Energy storage apparatus

An energy storage apparatus, comprising:

• an input unit configured to receive a DC power from a solar cell;
• a sensing unit configured to sense and output a voltage level of the solar cell;
• a signal generating unit configured to generate a periodic signal whose magnitude is periodically changed;
• a voltage generating unit configured to generate a reference voltage corresponding to the periodic signal;
• a control signal generating unit configured to generate a duty control signal by using time intervals in which the periodic signal has a magnitude lower than or higher than the reference voltage;
• a charging unit configured to perform a charging operation by means of an on/off switching operation in response to the duty control signal;
• a battery unit configured to charge an energy by means of the charging operation of the charging unit;
• and
• a main control unit for causing the voltage generating unit to adjust the reference voltage to a lower level when a current solar cell voltage is lower than a previous solar cell voltage and to adjust the reference voltage to a higher level when the current solar cell voltage is higher than the previous solar cell voltage.