One year of solar power & the Volt—how did we do?
Short answer: “Everything is going according to plan,” to quote Emperor Palpatine. The solar production exceeded our expectation; the Volt cost 2 cents per mile to drive; and we cut our CO2 by over 70%. Still we have a ways to go to be truly sustainable.
The Analysis:
What was our plan?
Our goal was to provide enough power with our solar panels to zero out our electric bill. Note that this does not mean that the solar panels would provide all the electricity to cover the car and the house. Because we charge the car in the off-peak at roughly 5 cents per kilowatt hour (kwh) and because the summer peak hour rate that our utility, Pacific Gas & Electric (PG&E), pays us for electricity that we generate is about 29 cents per kwh, the solar panels do not have to generate all the house/car’s electricity to zero out the bill. Because PG&E will not pay for any extra electricity that we generate—i.e. there is no feed-in-tariff-- it would not pay to produce more electricity than PG& E will reimburse.
Comparing the numbers to the estimate
Our estimate was that the panels would generate 4200 kwh , the house would consume 3600 kwh, and the car would use 3000 kwh for a total of 6,600 kwh for the year. So what are the final numbers?
The solar panels worked like a champ: 4,371 kwh!
Total electricity consumed: 6,460 kwh
Car electricity consumed: 2,400 kwh
House electricity consumed: 4,060 kwh
Final Electrical Bill: Summer peak: -371 kwh x $0.28 = $103.88 (credit)
Partial peak: 36 kwh x $0.09 = $ 3.24
Off peak: 2423 kwh x $0.04 = $ 96.92
Final Total Cost for the year: $ 3.72 (credit)
So the numbers came out pretty close to what we expected. Note that there is an $11 minimum charge per month in addition to this total. Therefore, the total electricity cost is $11 x 12 months = $121. Also, this is not a final exact amount. I’ll let you know if the final numbers have any big surprises from PG&E.
Did the Solar Panels save us money?
Yes! For the 6,460 kwh that we used we paid $121 fixed cost for the electricity. The solar panels cost $12,000 after the 30% solar tax credit. Spread over 30 years that comes to $689 per year. So the cost per kwh was ($121 + 0 + 689) ÷ 6,420 kwh = 12.6 cents per kwh. This is less than PG&E’s low Tier 2 rate for most residential users, which is 13.9 cents per kwh. Our rates would have been above Tier 2 if we did not have solar. The solar panels run the meter backwards, so we never get out of the low tier Tier 1 rates.
In our case, we also spent about $3,500 upgrading our 1927 house’s electrical circuits up to current standards for the solar panels and electric car. This brings our cost up to about 15.7 cents per kwh, which is still less than PG&E’s average rate for residential use, which is 18.6 cents/kwh. Using that average rate, we saved $183 with our solar panels (our electricity cost was $1,011, counting the electrical upgrade, while the average rate cost would have been $1,194).
Also, the cost of solar panel installation has now dropped to under $5 per watt, a 5% savings compared to one year ago, so the cost today would be about 12.1 cents per kwh, virtually the same as PG&E’s Tier 1--i.e. lowest regular residential rate of 12.2 cents per kwh. Also, solar rates are not subject to inflation, so the savings should get better with time.
The only puzzle to me is why anyone who uses more than the baseline of 300 kwh or so per month would not install solar panels—i.e. most people in California, especially if their house is already up to current electrical standards, and they can qualify to refinance.
If you live in the San Francisco’s East Bay, I suggest you give the guys at Super Solar, who installed our panels, a call. Actually now is a perfect time to refinance since interest rates are at record lows.
Did the Volt save us money?
The car on the day we bought it a year ago with new electrical conduits and panels installed (we've since painted them white to match the house).
So what did it really cost to drive the Volt? As reported in the previous post on this blog, we drove 7,900 miles on electricity and 4,800 miles on gas. On gas, the car gets 37 miles per gallon so that’s about 10 cents a mile, or $480 for the year. On electricity the car gets about 3.3 miles per kwh, so it used about 2,400 kwh. This is less than the 3,000 kwh we estimated. Since most of that charging was at night, the cost for driving the car was 2,400 kwh x .04 = $98.00. Note that I’m assuming that the household electricity use during the off-peak is about zero since the solar panels produce electricity on the weekend during off-peak times. If we add the fixed cost of $11 per month and spread it over the average of 535 kwh per month, that adds 2 cents per kwh, so the off peak cost becomes 6 cents per kwh, and the total cost for the car becomes 2,400 kwh x .06 = $144. This gives a cost of $144 ÷ 7,900 = $0.018 cents per mile, say 2 cents per mile.
Our previous car was a 1991 Honda Civic that got 25 mpg. Assuming an average of about $3.75 per gallon for the year (as you know gas prices have been going up and down), the Honda would have cost us $0.15 per mile for gas for a total of $1,905 for gas for the year. The Volt cost $480 for the gas miles and $144 for the electric miles for a total of $624. So we saved $1,281 this year.
