A POWER BALANCING RESERVE FOR AN ELECTRICAL GRID

According to an example embodiment, a power balancing reserve (PBR) apparatus (120) for an electrical grid (100) is provided, the PBR apparatus (120) comprising: an energy storage (121) for storing electrical energy and having a minimum allowable state of charge, SoC, level and a maximum allowable SoC level defined therefor; and a controller (122) for controlling transfer of electrical energy between the energy storage (121) and the electrical grid (100) in dependence of an observed AC frequency of the electrical grid (100) in view of said minimum and maximum allowable SoC levels using one of a plurality of operating modes via adjustment of an instantaneous charging power that indicates the amount of electric power currently transferred from the electrical grid (100) to the energy storage (121), the controller (122) arranged to: receive respective indications of a first operating mode selected for a first time period and a second operating mode selected for a second time period, where the first and second time periods are consecutive time periods in a sequence of time periods and where the second time period follows the first time period in said sequence, and control the instantaneous charging power during the first time period in accordance with the first operating mode in dependence of said observed AC frequency and at least partially in dependence of the second operating mode selected for the second time period.