Pumped Storage

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Navigate the Resource Guide: Table of Contents Major Topic Sections Related topics in this section		*Pumped Storage Hydroelectricity*

		Background
		Pumped storage hydroelectricity is a method of storing and producing electricity to supply high peak demands by moving water between reservoirs at different elevations. At times of low electrical demand, excess electrical capacity is used to pump water into the higher reservoir. When there is higher demand, water is released back into the lower reservoir through a turbine, generating hydroelectricity. Reversible turbine/generator assemblies act as pump and turbine (usually a Francis turbine design). Some facilities use abandoned mines as the lower reservoir, but many use the height difference between two natural bodies of water or artificial reservoirs. Pumped storage projects are net consumers of energy in that for every one kWh of energy generated during peak periods, more than one kWh of off-peak energy is required for pumping. Due to evaporation losses from the exposed water surface and mechanical efficiency losses during conversion, only between 70% and 85% of the electrical energy used to pump the water into the elevated reservoir can be regained in this process. Still, this system is economical as it flattens out the variations in the load on the power grid, permitting base-load power stations to continue operating at their most efficient capacity, while reducing the need to build special power plants which run only at peak demand times using more costly generation methods. Because of the energy losses inherent in pumped storage, the CO2 emissions associated with its use will be higher than that of the original power source. When coal-fired power is the driver of the pumped storage, there is likely a net increase in system CO2 emissions. However, a net reduction in greenhouse gas emissions can be realized with pumped storage when the fuel providing electricity for pumping has a lower carbon content (or no carbon content as in the case of wind energy or nuclear power) than the fuel being displaced by the pumped storage generation. Click here or on "Add PPRG Content" above to offer your comments to the PPRG.
		Power Partners℠ Projects
		*Exelon Generation, a subsidiary of Exelon, operates both the 536-MW Conowingo Hydroelectric Generation Station and the 1,071-MW Muddy Run Pumped Storage Facility. Each of these facilities produces, on average, more than 1.6 billion kWh of electricity annually. Through uprate and efficiency projects at these facilities, more than 800,000 tons of CO2 emissions have been avoided since 2000. Exelon continues work on a $39-million project to replace four of the 11 turbines at Conowingo. The last of these turbines will be operational in 2008. Click here or on "Add PPRG Content" above* to add your organization's projects.
		References, Sources, and Other Useful Data
		Electricity Storage Association, “Technologies: Pumped Storage Hydro” http://www.electricitystorage.org/tech/technologies_technologies_pumpedhydro.htm The Electricity Storage Association is a trade association established to foster development and commercialization of energy storage technologies. Its mission is "to promote the development and commercialization of competitive and reliable energy storage delivery systems for use by electricity suppliers and their customers." This article includes a brief overview of the technology, and links to a chart listing about 40 worldwide pumped hydro installations, 1000 MW and larger. Duke Energy, " Generating Electricity with Pumped-Storage Hydro" http://www.duke-energy.com/about-energy/generating-electricity/pumped_storage_hydro.asp In addition to their 29 traditional hydroelectric plants, Duke Energy has two pumped-storage plants in the Carolinas—Jocassee and Bad Creek. When demand for electricity is low, Duke Energy operators can refill the lake, as if they were recharging a battery. Using power from other Duke Energy stations, the huge turbines spin backward and pump water back up the power tunnels into the upper lake. Water is generally pumped back to the upper reservoir at night and on weekends. These pumped-storage plants typically generate power during times of peak electric demand. In southeastern part of the country, peaks are usually on hot summer afternoons and cold winter mornings during the work week. When used in a well-planned generating scheme, pumped-storage plays an important role and can be one of the most economical forms of electric power generation available today. International Hydropower Association (IHA), “Benefits of Pumped Storage” http://www.hydropower.org/psd/articles/benefits.html The International Hydropower Association, founded in 1995, is a UK-based non-governmental mutual association of organizations and professionals. This article, written by Hiroshi Tanaka, focuses on the rationale for Pumped Storage, explaining the benefits to the general public. Wikipedia, “Pumped-storage hydroelectricity” http://en.wikipedia.org/wiki/Pumped-storage_hydroelectricity From Wikipedia, the free encyclopedia, is an overview of pumped storage, its role in a larger power system, and its history. The article includes a worldwide list of pumped storage plants, with links to many of them. Click here or on "Add PPRG Content" above to add additional references and sources.


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