This graph from Agora Energiewende demonstrates how little renewable energy contributed to the overall energy mix of Germany in December 2016 – and the intermittency of supplies.
This is the primary problem for renewables – the sun does not shine 24/7, neither does the wind blow round the clock. Electricity from renewables has been extremely low for several weeks in Germany.
Lessons from Germany’s 2017 winter situation teaches us in the most profound way that we need base-load power to support reliable, stable electricity grids. This means power that can run 24/7. Coal is the backbone of many power systems today and currently provides 41% of global electricity generation.