A method for retrieving items from a storage system comprising a grid structure of storage columns, arranged to accommodate a vertical stack of storage bins arranged in storage cells covered by removable covers, the method comprising the steps of: a. providing a plurality of remotely-operated vehicles arranged to move horizontally along rails at the top level of the grid structure, at least one of said vehicles comprising a device capable of lifting and replacing covers and at least one vehicle comprising a device capable of lifting and replacing bins, said vehicles further comprising positioning sensors for detecting the vehicles' position on the grid, b. providing a computerized control system in electronic communication with the vehicles, said control system arranged to receive position information signals from the vehicles, and further arranged to send movement and position commands to the vehicles, said control system yet further arranged to record the position of bins in the grid structure and the position of bins within a stack, c. determining the position of a target bin to be retrieved in a target storage cell, characterized in that the method comprises further the steps of: d. instructing a plurality of vehicles to be proximately arranged in series and arranged to move in tandem and thus to form a train of vehicles adjacent to the target storage cell by transmitting movement commands to the vehicles, e. instructing the train of vehicles to move over the target cell in tandem by transmitting further movement commands to the vehicles, said vehicles consecutively lifting the insulated cover, any non-target bins above the target bin, and finally the target bin, f. instructing any vehicles of the train holding non-target bins to replace said non-target bins within the target storage cell, g. instructing a vehicle of the train to place a cover over the target storage cell, whereby a vehicle of the train is substantially at all times located above the open target storage column while the retrieval operation takes place. a. providing a plurality of remotely-operated vehicles arranged to move horizontally along rails at the top level of the grid structure, at least one of said vehicles comprising a device capable of lifting and replacing covers and at least one vehicle comprising a device capable of lifting and replacing bins, said vehicles further comprising positioning sensors for detecting the vehicles' position on the grid, b. providing a computerized control system in electronic communication with the vehicles, said control system arranged to receive position information signals from the vehicles, and further arranged to send movement and position commands to the vehicles, said control system yet further arranged to record the position of bins in the grid structure and the position of bins within a stack, c. determining the position of a target bin to be retrieved in a target storage cell, characterized in that the method comprises further the steps of: d. instructing a plurality of vehicles to be proximately arranged in series and arranged to move in tandem and thus to form a train of vehicles adjacent to the target storage cell by transmitting movement commands to the vehicles, e. instructing the train of vehicles to move over the target cell in tandem by transmitting further movement commands to the vehicles, said vehicles consecutively lifting the insulated cover, any non-target bins above the target bin, and finally the target bin, f. instructing any vehicles of the train holding non-target bins to replace said non-target bins within the target storage cell, g. instructing a vehicle of the train to place a cover over the target storage cell, whereby a vehicle of the train is substantially at all times located above the open target storage column while the retrieval operation takes place. d. instructing a plurality of vehicles to be proximately arranged in series and arranged to move in tandem and thus to form a train of vehicles adjacent to the target storage cell by transmitting movement commands to the vehicles, e. instructing the train of vehicles to move over the target cell in tandem by transmitting further movement commands to the vehicles, said vehicles consecutively lifting the insulated cover, any non-target bins above the target bin, and finally the target bin, f. instructing any vehicles of the train holding non-target bins to replace said non-target bins within the target storage cell, g. instructing a vehicle of the train to place a cover over the target storage cell, whereby a vehicle of the train is substantially at all times located above the open target storage column while the retrieval operation takes place.