Stationary Storage Device for Temporarily Storing Electric Energy in an Electric Supply Grid, Operating Method, and Retrofitting Module for the Stationary Storage Device

A stationary storage device configured to temporarily store electric energy in an electric supply grid includes at least one electric storage unit, each being connected to a common DC bus by a respective DC-DC converter. The storage device further includes a bidirectionally operated AC-DC converter for coupling the common DC bus to the supply grid, and a charging device configured to exchange energy with an electrically operated motor vehicle. The charging device includes a connection device configured to connect the electrically operated motor vehicle in order to exchange said energy, and a charge control device configured to control exchange of said energy. A coupling device is provided which is configured to electrically connect the connection device to the common DC bus via one or more DC-DC converters in order to exchange said energy.