A method for controlling a power plant for providing frequency support to a power grid, the power plant comprises an electrical storage unit and a power generating system comprising one or more power generating units including at least one wind turbine generator , where the power generating system is connected to an electrical power grid for supplying power to the electrical power grid, and wherein the electrical storage unit is electrically connected with the power generating system and is controllable to charge or discharge dependent on a power set-point (Pset_esu), wherein the method comprises - setting a frequency control period, wherein the electrical storage unit is scheduled to charge or discharge according to a first power set-point (Pset_esu1), - at a start of the frequency control period, charging or discharging the electrical storage unit according to the first power set-point (Pset_esu1), - in case the grid frequency (f) exceeds a first grid frequency (f1) located above or below a frequency threshold (fT), resulting in a first frequency deviation (Δf1) within the frequency control period, determining a first power change (ΔP1) of the power from the electrical storage unit based on the first frequency deviation (Δf1), - determining a second power set-point (Pset_esu2) based on the determined first power change (ΔP1), - providing the frequency support by controlling the electrical storage unit to charge or discharge according to the second power set-point (Pset_esu2) the method is characterised in that the method further comprises, - forecasting a period of time wherein the power plant is capable of generating a plant production power (Pplant_f) which is higher than a planed required plant production power (Pplant_req_f), and - setting the frequency control period within the forecasted period of time, wherein the electrical storage unit is scheduled to charge according to the first power set-point (Pset_esu1), hereby providing power capacity of the electrical storage unit to support an under frequency event. - setting a frequency control period, wherein the electrical storage unit is scheduled to charge or discharge according to a first power set-point (Pset_esu1), - at a start of the frequency control period, charging or discharging the electrical storage unit according to the first power set-point (Pset_esu1), - in case the grid frequency (f) exceeds a first grid frequency (f1) located above or below a frequency threshold (fT), resulting in a first frequency deviation (Δf1) within the frequency control period, determining a first power change (ΔP1) of the power from the electrical storage unit based on the first frequency deviation (Δf1), - determining a second power set-point (Pset_esu2) based on the determined first power change (ΔP1), - providing the frequency support by controlling the electrical storage unit to charge or discharge according to the second power set-point (Pset_esu2) the method is characterised in that the method further comprises, - forecasting a period of time wherein the power plant is capable of generating a plant production power (Pplant_f) which is higher than a planed required plant production power (Pplant_req_f), and - setting the frequency control period within the forecasted period of time, wherein the electrical storage unit is scheduled to charge according to the first power set-point (Pset_esu1), hereby providing power capacity of the electrical storage unit to support an under frequency event. <EOS>