Upgrade of the MGB Electric Sports Car

Analysis by Warren Winovich

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Battery pack cycle life. A distinct advantage of lithium-ion batteries over their traditional lead-acid counterparts is a much greater cycle life. The table below compares expected cycle life for both versions of the MGB electric sports car. Cycle life for the lithium-ion pack and the lead-acid, gel-cell pack represent the latest, most reliable, values. The sources are:

lithium-ion chemistry:Andrew Burke, UC Davis, Institute of Transportation Studies; reported at M.Brown Seminar, Jan. 30, 2010.
lead-acid gel-cells:Christopher LaForge, Battery Survey, Home Power, Vol.127, p. 80, October/November, 2008.

For lithium-ion batteries: c = 12900 x e-DOD/43, where DOD is in percent.

For lead-acid, gel-cells: c = 6240 x e-DOD/27, where DOD is in percent

A related property of the two battery systems is the specific cost, $/kW-hr, used to determine the amortized battery cost which can dominate operating cost. In the following table, electric car operation is for highway driving, 50 mph.

Table. Cycle life and specific cost: MGB batteries.

MGB with upgraded Li-ion packMGB with original Pb-A pack
range, highway, 75 % DOD 74 mi range, highway, 60 % DOD 12 mi
cycle life @ 75 % DOD 2255 cycle life @ 60 % DOD 676
pack failure mileage 166870 mi pack failure mileage 8112 mi
lifetime @ 40 mi/day 11 yrs lifetime @ 12 mi/day 1.85 yrs
specific cost, $/kW-hr 350 specific cost, $/kW-hr 290
MGB pack cost (China) $ 10990 MGB pack cost (us source) $2784
amortized pack cost 0.066 $/mi amortized pack cost 0.343 $/mi

With the original 9.6 kW-hr, lead-acid, gel-cell pack, expected lifetime for driving 12 miles daily is 22 months (i.e., 1.85 years). Cost difference of the upgraded Li-ion pack is $ 8206 (= $ 10990 - $ 2784). A sinking fund to raise this amount over the time period is $375 per month - $ 12.15 daily. In effect, this represents the cost of obtaining an electric car with outstanding performance with regard to range and battery life.

Operating cost. Operating cost of an electric car consists of two components:

1.energy cost for charging

energy cost = (economy, kW-hrs/mi/charge eff.)x(utility rate)

2. battery amortization cost

Determined in the table above.

Total operating cost for the two versions of the MGB electric sports car are compared below.

MGB: upgrade Li-ion packMGB: original Pb-A pack (gel-cell)
energy: (0.245/0.90)x(0.225):0.061$/mienergy: (0.246/0.75)x(0.225):0.074$/mi
battery amortization cost: 0.066$/mi battery amortization cost:0.343$/mi
total:0.127$/mitotal: 0.417$/mi

By the time that the upgraded version of the MGB electric car is driven 28300 miles, the difference in total operating costs will make up the additional cost of the lithium-ion battery pack. Then, for driving beyond 28300 miles, there will be an accrued savings (equal to 0.290 $/mi).

For comparison, operating cost of a Honda Civic hybrid is found below.

energy, $ 3.10/gallon, 35 MPG: 0.089 $/mi
maintenance, routine service: 0.021 $/mi
total:0.110 $/mi

Total operating cost of the hybrid is only slightly less than that of the MGB.

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