Claims:1. A horizontal single axis solar panel array sun tracking system, said tracking system including electro-mechanical actuator drive means for moving a plurality of solar panels in an array through a range of positions, said system comprising of
- a plurality of vertically disposed array posts,
- a rotational torque tube, mounting support rail assembly disposed between atleast two of said vertically disposed array posts, said mounting rails connected to one or more solar panels
- the said arrangement characterized in that the solar panels are mounted with a tilt between 3º to 10 º on the support rails, one on each of the two sides of the mounting rail, and such that the tilt angle maintained on each side mounting rail lip is offset same degree but in opposite direction to accommodate panel.

2. The horizontal single axis solar panel array as claimed in claim 1 includes plurality of fasteners means, such that each of fastening means, fastens two adjacent modules onto the mounting rail.

3. The horizontal single axis solar panel array as claimed in claim 1 includes arranging the solar modules in a portrait condition, thereby achieving lowest tracker row length for a specific number of modules and tilt.

4. The horizontal single axis solar panel array as claimed in claim 1, wherein the said electromechanical actuator drive means comprising atleast a gear and a motor which drive the number of rows having solar modules.

5. The horizontal single axis solar panel array as claimed in claims 1 and 4, wherein the said electromechanical actuator drive means includes a two state mechanical torque limiter as a safety interlock means, the said means arranged between the gear and motor of electromechanical actuator drive means, such that the limiter engaged in its first state selectively allows motion of the motor to be transferred to the gear and in its second disengaged state selectively disallows motion of the motor to be transformed to the gear, thereby electromechanical actuator drive with mechanical torque limiter means is an overload protection safety device.

6. The horizontal single axis solar panel array as claimed in claim 1 which includes two state external limit switches as a safety interlock means, the said means to selectively switch off the motor of the electromechanical actuator drive means, the said limit switch is mounted externally on the electromechanical actuator body, along the actuator screw cover, fixed at the end at the maximum desired travel limits, such that limit switch in its first disengaged state allows the motor to be ON and in its second engaged state when the screw hits the limit switch to open the NC (normally closed) contacts and close the NO (normally open) contacts, which in turns switches off the motor.

7. The horizontal single axis solar panel array as claimed in claim 1 which includes two states external limit switches, with contacts designed to open NC (normally closed) contacts and close the NO (normally open) contacts when actuated.

8. The horizontal single axis solar panel array as claimed in claim 1 includes a hand-wheel means arranged operatively with electromechanical actuator as a safety interlock means to assist moving the solar photovoltaic modules back to stow position during emergency.

9. The horizontal single axis solar panel array as claimed in claim 1, wherein the rotational mounting supporting rail assembly includes a long horizontal torque tube supported on bearings mounted upon array post/frames/pylons, such that the axis of the tube is horizontal in north-south line and the photovoltaic panels are mounted upon the said tube and the said tube will rotate on its axis to track the apparent motion of the sun through the day, and thereby rotating the mounted solar modules east to west throughout the day.

10. The horizontal single axis solar panel array as claimed in claim 9, wherein the bearings are polymer bearing bushes provided with male and female coupling thus eliminating the collar

11. The horizontal single axis solar panel array as claimed in claim 9, wherein the bearing sits on bearing circular pipe section to be used eliminating instead of two journal halves.

12. The horizontal single axis solar panel array as claimed in claim 1 includes a controller with backtracking means with associated feedback means operable with backtracking algorithm taking into account the criticality of angle of incidence and direct irradiance into quantification of the performance of the tracker.

13. The horizontal single axis solar panel array as claimed in claim 1, wherein the system proposes actual vs estimated diffused component of global horizontal irradiance as a criterion to qualify the PR value for a day in an acceptance test The values of irradiance gain and performance ratio are valid for comparison and confirmation with estimated or guaranteed values of gain and PR, only if the fraction of diffuse irradiance in actual or on-site GHI measurement (F_diffa) is lesser than or equal to the fraction of diffuse irradiance on estimated GHI (F_diffe). This procedure eliminates undermining the tracking accuracy and effectiveness due to extrinsic environmental factors and provides a way to account for the aptness of tracking algorithm employed.

