Solar Panel Tool

The Solar Panel tool enables you to model the exposure of solar panels mounted on spacecraft, aircraft, and ground vehicles over a given time interval. The result of the analysis can be used to determine varying availability of electrical power for operations to be performed by the vehicle and onboard apparatus.

To access the Solar Panel tool for a particular object, highlight the object in the Object Browser and select Solar Panel... from the <object> menu.

The Solar Panel tool contains:

  • Solar Panel View window. This window enables you to see the changes in the position of solar panels during animation. Use the Animation toolbar to set your scenario in motion. Use the button on the Default toolbar to access the Solar Panel window.
  • Solar Panel window. This window enables you to identify obscuring objects, define the time period during which data is reported, and report data related to vehicle solar panels.

The Color Quality setting for your system display must be set to at least 24-bit color in order for the Solar Panel Tool to work.

You cannot use the Solar Panel tool on any model that contains the FaceEmissionColor parameter or on any model that has a texture on the solar panel.

By default, the solar panel attempts to use the GPU to accelerate the solar panel calculations. If you encounter an error, open the Preferences panel (Edit > Preferences...) and clear the GPU Accelerated Analysis check box.

Obscuring Objects

The Obscuring Objects list is automatically populated with scenario objects, excluding stars and planets, that are candidates for obstructing sunlight directed at the subject vehicle's solar panels.

The Earth (or central body) is always taken into account in the analysis, as, for example, when the vehicle passes into the Earth's umbra or penumbra. In addition, instances in which the subject's own body obstructs sunlight from reaching its solar panels are automatically calculated.

Select All button. Selects all items in the Obscuring Objects list.

Deselect All button. Clears all items in the Obscuring Objects list.

You can also use the mouse to select individual items in the Obscuring Objects list.


Use to set an appropriate view for the solar panel exposure analysis, define a bound radius, and select among solar panel groups on a vehicle that has two or more such groups.

Bound Radius. Tailors the view to yield the optimal display for visualization and analysis. The field of view for solar panel illumination analysis is defined in terms of a rectangular plane rather than a linear boresight or direction of gaze. You can limit the size of that plane by specifying the radius of a circle centered in the rectangle and touching its long sides; that is, a circle having a radius equal to one-half the length of one of the short sides of the rectangle. This ensures that, once the optimal dimension is set, the vehicle remains within view even when rotated.

Solar Panel Groups. Select one or more solar panel groups to be highlighted in the Solar Panel View window and taken into consideration in the solar panel illumination analysis.

The projection is orthographic; that is, without perspective, with the sun's rays treated as parallel rather than radial. The impact on the solar illumination analysis is insignificant, given the dimensions involved here.

The Solar Panel View window displays the vehicle in black against a red background, with the solar panels shown in gray if illuminated.

The greater the effective area of solar illumination of a panel, the brighter the shade of gray in which it is displayed. The effective area is the area of the projection of the solar panel onto a plane perpendicular to the direction of the solar rays striking the panel.

To compute the electrical power captured by the solar panels at a given point in time, the Solar Panel tool applies the following Basic Power Equation:

Power = Efficiency X Solar Intensity X Effective Area X Solar Irradiance


  • Efficiency is specified for the solar panel in the vehicle model file and ranges between 0 and 100 (%).
  • Solar Intensity ranges from umbra (0) through penumbra (0  <   i  <   1) to full sunlight (1).
  • Effective Area is the cross-sectional area defined above.


The Solar Panel tool computes solar illumination over time by animating the scenario and periodically counting the pixels corresponding to illuminated portions of the solar panels under consideration. For this reason, you can specify a Start Time, a Stop Time and a Time Step for the analysis. If you do not set these parameters, they default to those set for the scenario.

Use Object Interval. If this option is enabled, STK asks for the interval for which the object or parent object is defined. If the object or parent object does not have an interval, the scenario interval is used. This option is used only during computation.

Interval and Start/Stop Times. The times during which solar panel data are reported. For more information on the options available for interval and start/stop times, see Time Options.

Time Step. The time step used to separate data points.

Compute button. Click Compute to calculate solar obscuration over the specified start and stop times. If you have already computed illumination data for this vehicle, STK displays a window that allows you to choose to delete existing data or cancel the compute.

Delete Data button. Deletes existing solar panel illumination data so that computer memory is restored once analysis is complete.

Changing the interval(s) does not force recomputation of the data.

Data Reporting

Once you compute solar panel data, you can display various data in report or graph form.

Type. The data to display in report or graph form:

    Power. The power captured by the solar panels at each time step, in the scenario power unit, and the solar intensity (ranging from zero to one).

    Area. The area of the solar panels illuminated by the sun (in the scenario distance unit squared), the effective area (defined above) and the solar intensity at each time step.

    Angles. For a selected time step, and over a range of angles from 0 to 90 degrees, the area and effective area of the solar panels struck by solar rays at each angle in the range. Angle information from the Solar Panel Tool has an accuracy within 0.35 degrees of the true angle.

Generate button. Once you choose a report or graph style and compute the solar obscuration, click Generate... to create the report or graph of choice.