Technology Benifits

Emerging EES systems (beyond traditional, but geographically limited, pumped hydroelectric storage) may provide several technical benefits for utilities, power system operations, and users. The traditional applications for energy storage are described below: (EPRI, 2003, EPRI, 2004, EPRI, 2006).

  • Grid Stabilization: EES can be used to help the transmission or distribution grid return to its normal operation after a disturbance. Energy storage can be used to remedy three forms of instability: rotor angle instability; voltage instability; and frequency excursions.
  • Grid Operational Support: In addition to stabilizing the grid after disturbances, energy storage can also be used to support normal operations of the grid. Four types of support operations can be performed through the use of energy storage:
    • Frequency Regulation Services: Energy storage can be used to inject and absorb power to maintain grid frequency in the face of fluctuations in generation and load.
    • Contingency Reserves: At the transmission level, contingency reserve includes spinning (or synchronous) and supplemental (non-synchronous) reserve units, that provide power for up to two hours in response to a sudden loss of generation or a transmission outage.
    • Voltage Support: Voltage support involves the injection or absorption of reactive power (VARs) into the grid to maintain system voltage within the optimal range. Energy storage systems use power-conditioning electronics to convert the power output of the storage technology to the appropriate voltage and frequency for the grid.
    • Black Start: Black start units provide the ability to start up from a shutdown condition without support from the grid, and then energize the grid to allow other units to start up. A properly sized energy storage system can provide black start capabilities, provided it is close enough to a generator.
  • Power Quality and Reliability: EES is often used to improve power quality and reliability. The vast majority of grid-related power quality events are voltage sags and interruptions with durations of less than 2 seconds, phenomena that lend themselves to energy storage-based solutions (EPRI 1998).
  • Load Shifting: Load shifting is achieved by utilizing EES for storage of energy during periods of low demand and releasing the stored energy during periods of high demand. Load shifting comes in several different forms; the most common is peak shaving (EPRI 2003). Peak shaving describes the use of energy storage to reduce peak demand in an area. It is usually proposed when the peak demand for a system is much higher than the average load, and when the peak demand occurs relatively rarely. Peak shaving allows a utility to defer the investment required to upgrade the capacity of the network. The economic viability of energy storage for peak shaving depends on a number of factors, particularly the rate of load growth (EPRI 2003). The $/kW cost of a distribution upgrade is usually much lower than the $/kW cost of energy storage. But the total cost of a distribution upgrade is usually much higher than the total cost of an EES optimized for deferral of a distribution upgrade for two to five years. AEP has justified the installation of NaS battery in Charleston, WV, for peak shaving based on savings from deferring the upgrade of a substation (Nourai, 2006).
  • Supporting the integration of intermittent renewable energy sources: Wind power generation is presently the largest and fastest growing renewable power source. The following applications are described in the context of wind power (EPRI 2004). Similar applications also exist for renewable energy sources other than wind power, such as solar photovoltaic (PV).
    • Frequency and synchronous spinning reserve support: In grids with a significant share of wind generation, intermittency and variability in wind generation output due to sudden shifts in wind patterns can lead to significant imbalances between generation and load, that in turn result in shifts in grid frequency. Such imbalances are usually handled by spinning reserve at the transmission level, but energy storage can provide prompt response to such imbalances without the emissions related to most conventional solutions.
    • Transmission Curtailment Reduction: Wind power generation is often located in remote areas that are poorly served by transmission and distribution systems. As a result, sometimes wind operators are asked to curtail their production, that results in lost energy production opportunity, or system operators are required to invest in expanding the transmission capability. An EES unit located close to the wind generation can allow the excess energy to be stored and then delivered at times when the transmission system is not congested.
    • Time Shifting: Wind turbines are considered as non-dispatchable resources. EES can be used to store energy generated during periods of low demand and deliver it during periods of high demand. When applied to wind generation, this application is sometimes called “firming and shaping” because it changes the power profile of the wind to allow greater control over dispatch.