14. The horizontal single axis solar panel array as claimed in claim 1 includes a stow-and-lock means which is mechanically and structurally incorporated into the support assembly such that the solar panels stop at a predetermined stow mode angle when the wind speed is greater than the prescribed allowable wind speed.

15. The horizontal single axis solar panel array as claimed in claim 1 includes maintenance means which is mechanically and structurally incorporated into the support assembly such that the solar panels stop at a predetermined maintenance mode angle, at which angle module cleaning is easy.

16. The horizontal single axis solar panel array as claimed in claim 1 includes a emergency means, which is mechanically and structurally incorporated into the support assembly such that the solar panels stop at a current angle position when an erroneous operation is identified by associated sensors.

17. The horizontal single axis solar panel array as claimed in claim 1 includes a rain means, which is mechanically and structurally incorporated into the support assembly such that the solar panels rotates throughout the -45 to + 45 degree cycle, through which angle rain water washes away the dirt from the modules.

18. The horizontal single axis solar panel array as claimed in claim 17 includes a rain means, which is mechanically and structurally incorporated into the support assembly such that the solar panel rotates once at a predetermined speed prior to panel stop, during which rotation rain water washes away the dirt.

19. The horizontal single axis solar panel array as claimed in claim 1 includes an offset means for the purpose of calibrating the field position sensors to an extent that actual structure position and sensor feedback to the tracker controller is same.
, Description:FIELD OF INVENTION
The invention relates to a Solar Tracking system.

BACKGROUND OF INVENTION
Tracker Controllers are devices that control the motion of the Solar tracking system to track sun for maximizing the solar energy production. Tracker controller runs sun position algorithm to find sun angle and control algorithm which collect inputs from field devices and decides to which angle, tracker structure is to be rotated. As a result, Tracker structure modules are inclined to such positions that the total output yield of the plant with respect to conventional fixed mount structures will increase.

OBJECTIVE OF INVENTION
A horizontal East West tracker is preferred over conventional fixed mount structures in India is mainly due to the geographic location of the country, with the sole moto of keeping tracker structure aligned with sun angle. If the pitch between two consecutive structures is low, then it is possible that shadow of one structure falls on the modules of other structure during morning and evening time, which harshly impact the generation as well as Module quality. Unique backtracking algorithm ensures maximum generation and improved module quality by calculating a new tracking position to avoid shadow effect altogether. Hence the main objective of having tracker controller is to calculate and control the optimum position of tracker structure so that maximum yield is obtained throughout the day out of the solar tracking system as per the invention by reducing shadow effect on modules. Distinctive mode of operations are implemented to reap maximum benefits.

DESCRIPTION OF INVENTION
The proposed system aims to control the motion of Horizontal single Axis Tracker (HSAT) to track the sun throughout the day from east to west (+ 45 to - 45 degrees) about a single horizontal axis. The system includes back tracking feature which helps to re-positon the structure to such an angle that shadow of one structure doesn’t fall on another structure while keeping an eye for maximum yield.
Tracker Controller system mainly consists of Programmable Logic Controller (PLC) section and Intelligent Motor Controller (IMC) section. PLC is major component of control System which is programmed in such a way that various operation modes of HSAT such as sun tracking mode, backtracking (shadow avoidance), wind stow mode, maintenance mode, emergency mode etc. form its basic framework. PLC runs sun position algorithm, back tracking algorithm and control algorithm. It collects input from field devices such as Inclinometer, Encoder & Anemometer (Wind speed sensor) and IMC section and decides the operation mode & rotation required and give command to IMC section accordingly to operate motor.

IMC section consist of Intelligent motor controller which receive command from PLC of controller panel, check status of connected field devices (east & west limit switch, emergency switch) and provide power supply to motor for forward and reverse operation.

HARDWARE ARRANGEMENT OF DESIGNED SYSTEM-
Tracker Controller Panel is mounted near Actuator of HSAT. Control system receives input from Inclinometer, Encoder, Anemometer & limit switches and communicates to SCADA. IMC section receive input from Limit switches and is connected to PLC.

