A system and method are provided for storing electric energy in the form of thermal energy. A thermoelectric energy storage system includes a working fluid circuit for circulating a working fluid through a heat exchanger, and a thermal storage medium circuit for circulating a thermal storage medium. The thermal storage medium circuit includes at least one hot storage tank, an intermediate temperature storage tank, and a cold storage tank connected together via the heat exchanger. A proportion of the storage medium is redirected to or from the intermediate storage tank from or to the hot or cold storage tank, joining another proportion which flows directly between the cold and hot storage tank.