It is good known that in theory, 41 % more sunshine is available by tracking the PV faculty to follow the day-to-day class of the Sun, comparative to fixed installings. The overall aim of this survey is to develop a control algorithm that improved public presentation and dependability the two-axis solar tracker. To accomplish this end, this survey dressed ore on optimising the LM3S811 based accountant board, thrust hardware and package.
Keywords: embedded system design, two-axis Sun trailing, control algorithm.
Solar energy systems and equipment such as PV and twenty-four hours illuming systems, solar aggregators, and solar-powered heat engines work best when their aggregators aim straight at the Sun. Adding a solar tracker to these systems increases their efficiencies at the disbursal of initial and operational costs and system complexness. It has been estimated that the usage of a trailing system, over a fixed system, can increase the power end product by 20 % – 40 % with cost addition 10 % -30 % [ 1-3 ] .
Since the Sun ‘s place in the sky alterations with the seasons and the clip of twenty-four hours, tracker is used to aline the aggregation system to maximise energy production. Several factors must be considered when finding the usage of trackers. Some of these include: the solar engineering being used, the sum of direct solar irradiation, feed-in duties in the part where the system is deployed, and the cost to put in and keep the trackers. Concentrated applications like concentrated photovoltaic panels ( CPV ) or concentrated solar power ( CSP ) require a high grade of truth to guarantee the sunshine is directed exactly at the focal point of the reflector or lens.
The two basic classs of trackers are individual axis and double axis. Single axis solar trackers can either hold a horizontal or a perpendicular axis. In concentrated solar power applications, individual axis tracker is used with parabolic and additive Fresnel mirror designs. Dual axis solar trackers have both a horizontal and a perpendicular axis leting them to track the Sun ‘s evident gesture virtually anyplace in the universe
This paper presents a control scheme for a two axes solar tracker that is executed in an ARM based Stellaris L3S811 microcontroller. Correct sun place is inferred from the GPS. The proposed control scheme consists of a combination between ; an unfastened cringle tracking scheme, and a closed cringle scheme. The overall aim of this survey is to develop a control algorithm that improves public presentation and dependability the two-axis Sun tracker. To accomplish this end, this survey concentrates on optimising the accountant board, thrust hardware and package.
Two-axA±s Sun tracker
The Sun ‘s beams can be decomposed into two constituents, one perpendicular to the panel surface, and the other analogue to the surface, where merely the former radiation can be received by the panel. Therefore, the angle between the Sun ‘s beams and the normal of the panel which is called the incident angle should be every bit little as possible. Incidence angle alterations with the diurnal and seasonal fluctuations. Therefore, the fixed-installed solar aggregators can non to the full absorb the solar radiation energy. If at any clip by automatically tracking solar aggregators, panel place can be adjusted harmonizing to the Sun ‘s flight to cut down the incidence angle ; it will be able to absorb more solar radiation energy than the fixed panels in the same irradiation conditions. The panel of dual-axis Sun tracking system rotates around the two reciprocally perpendicular shafts, AZ shaft and lift shaft, shown in Fig 1. It will track the Sun ‘s AZ angle and lift angle, so that the panel can accomplish incident angle of 0.
Two methods are normally used in solar trailing to place and follow the place of the Sun at any blink of an eye of clip between dawn and sundown: the closed cringle control method and the unfastened cringle control method. The closed cringle control method uses several feedback detectors such as LDR, photodiode, light-intensity detectors, mention cells and a signal processing circuit [ 4-6 ] . The signal processing circuit compares the end product signals of the detectors and operates on a feedback cringle with the coveted signal status. The end of the cringle is to bring forth maximal entire mistake signal from detectors by continuously seting the tracker way until the shadow on the detectors is the lower limit. A drawback of the closed cringle control method is that it can non efficaciously track the Sun on a cloudy twenty-four hours without a robust algorithm.
Fig. -Structure of the two-axis Sun tracker.
The unfastened cringle control method uses the longitude and latitude informations of the solar tracker location to find and track the place of the Sun [ 7, 8 ] . It has the advantages of easy scheduling and high truth. The system is simpler and cheaper than the closed-loop type of Sun tracking systems [ 9 ] . It does non detect the end product of the procedures that it is commanding. However, a fixed get downing way of the tracker at dawn every twenty-four hours is required in this method. Therefore, the get downing way of the tracker must be corrected from clip to clip. Consequently, an open-loop system can non rectify any mistakes so that it could do and may non counterbalance for perturbations in the system.
