# Cumulative US Plug-In Vehicle Sales Chart Shows Incredibly Predictable Exponential Growth

2 years ago by Eric Loveday 20Comments

Sometimes a lone chart (notice there’s no other image contained within this post. That’s an InsideEVs no-no) tells the entire story.

Such is the case here.

What you’re gazing upon is a chart showing cumulative US sales of plug-in vehicle from December 2010 (that’s when both the Chevy Volt and Nissan LEAF launched in the US) through March 2013.

The curve of the chart show that the cumulative sales of plug-in vehicles are exponential.

What’s more is that the chart follows almost a perfect exponential curve, which means the the future growth of the plug-in vehicle segment is rather predictable.

So, if we extended the chart out to (fill in the blank, as this is what we’d call an interactive post) and drew a fancy exponential curve line, then the result would show that cumulative US sales of plug-in vehicles at that time would be approximately ?????? units.

While we could fill in the blanks for you, there are simply too many scenarios to cover. What will cumulative sales be in January 2020? How ’bout March 2014? Maybe mid year 2018? We’re not sure what numbers you’re seeking, but if you’ve got some graph paper (or at least a ruler and a notebook) and a pencil (maybe a printer, too) then the answers to your questions are just a few simple steps away.

Go ahead. Give it a try. Let us know in Comments what you discover.

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### 20 responses to "Cumulative US Plug-In Vehicle Sales Chart Shows Incredibly Predictable Exponential Growth"

Are you sure it is exponential? Maybe it is bi-linear… lower sales rate from Jan 2011 through March 2012, then a higher sales rate after that.

try y=105*x^2 in any online graph tool, it looks pretty close

You have described quadratic growth:

http://en.wikipedia.org/wiki/Quadratic_growth

Exponential growth is much faster than that:

http://en.wikipedia.org/wiki/Exponential_growth

Plug-in vehicle growth is not exponential.

yeah i know

but what is bi-linear function?????

I’d be more impressed if it were not cumulative sales, rather just sales in general. When calculating cumulative sales, the bar graph will always go up each month, even if just a single car is sold. And even if no cars are sold, the graph will not go down unless you start subtracting cars that were wrecked or otherwise removed from the fleet.

Still.. having said that, I’ve been following the plug-in market very closely. And while individual sales of specific vehicles remains somewhat flat, it is important to remember that we keep adding more variations of plug-in vehicles on the market. Each new plug-in on the market seems to grab additional plug-in sales, rather than pull from an existing model (for the most part).

Can you explain what “New sales that month” means?

It’s an accumulative graph. So the red is what was sold that month. Check out my chart, where I leave the individual sales separate.

(it this pic doesn’t work, go to kdawg.com and click on the Plug In Sales Tab, then scroll down)

[IMG]http://i901.photobucket.com/albums/ac211/kdawg2011/PHEVSales2013-04-18_zps8ab67b90.jpg[/IMG]

Translation: I’m an idiot, haha. For some reason I visually missed that the red portions were merely the increase from the last month, my bad!

Eric, if you want to prove that it is an exponential curve, then you need to plot the data on a logarithmic scale Y-axis, which would reveal a straight line angled upwards. I suspect, that when you do plot this line, you will see an upwardly oscillating line, reflecting the ebb and flow of cyclical buying patterns throughout the year, over which you could plot a straight line to “linearize” the trend, then approximate your exponential growth rate.

I haven’t run numbers yet, but I think 1 million cumulative sales is an important milestone because 1) Obama has mentioned that number specifically in his SOU address and 2) it’s just a cool number!

My graph shows 143k to the end of 2013, 250k to the end of 2014, 390k to the end of 2015, 565k to the end of 2016, 760k to the end of 2017, 1m to the end of 2018, 2.6m to the end of 2023.

Looks easy achievable. Even too slow!

I have to partially agree with David Murray & Jason M. Hendler on this.

Don’t want to rain on anyone’s parade, but . . .

one thing I learned in my engineering career was the sheer folly of attempting to extrapolate (i.e. estimate outside the data range) from a curve fit to observational data.

It’s quite difficult to explain why to people who want to believe what they think they see in the nice curve. It has to do with the arbitrary nature (Exponential? Why not?) of the chosen curve.

Having said that – the cumulative chart is actually a superb visual tool for promotional purposes and confronting naysayers. Adding the red bars on top the blue (double counting) is pure marketing genius. Even pathological ideologues like Sarah Palin and friends might hesitate just a little before coming up with the next rant on so many “losers” buying all those “loser” electric cars.

So three cheers for good visual messaging. Just tread carefully with the projections.

I wouldn’t worry too much about whether or not the word “exponential” is truly appropriate. Suffice it to say that sales are accelerating at a steady pace, as the graph shows. Sales tripled from 2011 to 2012. And I think that maybe sales will triple again from 2012 to 2013. (or at least double). As the momentum builds, it will be harder for naysayers to have an argument.

MikeM, the red bars are not double counting. Observe that the bottom of one red bar lines up with the top of the previous bar.

That said, to my eye this looks closer to quadratic than exponential.

quadratic cumulative linear growth

@bitguru

Are too! – in the sense that the size of a red bar has to equal the step increase that just appeared in its associated blue bar.

But you’re right overall in that the proportionality is retained at the tippy tops of the red bars.

It’s only a quibble really since the red/blue ratio has to decrease with time/sales anyway, and I’m greatly in favor of throwing every piece of helpful visual imagery possible at the issue.

Let’s hope this graph gets widely circulated.

Though the graph looks good I think it’s pretty much irrelevant, at some point all the factors: gas prices, range, price, charging infrastructure, ect. will fall into place and it will look stupid to buy anything else. At that point it WILL go exponential and become supply constrained, OEMs can only make cars so fast. Part of this is herd mentality, it’s difficult for most people to make a decision that falls too far out of the norm, no matter how much sense it makes, they just think “there must be a catch”. I personally think a lot of people will go EREV or PHEV, as even the Tesla supercharger can’t refuel a car as fast as gasoline, even though they may only take a road trip 2-3 times a year this will be seen as a drawback (I personally drive an EV). But as the Volt owners are showing these cars use so little gas it won’t matter for a long time.

I also think that many people who buy Volts will realize 1) they don’t really need “infinite” range and 2) 40 miles of electric can become frustratingly short. In time, these people will likely replace their EREVs with a BEV.

The die hard electric fans, but not the masses, IMHO.

Percentage of new car sales is a good measure also….

MrEnergyCzar

http://electricdrive.org/index.php?ht=d/sp/i/20952/pid/20952

If you would like the numbers that go with the graph, here is the link to the story that I was working on.

Just the facts mam…… (also in the story)