Is solar generation increasing? (Yes) The perils of cumulative totals

This graph was tweeted by Greenpeace

Which immediately brought me back to a recent Stats Chat post on cumulative totals. Cumulative totals tend to go up. And on the face of it, it doesn’t really look like growth has been accelerating recently. Growing yes, but not “skyrocketing”.

I followed up on the post, and found the original data here. Turns out it’s quite a bad graph. It’s not installed solar capacity (as the label says), but rather solar generation. Though that at least explains why the value dropped in 2012 – it’s possible that generation could decrease (less sun?), but it would seem strange that lots of people would uninstall solar panels. Worse, it turns out that they are only using real data until 2013, and the 2014 and 2015 numbers are projected.

So here is a more accurate version of the graph (dotted are estimated figures)

production

But if you were to draw a line through 2009-17, it doesn’t really look like exponential “skyrocketing” growth, only linear straight-line growth.

And if you plot the annual increase, not such a flash picture emerges.

increase

Solar generation is definitely increasing (a good thing), but not skyrocketing.

UPDATE – One of the important things about being a scientist is that in the face of new information you should always re-evaluate your position. So it turns out that my conclusion was wrong. Solar installations are increasing exponentially. The data in the original greenpeace graphs was production as in fabrication, not generation. My bad. But still *not* installations.

So here is the actual world installed solar capacity.

install

It is pretty hard to tell whether that is actually just a straight line, or if the rate of installation is continuing to increase. So here is rate of annual installation.

inc

So rather cheeringly, solar installations are skyrocketing.

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About James

I'm a scientist. Sometimes I get distracted.
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