A method of controlling a power network comprising a plurality of power generation facilities (30, 31) connected to an electricity grid and a plurality of power storage facilities (40, 41, 42) electrically connected to the power generation facilities (30, 31), a power generation facility (30, 31) comprising any of a wind power plant, a tidal power plant, a solar power plant, a power storage facility (40, 41, 42) comprising any of a thermal storage facility; a battery storage facility; a flywheel storage facility; a compressed air storage facility; a hydro-electric facility; a synthetic natural gas storage facility, the method characterized in comprising: monitoring a production capacity and any ancillary service capability of the power generation facilities (30, 31); monitoring a storage capacity and any ancillary service capability of the power storage facilities (40, 41, 42); determining a grid requirement (Pdemand, Psched) to be fulfilled by the power network; determining an optimal facility control plan on the basis of the storage capacity and the production capacity, wherein the step of determining an optimal facility control plan comprises performing a revenue projection for a combination of energy and ancillary services on the basis of one or more of the set of forecast variables comprising: weather forecast; energy forecast; energy price forecast; spinning reserve price forecast; reactive power price forecast; ramping capability forecast; inertial response forecast; frequency response forecast; and operating the power network, according to the facility control plan, to feed power from the power generation facilities (30, 31) into the electricity grid and/or to transfer power from the power generation facilities (30, 31) to the power storage facilities (40, 41, 42) and/or to consume power from the power storage facilities (40, 41, 42), wherein the step of operating the power network to transfer power from the power generation facilities (30, 31) to the electricity grid is performed so that a net power at a grid connection point fulfils the grid requirement (Pdemand, Psched). monitoring a production capacity and any ancillary service capability of the power generation facilities (30, 31); monitoring a storage capacity and any ancillary service capability of the power storage facilities (40, 41, 42); determining a grid requirement (Pdemand, Psched) to be fulfilled by the power network; determining an optimal facility control plan on the basis of the storage capacity and the production capacity, wherein the step of determining an optimal facility control plan comprises performing a revenue projection for a combination of energy and ancillary services on the basis of one or more of the set of forecast variables comprising: weather forecast; energy forecast; energy price forecast; spinning reserve price forecast; reactive power price forecast; ramping capability forecast; inertial response forecast; frequency response forecast; and operating the power network, according to the facility control plan, to feed power from the power generation facilities (30, 31) into the electricity grid and/or to transfer power from the power generation facilities (30, 31) to the power storage facilities (40, 41, 42) and/or to consume power from the power storage facilities (40, 41, 42), wherein the step of operating the power network to transfer power from the power generation facilities (30, 31) to the electricity grid is performed so that a net power at a grid connection point fulfils the grid requirement (Pdemand, Psched). weather forecast; energy forecast; energy price forecast; spinning reserve price forecast; reactive power price forecast; ramping capability forecast; inertial response forecast; frequency response forecast; and operating the power network, according to the facility control plan, to feed power from the power generation facilities (30, 31) into the electricity grid and/or to transfer power from the power generation facilities (30, 31) to the power storage facilities (40, 41, 42) and/or to consume power from the power storage facilities (40, 41, 42), wherein the step of operating the power network to transfer power from the power generation facilities (30, 31) to the electricity grid is performed so that a net power at a grid connection point fulfils the grid requirement (Pdemand, Psched).