NOVELTY - The storage (1) has first and second released state of charge (SOC) regions (3, 5) provided for a power supply, a third released SOC region (4) provided for internal consumption and the power supply, and two blocked regions (6, 7). A control device adapts an actual charge state of the storage such that a fixed positive or negative energy quantity is provided for the power supply for a fixed time window at a fixed time of the storage. The first SOC region amounts to 10 % to 40 % of a capacity of the storage. The second SOC region amounts to 80 % to 90 % of a capacity of the storage.    USE - Energy storage such as an electrical accumulator such as an lead accumulator e.g. lead-acid battery, lead-gel battery, and lead-fleece batter, and a lithium-ion accumulator e.g. lithium-ion-lithium-cobalt dioxide battery, lithium-polymer battery, lithium-manganese battery, lithium-iron phosphate-battery, lithium-titanate battery, lithium-sulfur battery, and lithium-metal-polymer battery for an energy storage-power plant (claimed) for a photovoltaic system of a building. Can also be used for a sodium-nickel chloride-high temperature battery, sodium-sulfur battery, nickel-cadmium battery, nickel-iron battery, nickel-hydrogen battery, nickel-metal-hydride battery, nickel-zinc battery, silver-zinc battery, vanadium-redox battery, zinc-bromine battery for a hydro power plant and a wind power plant.    ADVANTAGE - The storage enables economic use of normally unused low and/or high capacity ranges of the energy storage for ancillary services that primarily targets on paid service provision such as minute reserve within hour time slices. The storage guarantees a positive power for feeding electrical power from the storage into a public power grid or negative power for receiving energy from the public power grid. The storage provides performance-based ancillary services in short time windows at a low and/or high charge state range and in the two capacitance regions of the energy storage with minimal negative impact on life of the storage. The storage provides additional revenue, and ensures early worth investment in the energy storage and photovoltaic system. The storage has an improved service life, and a high power strength. The storage is efficiently, comfortably and economically operated.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for the following:    (1) an energy storage-power plant    (2) a method for operating an energy storage.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic block diagram of an energy storage.'(Drawing includes non-English language text)'    Energy storage (1)    Released SOC regions for a power supply (3, 5)    Released SOC region for internal consumption and a power supply (4)    Blocked regions (6, 7)