The linear Fresnel (pronounced Freh-nel) reflector is arguably the hottest new solar power technology being developed today—not only for its inventiveness, but the temperatures it can produce are upward around 800 degrees Celsius.
It’s the latest innovation in concentrating solar power (CSP) technologies, a family of approaches to providing solar energy for power utilities—we’re talking hundreds of megawatts as opposed to photo voltaic cells, which are ideal for small scale use in the kilowatt range.
As a group, CSP technologies, also referred to as solar thermal technologies, rely on mirrors to reflect and concentrate solar radiation to generate heat. In turn, the heat is used to produce steam, which powers a turbine to produce electricity. CSPs are credited with solving the irregularity of solar power availability, which vacillates with cloud cover and nightfall. By converting solar power into thermal energy, it can be stored and deployed whenever needed. As the crowned king of solar thermal power, Fred Morse, says, “CSP is game-changing.”
Morse, who investigated the feasibility of solar power for President Nixon, and then managed solar within the Department of Energy for Carter and Regan, says power companies face a bleak road ahead, and would do well to look into CPS. Nuclear is expensive and has waste and storage problems. In the face of a carbon-constrained economy, coal has become difficult to finance. The price of natural gas has shot up and will always be subject to variability. Given those options solar thermal is looking increasingly attractive. As for the viability of the emerging linear Fresnel reflectors, Morse says, “The market will decide. The banks and the EPC contactors will decide. But the technology is wonderful.”
Linear Fresnel reflectors differ from other CSPs in that their long, low mirrors reflect sunlight onto a single, horizontal tubular receiver, where as other CSPs require multiple receivers. Developers of the Fresnel technology say their strategy lowers costs (all the CSP technologies are aiming for .10 cents a kilowatt hour). Linear Fresnel reflectors also require fewer acres because more mirrors can be squeezed onto a smaller parcel of land. And significantly, they can produce high temperatures, which leads to a more efficient conversion of sunlight into electricity.
“There are some real innovations there,” says Travis Bradford, the founder and president of the Prometheus Institute, a non-partisan group devoted to researching the solar energy industry. “But this is an evolutionary change, not a revolutionary change.”
Tell that to the handful of companies developing the technology. They appear (and not surprisingly) fairly confident they’ve cast the key to our energy future. The privately held company Ausra, which received funding from renowned Silicon Valley venture capitalist Vinod Khosla, produced a study showing that “over 90 percent of the U.S. electric grid and auto fleet's energy needs could be met by solar thermal power.”
At the end of June, Ausra opened a reflector production facility in Las Vegas, Nevada, with Senate majority leader Harry Reid (D-NV) in attendance at the launch ceremonies. The site will manufacture hardware for the 177 megawatt plant it plans to build in San Luis Obispo County, California, with a power purchase agreement from the state’s Pacific Gas and Electric Company. It says it will begin providing electricity for some 120,000 homes by 2010.
Also last month, the German company Solar Power Group announced it would build a 10 megawatt plant in Gotarrendura, Spain, using its linear Fresnel reflector technology. And a third player in the CSP market, SkyFuel, received a $435,000 grant from the Department of Energy in November, to pursue Linear Power Tower technology—its trademarked version of Fresnel.
Two variables distinguish these CSP solar power companies from one another. First, not all mirrors reflect equally. Second, not all fluids successfully heat to the same temperatures. Linear Fresnel engineers are jockeying to maximize output and patent the resulting techniques.
“What’s revolutionary from our perspective,” says SkyFuel president and CEO Arnold Leitner, “is that we are able now to form high-precision mirrors on any focal length to let the linear Fresnel system reach a high temperature. That has not been possible until a few years ago.”
Leitner, clearly passionate about the technology, explains with exuberance that because the receiver tube is large and stationary, “It allows you to introduce molten salt as the heat transfer fluid.” Molten salt, a mixture of nitrates, becomes liquid when heated and can withstand temperatures well above 400 degrees Celsius. “This has never been done before and the DOE recognizes that there has been a paradigm shift in the materials available,” says Leitner.
But from an outside perspective, technology is only one of many hurdles these companies must clear. Bradford says, “They still need to build these things. And to do that they not only have to get the technology right, they have to get the financing. They have to get utility companies that are going to take their electricity. They’ve got to get insurance and permits…it’s hard to do all this stuff.”
It would seem then what’s needed is the will to conquer the bureaucracy, woo partners, and master the technology. Leitner just may have energy enough to do all three.
Story by Victoria Schlesinger. This article originally appeared in "Plenty" in July 2008.