Compact Linear Fresnel Reflector

A compact linear Fresnel reflector (CLFR) – also referred to as a concentrating linear Fresnel reflector – is a specific type of linear Fresnel reflector (LFR) technology. Linear Fresnel reflectors use long, thin segments of mirrors to focus sunlight onto a fixed absorber located at a common focal point of the reflectors. These mirrors are capable of concentrating the sun’s energy to approximately 30 times its normal intensity. This concentrated energy is transferred through the absorber into some thermal fluid (this is typically oil capable of maintaining liquid state at very high temperatures). The fluid then goes through a heat exchanger to power a steam generator. As opposed to traditional LFR’s, the CLFR utilizes multiple absorbers within the vicinity of the mirrors.

The first linear Fresnel reflector was developed in Italy in 1961 by Giovanni Francia of the University of Genoa. Francia demonstrated that such a system could create elevated temperatures capable of making a fluid do work. The technology was further investigated by companies such as the FMC Corporation during the 1973 oil crisis, but remained relatively untouched until the early 1990s. In 1993, the first CLFR was developed at the University of Sydney in 1993 and patented in 1995. In 1999, the CLFR design was enhanced by the introduction of the advanced absorber. In 2003 the concept was extended to 3D geometry. Research published in 2010 showed that higher concentrations and / or higher acceptance angles could be obtained by using nonimaging optics to explore different degrees of freedom in the system such as varying the size and curvature of the heliostats, placing them at a varying height (on a wave-shape curve) and combining the resulting primary with nonimaging secondaries.

The reflectors are located at the base of the system and converge the sun’s rays into the absorber. A key component that makes all LFR’s more advantageous than traditional parabolic trough mirror systems is the use of "Fresnel reflectors". These reflectors make use of the Fresnel lens effect, which allows for a concentrating mirror with a large aperture and short focal length while simultaneously reducing the volume of material required for the reflector. This greatly reduces the system’s cost since sagged-glass parabolic reflectors are typically very expensive. However, in recent years thin-film nanotechnology has significantly reduced the cost of parabolic mirrors.

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