DESC:TECHNICAL FIELD

The present subject matter generally relates to controlling of solar trackers in solar power plants and particularly relates to an electronic or electromechanical controlling system and method for solar trackers which can sequentially control multiple dual and / or single axis solar tracker tables.

BACKGROUND

Solar power plants have become one of the leading sources of renewable energy in the world due to the abundance of solar power. One of the methods of generating solar power involves the use of photovoltaic solar panels, containing solar cells. Solar cells absorb solar energy, and this solar energy is then converted into electricity with the help of solar power panels.

In order to enhance energy production, solar panels have to be oriented such that solar radiations received by the panels are maximized. For this purpose, solar trackers are used for tracking the sun’s movement throughout the day. Installation of a tracking system is highly beneficial in areas where land cost is high, and/or is limited, or in challenging terrains like mountainous regions where a large patch of flat land is not available. Other examples include industrial rooftops, housing societies and corporate rooftops. Solar tracker controllers are known in the art and are used to optimize positioning of solar panels. Solar panels perform most efficiently when the incident rays of the sun are perpendicular to the absorbing surface. Since the position of the sun is constantly changing on account of the earth’s movement around the sun, solar tracker systems are used to optimize the position of the solar panels in relationship to the real time position of the sun. Tracking system increases the energy yield per unit area significantly with a fractional increase in upfront capital cost.

A dual axis solar tracker table can be moved along two axes, namely Azimuthal and Zenith (or Elevation) as represented in Figure 1. By enabling the movement of the panel in these 2 axes, it can be ensured that the table is always facing perpendicularly to the incident sun rays. Figure 2 shows a tracker table movable in 2 axes. To enable the automatic movement of the panel in these 2 axes, two independent actuators / motors are required, and separate electronic or electromechanical controllers are required which track the position of the sun and align the tables towards the sun.

As per the solutions available in the prior art, each solar tracker is provided with a controller. A significant drawback of this solution of having one controller for each tracker is that each tracker controller requires several auxiliary devices for the operation, like an AC or DC power supply, batteries, battery charger, wind speed sensor, light sensor, etc. For a large utility scale solar tracker plant, which generally ranges from few 100 MWs to few thousand Megawatts, the number of such controllers and auxiliary devices required becomes very large, which not only results in higher costs, but the larger number of components leads to higher maintenance and complexity. As a result, monitoring of the system becomes complex and difficult.

Thus, there exists a well felt need for a system and method that optimizes the resources employed in solar power plant systems by reducing the number of components and controllers and hence, ensuring a substantial reduction in cost and complexity of solar power plant systems. There also exists a need for a system that optimizes the energy production by solar trackers and at the same time assists the user in predicting energy output in solar power plant systems.
SUMMARY
It is an object of the present subject matter to provide an electronic or electromechanical controlling system and method for a solar tracker which is compatible with both single and dual axis solar trackers.

It is another object of the present subject matter to provide a single electronic or electromechanical controlling system for controlling multiple solar trackers in a cost – effective manner.
It is yet another object of the present subject matter to provide a system in which solar trackers are controlled by a single electronic or electromechanical controlling system by using components in an efficient manner.
It is yet another object of the present subject matter to provide a system in which solar trackers are controlled by a single electronic or electromechanical controlling system by using components in a cost-effective way.

It is yet another object of the present subject matter to provide a system in which multiple solar trackers are controlled by a single electronic or electromechanical controlling system by using a sequential mode of operation.

It is yet another object of the present subject matter to provide a system which requires relatively low maintenance and service.

It is yet another object of the present subject matter to provide a system which can collect different parameters of solar tracking so as to optimize the energy production.

The proposed system is an electronic or electromechanical controlling system that is configured to sequentially control multiple dual/single axis solar tracker tables, and at the same time, record real time data.

The subject matter relates to a solar tracker controller system for sequentially controlling multiple solar tracker tables of a solar power system, the solar tracker controller system comprising a processor configured to select one or more solar tracker tables to be controlled by actuating a multiplexing unit, calculate a desired position of the one or more selected solar tracker tables, and supply a voltage from a motor driver to the solar tracker tables for controlling the movement of the solar tracker tables about one or more axes based on the desired position calculated by the processor.

