have to look at both and decide which is better for the way you drive. Of course, people won't like seeing 4 MPkWh since the number will be so small, so maybe you could use miles per 10 kWh. Then the numbers would be like 40. In Europe, they use L per 100 km for the same reason. Of course the salesman would have to explain to the buyers (who flunked out of high school) that 40 on electric is better than 50 on gas even though 40 is a smaller number. Then there's the problem of which kWh to use. kWh in the battery (useful for calculating range) or kWh from the plug (useful for knowing cost). I wouldn't want manufacturers to supply cheapo inefficient chargers since they don't affect the numbers. If you tried to test a car, how do you measure charge in the battery (to do a before and after)? It's not that straightforward. You could charge it back to 100% (or whatever charger cutoff) and measure power taken from the plug. That wouldn't be hard. Overall I'd rather see miles per 10 kWh as measured from the plug so the full system gets measured, along side numbers for miles per gallon. This brings up another question. When they measure the Prius over the driving cycle, how do they make sure the battery starts and ends at the same SOC?
Not sure if you guys saw the news today, but the fuel economy section of the Volt's window sticker was revealed on the likes of Autoblog and TTAC. It has an all-electric MPG equivalent and a gasoline-only MPG number. The label will also show charging time, a range estimate for electric and gasoline, and a comparison with other cars.
