New patent enhances grid resiliency by extending energy storage duration

(Palo Alto, California, April 21, 2021) A new invention can double the duration of energy storage systems by continuing to operate at part load after it has been fully discharged. U.S. Patent No. 10,982,570 for DISPATCHABLE STORAGE COMBINED CYCLE POWER PLANTS issued on April 20, 2021 enhances the capabilities of Liquid Salt Combined Cycle™ (LSCC) technology. This new capability adds resilience to deliver additional electric power when needed for grid reliability in the face of extreme events, like polar vortex, heat waves, or wildfires.

LSCC technology integrates proven thermal energy storage with proven gas and steam turbines in utility-scale hybrid energy storage systems that deliver exceptionally low-cost storage and high fuel efficiency. During charging, the LSCC technology uses excess renewable electricity to heat molten salt to about 427°C for storage in a hot tank; during discharge the hot salt produces steam for power generation and is held in a “cold” tank at a temperature of about 250°C.

When added to a gas turbine, LSCC technology doubles power output without consuming more fuel, effectively cutting GHG emissions in half. The LSCC arrangement de-couples the steam and combustion cycles to improve flexibility and remove startup constraints. Electric charge heating can be independently sized to better couple with solar and wind generation profiles and reduce renewable curtailment. LSCC technology triples storage density, so a pair of industry standard 120-foot diameter tanks can deliver 1600 MWh of AC power, with marginal storage cost less than $30/kWh.

The new invention by Dr. William M. Conlon, P.E., Pintail Power founder and President, extracts an additional 1000 MWh from the “cold” salt after the hot tank is empty. By operating at reduced steam pressure, the boiling point of water falls below the ‘cold’ salt temperature to allow more heat to be transferred. With the gas turbine continuing to operate, steam temperature at the steam turbine remains constant. The steam turbine produces less power under these conditions, but the fuel efficiency remains superior to a combined cycle power plant using the same gas turbine.

The invention will be commercialized by Pintail Power LLC, which bridges renewable and conventional generation by coupling thermal energy storage to proven generating equipment. The Pintail Power approach offers low-cost, long duration storage to reduce renewable curtailment, cut GHG emissions, and improve the flexibility and reliability of the electric grid. Pintail Power provides long-duration energy storage technology, systems and services to utilities, independent power producers and developers to accelerate the transition to low-carbon electricity. In addition to LSCC technology, Pintail Power also provides Liquid Air Combined Cycle (LACC) technology that uses cryogenic liquid energy storage capable of safely holding more than 50 Gigawatt-hours of energy in a single tank.