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Large Aperture Trough (LAT) 73 Frequently Asked Questions

Frequently Asked Questions

What is Large Aperture Trough (LAT) 73?

LAT 73 is a complete parabolic trough solar collector and tracking system, engineered by 3M and Gossamer, that utilizes 3M™ Solar Mirror Film 1100 as a reflective surface for concentrating sunlight into a receiver tube containing heat transfer fluid. The heated transfer fluid is then converted into useful energy.

What are the advantages of a LAT 73?

LAT 73 has a 7.3 m aperture, the largest operating aperture of a parabolic trough system, and unprecedented optical accuracy of 99.3% intercept factor. This large size and precise accuracy results in significant solar field cost reductions.

Compared to an RP3 system,* LAT 73:
  • Requires 41% fewer components
  • Offers 20% cost reduction in materials
  • Translates into 17% cost reduction in EPC direct costs
*Large Aperture Trough (LAT) 73, 7.3 meters aperture combined with unprecedented optical accuracy yields a solar field with significant reductions in Levelized Cost of Energy (LCOE) when compared to traditional systems.

What is the size of one trough?

One trough has 20 solar mirror reflectors and is 12 meters long; two (sets of ten) reflectors are used to form the parabola with an aperture of 7.3 m. The aperture area of one complete trough is 86.87 square meters.

Why is the size of the aperture important?

The size of the aperture is very important because there is an inverse relationship between the aperture size and the total number of components required in the field. With a larger aperture we are able to deliver the reflective surface needed with a smaller amount of land, frames, receiver tubes, drives, etc. In an internal study comparing LAT 73 with a standard CSP system, it was determined that there is a reduction of 40% in the number of components needed for an equivalent field.

What is the intercept factor and why is it important?

Optical accuracy of a CSP installation is a key component of its performance. To help evaluate the optical accuracy of the LAT 73, the National Renewable Energy Laboratory (NREL) used their Video Hartmann Optical Tool (VSHOT) to measure local surface slope imperfections and expected amount of incident solar light that would strike a 70 mm receiver tube. The results matched previous 3M tests and validated that on average the intercept factor is 99.3%. This means that 99.3% of the light that strikes the 3M Solar Mirror Film is reflected on the receiver tube. This intercept factor includes errors from the supporting frame and structure of the LAT 73.

What is concentration ratio?

Concentration ratio (geometric) is the ratio of the size of the aperture to the size of the receiver tube. In the case of the LAT 73: 7.3 meters of aperture to 70 mm (.07 m) of diameter of receiver tube = 103 xs.

What are the main advantages of using reflective film over traditional glass?

3M Solar Mirror Film reflectors are lighter than glass, do not break like glass, do not contain lead and have the highest optical accuracy in the industry. 3M Solar Mirror Film compares favorably to solar weighted hemispherical reflectance at 94.5% and for specular reflectance at 95.5%. The advantages of using 3M Solar Mirror Film on the LAT 73 allows for design flexibility where the objective is to increase the size of the aperture while maintaining the highest intercept factor. This would be very difficult to achieve with glass mirrors.

How do you determine the size of a LAT 73 system?

Site location latitude and longitude, and Direct Normal Irradiation (DNI) is modeled for an expected thermal output to determine the size of the field required.

Where are the components manufactured?

Currently all the components—with the exception of the receiver tubes—are manufactured in the United States. Localized procurement of some components is possible depending on the location and size of the site.

How easy is it to install?

The trough collectors are very easy to install and can be done directly on-site. No pre-assembly is required and only simple tools are needed. No field alignment is necessary.

How is it cleaned?

The reflectors are cleaned with deionized(DI) water and contact cleaning using a 3M™ Microfiber Cloth.
Please see Cleaning Procedure here.

How resistant is the LAT 73 to wind load?

The LAT 73 is designed to maintain an intercept factor of over 99% under a 50 mph wind load. In adverse conditions, where a glass mirror construction may be stowed due to either fear of breakage or low shape efficiency, a LAT 73 construction may continue to produce on-target solar flux with high efficiency.

Modeled and simulated wind load testing also shows that the LAT 73 reflector panels do not permanently deform for wind gusts up to 130 mph. The design of the panels offers a key benefit—enabling larger geometry collector configurations. The patented Organic Connector™ trough frame system offers industry-leading frame accuracy and stiffness, even under wind load.

How do I get an estimate?

Contact 3M Renewable Energy to speak with a sales representative and receive a free estimate.