Chevy Volt's 230 MPG, view of an outsider

Chevy Volt's 230 MPG, view of an independent scientist

8/24/2009

General Motor just announced a 230 mile per gallon Chevy Volt on 8/11/2009, according to a press release of GM. For source please visit, GM press release.

Chevy Volt's 230 MPG is wrong

If an average 4-door sedan can go at 20 MPG, Chevy Volt's 230 MPG makes it 10X more efficient. Volt's overall efficiency will be over 100%. That is simply impossible. Something got to give.

I will try to explain the basis for those numbers. The following is a table on a gallon of gasoline's heating value and how EPA treats the value.

Terms	Abbrev	Energy values in Btu	Gasoline-equivalent in Wh at 100% efficiency	Relative values	Notes
Lower heating value	LHV	116,100	34,000	100%	Water is vapor in the final state.
Higher heating value	HHV	124,340	36,420	107%	Water vapor condenses into liquid water, giving off extra heat.
EPA corporate average fuel economy	CAFE	42,000	12,307	36%	Assumes a reasonable conversion efficiency of 36% from heat to electricity.
EPA doesn't use petroleum incentive adjustment bonus	EPA bonus	280,000	82,049	241%	Bonus=6.6667*CAFE

A gallon of gasoline has a lower heating value or LHV at 116 mBtu, with a higher heating value (HHV) at 7% higher. The difference between LHV and HHV is the condensation energy of water vapor. HHV = LHV + water vapor condensation energy. EPA's corporate average fuel economy is at 42 mBtu, or 36% or LHV. This value assumes a reasonable conversion efficiency of 36% from heat to electricity. Generally electricity is made from a coal power plant, not from gasoline. Currently, modern coal utility boiler efficiency is 34%. By comparison, natural gas combined cycle turbine efficiency can be as high as 53%. For a vehicle doesn't use petroleum, EPA oddily has an incentive adjustment bonus of 6.6667 times CAFE. For this value is 280 mBtu/gallon or 82 kWh/gallon.

The next table assumes 25 kWh per 100 mile, which is reported in the GM press lease

Terms	Abbreviations	Energy values in Btu	GGasoline-equivalent in Wh at 100% efficiency	MPG at Efficiency at 25 kWh_plug/100 mile
Lower heating value	LHV	116,100	34,000	136
Higher heating value	HHV	124,340	36,420	146
EPA corporate average fuel economy	CAFE	42,000	12,307	49
EPA doesn't use petroleum incentive adjustmentbonus	EPA bonus	280,000	82,049	328

The MPG is estimated from 49 to 328. As you can see, this number of MPG is totally depend on the gallon gasoline equivalent. The higher equivalent, the high MPG. For a gallon of gasoline, total heat is HHV at 124 mBtu. Convert this amount energy into electricity at 100% is 36 kWh and we get 146 MPG. Laws of thermodynamics tell us that 100% conversion is impossible. With CAFE number, I get a 49 MPG. Using EPA bonus which is 6.6667*CAFE =328 MPG. Those MPGs are also show below in a picture.



But wait a minute, a gallon is a gallon. You have to decide how much energy you can get out of a gallon gasoline. To me, as a scientist, the value is 42 mBtu or 49 MPG for Chevy Volt which reported 25 kWh/100 mile. 49 MPG is not shabby at all, and actually it is a super good number. I can tell you how difficult to increase mileage just by 1 MPG. You are talking about a leap from 20 MPG to 50 MPG, that is a revolution. But how GM spins it is just poor management.

How did GM get to 230 MPG

How does GM got the 230 MPG?	MPG	Mile driven in a testing	Weight	Contributing MPG
Energy stored in battery	328	12	67%	219
Energy from gasoline	49	6	33%	16
MPG reported by GM 230				235