The end of August marked the end of our fifth trouble-free and happy month, and over 4,100 miles with our LEAF.
That statement deserves some emphasis.
This is the first mass produced highway capable electric car at an affordable price point. It is absolutely remarkable to be able to say with confidence that I have had ZERO problems with the reliability or any other aspect of the car. I may have some preferences for improvements for the next generation LEAF, but none of these causes me to be anything less than extremely satisfied with this car. That is saying a LOT for a car that is ground breaking in its technology for a mass market product and represents a radical change in the fuel source and required refueling behavior.
Cost of Driving:
The LEAF continues to be our primary car for all trips within 35 miles of our home. This turns out to be the majority of our driving. We drive our Prius for longer trips. We've only had to put gas in the Prius about once a month over the past two months, about 7 gallons of gas usage each month. Since our electricity cost for charging the LEAF is likely to be zero for the year, because of our household solar PV system, our only fuel cost for our household driving will come from these monthly Prius fill-ups. We drive the LEAF about 1,000 fuel cost-free miles per month and the Prius takes 7 gallons for 300 miles of driving, so we use 7 gallons of gas for 1,300 miles of total driving, or a household miles-per-gallon of 186 mpg! At $4 per gallon of gas, our total fuel cost is about 2.1 cents per mile. Obviously, we're very happy about this.
For August, we used more power from the utility grid than in any prior summer month, 234 kWh. This was because we had more family members living with us as well as the fact that we were charging the LEAF for 1,028 miles of driving, more miles than in any prior month. So did our electrical bill for the month show a large expense? No, it showed a CREDIT of $52.90! As in the previous summer months, this was because our solar PV system generated power during the expensive, high demand Peak hours and we used power during the less expensive Off Peak and Super Off Peak hours. So our credits for producing lots of power during Peak hours were higher than our costs for our power usage during hours when power was in lower demand. This is the big benefit of home solar power and Time of Use rates.
Compared with a Plug-In Hybrid:
It's interesting to compare the costs of driving a Battery Electric Vehicle (BEV) like the LEAF with the cost of driving a plug-in hybrid. If I had chosen a plug-in hybrid like the Chevy Volt, instead of the LEAF, my maximum miles per day on electricity would have been about 40 instead of the 75 or so miles with the LEAF. In August, there were 12 days of the 27 days we that drove the LEAF when we drove over 40 miles. For those days, we drove a total of 161 electric miles in the LEAF for which the Volt would have used gasoline. At about 35 mpg when the Volt burns gasoline, this would have cost about $19.80 more for the month, or $237 more for the year.
If we replaced our 2007 Prius hybrid with a plug-in hybrid like the Volt, however, we would fare even better than we do now. Though we use the Prius for trips that are longer than the range of the LEAF, such as trips to Los Angeles or San Diego, most of the Prius trips are local because we need to drive two cars that day. Most of the miles for these local trips would be electric miles in a Volt, and would likely be at no cost due to our home's rooftop solar power system.
So for a two car household like ours, with most trips within a 35 mile radius, the combination of a BEV and a plug-in hybrid would work very well. However, every driver's needs and driving are different. If both drivers have a 70 mile daily commute, for instance, 30 miles of one person's daily driving would be on gasoline in the Volt. At 21 workdays per average month, that would amount to 630 gasoline miles, or 18 gallons of gas and $77 per month in gas costs. Compared with a Prius, at 50 mpg, the Prius would cost $117 per month for this commute, so the plug-in hybrid still beats a hybrid by $40 per month if the family has solar power and pays nothing extra for electricity to charge the car. If the family pays an average of 11 cents per kWh, the difference between the Prius and the Volt drops to only about $11 a month in favor of the Volt.
However, if one had a Volt instead of a Prius and were going to take it on a driving vacation, the Prius would begin to make more sense. If the driving trip was 1,000 miles, a round trip from Los Angeles to San Francisco, the first 40 miles in the Volt would be on electricity, but the rest of the miles would likely be on gasoline. Lets even assume that 80 miles are electric, since the driver might be able to charge up at the destination. Then 920 miles would be on gasoline. The Prius would take 20 gallons for this trip. The Volt would take 26.3 gallons. The cost difference at $4 per gallon would favor the Prius by about $25 for the trip.
Considering that most people don't make more than a couple of driving trips like this per year, that amount of savings of a pure hybrid over a plug-in hybrid is pretty minimal. If the family goes on lots of long drives, though, the pure hybrid with better gas mileage makes more sense than a plug-in hybrid with lower gas mileage. Of course, if the plug-in hybrid has similar gas mileage to the pure hybrid, an example being the soon-to-be-released Prius Plug-In, the advantage goes to the plug-in hybrid. This is an example of why the choice of a fuel efficient car is an individual decision and depends on a variety of factors, including the family's driving behavior and needs, the cost to buy or lease the car, including available rebates and incentives, and the family's willingness to do the additional daily planning and thinking that owning a plug-in car requires.
