Solar Tracking Controller

Solar Tracking Controller User Guide The solar tracking controller is an autonomous unit which, once configured, requires minimal interaction. The final tracking precision is largely dependent upon the accuracy of configuration and calibration. This user guide is for a two-axis controller configured to point a payload directly at the sun when tracking. Alternative configurations are available to reflect the sun with a mirror onto a target, or to support both direct and reflective types of operation. At GoshLab, we are continually working to develop and improve our products. Therefore, future versions of our tracking controller may not behave exactly as described in this manual. We welcome your feedback. Contact Details Email: info@goshlab.com.au Web: www.goshlab.com.au Address: Unit 4, 106 Mawson Place Mawson ACT 2607 Australia

1 General Operation 1.1 Operating Modes The solar tracking controller has two main modes of operation: automatic mode and manual mode. Typically, the tracking controller will be left in automatic mode, where it will track the sun during the day and go to sleep at night. Manual mode will be used when automatic tracking is not required, and for set up and maintenance. A third mode, not safe to operate mode, is available to handle unusual conditions such as extreme weather events. 1.1.1 Automatic Mode Automatic mode is the normal mode of operation, where the controller will move the payload to track the sun during the day, and go to sleep at night. When sleeping, the controller will move the payload to the stow position. When the controller is in automatic mode, there is a standby state available. In standby state, the controller will move the payload with the sun, but will point at a fixed offset from the sun rather than directly at the sun. Standby state allows the controller to respond quickly and with low energy usage to repeated requests to track or not to track. In automatic mode, the controller will switch between actively tracking and sleeping depending on the position of the sun. When the sun is below the tracking horizon, the controller will sleep. If the tracking hardware is not capable of the full range of motion required to track the sun in all positions, the controller will also go to sleep when it detects that the currently required position to track is outside of the available range of motion. In summary, the four potential states in automatic mode are: Tracking, active Tracking, sleeping Standby, active Standby, sleeping. To determine whether automatic mode is active from a web page: the Auto mode box will be highlighted in green when the automatic mode is active. The Trk radio button will be highlighted if the controller is in the tracking state; the Std radio button will be highlighted if the controller is in the standby state; the Act light will be on if the controller is active; the Slp light will be on if the controller is sleeping. To activate automatic mode from a web page: select the Trk radio button to start in the tracking state, or select the Std radio button to start in the standby state. The controller will determine whether it should be active or sleeping. To switch between tracking and standby states from a web page: select either the Trk or Std radio button. To leave automatic mode from a web page: activate one of the other modes. To leave automatic mode and stow the payload, select the Stow button. To leave automatic mode but leave the payload where it is, select the Motion control radio status button. To leave automatic mode because it is currently not safe to operate, select the Not Safe button. 1.1.2 Manual Mode Manual mode is used when automatic mode is not required. When in manual mode, the controller will only move the payload in response to user commands. There are two types of manual motion control commands: Manual seek commands move the payload to a predefined position. Motion control commands control the motion of the two motors directly. Document ID: STC-UD-001 GoshLab 2011 Page 1 of 17

