# Cost of Driving a Hybrid…

## Cost of Driving a Hybrid…

This isn’t an easy problem. I asked an engineer friend of mine from Canada to try to explain. Here’s what I received.

A ‘plug-in hybrid’ (PHEC) would have about a 30 to 40KW battery system.  Such a battery typically has a usable capacity of  12 to 16 KWH, and therefore takes more than that to charge. (Charging not 100% efficient.) A battery-only vehicle would have a 80 KW battery to provide about 35 KWH per charge.

On a simple 120 volt 20 amp household plug in circuit, the literature indicates we should expect a  PHEC would take 11 to 15 hrs to charge. Actual charging current would be at about 17 amps (a home circuit of 20 amps would be only loaded to about 17 amps if used continuously, to avoid blowing the 20 amp breaker). So at 120 volts that’s 2 KW, which over 14 hrs (being conservative) is 28 KW hrs. Up here, electricity is about 12 cents a KWH, but lets assume 15 cents as a more usual figure. (Europe is considerably higher — not sure what California is, but probably at least 15 cents.) So it costs 2KW X 14hrs X \$0.15=\$4.25 to fully charge an average Plug-In Hybrid overnight. Assuming you also use the gas engine for acceleration, hills, etc, I added another \$5.00 for gas a day —- purely a ‘guesstimate’. The larger BEV batteries would take 24 hrs, at that same power level, so would take 50 KWH, and cost \$7.35 to charge from empty.

(For the GM Volt the company says it will use even less gas, as it only has a small generator on board so you don’t get stuck out there on the road somewhere. The Volt is sort of a cross over between a PHEC and totally battery vehicle (BEV) like the Tesla.)

For a Level 2 charger based on 240 volts 40 Amp breaker, assuming 32 amp continuous load gives 7.7 KW available for charging. The data I’ve seen suggested that the 40 KW PHEC hybrid would therefore take less than 3 hrs. Which would be about 7.7 X 3 X .15 = \$3.50 in electricity cost each charge. (Again assuming almost empty when you plug-in.) For the BEV, needing about 5 hrs, it would cost 7.7 X 5 X .15 = \$5.75

The Level 3 service centre system a garage (or parking lot?) might install, putting out 60 KW of power, can charge up that 30 KW PHEC in about 18 min, or less thatn 1/3 hr which is about 20 KWH, which is \$2.70 per charge.  And for the BEV, 60KW for 35 min which costs \$5.25 per charge.

(You’ll notice that the bigger / faster the charge rate, the more efficient the charging process and the less it therefore costs.)

Therefore, depending on the charger, and the state of charge when you plug in, the electricity cost would be between \$2.70 and \$4.25 for the PHEC, and between \$5.25 and \$7.35 per charge assuming 15 cents a KWH for power.  This is assuming a full charge from near empty in each case. Of course, if you’re in a hurry you can always leave with a partial charge, in much less time. And a ‘Top up’ charge while visiting someone or at an appointment would cost less, of course. Might be a good business for parking lot operators to get into, at some point in the future.

Got it?

JVH

#### John Van Horn

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