In an embodiment, the processor is configured to calculate the desired position of the one or more solar tracker tables based on the current position of the one or more solar tracker tables and real time position of the sun.
In another embodiment, the processor is configured to calculate real time position of the sun based on the data pertaining to GPS location, wind load, time, date, year and the like.

In yet another embodiment, the processor is configured to collect data pertaining to parameters comprising frequency of tracking, the time after which alignment is required and so on.

In yet another embodiment, the multiplexing unit comprises one or more electronic or electromechanical multiplexing units.

In yet another embodiment, the multiplexing unit comprises a brush sub-assembly comprising a plurality of brushes, a plurality of brush cables, a plurality of brush holders, a plurality of springs, for sequentially routing a voltage to the solar tracker tables via a rotatable split disc, the rotatable split disc being driven by a motor.

In yet another embodiment, the driving unit is configured to actuate the motor for rotating the rotatable split disc for routing a voltage from the motor driver to the solar tracker tables.

In yet another embodiment, the solar tracker controller system further comprises a real time clock module configured to keep track of the day, date, and time and supply the same to the processor.

A method for sequentially controlling multiple solar tracker tables of a solar power system is also described, the method comprising selecting one or more solar tracker tables to be controlled by using a multiplexing unit, calculating a desired position of the one or more selected solar tracker tables, routing, in a sequential manner, a voltage to the solar tracker tables for controlling the movement of the solar tracker about one or more axes based on the desired position calculated by the processor.

In an embodiment, the desired position of the one or more solar tracker tables is calculated based on the current position of the one or more solar tracker tables and the position of the sun.
BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS
The present invention, both as to its organization and manner of operation, together with further objects and advantages, may best be understood by reference to the following description, taken in connection with the accompanying drawings. These and other details of the present invention will be described in connection with the accompanying drawings, which are furnished only by way of illustration and not in limitation of the invention, and in which drawings:

Figure 1 depicts the axes along which a dual axis solar tracker table can be moved.

Figure 2 depicts a table tracker which can be moved along 2 axes.

Figure 3 depicts a solar tracker controller system for sequentially controlling solar tracker tables of a solar power plant in accordance with one embodiment of the present subject matter.

Figure 4 depicts a front view of an electromechanical multiplexing unit of the solar tracker controller system in accordance with one embodiment of the present invention.

Figure 5 depicts a side view of the electromechanical multiplexing unit of the solar tracker controller system in accordance with one embodiment of the present invention.

Figure 6 depicts a top view of the electromechanical multiplexing unit of the solar tracker controller system in accordance with one embodiment of the present invention.
DETAILED DESCRIPTION
The following presents a detailed description of various embodiments of the present subject matter with reference to the accompanying drawings.

The specification may refer to “an”, “one”, “different” or “some” embodiment(s) in several locations. This does not necessarily imply that each such reference is to the same embodiment(s), or that the feature only applies to a single embodiment. Single features of different embodiments may also be combined to provide other embodiments.

As may be used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless expressly stated otherwise. It will be further understood that the terms “includes”, “comprises”, “including” and/or “comprising” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein, the term “and/or” includes any and all combinations and arrangements of one or more of the associated listed items.

Persons skilled in the relevant art will appreciate that the solution disclosed in the present subject matter can be achieved through several design iterations and approaches. The end result can be achieved both using an electronic system as well as electro-mechanical system.

The present subject matter relates to a system wherein multiple solar trackers can be controlled by a single controller. The challenges of the conventional systems do not overcome merely by having a single controller with a large number of components, or multiple number of controllers in one enclosure. The present invention provides a central processor which is configured to sequentially control a higher number of panels by using optimum resources, thereby reducing the cost and complexity, and increasing efficiency of the system.

Another challenge facing the renewable energy sector is the unpredictability of energy output on account of the limited data available. The system according to the present invention is configured to collect different parameters of solar tracking such as the frequency of tracking, the time after which alignment is required, etc., which helps in optimising the energy production by the solar tracker. Such a system also helps the user in predicting the energy output.