Some of the manual seek commands and the motion control commands are typically only used during set up and maintenance, and are not present on the Basic web page. After a manual seek command is completed, the controller will return to the motion control state. The basic manual seek commands are used to seek positions that are predefined during the set up of the tracking controller: Stow: move the payload to the stow position, which is a position configured to be the position the payload should be in when not in use, and which is also the position that is used when the controller is sleeping. Windsafe: move the payload to the windsafe position, which is a position configured to present a low profile to the wind, and which is also the position that is used by not safe to operate mode. Preset 1, Preset 2, Preset 3: move the payload to one of the preset positions, which are additional positions configured for site-specific use (for example, they may be positions used for washing or payload maintenance). The additional manual seek commands available from the advanced web pages are: Home: move the payload to the position with sensor coordinates (0,0). Point @ Sun: move the payload to the position that would point it directly at the sun at the time the button is pressed. (This is a one-off seek, not continuous automatic tracking.) World Direction Seek: move the payload to a position that will point it in a direction that is a fixed rotation from the current direction it is pointing. The available angles of rotation (100, 10, 5, 2, 1) are specified in milliradians. The Left and Right rotations are rotations around the world vertical axis, the Up and Down rotations are rotations around a world east-west axis. The motion control commands available from the Advanced and Calibration web pages allow direct control of the motors driving axis 1 and axis 2. The motors can be driven at variable speeds, in the positive or negative directions. The Stop button will stop motion of both motors. The currently selected motion control motor drive velocities are reported as Vel, as a signed fraction of the maximum velocity. To determine whether manual mode is active from a web page: the Manual mode box will be highlighted in green when the manual mode is active. The Manual seek light will be on while a manual seek is in operation, otherwise the Motion control radio button will be highlighted. To activate manual mode from a web page: select any of the manual seek or motion control command buttons, or select the Motion control radio status button. To leave manual mode from a web page: activate one of the other modes. To return to automatic mode, select one of the Trk or Std radio status buttons. To leave manual mode because it is currently not safe to operate, select the Not Safe button. 1.1.3 Not Safe to Operate Mode Not safe to operate mode is used to respond to extreme weather events or other conditions that may make it not safe to operate the tracker. Some controllers are configured to have an external safe to operate signal that will trigger this mode if it is removed; otherwise, a user command will be required to trigger this mode. The tracker may also enter not safe to operate mode in response to communication failures, potential mechanical failures, or other tracking problems. When the tracking controller enters not safe to operate mode, it will attempt to move the payload to the windsafe position, if it has enough information to do so. After the payload is in the windsafe position, or if the windsafe position can not be reached, the tracking controller Document ID: STC-UD-001 GoshLab 2011 Page 2 of 17

will enter a standby state where no further operation will be attempted until the controller is taken out of not safe to operate mode. To determine whether not safe to operate mode is active from a web page: the Not Safe mode box will be highlighted in green when not safe to operate mode is active. The Seek status light will be on while the tracker is seeking the windsafe position, then the Standby status light will be on. To activate not safe to operate mode from a web page: select the Not Safe button. To leave not safe to operate mode from a web page: activate one of the other modes, but only after you have investigated the situation and determined that it is now safe to operate. To return to automatic mode, select one of the Trk or Std radio status buttons. To enter manual mode, select the Stow button, or the Motion control radio status button. 1.2 Advanced Operating Principles This section contains more detailed information about the operation of the solar tracking controller. It is not necessary to be fully familiar with all of this material to operate the controller, but some of it may be helpful in understanding the web browser interface and the behaviour of the controller. 1.2.1 Tracker Mechanism A two-axis solar tracker has two axes of rotation for moving a payload to point at the sun. Axis 1 is the axis that is fixed with respect to the ground; axis 2 rotates around axis 1 with the payload. Each axis is typically fitted with a motor and a position sensor. The motor can be driven forward or backward at variable speeds. The position sensor measures the angle of rotation around the axis. The tracking controller is designed for use with position sensors that can only measure a change in angle of rotation rather than an absolute angle. Therefore, the absolute angle must be measured as an accumulated change in angle of rotation from some fixed index position. When the controller is first powered on, or after it has been restarted, it can not determine the absolute rotations around either axis without first finding the index positions. The operation of safely finding the two index positions is called homing. When an index position has been found for a position sensor, the sensor is said to be indexed. It is possible for information about the indexed position to be cached by the controller during a software reset. The cached value is an approximation that makes safe motion and homing possible, but not precise seeking or tracking. When an index position has not been found for a position sensor, but there is a cached value, then the sensor is said to be operating from a cached index. The controller will still need to find the actual index before it can seek a position. In general, the motors and position sensors of the solar tracker operate independently. The motors drive to move the payload, and the position sensors detect the change in position. When a drive signal is being sent to the motors but no motion is detected by the position sensors, the condition is called a motor stall. A motor stall condition can be caused by mechanical interference or a collision between the payload and something in the environment. It can also be caused by a fault in the motor, a fault in the position sensor, or a fault in the configuration of the tracking controller. Some motor stall conditions are expected and will arise during correct operation of the tracker, for example, during homing (see below). When an unexpected motor stall occurs during automatic operation, the tracking controller will change to not safe to operate mode until the situation can be investigated and resolved. Feedback about the current state of the tracker mechanism is available on the Advanced web page in the Tracker Mechanism section. For each axis, the Ind status light indicates if the sensor for that axis is indexed, and the Cch status light indicates if it is operating from a cached index. The Zero button will reset the state of both sensors to not indexed, with relative position zero. The Position (rad) number gives the measured sensor position as a rotation angle in radians. If the sensor is indexed, then the position is a precise value measured from the index position, otherwise it is just measuring change in position from an unknown Document ID: STC-UD-001 GoshLab 2011 Page 3 of 17

