# solstice(1) Manual Page

## NAME

solstice - compute the power collected by a concentrated solar plant

## SYNOPSIS

    solstice
    solstice [option]… [file]
    solstice -g <sub-option[:…]> [option]… [file]
    solstice -p <sub-option[:…]> [option]… [file]
    solstice -r <sub-option[:…]> [option]… [file]

## DESCRIPTION

solstice computes the total power collected by a concentrated solar plant, as described in the solstice-input(5) file. If the file argument is not provided, the solar plant is read from standard input. To evaluate various efficiencies for each primary reflector, it computes losses due to cosine effect, shadowing and masking, orientation and surface irregularities, materials properties and atmospheric extinction. The efficiency for each one of these effects is subsequently computed for each reflector.

The entities on which computations must be performed are listed in the solstice-receiver(5) file submitted through the -R option. The estimated results follow the solstice-output(5) format and are written to the output file or to the standard output whether the -o output option is defined or not, respectively. Note that the solstice algorithm is based on the Monte-Carlo method, which means that every result is provided with its numerical accuracy.

solstice is designed to efficiently handle complex solar facilities: several reflectors can be specified (planes, conics, cylindro-parabolic, etc.) and positioned in 3D space, with a possibility for 1-axis and 2-axis auto-orientation. Multiple materials can be used, as long as the relevant physical properties are provided. Spectral effects are also taken into account: it is possible to define the spectral distribution of any physical property, including the input solar spectrum and the transmissivity of the atmosphere, at any spectral resolution. Refer to solstice-input(5) for more informations.

In addition of the aforementioned computations, solstice provides three other functionalities. The -g option can be used to convert the solstice-input(5) geometries in CAO files. The -p option saves the sampled radiative paths used by the estimates, allowing to visualise them externally which may be a great help to identify a design issue. Finally, the -r option is used to render an image of the submitted solar facility. Note that these three options are mutually exclusives, and once defined, they replace the default solstice behaviour.

Please note that any coordinate-related question in Solstice must be considered with the right-handed convention in mind.

## OPTIONS

-D <alpha,beta[:…]>

  List of sun directions. A direction is defined by two angles in degrees. The first one, here refered to as alpha, is an azimuthal angle in [0, 360[ and the second one, here refered to as beta, is an elevation in [0, 90]. Each provided sun direction triggers a new computation whose results are concatenated to the output file.

  Following the right-handed convention, Solstice azimuthal rotation is counter-clockwise, with 0° on the X axis. Solstice elevation starts from 0° for directions in the XY plane, up to 90° at zenith. Thus -D0,0 -D90,0 -D180,0 and -D270,0 will produce solar vectors {-1,0,0} {0,-1,0} {+1,0,0} and {0,+1,0} respectively, while -Dalpha,90 will produce {0,0,-1} regardless of alpha value.

-f

  Force overwrite of the output file.

-g <sub-option:…>

  Generate the shape of the geometry defined in the submitted file and store it in output. Available sub-options are:

  format=obj

    Define the file format in which the meshes are stored. Currently, only the Alias Wavefront OBJ file format is supported.

  split=<geometry|object|none>

    Define how the output mesh is split in sub meshes. A sub mesh can be generated for each geometry or for each object as defined in the solstice-input(5) file format. The none option means that only one mesh is generated for the whole solar facility. By default, the split option is set to none.

-h

  List short help and exit.

-n experiments-count

  Number of Monte-Carlo experiments used to estimate the solar flux. By default experiments-count is set to 10000.

-o output

  Write results to output with respect to the solstice-output(5) format. If not defined, write results to standard output.

-p <sub-option:…>

  Register the sampled radiative paths for each sun direction and write them to output. Available sub-options are:

  default

    Use default sub-options.

  irlen=length

    Length of the radiative path segments going to the infinity. By default, it is computed relatively to the scene size.

  srlen=length

    Length of the radiative path segments coming from the sun. By default, it is computed relatively to the scene size.

-q

  Do not print the helper message when no file is submitted.

-R receivers

  solstice-receiver(5) file defining the scene receivers, i.e. the solar plant entities for which solstice computes Monte-Carlo estimates.

