Predicting Chevy Volt Sales: Is California Inventory The Key?

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2013 Chevrolet Volt  -  Driven, December 2012

2013 Chevrolet Volt - Driven, December 2012

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Analyzing electric-car sales numbers and prognosticating on them is somewhere between a parlor game and a black art.

Now one blogger has applied some Nate Silver-like statistical analysis to try to divine predictive patterns in sales of the Chevrolet Volt, the range-extended electric car that's currently the best-selling plug-in vehicle in the U.S.

Ryan Turner, of Raleigh, North Carolina, who writes the My Chevy Volt blog (he's also @VoltDriver on Twitter), suggested yesterday in a post that looking at Volt inventory in California gives some clues to future Volt sales.

He notes that he had not predicted the fall in Volt sales that took place last November, though he did expect reduced numbers last month as buyers who wanted to take advantage of the $7,500 Federal income-tax credit would rush to buy before December 31 of last year.

But now he thinks he's found the way to predict the monthly numbers: Reported Volt sales track inventory in the car's key market, California, where more than 50 percent of Volts are reportedly sold.

And he has a very nice graph to map the two trend lines, which we've taken the liberty of reproducing here (but, you should go read his whole analysis).

Specifically, he looks at the number of Volts available for sale within a 30-mile radius of the 90210 ZIP code. That's Beverly Hills, in case you never watched the famous Nineties TV show on Fox.

He's tracked those inventory numbers since last May, so he's got most of a year's worth of data built up now.

And the graph is pretty revealing.

Chevrolet Volt sales vs. Volt inventory around ZIP 90210, May 2012-Jan 2013 []

Chevrolet Volt sales vs. Volt inventory around ZIP 90210, May 2012-Jan 2013 []

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We'll be testing out his premise in months to come, to see if it holds up.

Meanwhile, we're curious: What other metrics would you use to predict the sales of the Chevy Volt--or indeed any plug-in car?

Leave us your thoughts in the Comments below.


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Comments (16)
  1. Since this is a correlation, it requires that you have current data to predict the other variable, and it would seem that previous national sales would be as good or better than concurrent California sales? Or am I missing something?

    That is, to predict sales nationally in X month, you have to have California sales for X month, so why is that better than using National sales for the month earlier or just getting the National sales at the same time as the California sales?

    Further, since as you point out, California sales are generally 50% of the national total anyway, then California sales numbers are MOST of what is contained in the national total. Or, the data/approach is using "X to predict X."

  2. You are missing something :)

    It isn't California sales. It is California inventory levels. California inventory levels are know real time.

    And the point of the blog wasn't really to make a model of sales. It 'can' do that in a reversed engineering base, but the intentions of the blog are to show that the lack of sufficient California inventory directly affects sales.

    I do say, in the blog, that an increase in California inventory will likely mean an increase in sales. But there will come a point where inventory is matched to demand, and this will cease to provide any real use.

    The point I am making is that the Volt market is artificially restrained.

  3. Read my blog entry, which is linked. I go into great detail.

    But don't confuse inventory with sales :) Two different things.

  4. I agree with this analysis absolutely. In my purchase experience in Northern California (Bay Area), it is the inventory that is the issue. Most Chevy dealers don't have many Volt sitting in the lot. They pretty much sell them out every 3-4 weeks (about my experience from dealer visit). So, if they got inventory, then they can sell them.

    I just don't understand why GM didn't figure it out. If they give enough inventory to LA and SF area, they can easily increase their California sales by at least 20-30%...

  5. One metric would be the level of spending by oil companies to continue spreading misinformation ;

  6. I think Ryan is confusing cause and effect. Chevy tooled up to make what? 40,000 per year or more, so if shortages are a problem, the answer would be to make more product. And he's ignoring some very key variables that need to be in the study: season, national election uncertainties, national disasters and advertising, among others. I leased my Volt directly as a result of advertised attractive lease incentives,and gas was in the $4.50 range with no relief in sight. Around election time, wonder of wonders, gas prices started down, Chevy STOPPED advertising the Volt on local network TV and it got really, really cold. Now gas prices are headed back up. (well, who knew??)
    The Chevy ad about going for weeks/months without a fillup was right on

  7. I'm not confusing anything. However, I think you are.

    I think it is very apparent from my data that lack of inventory in California pulled down sales significantly. You don't even need to believe me. GM has said it repeatedly, but they've never really backed it up with real data. It left them vulnerable from critics that said that reason was incorrect.

    Do you think that the Volt suddenly got unpopular in November, then people decide to like it again in December, then hate it again in January?

    There is always going to be variability for a multitude of reasons. But the supply disruptions for almost 2 full months in the second hand of the year was absolutely THE primary reason for poor sales.

    Read by blog, not this post.

  8. Typos. Read my blog, not this post.

  9. And by that, I mean that John is just presenting a small piece of my work. The blog posting has much more.

  10. Put another way. At one point in January there was less than 50 Volts to service an area of almost 5 million people. There were 65 Volts in the Raleigh area to serve 750,000 people. GM has not figured out the right supply, but considering 50% of their Volt sales are in Cali, they better figure it out soon.

  11. I totally agree. It seems the GM "distribution" manager is totally clueless. When I was getting my Volt in June, 2012, NO inventory at all for the entire Bay Area. I was calling all dealers on a day to day basis.

    If they had shipped more AT-PZEV Volts for California, they would have sold more each month...

  12. Either Chevrolet is making and shipping very few Volts or dealers aren't very interested in selling them. My {small town} local dealer has 50 Silverados on the lot and once in a while has a Volt.

  13. I live in a housing complex here in California. Townhouse not apartment. Our garages all share a common power source that is paid by the home owners association, I've been wondering for a while now how people like us will be able to charge our cars. If I got a new vehicle it wouldn't be hooked up to my power supply, unless I ran some weird power cord. This is deffinitly something that future housing developments will have to think about.

  14. If CA has a shortage of Volts, well, what's GM's problem getting cars to where they're wanted?

    Nationally, there is little correlation.
    Cumulative Volts built less Volts sold, Volts sold that month and PCT of avlble Volts sold that month:

    Mon Unsold Sold Pct of Avail
    12Jan 7129 603 8%
    12Feb 8453 1,023 12%
    12Mar 7350 2,289 31%
    12Apr 7450 1,462 20%
    12May 9831 1680 17%
    12Jun 9212 1760 19%
    12Jul 10757 1849 17%
    12Aug 11614 2831 24%
    12Sep 9977 2851 29%
    12Oct 8726 2961 34%
    12Nov 9512 1519 16%
    12Dec 8388 2633 31%
    13Jan 10197 1140 11%
    13Feb 11869 1626 14%

    Volts sold well Aug-Sep during declining inventory, selling up to 24% of available and have tanked despite increasing inventory, especially in the most recent two months.


    Green Cars have a dirty little secret. Informative, but has nothing to do with the Volt's inventory, GM's channel stuffing.

  16. @Ash: I trust you're aware of the many methodological flaws and inconsistencies in the study cited in the Wall Street Journal OpEd ... which the author conveniently omitted?

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