Intermittency and time averaging of renewable electric productions

The expressions, "There's always wind somewhere". "There's sunshine in the middle of the day when the need for electricity is greatest", generally stated without reference to any figures, seem to be common sense. In recent years, however, these imprecise phrases have been elevated to the status of concepts by the promoters of renewable energies. They are referred to as "abundance" and, in the case of photovoltaic electricity, "production/consumption adequacy", which are said to have the virtue of smoothing or adjusting a country's or a continent's production to needs. This concept applies to both wind and solar power.

In so doing, we seek above all to minimize a major weakness of these productions: they are essentially intermittent (this work deals jointly with the climatic intermittence of wind and solar power and the daily and seasonal variability of the latter) and very poorly predictable. As we shall see, they become difficult to manage as soon as their contributions exceed a certain level. Indeed, an examination of detailed generation data, both in France and in interconnected Europe, shows that intermittency is always very pronounced. The amplitude and kinetics of production variations can, even for modest-sized wind or solar farms, rapidly exceed those of consumption, so that they only imperfectly meet needs and often create new ones.