"An economist is an expert who will know tomorrow why the things he predicted yesterday didn't happen today." "Nimblefinger" at xkcd forums

Saturday, February 20, 2010

The Nissan Leaf

I've posted a couple of times on supplying the necessary electrical energy to replace our passenger automobile fleet with electric vehicles, and I also discussed the Chevy Volt. An all-electric vehicle appears ready to enter the fray in late 2010 - the Nissan Leaf. While Nissan seems to be playing it close to the vest (the vehicle's weight and price as well as many other specifications are not given), between Nissan's site and Autoblog's site some conclusions can be reached.

Let's look at the combined aerodynamic and rolling resistance efficiency of the vehicle. The Leaf is claimed to deliver about 100 miles on a full charge, the lithium ion battery pack capacity is stated to be 24 kilowatt-hours or about 86.4 megajoules. The electric motor is less than 100% efficient in its use of the energy in its source. Based on this page and the 80 kilowatt (or 107 horsepower) motor in the Leaf I'll use 92% (the table shows the minimum as 91.7%). Also, the Leaf site discusses "0% to 100% charge" so I'm going to assume that the vehicle uses all 24 kilowatt-hours of energy in the battery pack to go 100 miles. Thus, the Leaf uses .92*24=22.1 kilowatt hours or 79.6 megajoules to go 100 miles.

How does this compare to "miles per gallon?" The 79.6 megajoules is the energy in about .66 gallons of gasoline, but the internal combustion engine is quite inefficient so I'll use 22%. Then we'd be considering a car that goes 100 miles on (0.66/0.22) or about 3 gallons. Thus, we're looking at a car whose efficiency in terms of aerodynamics and rolling resistance is about that of a gasoline burning car getting 33 m.p.g. Seems quite reasonable, though certainly not awe inspiring.

How about cost? I drive about 62 miles per day year around, so I'd use about 62/100 of a full charge, or about 14.9 kilowatt-hours from the battery pack. Let's assume the charging system is 85% efficient, so I need (14.9/.85) or 17.5 kilowatt-hours of electricity. This would probably be at a marginal rate of $0.17/kilowatt-hour since I'd invariably be over my baseline rate with the City of Anaheim. So I'd spend 17.5*0.17 or  $3.01 per day on energy to drive. This is, of course, $3.01/62 or $0.049/mile. Right now in my Land Rover LR3 HSE I'm spending about $0.14/mile on gasoline. The Leaf would provide considerable savings, amounting, in the course of a year, to about $2,060. Certainly, that's nothing at which to sneeze (grammatical pedant that I am).

As to performance, the Leaf boasts a torque (from a dead stop) of  280 Newton-meters (208 pound-feet) and a top speed of over 140 km/h (87 mph). It will accept a full charge from a compatible 220 volt system in about 8 hours, about twice that from a 110 volt circuit. At a suitable quick charge station, it will take an 80% charge in under half an hour and a boost good for about 35 miles in about 10 minutes. Such suitable stations are, at the moment, mostly a distant dream however.

What about creature comforts? It appears to be quite comfortable, modern, and light. It will have room for at least four adults, MP3 connections via USB, a proprietary system built into the satellite navigation system to indicate charging facilities within range, systems to allow one to receive emails from the car on their smart phone and to control certain functions (heating, cooling, etc.) remotely via that smart phone. All things considered, I'm going to look very closely at the vehicle when it becomes available.

Addendum: How much might I reduce my costs if I built a solar charging system to charge the vehicle's battery pack during my working hours? I went here to find the insolation available, using average insolation, the month of March, and a horizontal flat plate to see this map:
Conservatively, 4.5 kilowatt-hours/meter^2/day are available on average. If I'm fortunate, maybe I can create a collector of 2 meter^2. If I'm even more fortunate and technology smiles, perhaps I can find cells with 18% efficiency and provide circuitry to charge the vehicle. Thus, I'd get 2*4.5 kilowatt-hours*0.18 or about 1.6 kilowatt-hours. This would be enough to bring the vehicle from, say, 65% charged to 71.7% or to go a little less than an extra seven miles.  To bring it from fully discharged to fully charged would take a little under 15 days. I can do perhaps a little under twice as well in June but still, seemingly not worth the trouble and expense.

3 comments:

Jonathan Friedman said...

Thank you. This is useful information for more than just Leaf buyers.

Anonymous said...

Wonderful analysis. Thank you. Would you consider adding a paragraph similar to the solar panel one that addresses wind power? That is, how far might a home wind turbine go toward charging the Nissan Leaf? -Donna, WA

King of the Road said...

It's significantly more difficult to look at wind because very local effects will predominate. For the sun, you're either able to expose the panels or you aren't, but for a wind turbine, the effects of buildings, trees, etc. will have an overwhelming effect on available energy.