My Lexus CT200h is EPA rated to get 42 miles per gallon combined. In it, over the 2 1/2 years I've had it, my total net has been 51.0 miles per gallon. The CT200h has a hybrid power train with a 1.4 kWh (kilowatt hour) NiMH (nickel metal hydride) battery. This battery is good for a mile or so at very low speed in so-called "EV mode." Plug-in hybrid electric vehicles (PHEVs) will have much larger batteries, enabling them to travel further and faster in EV mode. For example, the Prius PHEV is estimated to be able to travel 11 miles and at a maximum EV mode speed of 62 m.p.h. It achieves this with a 4.4 kWh battery pack. And the Chevy Volt now sports a 16.5 kWh battery pack that is estimated to provide an EV mode range of 38 miles.
I wondered if it would be possible to install a larger battery back and charging capability to my CT200h to convert it into a PHEV. As it happens, the answer is yes. And a huge variety of installations are possible, all the way from 2 kWh to 15 kWh capacity. Note that the Nissan Leaf, a pure electric vehicle (EV), sports a 24 kWh battery pack and a claimed range of 75 miles.
Should I install any conversion and, if so, which one? This can be looked at from an economic viewpoint and from a CO2 emission viewpoint. I'll look at both. As a baseline, my most common drive is the daily commute from my home in Anaheim Hills to my office in Long Beach. This round trip is about 62.5 miles and I do it, on average, four times each week. I'd be able to charge the vehicle at work, though I'd have to park at our laboratory facility about two blocks from our corporate offices. Such a strategy would enable me to utilize a battery pack with a 35 mile range to, on a typical day, never have to use the internal combustion engine.
What would this look like? The 7 kWh pack theoretically provides this 35 mile range, and I'd assume it would do so by discharging no more than 90%, but let's be conservative and assume that I'd need 14 kWh of charging per day. Assuming the charge system is 85% efficient, I'd draw about 16.5 kWh from the grid. At $0.16/kWh, this would cost about $2.64. I'll round down to $2.50 because I don't really quite go 70 miles on my daily commute.
Currently, with my 51 m.p.g. average, I use about 1.22 gallons of fuel in my commute. At a current price of $3.699/gallon, this costs about $4.50 per day. Thus, the conversion would save me something like $1.86 per day and, for 200 trips per year, I'd save $372/year. It's not completely clear from Plug In Supply's pricing page but it looks like I'd pay $9,875 for the 7 kWh system fully installed. Clearly, from a purely financial point of view, this makes no sense.
As to CO2 emissions, this is a bit more problematic to compute. I'd be getting half of my electrical energy from our house, where the City of Anaheim provides our electricity, and the other half in Long Beach, where Southern California Edison is the provider. And, assuming that some combination of coal, nuclear, and natural gas provides almost all of the electricity, I won't figure in emissions resulting from extraction and transportation of these fuels. This is reasonable, I'm not figuring the emissions resulting from extracting, refining, and transporting the gasoline I burn.
The calculation for the CO2 emissions from burning 1.22 gallons of fuel can't be exact as I don't know how much ethanol is in the fuel, and the mix of the various hydrocarbon chain lengths. I'm going to assume that the gasoline consists of n-heptane, C7H16 at that its density is 6 pounds per gallon. The chemical reaction would be C7H16 + 11O2 → 7CO2 + 8H2O. A mole of heptane has a mass of 100.2 grams. This mole results in 7 moles of carbon dioxide, each with a mass of 44 grams for a total of 308 grams.
Now, I'll be a bit general and figure that I use 1/51=0.0196 gallons of gasoline per mile. This gasoline weighs 0.118 pounds or 53.4 grams. This produces (308/100.2)*53.4 or 164 grams of CO2 per mile (this is the typical metric for vehicular carbon dioxide emissions) for a total on my commute of 62.5*164=10,250 grams or 10.25 kg of CO2.
That was the easy part. The electrical emissions are much more problematic because I've not been able to determine the mix of sources for Long Beach electricity. I'll just speculate. In any case, I need to determine the emissions related to 7 kWh from the City of Anaheim and 7 kWh from Southern California Edison in Long Beach.
I'm not able to find the appropriate mix of generating facilities to use to calculate for Long Beach, so I'll back into it from information from California State University Long Beach on this page, where it's stated that the renewable generation of 656,000 kWh avoided the emission of 471 metric tons of carbon dioxide. CSULB is only a couple of miles from our office, so this will have to suffice. So the generation of 7 kWh would involve the emission of 8.25*(471,000,000/656000) or 5,923 grams of CO2.
From Anaheim, I'll use the figures from my previous post on the Nissan Leaf. Using those numbers (and sparing my readers the gory details) I can figure that those 8.25 kWh involve the emission of 9,051 grams of CO2. The total emissions are thus 9,051+5,923 or 14,974 grams of carbon dioxide. Call it 15 kg. This is half again as much as my CT200h emits burning gasoline and the main culprit, as was the case for the Nissan Leaf I looked at, is that the City of Anaheim derives a surprising amount of its electricity from the burning of coal. And this information comes straight off of our bi-monthly bill!
So, when all is said and done, it makes no economic sense, and certainly no sense with respect to CO2 emissions, to undertake such a conversion. That's comforting because I don't have a spare $10K to throw at such a project!
And all of this probably overestimates the gains. The careful reader may have noticed that the Chevy Volt uses a 16.5 kWh pack to go 38 miles or 0.43 kWh/mile. The Nissan Leaf uses a 24 kWh pack to go 75 miles, or 0.32 kWh/mile. The Plug-In Supply site, where I got these figures, claims 35 miles on 7.33 kWh or 0.29 kWh/mile. It's true that these figures represent a Prius rather than a CT200h but I'm skeptical that the Prius is that much more efficient in terms of aerodynamics and rolling resistance than a Chevy Volt or a Nissan Leaf.