Now that’s not enough to cover the cost of the Volt, especially since the Honda had been paid off long ago. However, it is enough to borrow $15,000 for 15 years at the current interest rate of 3.25%. Since the Volt costs $40,000 minus a $7,500 tax credit it has a total cost of $33,500. Since the savings in gas are worth $15,000, the cost of the car is equivalent to $18,500 for a car that gets 25 mpg, i.e. about the same as an average new car today.
My secret plan
OK, so the car “only” breaks even compared to a new car that gets 25 mpg. But wait, I’m a very conservative person. I never plan to buy another car again. We financed the car for 30 years at 4 per cent interest. Now I do assume that I will need to buy new batteries in about 10 years, but I think they’ll be modestly priced, no more than regular auto maintenance would have cost. So how do the Volt numbers look with my 30 year plan?
A gas savings of $1,281 per year is enough to borrow $22,151 at 4% for 30 years. This means that the cost of the Volt is comparable to paying $33,500 – 22,151 = $11,349 for the car. And this does not assume any increase in the price of gas! Anyone want to bet that gas won’t go over $5.00 in the next ten years?
Thus my slogan for buying electric cars—“Save money, Save the planet”
What was the carbon footprint?
The big advantage of a Volt is that it produces a lot less CO2 and other pollutants, especially when combined with solar panels. Our Honda would have used 508 gallons of gas to drive the 12,700 miles that we drove last year. At 27.5 pounds of CO2 per gallon (see: How Clean are Electric Cars?)that would total 7 U.S. tons of CO2.
Our Volt used 129 gallons of gas for a total of 1.77 tons of CO2. The electricity for our house was 68% solar/32% from PG&E. PG&E estimates 0.524 pounds (238 grams) of CO2 per kwh (see the same post referenced above), so I calculate 2400 kwh for the Volt x 0.524 lbs/kwh x 32% PG&E electricity = 402 pounds CO2 = 0.2 tons.
Therefore, the total CO2 from the Volt was 1.97 tons, a 71% reduction compared to the Honda. Note that these numbers are for our car. I read that the average Chevy Volts is getting 111 mpg, so we are guilty of using more gas than the average Volt owner. We’ll try to behave better this year.
Is our Volt/household use sustainable?
Unfortunately, not really. I’ve argued that the earth can only absorb 7 billion tonnes (7.7 billion U.S. tons) of CO2 per year, so we really only get one tonne each. Our Volt produced a little less than 2 tonnes. Since we use about 3 tonnes just on natural gas for our stove, hot water, and household heat, and that doesn’t even count the CO2 produced at workplaces, we really need to eliminate CO2 from our transportation system if we are to have any hope of getting down to a sustainable level.
Fortunately for the Volt, this is not unreachable. If the gas we used were a low CO2 biofuel, that would put our gas driving down to the same range as our electric driving, say 0.2 tonnes total. And if batteries in the future can deliver two or three hundred miles on electricity, we would use much less gasoline on our trips.
What’s next?
So we aren’t there yet, but the Volt is a big step in the right direction, unlike mining the Canadian tar sands, which is a big step in the wrong direction. Let’s hope that the will for self preservation wins out over the oil companies will for profit this year. (Thank you President Obama for saying NO to the Tar Sands once again!—see: http://www.washingtonpost.com/national/health-science/obama-administration-to-reject-keystone-pipeline/2012/01/18/gIQAPuPF8P_story.html )
Another step in the wrong direction is that PG&E is proposing to raise the rates for electric vehicles from 4 cents per kwh to 11 cents in the off-peak. While this is still cheaper than gas, it reduces the cost savings for driving electric. Since electric vehicles are still new, I am encouraging PG&E to retain their rates at least for another two years, when all the rates will be reexamined.
Other steps that we should try to take this year include:
· Establishing a royalty/severance tax on oil in California. I just read in Greg Palast’s book, Vulture’s Picnic, that BP bribed the corrupt dictator of Azerbaijan so they would only have to pay a 10% royalty on the oil they extract. But in California we collect ZERO, nada, zip—we’re giving it away for free! How outrageous is that. Even Texas collects 25%.
· End oil subsidies, such as the modest steps that Obama has suggested, and more
· Stop the Keystone XL pipeline, no matter what route it takes
· Add warnings on gas pumps that burning gasoline increases the risk of catastrophic climate change, and encourages people to conserve fuel, to walk, and to use public transit, bicycles, and electric vehicles
· Support a constitutional amendment that declares that corporations are not people, and dollars are not free speech. (See http://movetoamend.org/)
And on the home front: The numbers show that our house used about 4,000 kwh instead of our estimated 3,600. It could be that the motion sensor floodlights we added in the driveway and around the house account for the extra, or it may be that we just need to turn off the lights more! I’m sure we can conserve if we work a bit harder. Also, household-electricity is more expensive than car-charging-electricity since it is more likely to occur during the peak and partial-peak daytime hours. Fortunately, our solar productivity was also above the estimate so the PG&E bill did zero out. I would also love to figure out an economical way to add solar water heating. It just doesn’t seem to pencil out like the solar panels do, especially with an electric vehicle.
Much to do, but it’s been a great year!
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