Overall, for a two car family with daily commutes and one or two driving trips per year, the combination of a BEV such as the LEAF and a plug-in hybrid with about 40 miles of electric range, such as the Volt, makes good sense. Of course, this doesn't take into account the purchase cost of these cars and the space and utility needs of the family. The good news, though, is that before too many years, there should be a good selection of BEVs and plug in hybrids with a variety of seating and interior space configurations to choose from, at increasingly reasonable price points.
For all of the above comparisons, as gasoline increases in price, as most people think is inevitable, the logic favors the plug-in car, either a BEV like the LEAF, or a plug-in hybrid even more strongly over a traditional gasoline fueled car or a standard hybrid, except for long driving trips, where the standard hybrid with better gasoline mileage will do better than a plug-in hybrid with lower gas mileage. New plug-in hybrids, like the Prius PHEV, may have similar gasoline mileage to the full hybrid version, though, so the PHEV will likely do better in all driving scenarios, although for a higher purchase price. This also assumes that the family can charge the plug-in car at low night time rates of about 10 cents per kWh without incurring a large penalty for any daytime uses such as air conditioning.
State of Charge Meter:
As I've written before, with an EV such as the LEAF, information about remaining driving range is the most important type of information for the driver to know. Unfortunately, it is even more difficult for an EV maker to make an accurate meter to show remaining range than it is for a gasoline powered car. This is because "State of Charge" is a more complex quantity than "gallons remaining" in a gas tank. The state of useful charge of a battery is influenced not only by the kWh of electrical charge remaining, but by the balance of charge between the battery cells, and the voltage of the lowest voltage cells.
The fuel gauge and range remaining instruments that Nissan included in the LEAF have limited usefulness. The "Miles Remaining" display is so influenced by recent past driving behavior, that the range shown when the battery is full is usually very optimistic. At lower levels of battery charge, the number displayed is probably more accurate, especially since Nissan updated the car's software and added what is effectively a "reserve" at the bottom end of the scale. The twelve bar "fuel" scale is more useful, and the "reserve" makes it less likely for drivers to run out of charge abruptly when the gauge reads zero bars. However, when there are less than about ten miles of actual remaining range, the display may show zero of twelve bars of charge and a flashing set of dashes for the miles remaining. This leaves the driver with no information at all with which to decide whether to stop immediately or go the extra five miles home.
Home Grown SOC Meter showing 93 of total 281 charge "counts".
SOC Meter showing 33% State of Charge
With a recent software update, the home grown SOC meter can now display battery voltage, amperage and instantaneous power use and regenerative braking charge in kW. With more experience in the hands of users, this data will become more valuable over time.
The Numbers:
Month: August 2011
Total Miles at Month End: 4,167 miles
Miles Driven in Month: 1,028 miles
Electric Power Used for Charging: 327.7 kWh (measured at wall power source, includes public charging)
Public Charging: 4.3 kWh
Home Charging: 323.4 kWh
Energy Efficiency, Month of August: 3.14 miles/kWh (wall to wheels)
Energy Efficiency, Lifetime: 3.14 miles/kWh (wall to wheels)
Most Electric Energy Used for Charging in a Day in August: 18.6 kWh (4.9 charging hours)
Least Electric Energy Used for Charging in a Charging Day: 6.4 kWh (1.7 charging hours)
Average Electric Energy Used for Charging in a Charging Day: 12.4 kWh (3.3 charging hours)
Household Power Used for Month: 790.6 kWh (without car charging)
Total Power Used for Month: 1,114 kWh (includes car charging)
Solar PV Power Generated for Month: 880 kWh
Net Power Used or Sent to Grid for Month: 234 kWh net used
Electric Bill, So Cal Edison, Schedule TOU-D-TEV: -$52.90 (A credit in this amount will be added to our net metering total credit for the year, offsetting future bills for months with lower solar output.)
Solar Net Metering Year Total kWh at Month #6: -136 kWh (Total of 136 kWh sent to the grid)
Solar Net Metering Year Total Cost at Month #6: -$357.84 (Total credit for the net metering year to date)
Cost for Charging Car in August: $0.00
Cost per Mile: $0.00
Cost for Charging Car, Lifetime: $0.00
Cost per Mile, Lifetime: $0.00
(If We Didn't Have Solar Power, Est Cost for Charging Car in August: $42.04)
(If We Didn't Have Solar Power, Est Cost per Mile in August: $0.041)
Average Miles per Driving Day: 38.1miles
Longest Day's Driving: 65.1 miles
Shortest Day's Driving: 20.7 miles
Number of Times we Took the Prius Instead of the LEAF Due to Low Charge: One
Unexpected Low Charge and Unable to Reach Destination: Never