Variable states
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Energy Quarterly 162
Variable states Corinna Wu Energy storage can help integrate wind and solar power into the electric grid.
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n August 14, 2003, a downed high-voltage power line in Ohio triggered a massive blackout across eight states in the Northeast and throughout Southeastern Canada. A total of 50 million people lost power for up to two days. The episode cost an estimated $6 billion and is considered to be the worst electrical system failure in the history of the United States. The cascade of failures—due to both human error and equipment malfunction—made clear the problems of the United States’ aging and balkanized electrical transmission grid. The blackout spurred Congress to pass the Energy Policy Act of 2005, which enforces mandatory reliability standards. Investment in the transmission grid had fallen during the 1980s and 1990s, but after the blackout, funding picked up again. Against this backdrop, power companies and regulating authorities now have another challenge to face: how to integrate variable and intermittent renewable resources such as solar and wind into the mix. Currently, electricity from non-hydro renewable resources accounts for 3.8% of the total electricity produced in the United States, according to the U.S. Energy Information Administration. In 2009, half of non-hydro renewable electricity came from wind and less than one percent from solar. However, that share is set to rapidly increase. Thirty states and the District of Columbia have established Renewable Portfolio Standards, regulations that require the increased production of energy from renewable energy sources. For example, California has set a goal of generating 33% of its electricity this way by 2020, and New York has set a goal of 30% by 2015. Although wind and solar are attractive because they do not produce greenhouse gases, they also pose difficulties because of their inherent variability. “If you look at wind and solar, their output changes dramatically,” said James Misewich, associate laboratory director for basic energy sciences at Brookhaven National Laboratory (Figure 1). The wind waxes and wanes, and the sun assuredly sets every night. Clouds can obscure solar panels, and even if only a portion of a solar array is shaded, it can have a big impact on how much electricity is produced. If wind and solar must supply a third of the energy generated, the job of meeting changing demand for electricity throughout the day becomes much more difficult. Power plant operators must meet the net load—the difference between user demand and this highly variable renewable output—by scheduling power generation from conventional sources. MRS BULLETIN
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VOLUME 36 • MARCH 2011
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www.mrs.org/bulletin • Energy Quarterly
One strategy that can help manage that net load variability is the use of storage technologies, including advanced batteries and superconducting magnetic energy storage (Figure 2). Storing electricity generated during periods of low demand—for example, when the wind blows at night—allows that energy to be deployed durin
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