Figure A shows Basic Tracker Controller Architecture

Figure B shows of Schematic Wiring of Control Section

Figure C shows of Schematic Wiring of IMC Section

KEY FEATURES OF INVENTION-

S. No. Particulars Details
1. Type of tracking Horizontal single axis
2. Tracking Angle ± 45° from Zenith
3. Tracking basis NREL – Sun tracking algorithm
4. Tracking Modes of Operation Tracking mode, Backtracking (shadow avoidance), Maintenance mode & Emergency mode
5. Components Controller, IMC, Inclinometer & Anemometer
6. Wind stow Mode Automatic sensing of wind speed and positioning the tracker to homing position. Uses anemometer for emergency wind stow
7. Control system Programmable Logic Controller (PLC)
8. Tracking Response Tracking Position calculation varies between 20 seconds to 120 seconds
9. Communication Bus Modbus RTU/ RS-485
10. Offset Adjustment Inclinometer/Encoder offset can be adjusted to get the actual and accurate field readings
11. Rain Mode Tracker modules can be cleaned from rain water by one full rotation of tracker structure

DETAILED SYSTEM OPERATION –
Tracker controller working in various operation modes is described here -

Figure D illustrates Control Flow Chart (Manual Mode)

Figure E illustrates Control Flow Chart (Auto Mode)

Figure F illustrates Backtracking Flow Chart

Tracking Mode – In tracking mode, sun angle is calculated using NREL algorithm and tracker structure is rotated accordingly to follow the sun so that maximum irradiation is received on solar modules plane. Tracker rotation is controlled in range of -45° to +45°. In evening, when sun angle is above 90°, tracker goes back to home position (i.e. 0° - horizontal plane)

This mode is always enabled. Tracker follows NREL algorithm and rotates the structure to align Modules according to Sun position within “-45 to +45 deg. range”. Tracker positions the structure at Stow (0 deg.) from Sunset (+90 deg.) till next day Sunrise hours (-90 deg.)

Backtracking Mode – If the pitch between two consecutive structures is low, then it is possible that shadow of one structure falls on module of next structure during morning and evening times. Energy generations will be effected due to this undesired arrangement and there is also possibility of module quality loss. To avoid this, a new angle (called Sun Set Point in flow charts) is calculated using backtracking algorithm and tracker moves from normal tracking angle to newly calculated angle to get the maximum yield.

Reduces shadow effect on modules, improves the Module quality thereby improvising Energy harvest and yield.

Backtracking - for maximum Energy harvest and improving Module quality
Backtracking is enabled when Sun position is within -90 to -60 deg. and +60 to +90 deg. The unique Backtracking logic works with inputs of Module dimensions and pitch (inter-row) distance, and calculates the optimized Module position set point, at which Module to Module (between rows) shadow effects are avoided.

Backtracking logic is implemented by other Market players in their tracker solutions, but L&T Tracker Backtracking logic is a unique customized algorithm in which Land undulation, Module type and Module orientation inputs are factored to provide the best set point angle to track the Sun

Tracker angle of 18.2.2016 is illustrated in figure 1

Backtracking results in
a. Improved Energy generation due to shadow avoidance on Modules across all sun hours
b. Improved Module quality
c. Longer exposure hours of Modules to Sunlight
d. Lesser impact to Module issues

Wind Stow Mode – Every tracker structure is designed to withstand up to a particular wind speed limit. Higher wind speed than that can cause damage to modules or even dislodge them from structure itself. Whenever wind speed goes above a particular limit, wind stow algorithm kicks start, in which tracker goes to home position for a particular period of time to minimize the impact of high wind speed on modules.

This mode is activated when Wind speed (at Tracker zone, feedback taken from Anemometer) exceeds the safe limit preset value. Heavy winds can cause module damage, dislocation of module from Structure. To avoid this damage, Tracker senses the wind speed, and during high winds, it actuates the structure to Stow position where impact of wind is lesser compared to other structural positions. When wind speed becomes low, the tracking gets resumed again.

Maintenance Mode – In maintenance mode, tracker structure always move to a pre-defined angle every time maintenance mode is enabled, which can be very handy during module cleaning, calibration of sensors etc.

This mode is activated manually by Operator for purpose of Module cleaning, calibration of sensors. When mode is activated, Tracker rotates the Modules to a preset set point angle at which, module cleaning can be done easily

In this mode, preventive maintenance activities and sensor healthiness checks can be worked.

