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As John pointed out, it's a marketing scam. More details: http://scienceblogs.com/goodmath/2009/08/the_chevy_volt_gets_230_mpg_on.php miles-per-gallon is obviously ambigious when referring to an electric car. But people will fall for it, GM will sell cars, and the marketing boys at GM will have champagne! Everyone is happy. N 2009/8/12 John Scull <[log in to unmask]> > Hi Alastair, > > It is my understanding that this number is an artifact of the EPA > measurement system which undervalues the energy stored when the car is > plugged in. If the car is rated as a hybrid like the Prius, the mileage > drops to about 50 mpg. As you point out, promoters of plug-ins seldom > consider the inefficiencies and carbon emissions inherent in the electricity > grid. > > Even GM can't avoid the laws of thermodynamics. > > John > > > ----- Original Message ----- From: "Alastair McIntosh" < > [log in to unmask]> > To: <[log in to unmask]> > Sent: Wednesday, August 12, 2009 2:14 AM > Subject: The Herald - GM's 230 MPG claim - does anybody understand the > thermodynamics? > > > http://www.theherald.co.uk/display.var.2525038.0.0.php?utag'076 > > Fascinating concept here from GM. But does anybody understand the > thermodynamics behind this? How does using an internal combustion engine to > charge a battery give such efficiency? It seems to me contrary to the > normal > entropic laws where you'd expect energy losses at each level of the system > - > from the engine, the battery, and the electric motor - rather than just > from > the engine as would be the case with a conventional direct drive system. > But > maybe it's to do with the charger engine being able to run at a steady > state > rather than being put through all the rigours of acceleration and > deceleration. Does anybody have an angle on this? > > Also, at some point, if you're going to be carrying a ton of metal around > as > your means of conveyance, you have to hit on the thermodynamic limits of > the > energy contained in a gallon of fuel. Beyond that limit further attempts at > efficiency would be impossible for a given type of primary fuel. Does > anybody know what that theoretical bottom line would be for average driving > conditions? It would be interesting to know as that figure would set the > theoretical bottom line for MPG. > > Incidentally, I am sceptical of some of the claims for electric > transportation because they rarely factor in the huge efficiency losses in > generating the electricity, or what the source fuels are. For example, > Eurostar claim an astonishing 18g of C02 per passenger kilometre. But they > buy a lot of their energy from France, which means nuclear. Again, does > anybody consider my scepticism on this unjustified? > > Cheers, > > Alastair. > > ************************************************************** > * Website: www.AlastairMcIntosh.com > * > * Email: [log in to unmask] > * > * Alastair McIntosh > * 26 Luss Road > * Drumoyne > * Glasgow G51 3YD > * Scotland > * Tel: +44 (0)141 445 8750 > * > * Hell and High Water: Climate Change, Hope and the Human Condition, now > * published by Birlinn, £8.99 - > www.alastairmcintosh.com/hellandhighwater.htm > * > * Soil and Soul: People versus Corporate Power is now in paperback and > * in French translation - www.AlastairMcIntosh.com/soilandsoul.htm > * > * Love and Revolution, collected poetry, is from Luath Press > * - www.AlastairMcIntosh.com/loveandrevolution.htm > * > * Rekindling Community: Connecting People, Environment and Spirituality > * is Schumacher Briefing No. 15 from Green Books, > * www.alastairmcintosh.com/rekindlingcommunity.htm > *~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > Alastair. >