-r <sub-option:…>

  Render an image of the scene through a pinhole camera, for each submitted sun direction. Write the resulting images to output. Available sub-options are:

  fov=angle

    Horizontal field of view of the camera in [30, 120] degrees. By default angle is 70 degrees.

  img=width x height

    Definition of the rendered image in pixels. By default the image definition is 800x600.

  pos=x,y,z

    Position of the camera. By default it is set to {0,0,0} or it is automatically computed to ensure that the whole scene is visible, whether tgt is set or not, respectively.

  rmode=<draft|pt>

    Rendering mode. In draft mode, images are computed by ray-casting; all materials are lambertian, the sun is ignored and the only light source is positioned at the camera position. In pt mode, the scene is rendered with the un-biased path-tracing Monte-Carlo algorithm; the materials described in the committed file as well as the submitted sun directions are correctly handled and an uniform skydome is added to simulate the diffuse infinite lighting. By default rmode is set to draft.

  spp=samples-count

    Number of samples per pixel. If rmode is draft, the samples position into a pixel are the same for all pixels. With rmode=pt the pixel samples are generated independently for each pixel. By default, use 1 sample per pixel.

  tgt=x,y,z

    Position targeted by the camera. By default, it is set to {0,0,-1} or it is automatically computed to ensure that the whole scene is visible, whether pos is set or not, respectively.

  up=x,y,z

    Up vector of the camera. If rmode is pt, this vector also defines the direction toward the top of the skydome. By default, up is set to {0,1,0}.

-t threads-count

  Hint on the number of threads to use. By default use as many threads as CPU cores.

-v

  Make solstice more verbose.

--version

  Output version information and exit.

## EXAMPLES

Launch two simulations for sun directions whose azimuthal and elevation angles are {45,70} and {50,75}. The solar facility is described in input.yaml and the receivers on which the integrations must be performed are declared in the rcvs.yaml file. 10000 experiments are used by the Monte-Carlo estimates and the results are written to output even though this file already exists:

    $ solstice -D45,70:50,75 -R rcvs.yaml -n 10000 -f -o output input.yaml

Generate a mesh for each geometry described in input.yaml, and save them in the output file with respect to the Alias Wavefront OBJ format. The meshes are positioned according to their orientation constraints, with respect to the sun direction whose azimuthal and elevation angles are {30,60}. Use the csplit(1) Unix command to generate an Alias Wavefront OBJ file per geometry stored in output. The name of the generated Alias Wavefront OBJ files are geom<NUM>.obj with NUM in [0, N-1] where N is the number of geometries described in input.yaml. Refer to solstice-output(5) for informations on the regular expression ^---$ used to split the output file:

    $ solstice -D30,60 -g format=obj:split=geometry -f -o output input.yaml
    $ csplit -f geom -b %02d.obj -z --suppress-matched output /^---$/ {*}

Trace 100 radiative paths into the solar plant described in input.yaml, with respect to the sun direction whose azimuthal and elevations angles are 0 and 90 degrees, respectively. Write the solstice-output(5) result to the standard output and postprocess it with the sed(1) Unix command to remove the first line that stores the sun direction from which the radiative paths come from. The remaining data that list the radiative paths geometry are redirected into the paths.vtk file:

    $ solstice -n 100 -D0,90 -R rcvs.yaml -p default input.yaml | sed '1d'>paths.vtk

Use the path-tracing rendering algorithm to draw the solar plant solplant.yaml with respect to the sun direction whose azimuthal and elevation angles are 180 and 45 degrees, respectively. Use 64 samples per pixel to estimate the per-pixel radiance and fix the up camera vector to {0,0,1}. Write the solstice-output(5) result to standard output and use the sed(1) Unix command to remove the first line which stores the sun direction used to draw the image. Finally, visualise the rendered picture by redirecting the remaining data to the feh(1) image viewer.

    $ solstice -D180,45 -r up=0,0,1:rmode=pt:spp=64 solplant.yaml | sed '1d' | feh -

## COPYRIGHT

solstice is copyright © 2016-2018 CNRS. License GPLv3+: GNU GPL version 3 or later http://gnu.org/licenses/gpl.html. This is a free software. You are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law.

## SEE ALSO

csplit(1), feh(1), sed(1), solstice-input(5), solstice-output(5), solstice-receiver(5)