reference. The Raw Edg number is a raw count of the number of falling or rising signal edges that have been detected from the position sensor. Its interpretation will depend on what type of sensor is being used. The Mot status light is on when a drive signal is being sent to the motor. The Drv number gives the current signed discrete drive speed. The Max status light indicates if this is the maximum discrete drive speed. The Stl light indicates if a motor stall condition is being detected. The Sk light indicates if the motor is currently being automatically controlled to seek a particular position. The Th light indicates that the position being sought on this axis has been reached. 1.2.2 Motion Limits The solar tracking controller will operate in a way designed to keep the position of the payload on the axes within set limits, and prevent the payload from colliding with the tracker structure. The controller implements motion limiting strategies to prevent unsafe motion. Under certain conditions, motion will be limited to allow the motors to drive only in particular directions. The conditions that will cause limited motion are: a position sensor is neither indexed nor operating from a cached index a position sensor detects that the position on an axis is outside the configured software limits for that axis the tracking controller detects that the payload has entered an area where a collision with the tracker structure is possible the initial tracking controller parameters have not been set, or the motion ok parameter has been set to false. In automatic operation, the tracking controller will automatically recover from these situations where possible. If the controller can not determine a safe direction to move to recover from a motion limit, the controller will change to not safe to operate mode until the situation can be investigated and resolved. Typically, this would only occur if the configuration parameters were set incorrectly. In manual operation, the motion limits can be overridden if it is necessary to move the tracker during set up and maintenance. In this case, motion of the payload should only ever be attempted when it is under close visual supervision to ensure that there are no unintended collisions or out-of-limit operations. Feedback about the current state of the motion limits of the tracker mechanism is available on the Advanced web page in the Tracker Mechanism section. The Lim status light comes on if any motion limits are active. The Col status light indicates if the limit is due to the payload being in the potential collision zone. The OK+ and OK- status lights indicate, for each axis, if motion is allowed for that axis in the positive and negative directions respectively. If none of these lights are on, no motion is allowed. The OVR check boxes allow the motion limits for each axis to be overridden so that the mechanism can be manually moved during set up and maintenance. 1.2.3 Seeking a Position The solar tracking controller uses a multi-state seeking strategy to move the payload to a desired position. The same strategy is used in several different circumstances: in automatic mode, during active or standby tracking, to seek the required position in automatic mode, at the start of sleeping, to seek the stow position in manual mode, to perform manual seek commands in not safe to operate mode, to seek the windsafe position. The seeking states are indicated on the web pages by status lights in the Tracking Control section: Sk: the motors are directly seeking the required position Hm: the controller is homing, to index the position sensors Document ID: STC-UD-001 GoshLab 2011 Page 4 of 17

Rc: the controller is moving to recover from a motion limiting condition Th: seeking has finished, the payload has reached the desired position Un: seeking has finished, the position was determined to be unreachable Fl: seeking has finished, the seek operation failed to reach the desired position. The response of the tracking controller to the various finish conditions will depend on the mode. In automatic mode, an unreachable position will cause the controller to go to sleep, and a seek failure will cause a change to not safe to operate mode. In manual mode, any finished seek will cause a change from the manual seek state to the motion control state. In not safe to operate mode, any finished seek will cause a change to the standby state. 1.2.4 Homing Homing is an operation the tracking controller uses to index the two position sensors. The homing operation is automatically initiated as part of the seeking operation if either of the two sensors is not indexed. The homing operation is indicated by the Hm status lights in the Tracking Control section of the web pages. The behaviour during homing will depend on the conditions that apply at the start of homing and the configuration of the tracker hardware. The following motions are possible: movement of either motor individually, in either direction movement of a motor to a hardware limit, movement back and forth at the limit movement back and forth across the predicted index position. The homing operation may fail if the tracker or tracking controller has not been configured correctly, or if there is a mechanical failure or interference. In that case, the associated seek operation will finish with a failure. Document ID: STC-UD-001 GoshLab 2011 Page 5 of 17

