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Large Aperture Trough (LAT) 73, engineered by Gossamer and 3M, leads the concentrated solar power (CSP) industry in optical performance.

Technical features include:
  • Highly reflective 3M™ Solar Mirror Film 1100, with a 94.5% solar weighted hemispherical reflectance and 95.5% specular reflectance (25 milliradian acceptance angle).
  • High accuracy reflective panel constructions, with less than 1.5 milliradian RMS slope error.
  • Integration with space frame that results in intercept factors exceeding 98% at a concentration ratio of 103.
With cost being a primary driver for CSP growth, LAT 73 has also been designed with a focus on both component and installed costs:
  • Compared to a standard 5.7 m aperture system, the LAT 73 requires over 40% fewer components resulting in a 20% reduction in bill of materials costs.
  • The high optical accuracy of the LAT 73 enables use of widely available standard 70 mm receiver tubes.
  • The high concentration ratio (103:1) results in higher heat flux per unit length, and minimizing receiver thermal losses.
  • High stiffness panelized reflectors enable high accuracy, even under wind load. The wider operating window increases the capacity utilization factor of the power unit.
  • The space frame and reflector assembly are designed to be self-aligning, so there's no need for mirror jigs or power tools in the field. Installation time per reflector is less than 3 minutes.

3M™ Solar Mirror Film 1100

Large Aperture Trough (LAT) 73 uses 3M™ Solar Mirror Film 1100* as a reflective surface for concentrating solar power.

Property
 

3M™ Solar Mirror
Film 1100 (%)

Thick Glass
Mirrors (4 mm) (%)

Aluminum (%)
 

Solar Weighted Hemispherical
Reflectance (ASTM G173)

94.5
 

94.8
 

87-91
 

Specular Reflectance at 25
mradian Acceptance Angle

95.5
 

95.5
 

79-86
 

* Source: S. Meyen et. al, Standardization of Solar Mirror Reflectance Measurements Round Robin Test, SolarPACES 2010.

Proven to Last

3M™ Solar Mirror Films have been tested extensively at NREL (over 168 months) and proven to have exceptional long-term outdoor durability.

Total Hemispherical Reflectivity 3M ECP 305+
Courtesy: Cheryl Kennedy, NREL, Golden Colorado

Optical Accuracy

Optical accuracy of any CSP installation is a key component of its performance. To help evaluate the optical accuracy of the LAT 73, NREL was engaged to use their field version of the Video Scanning Hartmann Optical Tool (VSHOT). This tool was employed to measure local surface slope imperfections and expected amount of incident solar light that would strike 70 mm receiver tube. Through the use of this tool, the teams were able to investigate the quality of the shape of the installed reflectors as compared to their ideal design. The best results matched previous well-controlled lab tests at 3M. These data validate that the 3M and Gossamer design demonstrates, on average, an intercept factor of 99.3%. This figure assumes a 70 mm receiver that is perfectly aligned, surfaces with ideal specularity, SCA with no tracking errors, and a standard sun shape. This is a remarkable result since it includes errors, not only from the reflectors, but also from the frame. The RMS slope errors of less than 1.5 milliradians is equally impressive, since mirror-frame systems are often in the 5 milliradian error range.

Slope error "heat map" for a LAT 73 reflector panel as tested at 3M's St. Paul laboratory VSHOT. The RMS slope error measured less than 1.1 milliradians for this panel over its entire surface of 4.8 m2. Values of less than 2.3 milliradians are considered to be very good.

"Acceptance envelope" plot for the LAT 73 collector as measured by NREL at SEGS I. The envelope represents the outer edges of a 70 mm tube at the focus of the parabola. For the LAT 73 panel shown, 99.8% of the laser beams reflected off the surface struck within the envelope.