Specifying Elevation and Azimuth Angles
The algorithm for Sun trailing uses the solar lift, i?±e and azimuth, i?±A angles computed at the solar tracker location. The tracker must be aligned horizontally to find the lift and AZ angles accurately along with the hr and decline angles with regard to the heavenly equator or plane as depicted in Fig.1. Solar lift, i?±e is the angle between the skyline and the line linking the beginning and the Sun that is, the complement of the zenith angle. Solar AZ, i?±A is the angular supplanting of the projection of the line to the Sun onto the horizontal plane from the south axis.
The solar lift angle, i?±e, of the orientation system in the perpendicular plane, ?e, can be calculated as follows [ 9 ]
sini?±e=sini?¤ sini?¦ +cosi?¤ cosi?¦ cosi?· ( 1 )
e is the lift angle of the system
i?¦ is the latitude.
is the hr angle ( 15 & A ; deg ; / hr ) , where ? = 0 at local midday.
is the solar decline, where ? is calculated from
Cooper ‘s equation,
( 2 )
N is the twenty-four hours of the twelvemonth ( 1 – 365 ) with N = 1 stand foring the 1st of January.
Fig. – The relation between lift and zenith angles.
The azimuth angle of the system in the horizontal plane, ?A, is calculated as [ 9 ] .
( 3 )
The solar trailing system normally returns to its initial remainder place after sundown, and starts to track the Sun after the Sun rises above the skyline. The dawn and sunset times can be calculated utilizing [ 13 ] for system location.
DesA±gn and application
3.1. Mechanical Design
The panels ‘ support construction was designed with two grades of freedom in order to change the disposition and orientation. Besides, the construct of the panel ‘s support every bit good as the system that allows this support to go around around the two axes was developed. The tracker is composed of a fixed base which is straight on the land, holding a mechanism that connects the base to the back uping construction of the panels. This mechanism consists of two parts, which have a grade of freedom ( from each other ) in two axes. For altering the disposition of the construction, extra linear actuator is mounted to the solar tracker control system.
Linear actuators are highly precise by design, particularly when compared to pneumatic and hydraulic solutions. Screw based mechanical additive actuators allow to progress or withdraw the motivation rod by highly little increases, which is required for the exact placement of solar tracker. Electric additive actuator consumes highly low electricity and are available in 12 Volts d.c. it can be powered by the solar panel itself supported by a battery. Linear actuators can be remarkably little, particularly when sing the scope of gesture that is required for traveling the Sun tracker. Photograph of the mechanical construction is shown in Fig. 3.
Fig. – Mechanical construction of the Sun tracker.
3.2. Hardware Design
The hardware design combines the embedded microcontroller with two DC motor drivers, rotational DC motor, DC motor controlled additive actuator, solar rotary motion mechanism, GPS, pyranometer, wind gauge, tilt switches and MEMBS based inclinometer. A general block diagram of the control system is shown in Fig. 4.
Global placement system ( GPS ) is connected to the microcontroller via a standard consecutive RS-232 port. GPS sends to the microcontroller sentences, that contains a twine of characters, continuously. These sentences chiefly include longitude, latitude, height, day of the month and clip for location where GPS is placed. Since microcontroller has the existent clip clock circuitry, it is moderately accurate over short periods, but it needs standardization sporadically. As a consequence, the GPS clock signal is used to update the microcontroller ‘s internal clip sporadically and therefore effects of the long term mistakes are eliminated.
As portion of the attempt to better solar tracker dependability and better understanding public presentation, a pyranometer is being added to solar tracker. This pyranometer allows the informations acquisition system to mensurate exactly the irradiance witnessed by the PV faculties on that tracker, and therefore better supervise the impact of the tracking algorithm on the energy end product of the system.
Solar tracker steps tilt angle with potentiometer that has long-run dependability job. A higher dependability option is a solid-state inclinometer. It has three chief advantages ; inherently higher dependability, higher declaration less than 0.1 & A ; deg ; , direct measuring of angle. In this undertaking, micro electromechanical systems based on electronic inclinometer ADXL345 is used [ 11 ] . Digital end product informations is formatted as 16-bit two ‘s complement and is accessible through either a SPI ( 3- or 4-wire ) or I2C digital interface The inclinometer would typically be mounted straight underneath a tracker ‘s plane, from where the disposition can be measured.
Fig. – Sun Tracker control system block diagram.
The solar tracker is fitted with bound switches to guarantee robust operation. A micro roller switch mounted on the base of the solar tracker prevents multiple revolution completion of the AZ tracking phase. The solar aggregator besides includes two more bound switches on the zenith tracking phase to forestall over travel harm to the additive actuator mechanism. The initial reset balance usage tilt switches. The mechanism include four tilt switches ( E, West, south and north ) To protect tracker constituents from over air current velocity, system besides requires an wind gauge to mensurate wind velocity.
