A method for operating a temperature control system for a temperature controlled goods vehicle, wherein the temperature control system comprises: a solar panel and a temperature control unit comprising: one or more temperature control components; a battery for providing electrical power for electrical components of the temperature control unit and electrical components which, in use of the temperature control unit, may be disposed within an interior of the temperature controlled goods vehicle, the battery being coupled to the solar cell for receiving a first charging current i 1 from the solar cell; an engine operative to supply a second charging current i 2 to the battery; and a controller, the method comprising: at the controller: monitoring a voltage of the battery; if the voltage of the battery exceeds a first battery voltage threshold for a first predetermined amount of time: determining a first energy count value representing an amount of energy delivered by the solar panel in a predetermined time period; if the first energy count value exceeds a first energy count value threshold: determining an average current value representing an average amount of energy delivered by the solar panel in the predetermined time period; and increasing a cycle threshold value that determines when the engine, having been activated solely to supply the second charging current i 2 to the battery, is deactivated so as to stop supplying the second charging current i 2 to the battery based on the average current value. a solar panel and a temperature control unit comprising: one or more temperature control components; a battery for providing electrical power for electrical components of the temperature control unit and electrical components which, in use of the temperature control unit, may be disposed within an interior of the temperature controlled goods vehicle, the battery being coupled to the solar cell for receiving a first charging current i 1 from the solar cell; an engine operative to supply a second charging current i 2 to the battery; and a controller, one or more temperature control components; a battery for providing electrical power for electrical components of the temperature control unit and electrical components which, in use of the temperature control unit, may be disposed within an interior of the temperature controlled goods vehicle, the battery being coupled to the solar cell for receiving a first charging current i 1 from the solar cell; an engine operative to supply a second charging current i 2 to the battery; and a controller, the method comprising: at the controller: monitoring a voltage of the battery; if the voltage of the battery exceeds a first battery voltage threshold for a first predetermined amount of time: determining a first energy count value representing an amount of energy delivered by the solar panel in a predetermined time period; if the first energy count value exceeds a first energy count value threshold: determining an average current value representing an average amount of energy delivered by the solar panel in the predetermined time period; and increasing a cycle threshold value that determines when the engine, having been activated solely to supply the second charging current i 2 to the battery, is deactivated so as to stop supplying the second charging current i 2 to the battery based on the average current value. monitoring a voltage of the battery; if the voltage of the battery exceeds a first battery voltage threshold for a first predetermined amount of time: determining a first energy count value representing an amount of energy delivered by the solar panel in a predetermined time period; if the first energy count value exceeds a first energy count value threshold: determining an average current value representing an average amount of energy delivered by the solar panel in the predetermined time period; and increasing a cycle threshold value that determines when the engine, having been activated solely to supply the second charging current i 2 to the battery, is deactivated so as to stop supplying the second charging current i 2 to the battery based on the average current value. determining an average current value representing an average amount of energy delivered by the solar panel in the predetermined time period; and increasing a cycle threshold value that determines when the engine, having been activated solely to supply the second charging current i 2 to the battery, is deactivated so as to stop supplying the second charging current i 2 to the battery based on the average current value.