Designing Linear Fresnel Reflector Arrays

By Charles Xie

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Linear Fresnel reflectors are a type of concentrated solar power that uses long, thin segments of mirrors to focus sunlight onto a fixed absorber located at a common focal line of the reflectors, similar to a Fresnel lens. The concentrated light energy is converted through the absorber into the thermal energy of a fluid, which then goes through a heat exchanger to power a steam generator or be used as process heat in industrial processes. It doesn't make sense to burn oil or coal to generate high temperature if we can get it from the sun. The simplicity, scalability, and flexibility of linear Fresnel reflectors make it an appropriate technology to consider.

Live model above (view in full screen)

There are many design options for a linear Fresnel reflector array. The key factors include the dimension and spacing of the reflectors, the height of the absorber tube, and the orientation of the reflectors (azimuth). There can also be multiple absorbers, as shown in the following model. In this design, the mirrors are laid out in the same way but they reflect the sunlight alternately to the two absorbers (e.g., 1, 3, 5, ... reflect to the absorber on the east side and 2, 4, 6, ... to the absorber on the west side).

Analyzing output of linear Fresnel reflectors with two receivers based on daily simulation

The effect of the receiver height

The higher we mount the receiver tube, the more energy the reflectors can collect. This can be easily studied using an Aladdin simulation shown below.

Comparison between two Fresnel reflector arrays aiming at receiver tubes mounted at different heights

The effect of the array azimuth

Linear Fresnel reflectors are usually aligned in the north-south direction. The following simulation compares the outputs of two arrays, one with zero azimuth and the other with 90° azimuth (meaning that the reflectors are essentially aligned in the east-west direction).

Comparison between two Fresnel reflector arrays aligned in different azimuths

Linear Fresnel reflector arrays around the world

Tucson Electric Power (TEP) and AREVA Solar constructed a 5 MW linear Fresnel reflector solar steam generator at TEP’s H. Wilson Sundt Generating Station — not far from the famous Pima Air and Space Museum. The following is an Aladdin model of the TEP station.

Live model above (view in full screen)

If you are interested, please click here to read about the analysis of the TEP station and explore more Aladdin models of existing Fresnel reflector arrays around the world.

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