Emergency Mode – Tracker motion stops in emergency mode and it stays fixed at its current position as long as emergency mode is activated. All sun angle calculations will keep running in back ground and tracking motion starts as soon as emergency mode is deactivated.

This mode gets activated automatically by Tracker in case of erroneous operation sequence / other faulty conditions. When activated, the tracker operation gets stopped thereby avoiding any risks. Tracking resumes only when this mode is de-activated.

Rain Mode – To utilize natural downpour to clean solar modules, rain mode acts as an add-on. In most likely scenarios, irradiation during rain period is low and solar energy generation is quite small. That period can be used to clean solar module from rain thus saving water and cost associated with module cleaning. Tracker makes one complete round of rotation (current location -> Nearest End angle (±45°) -> Opposite End angle (±45°) -> Sun set point)

By sensing Rain (feedback from Rain gauge), Tracker rotates the modules such that, Modules can be cleaned utilizing rain water by one full rotation of tracker structure thereby reserving the underground Water

Auto Offset Adjustment – As it is possible to that inclinometer and encoder drifts away over the course of time. Inclinometer/Encoder offset can be adjusted to generate actual field readings so that tracker motion is controlled over desired positions. Once the inclinometer/Encoder is calibrated, offset can be re-adjusted.

Inclinometer/Encoder offset is done to calibrate the field position sensors such that, actual module/structure position and sensor feedback to Tracker controller remains same.

Drifting of sensor accuracy due to ageing is unavoidable, but offsetting option maintains tracking accuracy (L&T Tracker accuracy is ± 1 degrees) by auto-adjustment of Sensor feedback with respect to the actual structural angle.

Teaching the sensors to maintain accuracy and avoid drifting of values, is a tedious task in case of large scale Utility solar plants where multiple Trackers are deployed. In these cases, Self-generating offset facility provides great support by reducing maintenance hours thereby reducing plant downtime and improving energy harvest.

SMS – Alerts on Tracker Status
Tracker operation status and Alarms is sent via SMS (Short Message Service) to authorized personnel. SMS is received automatically on daily basis and if required, SMS can be received on Demand basis at any time. Pioneer step in tracker technology – A New design feature implemented

Horizontal Single Axis Solar Tracker with Tilted module
Concept behind the invention

Horizontal single axis solar tracker follows sun east - west movement during day time to yield more energy than fixed tilt solar PV installation. Yield gain with respect to fixed tilt system considerably reduces at latitudes above 15° due to sun position. The module tilt towards true south from flat position will help to improve yield gain. L&T Solar unique module mounting rail design helps to achieve optimum tilt angle on horizontal single axis tracker. This unique design applies for module mounting in portrait condition.

Unique features:
- The mounting rail design dimensions are unique to maintain the module tilt and essential angle (3° to 10°) arrangement in solar tracker.
- The tilt angle maintained on each side mounting rail lip is offset by same degree but in opposite direction to accommodate module.
- This optimum mounting profile design shares two modules to reduce the fasteners and installation time of tracker
- The unique mounting design in portrait condition engineered to achieve lowest tracker row length for given number of modules and tilt.
- This profile is manufactured with 1.6mm/ 2.0mm thickness pre galvanized steel sheet

Figure 2 illustrates the Module with tilted towards south compared flat one in adjacent row

Benefit: Module tilt towards south yields better energy at high latitudes than HSAT with zero tilt
Solar Tracker Electro Mechanical Actuator safety interlocks
A solar tracker is a device used to track the sun to maximize the solar generation. Each row of solar tracker comprises PV modules fixed over purlins. Number of rows arranged in ganged beam is driven by an electro-mechanical actuator.

An electro-mechanical actuator is a robust system with high accuracy, efficiency & designed for long term maintenance free operation. For higher degree of reliability and safety it is necessary that interlock equipment are provided.

Unique Feature -
Following unique features are incorporated in the electromechanical actuators –

1. Use of Mechanical torque limiter
2. Use of external limit switch
3. Provision of hand wheel for manual operation during emergency

Figure 3 illustrates Electro-Mechanical Actuator with Unique parts

Mechanical torque limiters are over load safety devices for overload protection. When a jam in the structure occurs it may result in excessive loading of actuator, the built-in torque limiter will reliably and quickly release to prevent system damage.

