Certain embodiments are directed to control methods, window controllers, and uninterruptible power supplies for determining tinting instructions for optically switchable windows to reduce power usage at a site during a reduced power event. In some cases, reduced power operations are initiated by a window controller upon receipt of a trigger signal from an uninterruptible power supply sent when it detects a power loss. In some cases, tinting instructions are based on the remaining charge left on the uninterruptible power supply. In some cases, reduced power operations are delayed for a period of time.