Measuring Power Generation of Solar Panels on a Satellite

STK Premium (Space) or STK Enterprise
You can obtain the necessary licenses for this tutorial by contacting AGI Support at support@agi.com or 1-800-924-7244.

The results of the tutorial may vary depending on the user settings and data enabled (online operations, terrain server, dynamic Earth data, etc.). It is acceptable to have different results.

Capabilities covered

This lesson covers the following STK capabilities:

  • STK Pro
  • STK SatPro

Problem statement

A NASA Earth science satellite, Aqua, was designed to last six (6) years. It launched in 2002, so it has surpassed its design life, yet, it is still doing useful work in space. Since the satellite is still used, you want to optimize the efficiency operations performed by the vehicle and on-board equipment. You will perform some long-term analysis of the potential power generation on-board the satellite.

Your job is to find an accurate way to determine how the solar panel power generation changes throughout the year. This information will help you predict your power budget should the satellite last for many more years.

Break it down

You have some information that may be helpful. Here’s what you know:

  • You need to analyze changes in power over an entire year, with focus on changes in power that occur when the sun is closest or furthest away during that year (the solstice and equinox times).
  • Your analysis period will start on the winter solstice 2016 and last until winter solstice 2017. Due to the Earth's elliptical orbit, the Earth is at perihelion ~2 weeks after the winter solstice, and at Aphelion ~2 weeks after the summer solstice.
    • Solstice Date Time (UTCG)
    Spring Equinox '16 20 Mar 2016 04:30
    Summer Solstice '16 20 Jun 2016 22:34
    Fall Equinox '16 22 Sept 2016 14:21
    Winter Solstice '16 21 Dec 2016 10:44
    Spring Equinox '17 20 March 2017 10:28
    Summer Solstice '17 21 June 2017 4:24
    Fall Equinox '17 22 Sept 2017 20:02
    Winter Solstice '17 21 Dec 2017 16:28
  • The End of Life Power (EOL) from the solar panels on Aqua is approximately 4860 W.
  • The area of the solar panels is 67.2 meters.

Solution

Use STK Pro and STK's SatPro capabilities to create a new STK scenario and perform power analysis using the Solar Panel tool.

Video guidance

Watch the following video. Then follow the steps below, which incorporate the systems and missions you work on (sample inputs provided).

Creating a new scenario

First you will create an STK scenario. You are interested in the potential power over the course of four seasons, beginning with the winter solstice of 2016 occurring on December 21, 2016 and ending with the winter solstice of 2017 occurring on December 21, 2017. Due to Earth's elliptical orbit around the Sun, the Earth does not consistently receive solar rays of the same strength from month to month or even day to day. The same applies to satellites. You will now explore how a satellite generates power over the course of one year.

  1. Click the Create a New Scenario () button.
  2. Enter the following in the New Scenario Wizard:
    3. Option Value
    Name Seasonal_Power
    Description How can I compare the power generation of my solar panels throughout the year?
    Location C:\Users\<username>\Documents\STK 12\
    Start 21 Dec 2016 00:00:00.000
    End + 366 days
  3. When you finish, click OK.
  4. When the scenario loads, click Save ().

Modeling Aqua

Aqua is a NASA Earth science satellite. It is equipped with a radiometer used for ground, ocean, and atmosphere observation. You will model Aqua in this scenario. Perhaps you should check STK Data Federate to see if an Aqua model that includes the on-board equipment has already been configured and saved by someone else. If such a model already exists, it will save you some scenario building time.

  1. Using the Insert STK Objects Tool (), insert a Satellite () object using the From STK Data Federate () method.
  2. When the STK Data Federate tool appears, select the STK Data Federate - Search tab.
  3. Enter Aqua in the Search terms field.
  4. Click Search.
  5. When the search results appear, select Aqua_27424.sa from the Data Source AGI's Standard Object Data Service.
  6. Click Open.

    7. If you don't have internet access, you can use the Local Database to insert the Aqua satellite.

Changing your perspective

Reposition your view so that you can get a better look at Aqua’s solar panels in 3D.

  1. Bring the 3D Graphics window to the front.
  2. Right-click Aqua_27424 () in the Object Browser and select Zoom To. This will set the satellite as the focal point in the 3D Graphics window.
  3. Use your mouse to adjust the perspective.

3D View: Aqua

Just like the real Aqua satellite, the Aqua model is equipped with 12 solar arrays. Each array can be defined as a group in the satellite model file. Having several individual arrays enables you to articulate the solar panels individually, rather than articulating one huge “solar panel wing.”

Checking out the 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. 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 zero (0) and one (1).
  • Solar Intensity ranges from umbra zero (0) through penumbra (0 < i <1) to full sunlight one (1).
  • Effective area is the cross-sectional area defined above.
  • Solar Irradiance is SolarFluxAt1AU/(distance^2), where distance is the apparent position of the sun relative to the satellite in AU.

You can use the results of the analysis to determine varying availability of electrical power for operations to be performed by the vehicle and on-board equipment.

  1. Right-click Aqua_27424 () in the Object Browser.
  2. Extend the Satellite menu.
  3. Select the Solar Panel... option.
  4. Bring the Solar Panel View window to the front.

    5. Solar Panel View: Aqua

  5. Now bring the Solar Panel tool to the front again.
  6. Take a quick look at the Solar Panel Groups section. Are any solar panel groups listed on the Solar Panel tool for Aqua?
  7. Close the Solar Panel tool.
  8. Close the Solar Panel view.

If you don’t see any solar panel groups, it is because they do not exist in the model file. You will have to use a model file that contains solar panel groups.