Mechanical torque limiters are provided between the gear and motor. During normal operation these are usually in engaged condition allowing motion to be transmitted from the motor to gear, however when the present disengaging force is exceeded then it disengages the gear & motor to prevent system damage.

External limit switches are provided on the electro – mechanical actuator body, these direct acting contacts are designed to open NC (normally closed) contacts and close the NO (normally open) contacts when actuated.

Limit switches are provided on actuator screw cover, fixed at the end at maximum desired travel limits. During normal operation actuator would operate within allowable travel limits, but due to any malfunction when actuator operates beyond the allowable range – the screw hits the limit switch to open NC (normally closed) contacts and close the NO (normally open) contacts

Once the NO and NC contacts gets operated, it gives feedback to both tracker controller and IMC to switch off the motor thereby ensuring Redundancy for the Stop operation.

Provision of hand wheel in actuator used for solar applications helps to move the solar PV modules back to stow position during emergency condition.

Self - locking Polymer Bearing bushes and Circular Bearing holder with Slot provision
A solar tracker is a device used to track the sun to maximize the solar generation. Each row of solar tracker comprises PV modules fixed over purlins. Number of rows arranged in ganged beam is driven by an electro-mechanical actuator.

Among the various components which make up a tracker, two components which are important for performance of the tracker are – Polymer bearing bushes & bearing journal. Improper design of polymer bush bearing & its journal would affect the smooth operation of a solar tracker and thus loss of committed generation.

Polymer bearings are used due to its very low coefficient of friction, extremely low moisture absorption & higher resistant to abrasion.

Horizontal Single axis solar tracker polymer bearing and its journal arrangement is shown below
FIG.

Figure 4: Old Assembly – comprises of upper journal, lower journal, polymer bush bearing (two halves)

Figure 5: New Design – comprises of single journal part, polymer bush bearing (two halves)

Unique Features
? Polymer bushes - self-locking arrangement in bushes. Circular polymer bushes are provided between the torque tube and the bearing holder. To avoid it getting slipped from the bearing holder the bushes were provided with collar (ref Fig 4). Our new design eliminates this collar and the fixing is ensured by means of male-female coupling (ref Fig 5).

? Bearing journal

• Bearing journal are usually fabricated assemblies comprising of two halves – bottom journal & top journals which are bolted at site during assembly as seen in Fig 1.
• Profile of the machined part which holds the bearing is critical for operation of the tracker assembly. Since the two journals are machined components, the quality of output needs to be very high to ensure smooth operation of bush bearing over it.
• New design offers circular pipe section to be used eliminating two journals (pieces), this design offers a quality finished single part to be used with bush bearing.

? The new design of journal & bearing bush can be assembled faster compared to the previous design.

? When compared to the previous design, fabrication of journal assembly in new design is easier and at the same time quality can also be ensured.

Unique criteria for quantification and acceptance of solar tracker performance
In order to maximize the incident irradiance on a solar photovoltaic system, arrays should be kept facing the sun at all times. Maximum irradiance will be collected by moving the array to face the sun and by maintaining the angle of incidence (angle between normal to the surface and a ray directly incident from the sun) as close to zero as possible – a method widely known as sun- tracking. By minimizing the incidence angle, tracking improves the collection of direct irradiance, the component of incident radiation that comes in a straight line from sun’s direction. Tracking in solar power systems is therefore more effective on direct irradiance.

Performance ratio (PR) is a metric used to define the operational efficiency of a solar photovoltaic (PV) system. PR is the ratio of actual energy generation to the energy that would have been generated if the energy conversion happened consistently at the rated capacity of the PV module. PR, however, is a function of system efficiency and weather.

TESTING PERFORMANCE OF A TRACKER:
Actual performance of a PV system, i.e. the energy generated, varies with respect to operating temperature, level and spectrum of irradiance, wind velocity etc… PR measurements should be corrected for the variance in actual weather parameters from the estimated values in order to eliminate any bias in the system performance representation. Correction for actual vs estimated operating cell temperature is most commonly applied on performance ratio for a solar PV power plant.