Consequently, we need powerful and cost-efficient microcontroller to link all these parts and manage to track the Sun. It must hold two consecutive port, ( UART ) one for communicate computing machine the other 1 for GPS, two PWM signals for motor A and motor B, one I2C port for solid-state inclinometer, hardware counter input for wind gauge, parallel input for pyranometer, at least four digital inputs for tilt switches. In add-on, these characteristics we need package development tools for microcontroller. Sing the computation of the mentioned before, 32-Bit Stellaris microprocessor LM3S811 which is optimized for small-footprint embedded applications, fits best to the Sun tracker system.
TI Stellaris LM3S811 microcontroller has a Reduced Instruction Set Coding ( RISC ) ARM nucleus, internal oscillators, timers, UART, USB, SPI, pull-up resistances, PWM, ADC, parallel comparator and watch-dog timers are some of the characteristics [ 10 ] .
The developed Sun tracking algorithm enables high-precision finding of Sun angles and times for dawn, solar midday and sunset year-round. The flow chart of the algorithm is drawn in Fig. 5. The computation of the Sun angles with the Sun tracking algorithm package merely requires the specification of the day of the month, clip and exact longitude, latitude and lift of the location through a GPS system.
Fig. – Flow chart of Sun tracking algorithm.
The algorithm we developed for the control of the Sun tracker is composed of two chief subdivisions. In the input subdivision, the solar lift and AZ angles every bit good as dawn, sundown, solar midday and present solar times are calculated harmonizing to subdivision 2 and used as shared variables in other parts of the package. When the system starts, Stellaris foremost sets tracker to the place place and so takes GPS information to cipher the Sun set and rise times. The present solar clip is compared with the dawn and sunset times to find whether tracking should get down or halt. At dark clip, it waits following sample clip. Sample clip period may be defined harmonizing to proficient restraints. First restraint is GPS hot start clip that is 1 second for GPS. It can non be shorter than this value. The other restraint is the energy consumed by motor A and B during one tracking measure. We set sample clip to 2 minute during experimental work. The present solar clip between dawn and sunset clip ‘s Stellaris reads pyronometer value to look into if there is adequate solar radiation to bring forth power. Otherwise, Sun tracker stays at place place until solar radiation rise to lower bound of solar radiation. After solar radiation reaches the coveted value, so algorithm reads anemometer value to specify whether the Sun tracker can travel safely. If non, Sun tracker stays at place place at least during one sample clip. Otherwise, it starts tracking the Sun.
In the end product subdivision of the algorithm, the package takes azimuth, ?A, and lift, ?e, angles from shared variables and converts them to drive gesture. The deliberate angles ?e, ?A, are so subtracted from the old place values. Harmonizing to the obtained angle difference and their marks, microcontroller sends PWM and way signals to the motor accountants. Motor A and motor B takes solar panel to the new place.
Motor A can drive solar panels to turn in the horizontal plane in order to track the alterations in AZ angle ; its positive place is westbound. Similarly, motor B can drive solar panels to turn in the manner of fliping so as to track the alterations of solar lift angle ; its positive way is downward. At the terminal of tracking, the place of mechanisms demands to be defined. The electronic inclinometer ADXL345 sends x, Y, omega axis values to the Stellaris. This digital axis values are converted to angles by the microcontroller. By comparing the mensural angles with deliberate angles, the two motors take different motions to complete come up to the coveted place of the solar panel. Finally, when this twenty-four hours is over, the system backs to the place place to wait for the following twenty-four hours.
ResultS and dA±scussA±on
Sun tracker was tested both in the research lab and out-of-doorss utilizing SM-55 solar panel [ 12 ] . During the out-of-door trial, the Sun tracking system was moved to outside of a edifice so that we could compare the consequences between fixed place and two-axis Sun tracking systems. During a 24-hour test period, the two-axis solar tracker was required to run for about 2 proceedingss every hr to keep proper alliance with the Sun.
Fig. – Outdoor trial consequences of sun tracker.
During the trial procedure, solar panel charged to the battery, and solar panel current and electromotive force values were measured and stored every minute utilizing a information lumberman. End of the twenty-four hours, the solar panel, charged the battery up to 408.2 Watt-hour energy for about 11 hours. The recorded information on the twenty-four hours 5.5.2012 proved that the two-axis solar tracking PV panel produced more energy than the fixed 1 with about 40.7 % .
In this survey, a cost effectual two-axis Sun tracker has been developed. The ARM Cortex-M3 nucleus microprocessor successfully calculated the tilt angle of the solar panel in order to look into the accurate Sun lift angle. The placement technique, which has been investigated by the DC motor and additive actuator, reduced the mistake in turn uping the lift AZ angles to 0.1 & A ; deg ; . The proposed tracker has increased the energy collected by 40.7 % .