You can also determine if the model file has solar panel groups through the model file. If the solar panel groups are defined as a component, you will see them mentioned at the top of the model file.

Changing Aqua’s model

For solar panel groups to show up in the Solar Panel Tool section, they must be defined in the model. Right now, Aqua is set to use the default catalog model file (aqua.glb). Switch that out and use a customized model that has been provided. The customized model includes solar panels defined as components.

  1. Open Aqua_27424’s () properties ().
  2. Select the 3D Graphics - Model page.
  3. Click the ellipsis button () beside the Model File option.
  4. Go to <STK install folder>\Data\Resources\stktraining\samples.
  5. Select the aquaSPGroups.mdl file.
  6. Click Open.
  7. Under Model - Articulations, click View.
  8. Select the Default solar panels to point at Sun check box.
  9. Click OK.
  10. Click Apply.

Ensuring the solar panels are pointed at the Sun

Since you changed the model file, you have to ensure that the solar panels are correctly pointed at the Sun.

  1. Open Aqua_27424’s () properties ().
  2. Select the 3D Graphics - Model Pointing page.
  3. Ensure that the Assigned Target Object for Solar_Arrays-000000 is the Sun.
  4. Click OK.

Reopening the Solar Panel tool

For the Solar Panel tool to take the new model file into account, you will close and reopen the tool. If you left it open and changed the model, the new solar panel groups would not have recognized the new model components.

  1. Right-click Aqua_27424 () in the Object Browser.
  2. Extend the Satellite menu.
  3. Select the Solar Panel... option.
  4. Bring the Solar Panel View window to the front.
  5. Arrange the view so you can see the Solar Panel Tool and the Solar Panel View at the same time.

Using the Visualization area

The options in the Visualization area enable you 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.

Setting Bound Radius

The 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, 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.

You do not have any other objects in the scenario yet, so there is no chance that anything will obscure your view of Aqua if you enlarge it. Increase the Bound Radius just a bit to ensure that Aqua’s solar panels are all in view.

  1. Bring the Solar Panel tool to the front.
  2. Enable the Bound Radius option in the Solar Panel Tool.
  3. Set the value to 13 m.
  4. Click Apply.

Selecting the solar panel groups

There are twelve solar panel groups. You need to ensure that all twelve solar panel groups will all be considered in the solar panel illumination analysis.

  1. Bring the Solar Panel tool to the front.
  2. Select all twelve solar panel groups from the Solar Panel Groups list.
  3. Click Apply.
  4. Take a look at the Solar Panel View window.

    Solar Panel View: Aqua

Setting the data time step

By default, the Solar Panel tool uses the scenario Analysis Period as the Data interval Start and Stop Times. You are interested in analyzing changes in power that occur when the sun is closest and farthest away during the year. Analyzing the entire year in one shot could take quite some time. To speed up the analysis, set the time step to one hour.

  1. Set the following options in the Data section:
    2. Option Value
    Start Time 21 Dec 2016 00:00:00.000 UTCG
    Stop Time +366 days
    Time Step 3600 sec
  2. Click Apply.

Computing the data

Now you can compute your first subset of data and determine if the Earth's elliptical orbit around the Sun has any effect on power generation. This will take some time.

  1. Arrange your workspace such that you can clearly see the Solar Panel tool window and it is not obstructing the view of either the Solar Panel View or the 3D Graphics window.
  2. Save () your scenario.
  3. Click Compute in the Data area on the Solar Panel tool.
  4. Watch the satellite animating in the Solar Panel View window.

The Solar Panel View window displays the vehicle with the solar panels illuminated. The greater the effective area of solar illumination of a panel, the greater the power generated. The effective area is the area of projection of the solar panel onto a plane perpendicular to the direction of the solar rays striking the panel.

Generating a data report

Now that you have computed the solar panel data, you can display various data in report or graph form. You are interested in the Effective Area report. The effective area report measures the solar panels illuminated by the sun and the effective area and the solar intensity at each time step.

  1. Locate the Data Reporting section of the Solar Panel tool window.
  2. Select Area for the Type.
  3. Select Report.
  4. Click Generate... .
  5. When the Solar Panel Area report displays, scroll down to the All Solar Panel Group section.

    6. You can also use the Jump To drop-down and select All Solar Panel Groups.

    The Solar Panel Area report for satellites provides data related to the area of the solar panels illuminated by the sun. The values reported as the Effective Area represent the solar panel area lit by the Sun and reduced by the cosine loss. This area can be readily incorporated in power computations.

  6. Leave the Effective Area report open.

Running the Power graph

The Effective Area changes during the solstice time and so does the power. Remember that power is directly related to the effective area as calculated by the Solar Panel tool:

Efficiency X SolarIntensity X EffectiveArea X Solar Irradiance= Power
  1. Bring the Solar Panel tool to the front.
  2. Return to the Data Reporting section.
  3. Select Power for the Type.
  4. Select Graph.
  5. Click Generate....

    This graph will change slightly every time the TLE for Aqua is updated. So your results may look different from the ones below.

    6. Graph: Power graph

  6. Double-click the graph.
  7. Select the Axes tab in the Customization window.
  8. Select Min.
  9. Set the min value to 8500 (W). This will enable you to focus on the peaks in the graph.

  10. Over the course of the year, you can see the measured solar power vary. The Earth's elliptical orbit and the satellite’s position in orbit and attitude have an effect on the total power generated.
  11. Close the Solar Panel tool.
  12. Close the Solar Panel view.

Save your work

  1. Save () your work.
  2. Close the scenario ().