In case of a tracker based system, effect of the composition of irradiance is an equally critical parameter since the gain from sun-tracking is most effective on the direct component of irradiance. Thus effectiveness of solar tracking depends on the atmospheric conditions and the composition of diffuse and direct components in the total irradiance. Higher the direct component, higher the total gain due to tracking. Net tracker gain is a weighted average of the gain in diffuse and direct constituents of irradiance as observed from detailed analysis at several locations (Fig.6).

Fig. 6A and 6B. Graphs depicting: a) percentage of diffuse and direct irradiance components in GHI b) gain of diffuse, direct and global irradiance on tracker plane upon the respective components on a horizontal surface

Current processes defined for performance acceptance tests does not take this factor into account, which is critical in case of provisional acceptance tests done over a short period of time; for instance, 7 days and commitment of PR is on monthly/yearly basis

UNIQUENESS:
The procedure defined by L&T for the provisional tracker performance measurement considers actual vs estimated diffused component of irradiance as a criterion to qualify the PR value for a day in an acceptance test. The values of tracker gain over horizontal installation is vetted for the estimated fraction of diffuse and direct components in the estimated global horizontal irradiance (GHI), computed from the meteorological database, which will be mentioned and agreed upon by all parties in the contract. The values of irradiance gain and performance ratio are considered valid only if the fraction of diffuse irradiance in actual GHI measurement (F_diffa) is lesser than or equal to the fraction of diffuse irradiance on estimated GHI (F_diffe).

The new PR acceptance procedure or trackers is defined as below:

• Global horizontal irradiance (GHI) at the project site is measured using a GHI pyranometer.
• An additional sensor, a shadow-band pyranometer, is installed in the project site for the measurement of diffuse component of irradiance in the horizontal plane. The actual daily fraction of diffuse irradiance (F_diffa) in the GHI is computed from the two pyranometer readings.
F_diffa = Actual diffuse irradiance / Actual GHI
F_diffa = Shadow-band pyranometer measurement / GHI pyranometer measurement

• Daily PR values as calculated on the basis of daily measurements of energy generation and insolation.
• If actual PR averaged over the measurement period is greater than OR equal to guaranteed PR (Guaranteed PR for the month) then the test is deemed successful.
• If actual PR averaged over the measurement period is lesser than guaranteed PR for the period of measurement, then the following checks and corrections are to be applied.
a. Correction for actual operating module temperature:
Corrected PR is calculated based on the given formula if actual PR is less than
guaranteed PR
PRCorr_Actual = PRActual X (1/Ctemp)
Correction coefficient for temperature is calculated based on given formula.
Ctemp = (1- a x (Te -Tm))
Te = estimated module temperature
Tm = actual / measured module temperature
b. Check on diffuse fraction of GHI:
If temperature corrected actual PR is less than guaranteed PR, then this could indicate the unavailability of estimated direct irradiance component on the day of measurement.

Check the actual fraction of diffuse radiation for the day is greater (F_diffa) with the average fraction of diffuse radiation as per the estimation conditions (F_diffe).
(Total diffuse radiation on horizontal plane for the day recorded by the shadow-band pyranometer and total GHI is recorded by GHI pyranometer.)
If F_diffa > F_diffe , the day is not considered for PR estimation.

PR acceptance test is to be carried out till weather parameters fall in the acceptable limits.

This procedure takes into account the criticality of angle of incidence and direct irradiance into quantification of the performance of a tracker at any location. It eliminates undermining the tracking accuracy and effectiveness due to extrinsic environmental factors and provides a way to account for the aptness of tracking algorithm employed.

In one aspect, the invention is a horizontal single axis solar panel array sun tracking system, said tracking system including rotational electro-mechanical actuator drive means for moving a plurality of solar panels modules in an array through a range of positions. The said system comprises of a plurality of vertically disposed array posts. A rotational torque tube mounting support rail assembly is disposed between atleast two of said vertically disposed array posts. The said mounting rails are connected to one or more solar panel modules. The said arrangement characterized in that the solar panel modules are mounted with a tilt between 3º to 10 º on the support rails, one on each of the two sides of the mounting rail, and such that the tilt angle on one side is same as tilt angle on the other side but tilt on second side is in opposite direction with respect to tilt on first side.

In another aspect, the invention includes plurality of fasteners means, such that each of fastening means, fastens two adjacent modules onto the mounting rail.

