61601 - Overview of Grid-Scale Energy Storage Systems and Technologies 

Grid-scale energy storage is needed to enable deep penetration of renewable power generators like solar photovoltaic and wind farms into the energy mix. The minute-by-minute, hourly, and seasonal variability associated with these renewable resources is poorly matched with power usage. Conventional power generation from fossil fuels or nuclear sources is typically required in order to provide sufficient power quality and reliability, although this approach results in operational profiles that require significant ramp rates and turndown, reducing the efficiency and life of conventional plants. Grid-scale energy storage systems would absorb power from the grid during periods of excess renewable generation, and release the stored energy to generate power when renewable sources are unavailable. Lithium-ion or other battery chemistries are being introduced as a potential solution, but all existing technologies are currently cost-prohibitive at the many Megawatt- or Gigawatt-scales for more than about 2-4 hours. There are many existing or developing machinery-based energy storage systems to fulfill this need, including pumped hydro, flywheels, compressed air, gravitational, liquid air, pumped thermal (example images below), and various thermochemical technologies such as hydrogen, ammonia, synthetic natural gas, sulfur, and other "Power-to-X" technologies. This tutorial reviews all of these technologies including basic working principles, role of turbomachinery, hybridization with existing power generators, state of development, advantages and disadvantages relative to other technologies, and research & development needs for system improvements and commercialization.