ELECTRIC ENERGY CONTROLLER

PROBLEM TO BE SOLVED: To purchase and sell electric energy efficiently while taking account of the reliability by providing means for purchasing electric energy from the other party setting a more expensive charge while taking account of the reliability. SOLUTION: Every time when power is purchased, a computer 102 is started to set an electric energy to be purchased. It is set not to exceeds the sum of power consumption and the allowable charging capacity of a battery 104. A party proposing a lowest unit price for a set electric energy to be purchased is then selected among a plurality of parties. In order to confirm the reliability of power system, system simulation is performed based on power flow calculation at the time of purchasing power and a decision is made whether a reliability problem of overload, abnormal voltage, or the like, is present in a specified region surrounding a transmission path to the other party. When reliability can not be ensured, a party proposing a next inexpensive unit price is selected and the reliability of power system is checked similarly.