I've always been a bit curious about this number. To do a proper conversion, you need to know how much my electricity costs per kilowatt hour and how much gas costs per gallon, both of which vary wildly. Does the car simply have some average numbers baked into the software, or is it somehow dynamic (e.g. receiving data over an RDS feed to update its internal conversion calculation periodically)? If the numbers are fixed, does anyone know what numbers they used?
The car nevers does an MPGe calculation. It only does mpg when in HV mode and kwh consumed during EV mode. To do MPGe you do not use the price but use the energy content... MPGe = total miles / total energy You can get from wikipedia. Mike
Ah, I was thinking MPGe was supposed to indicate cost equivalency. As in, you went X miles and used $Y in electricity, which would have bought you Z gallons of gas, so you got X/Z MPG equivalent. It makes much more sense when you just compare the energy content. Thanks.
Random tangent, but this reminds me of the interesting observation made in this XKCD post: gas mileage is actually a unit of area. Droppings . Now when I drive, I picture myself leaving a little thread of gasoline everywhere I go.
33.7 KWH = 1 GALLON and PIP kWh = 85% of Kill A Watt meter kWh due to charging loss. Then wouldn't MPGe = Total Miles /[Pump Gallons + (.85 * Kill A Watt kWh/33.7)] ? Seems correct. However, drinnovation, who helped setup the formulas of the MPG Spreadsheet, is using MPGe = Miles*33.7/(Gallons*33.7+1.15*kWh) Are the formulas equivalent? Miles*33.7/(Gallons*33.7+1.15*kWh) Miles/(Gallons*33.7+1.15*kWh)/33.7 Miles/[(Gallons*33.7)/33.7 + (1.15*kWh)/33.7] Miles/[Gallons+ (1.15*kWh/33.7)] DR.Innovation, I need your help !!!
MPGe = Miles*33.7/(Gallons*33.7+1.15*kWh) ?? So 500 miles and 10 gallons and 3 kW gets you 49.5 ?? Less than 500/10=50mpg?? Then why plug in? Personally I think the whole MPGe is bogas.
Only plugging in once per tank, as with your example, is basically not plugging in. Far more realistically is plugging in every night. The result is both higher MPG and higher MPGe.
Consider the cost of the relative efficiencies of the two fuels. In my area gas cost $3.90/gallon & a kWh of electricity cost 12 cents. 33.7 kWH = 1 gallon of gas To account for charging inefficiency 33.7 kWh x 1.15= 40.7 kWh Cost of gallon equivalent kWh from wall plug $4.88 Consider the relative efficiency of the two fuels PIP Gas 41.5 miles using 10 gallons 41.5 mpg Electric 912 miles using 265 kWh Account for 15% charging inefficiency 304.8 kWh (300 x 1.15) Convert to gallon equivalent 304.8/33.7 = 9 MPGe = 912/9 = 101.33 It takes 2.44 gallons of gas to drive 101.33 miles at a cost of $9.51 Cost per 100 miles Gas $9.4/100 miles KWh $4.82/100 miles
Breaking out cost like that doesn't work with a plug-in hybrid, since there's so much blending... which complicates the understanding of MPGe. Here's my real-world data: 17,194 miles 221.7 gallons 1,578.3 kWh (including charging loss) (((221.7*3.9)+(1578.3*0.12))/17194)*100 = $6.13 / 100 miles That's overall, of course, which doesen't necessarily reflect what was actually paid. It just gives an idea of the efficiency itself.
You are correct! However given JamesBurke's comment my goal was to demonstrate the relative cost/efficiency advantages of using kWh as opposed to gas.
