Something like a quarter of US energy consumption is in transportation. As you mentioned, the storage density of electricity still far lags behind petroleum. It also takes an hour at a supercharger to "fill up" an electric car vs. a few minutes at a pump. Hydrogen and biofuels (in the US) are generally seen as energy sinks (they take more energy to produce than they give off), but what they lose in conversion they make up for in suitability towards a transportation fuel.

The point is transportation is a tricky application for renewables, and the amount of storage needed to make it work is mind-boggling huge, even assuming decades of compounding growth.

According to LLNL [1], the US consumption of energy in transportation is 27.7 quads. A quads is a measure of a lot of kWh. Specifically, 27.7 quads is 8,118,068,643 MWh.

Tesla's gigafactory is slated to produce 35 GWh worth of battery storage production per year at full capacity (slated for 2018) [2].

So, our annual energy consumption in transportation alone is 8,120,000 GWh, and our largest factory will, in two years, produce about 35 GWh per year worth of capacity.

Lets assume some compounding magic and imagine the gigafactory will be only the first of many self-replicating automated tesla factories. Say we grow our capacity at 5% every year... after two decades, in 2038, that puts annual capacity at 92 GWh, with a cumulative installed capacity of 1,250 GWh.

We're trying to hit 8,120,000 GWh. That's not gonna work.

Okay, lets assume instead of 5% growth, we somehow get 50% growth (we need more gigafactories, but lets say we also get better at building batteries, something closer to moore's law). Now after two decades of 50% growth, in 2038 our new annual storage production is 116,000 GWh, with something like 350,000 GWh of cumulative installed capacity.

Still short of 8,120,000 GWh.

(But this exponential growth is only starting to hockey-stick upwards at this 50% growth... we WOULD hit our goal within the third decade)

So, even assuming very optimistic conditions where the storage capacity production is exponentially growing, consumption stays flat, and capacity does not degrade once installed, electric cars still will barely make a dent in petroleum usage in transportation after two decades.

I hope I made some error on my metaphorical napkin here (like a battery can be recharged... if you have 365 Wh of annual consumption, that can technically be serviced by a 1 Wh battery being used every day, right? So we don't quite need to match the 8,120,000 number exactly, right? Maybe like 1/10 or 1/100th of that?) Because if I didn't, that means we need an Apollo-level effort sustained for a few decades to have a meaningful path off fossil fuels.

[1]: https://flowcharts.llnl.gov/content/assets/images/energy/us/... [2]: https://www.tesla.com/gigafactory