It has taken off exponentially. That’s what the growth curve you’re looking at is called. :)

No, it has not taken off exponentially yet in the way the Tony Seba video demonstrates with a picture of 5th Ave in NYC in the year 1900 where there are lots of horses used for transportation, and only one car, compared with a picture of the same street in 1913, where the street is full of cars, and there is only one horse to be found.

Scroll down the page I linked to the graph "Exponential Growth of Solar PV". A straight line on a log graph is exponential by definition.

There's the formal definition of "exponential", and then there is "exponential" in the sense of completely disruptive and transformative as in the example Tony Seba gives. I am referring to the latter.