An energy storage system stores power received from a power grid as potential energy in compressed earth materials. The energy storage system includes a motor-generator coupled to an anchor via a tensile member. The motor-generator is configured to apply a tensile force to the tensile member. The tensile force causes the motor-generator and the anchor to apply a compression force to the earth materials in the ground, and causes the anchor to displace, thereby storing the received power as potential energy. The energy storage system provides power to the power grid by relieving some of the tensile force on the tensile member and thereby relieving some of the compression force on the earth materials. The anchor displaces towards its original position, and thereby causes the motor-generator to generate electrical power from the stored potential energy.