The present invention provides a solar tracker controller system for sequentially controlling multiple solar tracker tables of a solar power system. The solar tracker controller system comprises a processor configured to select one or more solar tracker tables to be controlled, calculate a desired position of the one or more selected solar tracker tables, and actuate a multiplexing unit based on the calculated position of the one or more solar tracker tables. The multiplexing unit is configured to route, in a sequential manner, a voltage from the motor driver to the solar tracker tables for controlling the movement of the solar tracker tables about one or more axes based on the desired position calculated by the processor. The processor is configured to calculate the desired position of the one or more solar tracker tables based on the current position of the one or more solar tracker tables and real time position of the sun. The processor is configured to calculate real time position of the sun based on the data pertaining to GPS location, wind load, time, date, year and the like. The processor is configured to collect data pertaining to parameters comprising frequency of tracking, the time after which alignment is required and so on. The multiplexing unit comprises an electronic or electromechanical multiplexing unit.

The multiplexing unit comprises a brush sub-assembly comprising a plurality of brushes, a plurality of brush cables, a plurality of brush holders, a plurality of springs, for sequentially routing a voltage, to the solar tracker tables via a rotatable split disc, the rotatable split disc being driven by a motor. The solar tracker controller system further comprises a driving unit, a motor to rotate the rotatable split disc for routing a voltage frm the driving unit to the solar tracker tables. The solar tracker controller system further comprises a real time clock module configured to keep track of the day, date, and time and supply the same to the processor.

The present invention also provides a method for sequentially controlling multiple solar tracker tables of a solar power system. The method comprises the steps of selecting one or more solar tracker tables to be controlled, calculating a desired position of the one or more selected solar tracker tables, and routing, in a sequential manner, a signal to the solar tracker tables for controlling the movement of the solar tracker about one or more axes based on the desired position calculated by the processor.

Figure 3 depicts a solar tracker controller system 100 for sequentially controlling solar tracker tables of a solar power plant in accordance with one embodiment of the present subject matter. The solar tracker controller system 100 according to the present subject matter comprises a plurality of components. For example, and by no way limiting the scope of the present subject matter, major components of the solar tracker controller system 100 according to the present subject matter include but are not limited to a central processor or microcontroller 102, one or more power converters 104, one or more driving units or motor drivers 106, a multiplexing unit 108 comprising multiplexing circuitry (not shown), and a real time clock (RTC) module 110.

The system 100 also comprises a sensor circuitry (not shown) for connecting various sensors comprising but not limited to one or more wind sensors 112 mounted on multiple solar tracker tables T1 to Tn, to the solar tracker controller system 100. In an embodiment, the system 100 according to the present subject matter provides for a sequential mode of operation of the electronic or electromechanical multiplexing unit 108 such that select group or groups of tables or individual tables T1 to Tn can be aligned first followed by another group of tables or individual tables. Adoption of a sequential mode of operation ensures that the number of components and parts required for the present system 100 are minimized, thereby reducing cost and complexity of the present system 100. In an embodiment, the solar panels are adjusted sequentially after a pre-programmed time interval throughout the day based on the input received from the central processor 102.

According to a preferred embodiment of the present subject matter, the central processor 102 is configured to sequentially control a plurality of solar tracker tables T1 to Tn. In different embodiments, the central processor 102 is configured to sequentially control single and / or dual axis solar tracker tables without departing from the scope of the present subject matter. In an embodiment, the central processor 102 of the present subject matter includes one or more processors. A processor in accordance with one embodiment of the present subject matter may include a logic circuitry for processing instructions. In other embodiments, the processor may be one or more of general-purpose processors, special purpose processors, digital signal processors (DSP), microprocessors, micro-controllers, controllers or the like.

The central processor 102 according to the present subject matter is configured to calculate the zenith and azimuth angle of the sun based on astronomical solar position algorithm. In one embodiment of the present subject matter, the central processor 102 utilizes data pertaining to the GPS location, time, date year as input and calculates the sun position in elevation and azimuth angles. In other embodiments, the central processor 102 may be configured to utilize other parameters as well. In an embodiment, central processor 102 is configured to utilize signal corresponding to the event of a thunderstorm and enable rotation of solar tables T1 to Tn such that the solar tables T1 to Tn are aligned in horizontal direction to minimize wind load on the panels. This allows the solar tables T1 to Tn to track the sun throughout the daytime, thus boosting energy production gaining approximately 25% to 40% more power per acre.

