Thermal Storage

A dispatchable, grid-scale thermal energy storage system based on a molten silicon storage medium. Excess electricity is converted to thermal energy to heat the silicon, stored in one of two large tanks. When demand arises, glowing-hot molten silicon is pumped through an array tubes that emit light, and special-purpose multi-junction photovoltaics convert the generated light to electricity.

IceBank makes ice during off-peak hours, and the HVAC chiller system works in conjunction with IceBank tanks during on-peak daytime hours to manage building energy loads.

The Echogen Power Systems team will develop an energy storage system that uses a carbon dioxide (CO2) heat pump cycle to convert electrical energy to thermal energy by heating a “reservoir” of low cost materials such as sand or concrete. The reservoir will retain heat that will be converted back into electricity on demand. To generate power, liquid CO2 will be pumped through the high-temperature reservoir to a supercritical state, after which it will expand through a turbine
to generate electricity from the stored heat.

The Brayton Energy team will develop an energy storage system that combines thermal storage and a gas turbine to generate power. When the system is charging, an electrically driven heat pump will accumulate thermal energy in a molten salt solution, which can then be discharged later by heating gas and sending it through the generation turbine. Brayton Energy’s innovation lies in their reversible turbine design, in which each turbine acts as the compression stage for the other, whether during charging or discharging. This approach simplifies the system and increases durability.

The National Renewable Energy Laboratory team will develop a high temperature, low cost thermal energy storage system using a high performance heat exchanger and closed loop Brayton cycle turbine to generate power. Electric heaters will warm stable, inexpensive solid particles to temperatures greater than 1100°C during charging. To discharge the system, the particles will be fed through the heat exchanger, heating a working fluid to drive the gas turbine attached to a generator. The electricity storage system is designed to be deployed economically anywhere in the United States.

Heat is stored in a salt (same type as used in reusable hand warmers), rather than traditional bricks.