As others have said, if nothing is done about the energy excess, it goes into an increase of the frequency. In Germany, there are 3 different steps to handle t

As others have said, if nothing is done about the energy excess, it goes into an increase of the frequency. In Germany, there are 3 different steps to handle this (I guess it's pretty much the same in other countries too). 1. The primary reserve power is short-term fine-grained capacity that takes effect automatically (is not requested by the TSO[1] explicitly) if the frequency leaves the +-0.01 Hz band around 50 Hz. The capacity is then provided proportionally to the distance, full capacity is supposed to be provided when the frequency goes under 49.8 or over 50.2 Hz. The tricky part is that the capacity needs to be supplied in both directions which can for example be done by modulating the frequency differences on a power plant running slightly under its full capacity. In Europe, this capacity is provided jointly spread over the whole grid and totals roughly 3 GW in both directions (e.g. simultaneous full outages of two large power plants). Broadly speaking, primary reserve power is supposed to stabilise the grid, i.e. to stop a frequency in/decrease. 2. Secondary reserve power is supposed to kick in after 5min, latest 15min of primary reserve power usage. This is done automatically by the individual TSOs (in Germany we have 4 because we can :)) if the reason for the deviation is in their grid, and sends a request to a controller in the providing power plants, which have to provide 1MW 1min after the request and full (sold) capacity after 5min. It's not as immediate as primary power as the to-be-produced capacity is not directly calculated from the frequency, but the request messages still change quite frequently, usually a few times per second. This part is supposed to move the frequency back to 50 Hz. 3. At last, if secondary reserve is drawn for too long, minute reserve power is activated. This is just a straight "you have 15min to provide 50 MW, 30min onwards after you start". It's essentially just an economical optimisation on the process, since due to the higher lead time, conventional power plants can actually start up to provide it, while for both secondary and primary reserve power they need to react so quickly, that a full ramp-up wouldn't be efficient. Back to your main question, on how negative reserve power is provided then concretely, this could be: - Downmodulating running power plants (primary, secondary and minute reserve) - Charging batteries (likely just primary and secondary reserve since minute reserve would exceed capacity) - Starting up additional consumers (minute reserve) - Running turbines without actually producing any power (worst case minute reserve) - Shutting of wind turbines by turning their rotor blades (likely just secondary, can't be provided guaranteed for long due to changes in the wind, would be fast enough for primary reserve but can only work in one direction) [1]: Transmission System Operator