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Non-Tech : Alternative energy -- Ignore unavailable to you. Want to Upgrade?

To: Jim S who wrote (7916)	4/22/2010 2:58:56 PM
From: Jacob Snyder	Read Replies (1) \| Respond to of 16955

re: energy storage efficiency: Most of the articles on this subject aren't clear, when they give a % efficiency, whether they mean round-trip or one-way. Here are some, that clearly give round-trip data, with efficiencies between 84% and 60%: Pumped Hydro Storage...The round trip efficiency in modern pumped Hydro Storage plant is over 80% and can be as high as 84%. This represents the percentage of electrical energy regenerated from 100% of the energy used for pumping. Turlough Hill is now over 30 years old and has a round trip energy efficiency of about 75%... ...Pumped hydro normally consists of two water reservoirs or lakes at different heights. These are connected by large diameter pipes or tunnels. Reversible pump / turbine machines are located in a power house connected to the pipes. These are first used to pump water from the lower to the upper reservoir, where it is stored as hydro energy. The pumps are powered by large electric motors, which can also act as generators in the reverse direction. When water is released from the upper reservoir, it flows back down through the reversible machines, which now act as turbines. The turbines are connected to reversible motor / generators, which were initially used as motors to drive the pumps, but now act as generators powered by the turbines and reconvert the hydro energy into electricity...there are over 200 such Hydro Electric Storage stations worldwide. These are robust plants. The oldest ones have been in operation for over 80 years. spiritofireland.org Pumped hydro efficiencies round-trip between 60% and 85%....80,000 dams in the U.S., only 3% with hydroelectric generators...78GW of pumped hydro storage capacity could be installed in existing dams... Compressed air facility in McIntosh, Alabama, built in 1991, has a round-trip efficiency of 66%... nicholas.duke.edu 72%-80% charge/discharge (round-trip) efficiency for "pumped heat" energy storage. Uses compressed air, and gravel to store the heat. green.tmcnet.com nationalgrid.com Greater than 70% round-trip efficiency for Pumped Hydro. Disadvantages are high capital cost, long construction times. hawaiirenewable.com At the present time the United States leads the world in the number of pumped hydroelectric installations of over 1,000 megawatts, followed closely by Japan. America’s largest such installation at Bath County, Virginia transfers water over a vertical height of 1,262 feet and is rated at 2,100 megawatts. energycentral.com