There is no exponential when it comes to renewables. The only source of energy we have that provides exponential is nuclear but unfortunately, there is a lot of pushback although it's both greener and provides more energy than wind and solar can ever do.

Furthermore, while they are renewable to they are also unreliable and need to have backup sources which makes them unfit as a enegy base. Remove the subsidies and you will see just how problematic they are.

And then we haven't even looked at the problem with producing them, maintaining them etc.

http://instituteforenergyresearch.org/topics/encyclopedia/so...