In a preferred embodiment, the real time clock module 110 comprising an onboard integrated real time clock is provided. The real time clock is configured to keep track of the day, date, and time and supply the same to the central processor 102. Tables T1 to Tn are then adjusted sequentially in a fixed interval of time throughout the day in an embodiment. According to a preferred embodiment of the present subject matter, the central processor 102 is also configured to tilt the tables T1 to Tn to zero degrees zenith angle in case the wind speed is above a certain threshold, thus keeping the wind loads under limits.

In an embodiment, the central processor 102 is also configured to obtain inputs from various sensors mounted on solar tracker tables T1 to Tn. Various sensors mounted on the solar tracker tables T1 to Tn and sending signals to the central processor 102 comprise but are not limited to tilt sensors, rotation sensors etc. In an embodiment, the central processor 102 is configured to obtain signals corresponding to real time tilt / rotation of the solar tracker tables T1 to Tn from the sensors mounted on the solar tracker tables T1 to Tn as inputs. In an embodiment, the central processor 102 is configured to operate in a closed-loop in which the central processor receives signals from the sensors mounted on the solar tracker tables T1 to Tn and rotate said solar tracker tables T1 to Tn up to a desired angle. In another embodiment, the central processor 102 is configured to operate in closed loop in which the central processor is pre-programmed to rotate the solar tracker tables T1 to Tn up to a desired time period in order to achieve the desired angle of solar tracker tables T1 to Tn. The central processor 102 according to an embodiment of the present invention not only controls the solar tracker tables T1 to Tn but is also configured to collect data pertaining to parameters, such as the frequency of tracking, the time after which alignment is required, etc. in the system 100.

The motor driver 106, also referred to as the driving unit, of the present invention is configured to actuate the solar tracker tables T1 to Tn. The motor driver 106 can be configured as H-bridge or relay based motor driver, or any other electromechanical or electronic motor drive system in accordance with different embodiments of the present subject matter.

The system 100 in accordance with the present invention communicates with the base station or ground station 114 on a real time basis. In an embodiment, the system 100 is connected to the base station or ground station 114 via a wired or wireless communication. Such collection of real time data in accordance with the present subject matter provides the users of the present system 100 with the ability to monitor and control multiple solar power plants from anywhere across the globe. Thus, the system 100 according to the present invention not only gives plant owners the ability to control and monitor but also helps them in predicting the production, thus giving them an edge in reputation of the new projects involving the system.

The multiplexing unit 108 according to the present subject matter comprises an electronic or electromechanical multiplexing unit that is configured to accommodate large number of sensor inputs and actuator outputs with a single processor, i.e., the central processor 102 and with a single motor driver 106. Figures 4, 5 and 6 illustrate a front view, a side view and a top view of an electromechanical multiplexing unit 108 in accordance with one embodiment of the present subject matter. Major components of the electromechanical multiplexing unit 108 according to the present embodiment comprises but are not limited to a brush sub-assembly comprising a plurality of brushes 116, a plurality of brush cables 118 electrically connected with respective plurality of brushes 116, a plurality of brush holders 120 for accommodating respective plurality of brushes 116, a plurality of springs 122 mounted in the plurality of brush holders 120 and biasing the respective plurality of brushes 116. The electromechanical multiplexing unit 108 further comprises a rotatable split disc 124 for indexing and routing a voltage to the solar tracker tables T1 to Tn, in a sequential manner, a mounting assembly 126 for mounting the brush sub-assembly, and a motor 128 for driving the rotatable split disc 124. This configuration of the multiplexing unit 108 significantly reduces the number of electronic components required for achieving a multi-channel controller. In a preferred embodiment, a plurality of multiplexing units is employed in the system. In yet another preferred embodiment, one multiplexing unit is employed for supplying power and one multiplexing unit is employed for transmitting signals. According to the present embodiment, only one motor driver 106 and one central processor or microcontroller 102 is sufficient to control several channels of tables T1 to Tn.

