Volker Quaschning talks in this Youtube video about the German transition to renewable energy (in German).
He calculated how long it will take to get to 100 percent renewable energy assuming the present policy under the 2014 Renewable Energy Law is kept in place. His result: Until 2155.
In contrast, to stay under a 2 degree Celsius warming path, Germany would need to get there until 2040.
It follows that the present speed is too slow.
That is unfortunate. It doesn’t make any sense to slow down deployment of solar when prices go down.
The problem with a fast transition to renewable energy is that coal power plants would need to be switched off in many time slots, since there would be no demand left for them on a sunny summer day. And closer to the goal of a completely fossil fuel free energy system there would be many time slots where supply would be double or more of available demand.
Actually, that’s a nice problem to have. And Quaschning notes lots of solutions. Batteries in homes, in electric vehicles, and making gas from wind or solar power are just some of the solutions he mentions.
Part of the problem is that lignite power plants have trouble reducing their output quickly. They are lacking in flexibility.
As it turns out, one solution to this problem is to add some gas to the fuel mix of a lignite power plant. That makes it possible to reduce more of its capacity over the daytime hours safely.
If you can use gas made from solar or wind power for that purpose, that would also help in reducing the CO2 emission per kWh of these dirty power plants.
Anyway, I agree with Quaschning. Things need to go much faster.
He also mentioned smart phones. When he asked his audience if they have one, over 90 percent raised their hands. That shows that it is easily possible to introduce this new technology in less than ten years.
There is no technical reason why it should take more than ten years for renewable energy to displace fossil fuel as well. And the stakes are much higher than with smart phones.