A system for providing a primary control power for a power grid by at least one energy storage device, wherein the system comprises an energy resource controller connected to said energy storage device, the energy resource controller has a state of charge control unit (SOC-CU) adapted to perform a state of charge power control of the energy storage device, wherein the energy resource controller has a primary power control unit (PPCU) adapted to perform a primary power control of the energy storage device depending on at least one observed grid parameter of said power grid, wherein a power conversion device connected between the power grid and the energy storage device is controlled according to power control signals calculated by said state of charge control unit (SOC-CU) and by said primary power control unit (PPCU) of said energy resource controller, wherein the state of charge control unit (SOC-CU) of the energy resource controller is configured to apply a state of charge response curve to said conversion device such that - in a first SOC range the energy storage device is charged, and - in a third SOC range the energy storage device is discharged, characterized in that the state of charge response curve is step-like, in an intermediate second SOC range the energy storage device is neither charged nor discharged, wherein the extent of the first SOC range of the step-like SOC response curve applied by the state of charge control unit (SOC-CU) is reduced and the extent of the third SOC range of the step-like SOC response curve applied by the state of charge control unit (SOC-CU) is expanded by said state of charge control unit (SOC-CU), if an electricity price is increased and/or a predicted demand for primary control power by said power grid is reduced. the energy resource controller has a state of charge control unit (SOC-CU) adapted to perform a state of charge power control of the energy storage device, wherein the energy resource controller has a primary power control unit (PPCU) adapted to perform a primary power control of the energy storage device depending on at least one observed grid parameter of said power grid, wherein a power conversion device connected between the power grid and the energy storage device is controlled according to power control signals calculated by said state of charge control unit (SOC-CU) and by said primary power control unit (PPCU) of said energy resource controller, wherein the state of charge control unit (SOC-CU) of the energy resource controller is configured to apply a state of charge response curve to said conversion device such that - in a first SOC range the energy storage device is charged, and - in a third SOC range the energy storage device is discharged, - in a first SOC range the energy storage device is charged, and - in a third SOC range the energy storage device is discharged, characterized in that the state of charge response curve is step-like, in an intermediate second SOC range the energy storage device is neither charged nor discharged, wherein the extent of the first SOC range of the step-like SOC response curve applied by the state of charge control unit (SOC-CU) is reduced and the extent of the third SOC range of the step-like SOC response curve applied by the state of charge control unit (SOC-CU) is expanded by said state of charge control unit (SOC-CU), if an electricity price is increased and/or a predicted demand for primary control power by said power grid is reduced.