Technology Overview

The company, 4th Power, uses renewable electricity to heat up a box of rocks to store energy. They have developed a big energy storage system that is utility-scale and can be as large as half a football field. The system uses liquid tin as a heat transfer fluid, chosen for its corrosion resistance and low melting point. The heat from the liquid tin is transferred to large blocks of graphite, which glow white-hot and store the heat. The stored heat can then be converted back into electricity using thermal photovoltaic (TPV) cells. The system can provide short-term response times and is designed to compete in the longer-duration storage market as well.