According to the present embodiment, the motor driver 106 is configured as H-bridge motor driver. The H-bridge motor driver 106 according to the present embodiment is configured to supply voltage to the brushes 116 via respective brush cables 118. The brushes 116 in accordance with a preferred embodiment are configured as carbon brushes. The brushes can be of any material comprising but not limited to carbon, copper carbon, silver carbon, etc. in different embodiments. As shown in Figures 4 and 5, each brush 116 is held in place inside the respective brush holder 120, and a spring 122 pushes the brush 116 outwards to maintain good electrical contact with the split disc 124. Each brush holder 120 comprises a provision to screw cables at the top as shown in Figures 4 and 5. In a preferred embodiment, the brush holders 120 are made of metal, and are electrically isolated from the mounting assembly 126 to avoid short circuit. In the present embodiment, two brush sub-assemblies are provided as shown in Figures 4 to 6. However, in other embodiments more than two brush sub-assemblies may be provided without departing from the scope of the present subject matter.

As shown in Figure 6, the rotatable split disc comprises a plurality of metallic sections 130, which are electrically isolated from each other. In an embodiment, each spring-loaded brush 116 is kept in contact with a section of the split disc 124. Thus, the current flows from the brush cable 118 to the corresponding metallic section 130 of the split disc 124 through the brush holder 120 and the brush 116. The current from the respective metallic section 130 of the split disc 124 then flows to the channel output cable (not shown). The channel output cables are kept slack at the bottom of the assembly to ensure smooth movement. The channel of tables to which output is to be provided is selected by rotating the split disc 124. A particular channel of tables is selected by rotating the split disc 124 at a pre-programmed angle. The rotation of the rotating the split disc 124 is achieved by using the motor 128. In different embodiments, the motor 128 comprises a servo motor, a stepper motor or any other motor, with or without a feedback system. In a preferred embodiment, the motor 128 comprises a servo motor for easier control and reduced complexity.

The central processor or microcontroller 102 monitors the movement of the motor 128 and the pre-programmed angle is achieved to route the voltage, from the driving unit to the desired channel of tables. To further change the channel of tables, voltage is first turned off by the central processor or microcontroller 102 through the motor driver 106 to avoid sparking, thereby increasing life of brushes 116 and the split disc 124. The rotation sequence is followed again in a similar manner for turning the other channel of tables.

According to an embodiment of the present subject matter, the zenith angles are measured through one of several devices selected from but not limited to an encoder, or an inclinometer, an accelerometer or tilt sensor.
According to one embodiment of the present invention, the feedback for zenith angles is taken via one or more acceleration sensors mounted on individual tables T1 to Tn via wired connections. In another embodiment the acceleration sensors are mounted on the tables T1 to Tn via wireless wired connections.

According to an embodiment of the present subject matter, the azimuth angles are measured through one of several devices selected from but not limited to an encoder, an inertial measurement unit (IMU), a gyroscopic sensor, a magnetometer, a combination of these devices or any other sensor / device capable of measuring yaw angle.
According to one embodiment of the present subject matter, the feedback for the azimuth angle is taken by the rotary encoders mounted on individual tables T1 to Tn via wired connections. In another embodiment, the rotary encoders are mounted on tables T1 to Tn via wireless connections.

In an embodiment of the present subject matter, the system 100 is configured to optimise the use of hardware and delivers better performance. The present invention provides one central processor 102, which is configured to control multiple channels of tables T1 to Tn, and which can be further extended by adding supporting circuitry. For instance, and merely as an example, 9 channels of tables T1 to Tn convert to 18 actuators/motors, 9 acceleration sensors and 9 rotary encoders in a dual axis system. Since each connection is a wired connection, and a connection length between 2 tables can reach well up to 50 meters, the system architecture has been designed in such a way that the extended cables do not create a problem. In a preferred embodiment, the communication between the acceleration sensor and the processor 102 is via a special digital communication system, which has been used because of long wired connections.

In accordance with the present embodiment, the system 100 is powered externally through a DC power source (not shown). The power converters 104 supply this power to the central processor 102, the multiplexing unit 108 and the rest of the circuitry (not shown). The central processor 102 takes wind speed data from the wind sensor 112. The central processor 102 also takes the time and date data from the on-board real time clock (RTC) module 110. The central processor 102 also communicates with the base station 114 through wired or wireless communication to exchange data.

