TECHNOLOGY FOCUS - ELECTRICAL POWER AND ENERGY - Preferred Components: The system includes power transformer (20), and two watt meters. The first watt meter is at the power transformer and measures the electricity generated by fuel cell generator. The second watt meter is at the power transformer and measures the actual demand for electricity from the external load. Load detector and heat usage pattern detector are at the system controller. The load detector is connected to the fuel cell generator and controls the electricity generation in the fuel cell generator based on the surplus electricity. The power transformer transforms direct current electricity generated by fuel cell generator in alternating current (AC) electricity and provides the AC electricity as power source for an external load. The power balancer is inside the waste heat recovery unit and includes electric heater transforming the surplus electricity into the heat source. The heat usage pattern detector is connected to a temperature sensor at the waste heat recovery unit. The temperature sensor is at the waste heat recovery unit and draws the heat usage pattern by repeatedly calculating the heat source decreased in waste heat recovery unit based upon a temperature measured by the temperature sensor. Preferred Methods: The method involves drawing the heat usage pattern by averaging the amount of heat consumption at each stage and repeating calculation of decreased heat at the waste heat recovery until at every predetermined time period prior to optimizing the operation of fuel cell generator, balancing power that provides the waste heat recovery unit with surplus electricity generated by fuel cell generator, detecting electricity generation that determines an economic coefficient based on electricity generation cost and commercial electricity supply price and controls the electricity generation in fuel cell generation when the heat source reaches the total amount of heat stored in waste heat recovery unit based on the economic coefficient after the optimizing of operation of fuel cell generator. The drawing step calculates the amount of decreased heat by detecting the temperature drop of the heat source with temperature sensor in waste heat recovery unit and the capacity of heat reservoir where the heat source is stored, and by setting each hour to one stage based on the 24 hour day and averaging the amount of heat consumption at each stage. The step of optimizing the operation of fuel cell generator operates the fuel cell generator at the appropriate stage in response to an average amount of heat demand by recognizing the heat stored in waste heat recovery until at an initial point in time and the total amount of heat usage pattern accumulated until a point in time, respectively.