A collector (SCA, solar collector assembly) is an individually tracking component of the solar field that includes mirrors, a supporting structure, and receivers.

Note. See the Troughnet website at http://www.nrel.gov/csp/troughnet/solar_field.html for more information about collectors.

On the Collectors page, you can define the characteristics of up to four collector types. On the Solar Field page, you specify how the different collector types are distributed in each loop of the field, assuming that the field consists of identical loops. Solar Advisor only uses data for collector types that you have included in the single loop specification on the Solar Field page

Collector Type and Configuration Name

Collector Type

Choose the active SCA type (1-4). Solar Advisor displays the properties of the active SCA type on the Collectors page. You can assign different properties to each of the up to four collector types. See Specifying the Loop Configuration for details on including different SCA types in the solar field.

Configuration Name

The name of library entry for the receiver type.

Collector Geometry

Reflective aperture area (m2)

The total reflective area of a single collector, used to calculate the loop aperture area of a loop, and number of loops required for a solar field with the aperture area defined on the Solar Field page.

Aperture width, total structure (m)

The structural width of the collector, including reflective and non-reflective area. Solar Advisor uses this value to calculate row-to-row shadowing and blocking effects.

Length of collector assembly (m)

The length of the collector assembly, used to calculate the length of a single assembly, and for a solar field with an "H" layout, the length of runner pipes.

Number of modules per assembly

The number of individual collector-receiver sections in a single collector.

Average surface-to-focus path length (m)

The average distance between the collector surface and the focus of the parabola. This value is not equal to the focal length of the collector. To calculate the value when you know the focal length and aperture width, use the following equation, where Favg is the average surface-to-focus path length:

Where a is the focal length at the vertex, and w is the aperture width

Piping distance between assemblies (m)

Length of pipes and hoses connecting collectors in a single row, not including the length of crossover pipes.

Length of single module (m)

The length of a single collector-receiver module, equal to the collector assembly length divided by the number of modules per assembly.

Optical Parameters

Incidence angle modifier coeff 1-3

Coefficients for a polynomial equation defining the Incidence Angle Modifier equation. The equation captures the degradation of collector performance as the incidence angle (theta) of the solar radiation increases.

Tracking error

Accounts for reduction in absorbed radiation error in collectors tracking caused by poor alignment of sun sensor, tracking algorithm error, errors caused by the tracker drive update rate, and twisting of the collector end at the sun sensor mounting location relative to the tracking unit end.

Geometry effects

Accounts for errors in structure geometry caused by misaligned mirrors, mirror contour distortion caused by the support structure, mirror shape errors compared to an ideal parabola, and misaligned or distorted receiver.

Clean mirror reflectance

The mirror reflectance input is the solar weighted specular reflectance.  The solar-weighted  specular reflectance is the fraction of incident solar radiation  reflected into a given solid angle about the specular reflection direction. The appropriate choice for the solid angle is that subtended by the receiver as viewed from the point on the mirror surface from which the ray is being reflected. For parabolic troughs, typical values for solar mirrors are 0.923 (4-mm glass), 0.945 (1-mm or laminated glass), 0..906 (silvered polymer),  0.836 (enhanced anodized aluminum), and 0.957 (silvered front surface).

Dirt on mirror

Accounts for reduction in absorbed radiation caused by soiling of the mirror surface. This value is not linked to the mirror washing variables on the Solar Field page.

General optical error

Accounts for reduction in absorbed radiation caused by general optical errors or other unaccounted error sources.

Optical Calculations

Incidence angle modifier

The incidence angle modifier equation calculated as a reference for the location in question at noon on the summer solstice. This value is not used in determining the design of the solar field.

End loss at design

Optical end loss at noon on the summer solstice due to reflected radiation spilling off of the end of the collector assembly. This value is provided as a reference and is not used in determining the design of the solar field.

Optical efficiency at design

The collector's optical efficiency under design conditions.

This section will describe equations for the calculated values on the Collectors page. It is currently under development. For general descriptions of the variables, see Input Variable Reference.

Incidence angle modifier

Where,

End loss at design

Optical efficiency at design