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Profile: Cara S. Libby
Cara S. Libby was a participant or observer in the following events:
Arizona Public Service (APS), the state’s largest utility company, is using a new project it calls Solana to store solar energy collected during daylight hours to serve power demands during the night, according to an article published in the New York Times. APS had a three-mile stretch of desert near Gila Bend, southwest of Phoenix, bulldozed flat, and installed a network of parabolic mirrors that focus the sun’s energy onto a series of black-painted pipes. The pipes funnel the heat to large tanks of molten salt, which traps the heat until the plant draws the heat out of the salt and uses it to generate steam and electricity. The Solana project is an attempt to overcome one of the largest drawbacks of solar energy, the dearth of energy when the sun is not shining. “We’re going to care more and more about that as time goes on,” says APS general manager Brad Albert. Other states are watching the Solana project closely; California has just approved a rule requiring the state’s utilities to install storage facilities by 2024. Robert Gibson of the Solar Electric Power Association says: “The impetus to require storage is definitely inspired by the success of solar. Hopefully the California initiative is going to kick-start this and bring down costs.” Battery storage has always been a promise, he says, but cost-effective storage “has always been a few years out.” The biggest challenge for Arizona solar users, mainly individuals with rooftop solar arrays, is generating power in the early morning hours, before the sun has risen enough to activate the panels. Arizona and California also face similar problems in the evening, when the sun is too low for the panels to work well and people are returning home. By 6 p.m., most solar arrays are working at half capacity at best, even if they are installed on tracking devices that tilt the panels to follow the sun across the sky. Solana was built with a $1.45 billion loan guarantee from the US Department of Energy. Another similar project, also built with federal loan guarantees, is the Ivanpah project in California (see September 22, 2013). Cara S. Libby of the Electric Power Research Institute says, “There will be a trend towards storage as we see more variable renewables like photovoltaics and wind being added to the grid.” The flexibility of such a system becomes more important as a utility adds higher volumes of inflexible renewables, Libby says. Solana is not the first renewable energy plant with storage; others use banks of electric batteries. But battery storage is so expensive that it is primarily used to smooth the output of the plant and not to store large amounts of energy overnight. Storing energy as heat is much cheaper, but is mechanically inefficient. [New York Times, 10/17/2013]
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