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May 2009
Electric Energy Storage
CLIMATE TECHBOOK
Quick Facts
• Electric energy storage (EES) uses forms of energy such as chemical, kinetic, or potential energy to
store energy that will later be converted to electricity. Such storage can provide three basic services:
supplying peak electricity demand by using electricity stored during periods of lower demand,
balancing electricity supply and demand fluctuations over a period of seconds and minutes, and
deferring expansions of electric grid capacity.
• Global EES capacity is 90 gigawatts (GW), which is only 3 percent of electric power production
capacity due to the high capital cost of EES compared to natural gas power plants which can provide
similar services, and regulatory barriers to entry in the electricity market. Of that global capacity, 22
GW of EES is in the United States (2.5 percent of U.S. power capacity).
• EES can potentially smooth the variability in power flow from renewable generation and store
renewable energy so that renewable generation can be scheduled to provide specific amounts of
power, which can decrease the cost of integrating renewable power with the electricity grid, increase
market penetration of renewable energy, and lead to greenhouse gas emission (GHG) reductions.
Background
Electric energy storage (EES) technology has the potential to facilitate the large-scale deployment of variable
renewable electricity generation, such as wind and solar power, which is an important option for reducing
GHG emissions from the electric power sector. Wind and solar power emit no carbon dioxide (CO2) during
electricity generation but are also variable or intermittent electricity sources. Wind power only produces
electricity when the wind is blowing and solar power only when the sun is shining, thus the output of these
sources varies with wind speeds and sunshine intensity. Since operators of the electricity grid must
constantly match electricity supply and demand, this makes variable renewable resources more ch