NOVELTY - The operating method involves acquiring power generated by power generator, load power consumed by power load and surplus power. The heat is generated in a heat pump using the increasing/decreasing power that follows the increases/decreases in the surplus power per unit of time. The power consumed by the heat pump conforms to the surplus power is reduced, when the amount of change in the surplus power acquired during a prescribed interval leading up to the present exceeds a preset threshold.    USE - Operating method for heat pump for electric power generating apparatus such as solar power generation device used in heat pump system (claimed) used in home.    ADVANTAGE - The tracking degree with respect to the surplus electric power of the electric power consumed by heat pump can be reduced, when the surplus electric power is changed rapidly. The rapid fluctuation of heat pump load electric power can be prevented instead of permitting some head tide and generation of electric power purchase so that heat pump can be operated stably. The stability of the electric power system can be improved, so that suppression of power rates in the case of operation of hot-water supply system or hot water supply and heating system can be prevented.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for heat pump system.    DESCRIPTION OF DRAWING(S) - The drawing shows a flowchart illustrating the calculation process of power consumption command value performed with HP control apparatus. (Drawing includes non-English language text)    Step for renewing surplus power history (S1202)    Step for acquiring information used in calculation of power consumption command value (S1203)    Step for determining whether surplus power history satisfy specific condition (S1204)    Step for transmitting power consumption command value conforming to immediately preceding surplus power to heat pump control unit (S1208)    Step for transmitting power consumption command value from last time to heat pump control unit (S1209)