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2 Web Browser Interface Reference 2.1 General Principles The GoshLab Solar Tracking Controller has a built-in web server that allows you to interact with the controller through a web browser. You will need a recent version of one of the major browsers that supports Javascript and XML, for example, Google Chrome, Internet Explorer, Firefox, Opera, Safari. To interact with the controller, you will need to know its IP address on your local network, for example 192.168.1.66. Type the IP address into the address bar of the browser as, for example: http://192.168.1.66/. The browser should load the Basic page, as described below. It is recommended that the browser not be left running for extended periods showing the current version of the solar tracking controller interface, as there are memory consumption issues with some browsers. The web browser interface consists of several pages. The Basic page is all that is required for normal day-to-day operation. The other pages are used during set up and maintenance. A page menu is shown across the top of each page, with the currently selected page highlighted. The information displayed on the web browser interface pages is not continuously updated in real time. The information will update more frequently during user interaction, but the displayed information may be seconds or minutes old. The liveness indicator on each section (see below) may assist with judging the age of the information. Several graphic conventions are used on the web pages to show states of operation: Off Mode On Mode Status light: indicates if a particular state or condition is off or on. Information only, not clickable. Radio status button: selects between one of a group of states. Click on an off radio status button to turn that state on and the others in the group off. Tick box: indicates if a particular state or condition is off or on. Click on an off tick box to turn the state on, and click an on tick box to turn the state off. Liveness indicator: indicates the age of the information displayed. When the ball appears to bounce, the information in the section has been updated within the last few seconds. When the ball is not bouncing, the information may be out of date. An update of the information can be triggered by moving the mouse within the section, clicking on the liveness indicator, or refreshing the whole page (F5 in most browsers). Mode indicator: indicates if a particular mode is off or on. Information only, not clickable. Document ID: STC-UD-001 GoshLab 2011 Page 7 of 17

2.2 Basic Page The Basic page is shown in Figure 1. It contains two sections: Tracking Control and Sun Observation. Figure 1: Basic Page 2.2.1 Basic Page Tracking Control Section The Tracking Control section is divided into three sub-sections for each of the three major modes of operation: automatic, not safe to operate, and manual. The current operating mode is highlighted in green. Each of the three sub-sections has further details about the state of operation within the major mode. Auto: the Direct @ Sun row Trk and Std radio status buttons indicate whether the controller is tracking or in standby (respectively), and allow you to select the automatic mode and choose between tracking and standby operation. The Act and Slp status lights indicate whether the controller is actively tracking or sleeping (respectively). These are described in Section 1.1.1. The remaining status lights (Sk,Hm,Rc,Th,Un,Fl) indicate a seeking state, as described in Section 1.2.3. Not Safe: the Seek and Standby status lights indicate whether the controller is seeking the windsafe position or in standby (respectively), as described in Section 1.1.3. The Not Safe button puts the controller into the not safe to operate mode. The remaining status lights (Sk,Hm,Rc,Th,Un,Fl) indicate a seeking state, as described in Section 1.2.3. Manual: the Manual seek state light is on when the controller is currently executing a manual seek command. The Motion control radio status button indicates if the controller is in the manual motion control state, and allows you to select the state when the controller is in another mode. The named seek position buttons (Stow, Windsafe, etc.) allow you to execute a manual seek command, as described in Section 1.1.2. The remaining status lights (Sk,Hm,Rc,Th,Un,Fl) indicate a seeking state, as described in Section 1.2.3. Document ID: STC-UD-001 GoshLab 2011 Page 8 of 17

2.2.2 Basic Page Sun Observation Section This section displays information on the most recently calculated sun position for the tracker site. Time (UTC): this is the universal coordinated time the controller is currently using to calculate the sun position. Sun Up?: this status light is on when the sun is above the tracking horizon, as configured by the tracking controller parameters. Azimuth, Elevation (rad): this is the current azimuth and elevation of the sun, measured in radians. North is azimuth zero, east is azimuth -π/2 and west is azimuth +π/2. Horizontal is elevation zero, and the zenith (directly overhead) is elevation π/2. Incoming ray (uvec): this is the unit direction vector of the incoming ray from the sun, in world coordinates. Document ID: STC-UD-001 GoshLab 2011 Page 9 of 17