The motors on the tables T1 to Tn are powered by the Motor Driver 106, which can be an H-bridge, a relay based, or any other type of motor driver. In an embodiment, the motor driver 106 can be achieved through an H-bridge architecture, or there can also be a relay based system, or any other electromechanical or electronic motor drive system. In a preferred embodiment of the present invention, an H-bridge has been used for increased reliability and lifetime. In an embodiment, the central processor or microcontroller 102 routes this power from the motor driver 106 to each motor mounted on the tables T1 to Tn one by one by controlling the multiplexing unit 108. The motor driver can power only one motor at a time in an embodiment. The multiplexer unit 108 acts like a selector switch that is configured to be used to select any one motor mounted on a table which is to be powered. The selection is done by the central processor 102. Similarly, inclination data from multiple tables T1 to Tn is read by the central processor 102 through the multiplexing unit 108. Thus, a single processor 102 and a single motor driver 106 is able to control multiple tables sequentially.

As can be seen from above, the system according to the present invention enables the user to control multiple solar tracker tables sequentially, which offers significant advantages in terms of reducing the number of components of the system. The systems existing in the art are capable of controlling only one table. While implementing solar tracker tables on a large scale (few MWs to few thousand MWs), the system as per the present invention reduces the required number of components significantly, thereby lowering complexity and cost, and aiding easier maintenance and monitoring.

While the preferred embodiments of the present invention have been described hereinabove, it should be understood that various changes, adaptations, and modifications may be made therein without departing from the spirit of the invention and the scope of the appended claims. It will be obvious to a person skilled in the art that the present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive.
,CLAIMS:I/We claim:

1. A solar tracker controller system 100 for sequentially controlling multiple solar tracker tables T1 to Tn of a solar power system, the solar tracker controller system 100 comprising:

a processor 102 configured to select one or more solar tracker tables T1 to Tn to be controlled by actuating a multiplexing unit 108, and

calculate a desired position of the one or more selected solar tracker tables T1 to Tn, and

a motor driver to supply a voltage to the solar tracker tables T1 to Tn sequentially for controlling the movement of the solar tracker tables T1 to Tn about one or more axes based on the desired position calculated by the processor 102.

2. The solar tracker controller system 100 as claimed in claim 1, wherein the processor 102 is configured to calculate the desired position of the one or more solar tracker tables T1 to Tn based on the current position of the one or more solar tracker tables T1 to Tn and real time position of the sun.

3. The solar tracker controller system 100 as claimed in claim 2, wherein the processor 102 is configured to calculate real time position of the sun based on the data pertaining to GPS location, wind load, time, date, year and the like.

4. The solar tracker controller system 100 as claimed in any one of previous claims, wherein the processor 102 is configured to collect data pertaining to parameters comprising frequency of tracking, the time after which alignment is required and so on.

5. The solar tracker controller system 100 as claimed in any one of previous claims, wherein the multiplexing unit 108 comprises one or more electronic or electromechanical multiplexing units.

6. The solar tracker controller system 100 as claimed in any one of previous claims, wherein the multiplexing unit 108 comprises a brush sub-assembly comprising a plurality of brushes 116, a plurality of brush cables 118, a plurality of brush holders 120, a plurality of springs 122, for sequentially routing a voltage to the solar tracker tables T1 to Tn via a rotatable split disc 124, the rotatable split disc 124 being driven by a motor 128.

7. The solar tracker controller system 100 as claimed in any one of previous claims, wherein the central processor is configured to actuate the motor 128 for rotating the rotatable split disc 124 for routing voltage to the solar tracker tables T1 to Tn.

8. The solar tracker controller system as claimed in any one of previous claims further comprises a real time clock module configured to keep track of the day, date, and time and supply the same to the processor 102.

9. A method for sequentially controlling multiple solar tracker tables T1 to Tn of a solar power system, the method comprising:

selecting one or more solar tracker tables T1 to Tn to be controlled by using a multiplexing unit;

calculating a desired position of the one or more selected solar tracker tables T1 to Tn; and

routing, in a sequential manner, a voltage to the solar tracker tables T1 to Tn for controlling the movement of the solar tracker tables T1 to Tn about one or more axes based on the desired position calculated by the processor 102.

10. The method as claimed in claim 9, wherein the desired position of the one or more solar tracker tables T1 to Tn is calculated based on the current position of the one or more solar tracker tables T1 to Tn and the position of the sun.