Wind turbines and solar systems deliver highly volatile amounts of electricity over days, weeks and months. The contribution of wind energy in particular fluctuates considerably from day to day making supply hardly predictable. For example, on several days in January and September 2017, as well as in summer 2018, wind turbines had practically nothing to the supply to the grid despite forecasts, whereas stormy weather in October 2017 caused wind power production in Germany to rise to a record.
Once there is such an overproduction, renewable generation systems are artificially switched off by the transmission system operators (TSO), because this surplus of electricity cannot be used and puts power grid stability at risk. If this excess power cannot be fed into the grid, for example when network capacity is at its limit or there is a risk of overload, the generating facility is entitled to compensation according to the 2009 renewables law “EEG 2009”. In simple terms, only in Germany taxpayers and households in past years payed billions of euros for dumped surplus of renewable energy, in amount of dozens of millions of megawatt hours.