2.3 Advanced Page The Advanced page is shown in Figure 2. The Advanced page is only recommended for use by experienced users during set up and maintenance. It contains three sections: Tracking Control, Sun Observation and Tracker Mechanism. Figure 2: Advanced Page 2.3.1 Advanced Page Tracker Control The Advanced page Tracker Control section is an extension of the Basic page Tracker Control section. There are additional Manual seek command options, and in the Motion control section, a set of buttons to drive the two motors of the tracker directly, as described in Section 1.1.2. The currently requested motion control velocity is also reported as Vel. The two numbers are the axis 1 and axis 2 requested signed fractional drive speeds. Document ID: STC-UD-001 GoshLab 2011 Page 10 of 17

2.3.2 Advanced Page Sun Observation The Advanced page Sun Observation section is the same as for the Basic page. 2.3.3 Advanced Page Tracker Mechanism The Tracker Mechanism section gives information about the position sensors, motors, motor control states and motion limits of the controller, as described in Sections 1.2.1 and 1.2.2. The Payload World Coordinates table reports the position and orientation of the payload, as calculated from the current sensor positions and the model of the tracker mechanism. No information will be displayed if the sensors are not indexed or operating from a cached index, or are outside their operating limits. The Position row gives the three dimensional world coordinate position of the origin of the payload. The Orientation row gives its three dimensional orientation, expressed as a unit quaternion rotation. The Direction row gives the direction that the payload is pointing, as a unit vector. Document ID: STC-UD-001 GoshLab 2011 Page 11 of 17

2.4 Calibration Page The Calibration page is shown in Figure 3. The Calibration page is only recommended for use by experienced users during set up and maintenance. It contains two sections: Tracking Control and Calibration Data. Figure 3: Calibration Page 2.4.1 Calibration Page Tracking Control Section The Calibration page Tracking Control section is the same as for the Advanced page. 2.4.2 Calibration Page Calibration Data Section The Calibration Data section allows calibration data points to be recorded in the controller. The calibration process is part of the set up and maintenance of the solar tracker, and involves recording data points under particular conditions. Some controllers may be configured to collect different types of points, and some will only have a single option. For example, the page shown in Figure 3 only allows points for Fit mount angles by pointing directly at sun. The other components of the calibration data section are as follows. The state light in the first column indicates which type of point was most recently recorded. The Record Point button records a new point. Document ID: STC-UD-001 GoshLab 2011 Page 12 of 17

The number in the bottom left hand corner indicates how many points have been recorded. The Undo Last button removes the most recently recorded point. The Undo All button removes all the recorded points. The xml link is a web link to download the recorded data points (right click and choose save target as ). Any recorded data points will be lost if the controller loses power or is restarted. A maximum of 32 points can be recorded at a time. The recorded points would typically be downloaded and used in the external calibration process. Document ID: STC-UD-001 GoshLab 2011 Page 13 of 17

