Introduction to Energy Storage

Energy storage is integral to small, decentralized power grids to support the balancing of electrical supply and demand. There are several important functions of energy storage that help to smooth out power supply and match power demand. Those functions consist of load leveling, load shifting, and maintaining an uninterruptible power supply (UPS). For instance, renewable resources such as wind and solar are variant and seasonal. As a result, renewable energy production is not always available when it is needed or, conversely, an excessive amount of energy may be produced. During an event of excessive power production, energy can be accumulated using storage technology. As the renewable energy source subsides, another form of electrical production, such as diesel generators, may be needed. During the transition phase between renewable power to diesel generation, energy is dispatched from the storage device to make up for the lack of power production. Storage technology can also be used to displace fossil fuel by storing energy from renewable resources during off-peak hours and dispatching that energy at the time of peak hours.

It should be noted that in centralized grid applications, storage is not an end in itself, but a bridge used as required to insure power quality or to simplify control. Storage is used to bridge a low-cost energy option like hydro or wind, to a higher-cost energy option like natural gas or diesel, allowing a seamless switch between the two. Long-term storage is typically not economical and when compared to the cost of providing power with conventional dispatchable generation, the capital and maintenance costs of storage technology are significantly higher.

Even so, the use of energy storage is considered by many as an essential component of future utility delivery infrastructure throughout the United States as more intermittent renewable energy is added to the system. As specified above, energy storage can be used in a wide range of applications to improve availability and reliability of delivered power, to support variable distributed generation, stabilize transmission and distribution lines, or time shift consumption through bulk storage to achieve the most efficient use of baseload generation. Many of these applications require short bursts of power to balance and control energy, with discharge times ranging from milliseconds to a few minutes, however, systems such as pumped hydro can store energy for days in order to provide load shifting capabilities.


Pumped Hydro Facility1.

Challenges in Energy Storage

For the most part, energy storage is still an emerging technology and has a high cost of implementation. There are also physical limitations with today’s energy storage technology that can hinder their applicability. Currently, most electrochemical technology has limited storage capacity, due to significant self discharge rates, and have a restricted cycle life. Additionally, these devices can generally only dispatch power over a short period of time. Contrarily, pumped hydro and compressed air energy storage are to able store and dispatch power over a longer timeline, however, are highly locational, depending on the presence of either an elevated reservoir or large underground cavern, respectively. Many of the new systems installed in rural Alaska are demonstration projects and require considerable troubleshooting, which amplifies the challenges of isolation and cost.

Although significant challenges still exist with energy storage, great strides have been made in the past decade and will continue with the progress of technology. For example, the advancement of new lighter and stronger materials has respawned interest in development of the flywheel, a storage device that’s amelioration has been slow due to the lack of suitable components. Similar to other emerging technologies, as energy storage matures, the cost of implementing these devices will decrease over time.

Energy Storage in Alaska

As rural communities in Alaska continue to invest in renewable energy, such as wind power, accession of availability and reliability through energy storage becomes increasingly important. Most rural power grids have small base load power needs, ranging from a couple hundred kW to a few MW, often less than the amount produced by commercial scale wind turbines. In the past, the method of dealing with excess power was to use electrical dump loads to convert the unused electricity into heat. The application of energy storage would allow for the excess energy to be stored for later use instead of being consumed as less valuable heat2. In communities hosting a renewable energy source with high penetration, storage devices can be used to bridge renewable and diesel generation, as specified in the introduction.

Presently, there are only a handful of energy storage projects in the State of Alaska (see project list below), most of which are still in the development phase. Several energy storage projects are anticipated to be operational by the end of 2013 or earlier, including Kokanok and Kodiak. The most notable project in the state is GVEA’s Battery Energy Storage System (BESS), which is one of the world’s largest energy storage devices and has helped to avoid multiple power outages across the city of Fairbanks3.



Energy Storage Options

Many strategies can be used for energy storage, including chemical storage (hydrogen, electrochemical (batteries), electrical (capacitors), mechanical (flywheels or pumped hydro), or thermal storage. In grid connected situations, only pumped-hydro is economic, but other storage is used for increased reliability for some applications, such as batteries for UPS systems for computers. All electrical storage systems add flexibility to the electric grid, increasing the options available for grid optimization and management. Which storage technology would perform best depends on local economics, the proposed application, and details of the site.

Storage can be classified by several key parameters:

  • Rated Power (kW) The rated power output available from the device under normal operating conditions.
  • Rated Capacity (kWh) The total amount of available energy within the storage system.
  • Response time (Hz) The speed at which the storage device can respond to changes in the power system.
Flywheels and Capacitors
Pumped Hydro and Compressed Air
Thermal Storage


Links and Resources

2012 Energy Storage Workshop


  • Australia Department of Primary Industries and Energy, 1993. Rural and Remote Area Power Supplies for Australia.
  • Crompton, T.R.. Small Batteries, John Wiley & Sons, New York. 1982
  • Desmettre D., Mattera F., Malbranche P. and Métais S. (2000), Publishable Final Report of project “Qualibat, Investigations for a QUicker Assessment of Lifetime and other key characteristics of photovotlaic BATteries”, GENEC, CEA Cadarache, F-13108 St. Paul-lez-Durance, France
  • Hunter, R., & Elliot, G. (1994)., “Wind Diesel Systems”, Cambridge University Press, Cambridge, UK.,1994.
  • Perez, R.A. (1995). The Complete Battery Book, First edition, Tab Books, Blue Ridge Summit, PA.
  • Wenzl H., Baring-Gould I., Kaiser R., Liaw B.Y., Lundsager P., Manwell J., Ruddell A., Svoboda V., (2004) Life Prediction OF BatterIES For Selecting the technically most suitable and cost effective battery, Proceedings of the 9th European Lead Battery Conference, 9ELBC, Berlin, Sept, 2004 and Journal of Power Sources.

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