Disclosed is an electric power system including a first unit (for example, a unit 201) equipped with a first power source (for example, a solar panel (201b)), a first rechargeable battery (for example, a unit storage battery (201c)) to which an output of the first power source is input, and a first power consuming portion (not shown) to which an output of the first rechargeable battery is input; a second rechargeable battery (for example, a shared storage battery (202)); and an electric power line (for example, a shared electric power line (203)) for sharing electric power between the first rechargeable battery and the second rechargeable battery.