# Converting Wh/mile into MPG



## martinwinlow (Sep 22, 2009)

That's US gallons, BTW. A UK (proper!) gallon contains 44016Wh. MW


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## IamIan (Mar 29, 2009)

The initial post gives the MPGe ... Miles Per Gallon Equivalent ... for energy Wh equivalent.

Remember the 36,650 wh or 36.65 kwh per gallon is for 100% Gasoline.
Other Blends E10 , E85 , etc ... have less wh per gallon.

The other 2 types of MPG comparison are:

MPGe ( $ Cost Fuel equivalent )

MPGe ( pollution equivalent )

- - - - - - - 
*MPGe ( $ Cost Fuel equivalent )
*
If you know your local cost $ per Gallon ... and the $ per kwh of electricity... use those more local numbers.

If the Gasoline is $3.40 per gallon.
$3.40 per gallon / 36.65 kwh per gallon = ~$0.093 per kwh of gasoline energy.

If the Electricity is $0.12 per kwh of electrical energy.

The Cost difference ratio per wh of energy = 0.093 / 0.12 = ~0.773

Use the already previously determined MPGe ( energy based ) and adjust for the cost different for that amount of energy.

The 300wh/mile example was ~122.2 MPGe ( energy )

Now multiply the MPGe ( energy ) by the cost ratio.

122.2 x 0.773 = ~94.4 MPGe ( Fuel Cost )

- - - - - - - - - - - - -
*MPGe ( Pollution )
*
Pollution is more complex ... not all ICE cars with the same MPG pollute the same ... not all kwh of electricity produce the same pollution.

Those other variable come in when talking about other charging sources ... is coal used? ... old dirty coal , or newer updated coal ? ... compared to what ICE tailpipe pollution ... a 50MPG PZEV will pollute less per gallon or mile than a SULEV that got the same 50MPG ... and the SULEV at 50MPG pollutes less than the ULEV ... and the ULEV less than the LEV ... etc ... even though they are all using the same 50MPG.

In general the BEV pollutes less in some cases ... but not in all cases ... even at the same MPGe.

One simplification is ... If your BEV is charged from a 'clean' electrical source ... hydro , wind, solar , etc ... it will pollute less ... than any equal or lower MPGe ICE.


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## JSHarvey1961 (Nov 1, 2014)

IamIan said:


> The initial post gives the MPGe ... Miles Per Gallon Equivalent ... for energy Wh equivalent.
> 
> Remember the 36,650 wh or 36.65 kwh per gallon is for 100% Gasoline.
> Other Blends E10 , E85 , etc ... have less wh per gallon.
> ...


For the dollar cost equivalent (and all the measure for that matter) you are neglecting the cost of replacing the batteries. That adds several cents per mile driven (anywhere from 7 to 20 depending on the type of battery) to the cost of an EV.


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## Vanquizor (Nov 17, 2009)

MPG also neglects maintenance costs as well- for what we spend on oil changes in my wife's vehicle I could have a new battery pack every 18 months.


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## IamIan (Mar 29, 2009)

JSHarvey1961 said:


> For the dollar cost equivalent (and all the measure for that matter) you are neglecting the cost of replacing the batteries. That adds several cents per mile driven (anywhere from 7 to 20 depending on the type of battery) to the cost of an EV.


Not neglecting .. those other things , like battery replacement .. were not the issue being discussed ... a year ago now, in the post you reference.

The MPG number listed for a ICE car does not include any maintenance type of life time costs of operation .. not 12V car starter battery replacements, not oil changes, brakes , spark plugs, Tax pay cost for oil wars, health care costs for pollution, etc.

MPGe is not the same thing as , total vehicle life time cost per mile.

If you want to instead of MPGe ... do a .. total vehicle life time cost per mile ... ownership + Maintenance ... feel free ... please post each step of your data analysis... both the ICE and BEV will both go up.

But if you like ... see attached .. as an example someone else did ... they found a Brand New OEM 100 Mile Range BEV breaks even with the ICE in ~5 years .. after that the BEV is cheaper overall ... even with buy new price and all those other costs .. and as technology gets better and oil keeps getting more expensive that will only continue to shift to shorter and shorter periods than that ~5 Years (in 2012)... so if you plan to drive for more than ~5 years ... the ICE is just costing you more money in total  ... and of course the DIYers .. like this site ... will be even shorter period than the brand New OEM time period.


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## Moltenmetal (Mar 20, 2014)

Converting a gallon of gasoline in BTU of HEAT energy directly to its numerical equivalent in kWh of electrical energy is misleading. A typical power plant converts heat in fuel to electricity with about 30% efficiency, so they aren't at all comparable. Combined cycle is more efficient but not used everywhere. 30% is a good US nat gas power plant average, which is why it sucks to see people wasting electricity (high value energy which can be converted to mechanical work with high efficiency) being used in resistance heaters to make low-grade comfort heat- it makes my blood boil!

If your source of energy is the grid, then the grid source energy balance is easy to look up. Here in Ontario it's about 11% nat gas, 2% coal, with the balance being nuclear and renewables. With a grid like that, the BEV wins hands down on both GHG emissions and toxic emissions against a hybrid or turbo diesel. But not all grids are this fossil-lean.

You also need to take into account the energy cost of refining and distributing gasoline, and grid losses, charging losses etc. for the BEV. Grid losses are about 6.6% on average! and charging is about 90% but can be higher. Round numbers, about 3% of the energy in a gallon of gasoline has been used as electricity in the refinery (ie. ~9% in source fuel terms) and a further 7% has been used in fuel gas in the refinery. So that 33.5 kWH per gallon is closer to 36.8 kWh of petroleum heat energy emitted to the atmosphere to refine and then burn it.


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## IamIan (Mar 29, 2009)

Moltenmetal said:


> If your source of energy is the grid, then the grid source energy balance is easy to look up. Here in Ontario it's about 11% nat gas, 2% coal, with the balance being nuclear and renewables. With a grid like that, the BEV wins hands down on both GHG emissions and toxic emissions against a hybrid or turbo diesel. But not all grids are this fossil-lean.
> 
> You also need to take into account the energy cost of refining and distributing gasoline, and grid losses, charging losses etc. for the BEV. Grid losses are about 6.6% on average! and charging is about 90% but can be higher. Round numbers, about 3% of the energy in a gallon of gasoline has been used as electricity in the refinery (ie. ~9% in source fuel terms) and a further 7% has been used in fuel gas in the refinery. So that 33.5 kWH per gallon is closer to 36.8 kWh of petroleum heat energy emitted to the atmosphere to refine and then burn it.


Also to keep in mind .. the ICE in the car also converting at roughly ~30% efficiency... the 36kwh of chemical energy in that 1 gallon of gasoline only yields ~12kwh of mechanical shaft energy... where 36kwh from the electrical outlet (even with losses in charger , batteries, etc) will net me out far more than ~12kwh of shaft mechanical energy.

Perhaps the easiest MPGe comparison to make is the (direct) $ based one .. because the $ at the pump , already includes all those distribution costs , refining costs ,etc ... and so does the price from the grid.

BEV __$ to buy the energy to go __ Miles.
ICE __$ to buy for the energy to go __ Miles.

In most places the BEV will win that MPGe (direct $ based) comparison.


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