NOVELTY - The method involves determining an amount of electrical energy. A current electrical output of a solar cell array (92) is sensed. Heating time period for heating a metal substrate converter (96) to predetermined operating temperature (94) is estimated using the solar cell array. A converter heater is energized with electrical power from the solar cell array to preheat the metal substrate converter to the predetermined operating temperature before the engine is started when the estimated heating time period is within predetermined time range less than current waiting time period.    USE - Method for reducing exhaust gas emissions on starting an internal combustion engine in a vehicle i.e. car, by allocating electrical power generated by a vehicle-mounted solar cell array. Can also be used for a hybrid-electric vehicle.    ADVANTAGE - The method enables reducing total vehicle tailpipe emissions by initiating converter heating prior to anticipated vehicle start time and input by a vehicle operator, so that the converter is at preferred operating temperature when an operator starts the vehicle. The method enables an on-board computer to receive and process sensor inputs from the converter and a solar cell to properly synchronize converter heating with a vehicle operator's schedule. The method enables reducing power demands on the battery so as to employ the solar cell array to generate a portion of the electrical energy needed to preheat the converter. The method enables integrating the power available from the solar cell array into a vehicle electrical system, so that the solar cell array can be properly managed and stored. The method enables preheating catalytic converters to operating temperature so as to reduce cold start emissions. The method allows a controller to use output from on-vehicle sensors and input data when a vehicle is operated so as to allocate power harvested from the solar cell array, thus efficiently reducing vehicle exhaust emissions.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for the following:    (1) a method for allocating electrical power generated by a vehicle-mounted solar cell array    (2) a system for reducing exhaust emissions from a vehicle, comprising vehicle-mounted solar cell array.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of a controller for directing power from a solar cell array to devices including a catalytic converter preheater.    Solar cell array (92)    Predetermined operating temperature of converter (94)    Metal substrate converter (96)    Controller (100)    Timer (102)    Clock (106)    Switch (114)    Battery (118)    Vehicle (120)