In another aspect, the invention includes arranging the solar modules in a portrait condition, thereby achieving lowest tracker row length for a specific number of modules and tilt.
In another aspect, the invention discloses and uses an electromechanical actuator drive means comprising atleast a gear and a motor which drive the number of rows having solar modules.

In another aspect, the invention discloses that the said electromechanical actuator drive means may include a two state mechanical torque limiter as a safety interlock means, the said means arranged between the gear and motor of electromechanical actuator drive means, such that the limiter engaged in its first state selectively allows motion of the motor to be transferred to the gear and in its second disengaged state selectively disallows motion of the motor to be transformed to the gear, thereby electromechanical actuator drive means is an overload protection safety device.

In another aspect, the invention includes two state external limit switches as a safety interlock means, the said means to selectively switch off the motor of the electromechanical actuator drive means, the said limit switch is mounted externally on the electromechanical actuator body, along the actuator screw cover, fixed at the end at the maximum desired travel limits, such that limit switch in its first disengaged state allows the motor to be ON and in its second engaged state when the screw hits the limit switch to open the NC (normally closed) contacts and close the NO (normally open) contacts, which in turns switches off the motor.

In another aspect, the invention includes two states external limit switches, with contacts designed to open NC (normally closed) contacts and close the NO (normally open) contacts when actuated.

In another aspect, the invention includes a hand-wheel means arranged operatively with electromechanical actuator as a safety interlock means to assist moving the solar photovoltaic modules back to stow position during emergency.

In another aspect, the invention discloses a rotational mounting supporting rail assembly which includes a long horizontal torque tube supported on bearings mounted upon array post/frames/pylons, such that the axis of the tube is horizontal in north-south line and the photovoltaic panels are mounted tiltingly upon the said tube and the said tube will rotate on its axis to track the apparent motion of the sun through the day, and thereby rotating the mounted solar modules east to west throughout the day.

In another aspect, the invention teaches that the bearings are polymer bearing bushes provided with male and female coupling thus eliminating the collar in the system. The bearing sits on single journal integrated circular pipe section type bearing instead of two journal halves.

In another aspect, the invention includes a controller with backtracking means with associated feedback means operable with backtracking algorithm taking into account the criticality of angle of incidence and direct irradiance into quantification of the performance of the tracker.

In another aspect, the invention proposes actual vs estimated diffused component of global horizontal irradiance as a criterion to qualify the PR value for a day in an acceptance test. The values of irradiance gain and performance ratio are valid for confirmation against estimated or guaranteed values of gain and PR, only if the fraction of diffuse irradiance in actual or on-site GHI measurement (F_diffa) is lesser than or equal to the fraction of diffuse irradiance on estimated GHI (F_diffe). This procedure eliminates undermining the tracking accuracy and effectiveness due to extrinsic environmental factors and provides a way to account for the aptness of tracking algorithm employed.

In another aspect, the invention includes a stow-and-lock means which is mechanically and structurally incorporated into the support assembly such that the solar panels stop at a predetermined stow mode angle when the wind speed is greater than the prescribed allowable wind speed.

In another aspect, the invention includes maintenance means which is mechanically and structurally incorporated into the support assembly such that the solar panels stop at a predetermined maintenance mode angle, at which angle module cleaning is easy.

In another aspect, the invention includes a emergency means which is mechanically and structurally incorporated into the support assembly such that the solar panels stop at a current angle position when an erroneous operation is identified by associated sensors.

In another aspect, the invention includes a rain means, which is mechanically and structurally incorporated into the support assembly such that the solar panels rotates throughout the -45 to + 45 degree cycle, through which rain water washes away the dirt from the modules.

In another aspect, the invention includes a rain means which is mechanically and structurally incorporated into the support assembly such that the solar panel rotates once at a predetermined speed prior to panel stop, during which rotation rain water washes away the dirt.

In another aspect, the invention includes an offset means for the purpose of calibrating the field position sensors to an extent that actual structure position and sensor feedback to the tracker controller is same.

The disclosure has been made as known to inventors and with specific examples and illustrations for the purpose of proper disclosure and better understanding of the invention. There can be other variations and modifications that will be obvious to skilled persons in the art. All of such variations and modifications are within the scope of invention.