G.M. Puts Volt’s Mileage in City in Triple Digits | Hacker News Reader

G.M. Puts Volt’s Mileage in City in Triple Digits

nytimes.com

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This announcement proves two points:

1. Moving forward, MPG is not going to be a good measure of efficiency or operating cost.

2. GM is run by salespeople, not engineers.

It begs the question, what is the proper measure?

MP$, MPKWH?

MP$ is what we really care about but it has to be adjusted for price fluctuations of power and gasoline, pretty impractical.

Maybe list MPG City, MPG Highway, MPKWH Battery on the sticker.

MPJ - Miles per Joule

As we move toward alternative fuels, we need a fuel-independent metric.

Agreed. It'll have to be a measure of energy consumption per mile. Consumers will also have to develop an understanding of the relative cost of different energy sources.

Maybe we rate cars in Miles/Joule and rate energy sources in Joules/$. Makes the math pretty simple.

You might need to add some cargo/people capacity in there. A tiny electric car will have a hard time beating a diesel MAC truck for efficiency when it's hauling a few tons :)

Just as a Vespa would have poor gas mileage carrying heavy truck cargo - this has nothing to do with the energy source.

I thought that was the idea - removing different energy sources from the picture and looking at which vehicles are more efficient.

There is no intuitive way to convey what you are proposing. If you tried to move 4 tons of cargo, a big rig would use less energy than a Civic. If you are trying to get yourself across town, a Civic will use less energy than a big rig. It would be complicated and expensive to calculate the full spectrum of efficiencies for a vehicle under different cargo loads. Personally, I would use the data, but I suspect the average person would find multiple efficiency graphs to be overwhelming.

But 1 Joule of one energy does not cost the same as 1 Joule of another, which is why MPG gasoline and MPG diesel are not directly comparable

GPM

Watt-hours per mile is common, and easy enough for a reasonable consumer to calculate the expense of given the cost of a kWh in their neighborhood.

EPA MPG estimates for electric vehicles are unfortunately purposely distorted for the purposes of giving electric vehicles higher MPG [ http://www.sae.org/mags/AEI/6559 ]. For instance, a gallon of gasoline contains about 33 kWh of energy, but an normal car wastes about 2/3 of this, netting only 11 kWh per gallon.

Logically, an electric car should arrive at an MPG by calculating the number of miles that it would travel on this same amount of energy. Instead, the EPA has told all-electric companies that they can do this computation using 82 kWh (almost 7.5 times more than the logical value), giving all-electric cars a huge benefit (Nissan's upcoming electric has claimed 367 MPG).

Plug-in electric cars use a different value, which is somewhere between the two, giving Chevy some magic number in between. Just to confuse matters, the EPA sticker on the electric Mini quotes kWh/100 mi, giving it "33" city and "36" highway, numbers that resemble current gasoline car mileages.

(more info: http://www.hybridcars.com/fuel-economy-numbers/confusion-ove...)

[EDIT: Also, it has been said that the gasoline engine in the Volt will provide around 50 MPG. Whenever you travel farther than 40 miles (assuming a full battery), this car is no more gasoline efficient than the Prius.]

And that plugins are going to be designed around the specifics of the EPA test. If the next plugin only needs the engine for half the time on this same route will that count as 500mpg?

Similarly my SUV does infinite miles per gallon on initial in-city mileage (only counting the 1/2 mi downhill stretch from my house)

Not true, idling consumes gasoline. Unless you have disabled your steering lock, and can do without power steering, headlights, AC, or brakes (not recommended :-) ), you are not getting ∞ MPG, even if your car tells you otherwise.

just to be clear, you save as much gas moving up from a 20 mpg car to 25 mpg car as you do going from 50 mpg to 100mpg. (think in terms of gals per 100 mile)

Well yeah, but in absolute terms only.

  Car 1: instead of needing 5 gallons you only need 4 gallons. Saved: 1 gallon (20%)
  Car 2: instead of needing 2 gallons you only need 1 gallon.  Saved: 1 gallon (50%)

But who makes comparisons like this in absolute terms? I rather save 50% than 20%, but maybe that's just me.

People have to pay for things in absolute money. :)

Not to mention that absolute savings are important when it comes to carbon reduction.

The lack of a plan on how to deal with urban customers or those who don't have a garage to park the car in (apartment dwellers) is really disconcerting. As the article says, these are the people who could benefit from this car the most.

That's so disingenuous to not count the cost of electricity for recharging it.

40 cents for 40 miles on electricity, it's in the article.

Compared to $2-4 for 30 miles on the average sedan, not bad.

Maybe this will finally spur Toyota to add a plug-in standard on the Prius.

That electricity cost is based on a single location. My electricity is 12.5cents per KWH, regardless of time of day. That turns into about 3 cents per mile, rather than 1 cent per mile quoted in this article.

Close, but not quite. The sentence right before their 40¢ a day claim, they say $2.75 per 100 miles. That works out to 82.5¢ for 30 miles, or $1.10 per 40 miles. 82.5¢ is 3 times better than the current $2.60 for a gallon of gas, but grid power is almost double the 11¢/kWh used for these calculations in some parts of the country.

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