The Green Machine will answer whether this added expenses of a far larger battery pack does anything for the planet or is it pure hype brought to you by the federal government that is now the largest shareholder in Congressional Motors sorry I meant to say general Motors. The US EPA has this bogus calculation for equivalent MPG for plug in hybrids like the Volt and the Raser Hummer. This bogus calculation does not assign either energy value or carbon footprint to the electricity that is used in the plug in to recharge the plug in’s large battery pack. At least Tesla is honest about its requirements for plug in power. The Tesla site states the Tesla will need 0.28 kilowatt hours from the grid for each mile it will travel. The Volt is a heavier vehicle, and also less aerodynamic than the Tesla so the Green Machine estimates the Volt will require 25% more energy to travel a mile. The Volt will therefore require 0.38 kilowatt hours of electrical energy to move a mile. The most efficient fossil fuel fired method to generate electricity is by combined cycle generation with natural gas. Without boring you all with the mathematical details the Volt will need approximately 0.0225 gallons of gas equivalent to travel the mile. The Prius with an EPA rating of 50 mpg only needs 0.02 gallons of gas to do the job of moving a mile. So the Prius is indeed 10% more efficient than the Volt.

On a truthful basis the Volt gets approximately 45 mpg when the natural gas that is needed to generate the electricity is accounted for. If the average efficiency of the electric grid is used the Volt gets no more than 30 mpg. Maybe the Congress and GM’s CEO had a typo in their press release and meant to claim 30 MPG not 230 MPG?

Since the EPA is for the entire US we should use the average CO2 emissions to generate a kilowatt of electricity over the entire US when calculating the Volt’s carbon footprint. This average amount of CO2 is 1.3 pounds per kilowatt hour. Therefore to move a mile the Volt will emit 0.494 pounds of CO2 per mile. The Prius will emit 0.4 pounds of CO2 to travel a mile when powered by gasoline. The Volt has 25% more CO2 emissions and is ten percent less energy efficient than the Prius. It is time for Congress to enact legislation that the EPA must use, that is based on thermodynamics rather than fantasy. This is no time for a tea party it is time that we Revolt against the Volt. Congressional Motors is a better sounding name then General Motors so instead of wasting the extra $15,000 to buy a General Motors Volt ES 230 MPG, we should all buy the Prius. After the Volt flops they will rename this car the Congressional Motors Revolt BS 45 MPG.

Lindsay -- in the previous article yoiu cited one analysis that shows the Tesla has a well-to-wheel ratio of 1.14; if your assumption about the Volt is correct and it is 25% less efficient that should give the Volt a well-to-wheel ratio of 0.86, compared with the well-to-wheel ratio of the Prius which is 0.56. So why is the Volt not 53% more fuel efficient than a Prius, giving it an EPA rating of 78MPG (1.56*50 mpg for the Prius)? Agreed this is still a far cry from the 230mpg they claim. But it would seem to me that a Volt should be a greener machine than the Prius any way you cut it -- and certainly more affordable than the Tesla.

ReplyDeleteRaelo You need further explanation. The volt needs 0.38 kwh per mile from the grid. The most efficient nat gas combined cycle is 50% efficient so we need 0.76 kwh per mile of input energy. This is 2593 BTUs of input energy. A gallon of gas has 115,000 BTUs (LHV) and this means 44.4 mpg. Had you gone to Iowa State and not Minn you would know this if you are the Raelo I think you are?

ReplyDeleteLindsay, great topic! However, whilst the desperate GM marketing boffins have somewhat overcooked the merits of the Volt, shouldn’t we overlook this somewhat and essentially be supporting a general move to electric propulsion? The rationale being that in the long-term it will (i) prove the technology (and make it more mainstream rather than ‘early adopter’) so that (ii) it will be significantly cleaner when an increasing share of the energy consumed is from renewable sources (some way off mind… but I live in hope), thereby enabling (iii) the symbiotic (when ‘plugged-in’ that is) relationship to renewable-sourced energy in that it could provide temporary energy storage for the somewhat unpredictable energy supply vs. demand…

ReplyDeleteLindsay,

ReplyDeleteAs always, provocative and interesting but this entry is a bit incomplete... You failed to address one very important factor that probably tips the scales ever so slightly in favor of the Volt... Namely, the TOTAL costs of delivering energy sources... How much energy is required to discover, remove, transport, refine, transport again, and deliver gasoline to every auto on the planet, let alone the Prius? Also the curb weight of the 2010 Prius is 3042 lbs. compared to 3520 lbs. for the Volt (15% greater not 25%) and, at city driving speeds, CoD differences between the two vehicles would be negligible with a slight advantage going to the Volt (from appearances)... And another thing, for all the wailing and teeth gnashing about the US stake in GM, nobody has suggested anything that would be better... And I mean, nobody... BTW, Toyota's financial unit requested an emergency "loan" of $3 billion from a state-back lender in March...

Paul and Blair. Thanks for the comments. You guys are great. Even if we have a million plug ins this will only be 15 million kilowatt hours of power stored. This is about 7 hours of the Hoover Dam output. The Hoover Dam provides less than one half percent of the US power generation. As for Toyota also loosing money and needing a bail out this is indeed true. I have no problem with The US owning Congressional Motors, I just want government of the people by the people and for the people so let's have the US buy Lincoln instead of Chevy

ReplyDeleteI am delighted that you wrote this piece.

ReplyDeleteThere is lots of minutiae that can be debated, but the bottom line is that 240 mpg is MISLEADING people who do not understand thermodynamics. I am outraged that we allow this kind of marketing nonsense to be amplified by the media at large. Unchecked, some people might actually think that the Volt is 5x (okay 4.6x, 230/50) better than the Prius in terms of fuel demand, which it is not.

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