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Old 04-28-2009, 04:18 PM   #4 (permalink)
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EV net efficiency flow chart

Yesterday,there was a discussion about the "actual" efficiency of a plug-in EV,from"wheeling" the power onto the grid,to the power delivered to the road surface from the traction drive in the car itself.I went into my records and found the following.The data is from GM Research Labs and Electric Power Research Institute.The numbers aren't current but may give some insight.

(1) Electric utility generation plants are given efficiencies from 34-50%,with a combined-cycle unit scoring the highest.

(2) Power transmission losses delivering the power over the grid to the household give an efficiency of 93-94%.

(3) Battery chargers are given a 90% efficiency.

(4) Storage batteries on board the car are given 80% efficiency ( this has nothing to do with it's power density).

(5) Controllers are given efficiencies as high as 98% ( Alan Cocconi's AC Propulsion using MOSFET and IGFET power transistors){his CRX loses 2kW in heat loss during full acceleration}.

(6) Electric motors are given a range of efficiency,from 75% for a conventional DC device,to 92% for a GM MagnaQuench,and 96% for Unique Mobility in Colorado.

(7) If the EV uses any type of powertrain from the motor to the drive wheel,it might be conservatively estimated at 95% efficiency.

Considering the chain of events to power down the road in my home-built Ghia EV,if I use coal-fired electricity from a conventional power plant,I might expect an overall thermal efficiency on the order of 15.4%,compared to the chemical energy of the coal.With the combined-cycle plant,overall efficiency would be 30.2%.

For a comparison,an IC-powered car,operating at constant speed at max BSFC can achieve 40% efficiency.This is why the Chevy VOLT is configured the way it is.Alternate,renewable forms of power wheeled onto the grid obviously get around the fossil-fuel CO2 challenge,however its important to realize how much energy is lost moving it around and from transforming it from one form to another.

I like Ed Begley Jr's rooftop PV array-charged EV. This is along the lines of what Hunter and Amory Lovins were advocating a couple decades ago.
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