Do intermittent sources of electricity cause problems? Technicalities concerning solar and wind power

The variability of certain forms of renewable energy, mainly wind and solar (photovoltaic) power, causes quite real problems that are often underestimated and poorly understood. Variability is not something new for persons who manage electricity grids. They have to constantly cope with variations in the demand for electricity and with incidents affecting the means of production or transportation and distribution networks. Introducing 'renewable' variables on a grid increases the need for flexibility, but does not create it. In any case, efforts should be undertaken for making grids more flexible. Let us take a look at the situation of France from now till 2020, before examining the questions that arise for most grids in the long run and then coming back to specific aspects of the French situation