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3 Glossary Active In automatic mode, the normal state of the tracker during the day when it is actively tracking the sun, as compared with sleeping. See Section 1.1.1. Actuator An alternative name for motor. Azimuth The horizontal angle of the sun or other object, measured westwards from north. Axis 1 and axis 2 The two axes of a two axis tracking system. Axis 1 is fixed relative to the world, axis 2 rotates around axis 1 with the payload. Automatic mode A mode of operation of the solar tracking controller where the controller will move the payload to track the sun during the day and go to sleep at night. See Section 1.1.1. Cached See operating from a cached index. Calibration The process of refining a model of the geometry of the solar tracker by collecting and analysing data. The calibration process is used to determine some of the configuration parameters of the tracking controller that allow precise pointing in the world. Collision zone An area within the range of motion where it is determined that the payload may be in danger of colliding with the tracker structure. Motion will be limited when the payload is in the collision zone. See Section 1.2.2. Configuration parameters A set of operating parameters that are configured during the set up of the tracking controller. The configuration parameters determine aspects of the behaviour of the controller. Encoder An alternative name for a position sensor. Elevation The vertical angle of the sun or other object, measured upwards from horizontal. Hardware limits Electronic limits fitted to the tracker that cut power to the motor, and thereby prevent unwanted motion. Compare with software limits. Home The position where the indexed position sensors will both read 0. Homing The operation of driving the motors to index the position sensors. Horizon See tracking horizon. Index position A reference position or angle from which others are measured. Used with reference to a position sensor. Indexed The state of a position sensor after the index position has been located and therefore the sensor can report a position measured with respect to the index. See Section 1.2.1. IP address The address of a device on an Internet Protocol network. Each solar tracking controller has a unique IP address. Manual mode A mode of operation of the solar tracking controller where the controller will only move the payload in response to user commands. See Section 1.1.2. Manual seek In manual mode, a command issued to move the payload to a particular position, or the state of the controller while executing such a command. See Section 1.1.2. Motion control In manual mode, a command issued to control the motors directly, including stopping motion, or the state of the controller while executing or waiting for such commands. See Section 1.1.2. Motor In a tracking system, one of the two motors used to drive rotations around the axes. See Section 1.2.1. Document ID: STC-UD-001 GoshLab 2011 Page 15 of 17

Motor stall A condition detected when a drive signal is sent to a motor but no motion is reported by the position sensor. See Section 1.2.1. Not safe to operate mode A mode of operation of the solar tracking controller used when it is considered not safe to operate due to weather or other conditions. See Section 1.1.3. Operating from a cached index The state of a position sensor where information about the index position has been restored from a cache. The position sensor can report only an approximate position with respect to the index. See Section 1.2.1. Override With respect to a motion limit, temporarily remove the limit so that the payload can be moved. Parameter One of the configuration parameters. Payload An object that is attached to the solar tracker that needs to be pointed relative to the sun. The purpose of the solar tracker is to point the payload. Position sensor A device used to measure the angle of rotation of the payload around one of the axes. See Section 1.2.1. Preset One of a set of positions chosen during configuration for site specific purposes, such as washing or payload maintenance. Range of motion The combined allowable range of motion of the payload, as defined by the software limits on each axis. Seek The operation of controlling the motors so that the payload is moved to a particular position, or a command to do so. Sensor See position sensor. Sleeping In automatic mode, the state of the tracker overnight or when the required tracking position can not be reached. When sleeping, the payload will be moved to the stow position. See Section 1.1.1. Software limits Limits on the allowable motion of the payload on each axis, configured in software as a parameter. Software limits on each axis define the range of motion. Compare with hardware limits. Solar tracker A complete system for moving a payload with respect to the sun, comprising a mechanical structure, motors, sensors, and a control system. Solar tracking controller The control system for a solar tracker. Stall See motor stall. Standby In automatic mode, a state of tracking where the payload is pointed at an offset from the sun rather than directly at it, see Section 1.1.1. In not safe to operate mode, a state of operation where the controller is idle, see Section 1.1.3. Stow To move the payload to the stow position. Stow position A particular payload position, chosen during configuration to be the position the payload should be in when sleeping or not in use. Tracking In general, the operation of the solar tracker in moving the payload relative to the sun. In automatic mode, the particular state of tracking by pointing at the sun directly, as compared with standby. See Section 1.1.1. Tracking horizon UTC The elevation of the sun configured to be the point above which tracking will operate. The sunrise and sunset horizons can be set independently. Typically, the tracking horizon will be above the actual horizon. Universal coordinated time, a global time system that is independent of the local time zone. Similar to the older Greenwich Mean Time. Document ID: STC-UD-001 GoshLab 2011 Page 16 of 17

Windsafe position A particular payload position, chosen during configuration to be a position where the payload presents a low profile to the wind, used in not safe to operate mode. World coordinates Coordinates (positions, directions, orientations) specified in a coordinate system relative to the real world or site, as opposed to coordinates specified relative to some part of the tracker mechanism or payload. XML A standard file format for storing information. The tracking controller uses the XML format for input and output of data. Zenith Directly overhead, that is, having an elevation of +90 (or +π/2 radians). Document ID: STC-UD-001 GoshLab 2011 Page 17 of 17