Saturday, January 18, 2014

Three years on solar power and our electric car

As luck would have it, we hit 50,000 miles on our Volt on January 11, 2014, exactly three years after we bought her.  So, once again, I have to sheepishly report that we drove too much!  A long road trip to the Southwest accounts for most of extra mileage, plus more  errands, appointments, meetings, . . .  we promise to cut back in 2014!
              2011                2012                2013                  Totals
Miles Driven 12,711 16,768 20,521 50,000
Gallons of gas 129 188 251 568
Miles per gallon 98 89 84 88
Miles on electricity      7,900 (62%)        9,827 (59%)    11,734 (56%)      29,461 (59%)

We did have two maintenance issues this year—we replaced the tires and the windshield wipers!  Actually the warning light came on one time, and I took it to the dealer; they found the problem, which was minor, and fixed it under the warranty.

The 50,000 mile mark is significant, since the Climate Central report, which was critical of electric vehicles, based its argument on an expected life of 50,000 miles for the batteries.  So far I have not seen any deterioration of the battery.  E.g. this morning, after charging overnight, the mileage estimate for the batter was 37 miles, which is pretty normal for our car.  A more likely battery life is well over 100,000 miles.

How about the solar panels?  Today is the three year anniversary of the start up of our solar panels.  I took a reading and found that our current total is now 12,954 kilowatt hours (kwh), which means that the panels produced 4,304 kwh in 2013. (subtracting last year's amount) This is actually more than in 2012—maybe because it almost NEVER rained in 2013, so there was a lot of sun.  The 4304 is 1.5% less than the 2011 production, so this is in line with an expected 20% drop in power production over 20 years.

Did we save money with solar power and electric car?

Absolutely!  We just received our PG&E "true up" bill for our annual electric charges.  See figure below.  The meter shows a net reading of 2,310 kwh for the year.  Since the solar panels produced 4,304 kwh for the year, we used a total of 6,614 kwh.  Our total PG&E electric bill was their minimum charge--$5.91 x 12 months = $71 for the year.  Our solar panels cost $12,000 and are financed at a 3.5% annual rate for an annual cost of $653.  So our total electric bill plus solar finance cost for the year was $724.  Dividing that by 6,614 kwh gives a cost of 10.9 cents per kwh.  This is less than the U.S. average of 12.3 cents per kwh and well below the California average of 15.4 cents/kwh. 

Even if we add the cost of our house's electrical upgrade--$3,500—that only brings the kwh cost up to 13.8 cents per kwh.  Using this number we saved 1.6 cents/kwh x 6,617 = $106 for the year compared to average PG&E utility rates.

So there is some savings with the electricity, but the real savings is in gas.  At 3.2 miles per kwh, we used 11,734 miles/3.2 miles per kwh = 3,667 kwh.  With almost all of this being charged at the low off-peak rate of about 6 cents/kwh (adding fixed charges) the cost of driving on electricity was $220.  With our old Honda, which got 25 miles per gallon, which is also the current U.S. average, and a cost per gallon of $3.75, the cost of driving on gasoline would have been 11,734/25 mpg = 469 gallons x $3.75 = $1,760.  So we saved $1,760 - $220 = $1540 in addition to the $106 we saved on the electricity.

Of course we did have to finance the car, which was expensive, but a savings of $1646 is more than enough to pay for the additional cost of the Volt over a similar gasoline car.  And, as noted here, the cost of electric cars keeps coming down, making them a better deal all the time.

Even more good news

If you look at our annual electricity usage in the figure below, you'll see that we used a net (total electricity used minus solar electricity generated) of 670 kwh in December.  This is a lot higher than the 448 kwh net in December, 2012 or the 292 kwh in December, 2011.  The reason for the extra usage this year is that in each of the last two years our total charge for electricity was well under the minimum charge.  In 2011 we could have consumed an additional $70 in electricity without additional charge.  In 2012, we could have consumed $122 more in electricity without charge.  So, in 2013, we added an electric heater to warm our bedroom, hallway, and bathroom every winter morning before 7 AM, which is when the electric time-of-use rate goes up.  For the year we were still $37 under the minimum, so we'll keep using that electric heater through the next few months—for free!

So 2013 was a great year to be driving an electric car with solar power.  As I've said in previous years, the main regret I have is that we are still using too much gasoline.  If we could buy a low carbon gas substitute—e.g. algae based biofuel—I would be happy to pay whatever it costs.

PS--also just for the record: GM sold 23,094 Volts in 2013 compared to 23,461 Volts in 2012.  However, electric vehicle sales overall nearly doubled in 2013 as many new models came on line.  There were more than 90,000 EVs sold in 2013.


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