A Study on Development of Azimuth Angle Tracking Algorithm for Tracking-type Floating Photovoltaic

System

Young-Kwan Choi 1,1, In-Soo Kim1, Sung-Taek Hong1 and Heung-ho Lee2

1 K-water (Korea Water Resources Corporation), Republic of Korea 2 Chungnam National University, Republic of Korea

Abstract. Since floating facility with mooring system has the overall structure move and rotate by wind or environmental variables, the error in azimuth angle must be compensated using GPS receiver and geo-magnetic sensor. Accordingly, when the existing photovoltaic tracking algorithm is applied to floating photovoltaic system as is, optimal photovoltaic tracking cannot be performed. In this paper, a tracking-type floating photovoltaic model was manufactured to develop an effective azimuth angle algorithm for photovoltaic tracking in floating condition, and the developed algorithm was applied for verification.

Keywords: floating photovoltaic system, solar tracking algorithm

1 Introduction

PV is divided into fixed-type where the angle of PV module is fixed at a certain angle, and tracking-type where the azimuth and altitude of the sun is tracked to receive the sunlight perpendicular to the module surface. The tracking-type PV is a high-efficiency generation system that produces a greater amount of electricity by adding real-time sun-tracking function to the PV module. In general, it is known that on the ground, the power generation of a dual-axis tracking-type is 30% greater than a fixed-type.

Tracking-type PV system is designed to detect the existence of effective PV to track the location of the sun with solar sensor, and automatically track the sun with precision by program even when it is cloudy or rainy. For this, a separate mechanical device is used to rotate the PV module, but the number of unit PV modules that can be rotated at once is limited, and frequent malfunctions and such require a great deal of effort in maintenance.

The tracking-type system used on the ground has limitations as to PV modules (below 3kW) that can be operated through a single tracker and the utility is also limited due to frequent malfunctions. Due to such factors, the structure must be designed with cantilever at a single rotation point, and as the cantilever length is limited due to the influence of self-weight or external force, there is the weakness that the cost of the structure rises as the unit module capacity increases.

In floating PV, the external forces including self-weight of the structure is

Advanced Science and Technology Letters Vol.51 (CES-CUBE 2014), pp.197-202

http://dx.doi.org/10.14257/astl.2014.51.45

ISSN: 2287-1233 ASTL Copyright © 2014 SERSC

transferred to the water through the buoyancy in the gravitational direction, so the length of the structure that can resist the gravitational direction can be designed with relatively more freedom. Also, as it floats on the water, it can rotate with a small amount of energy even if the unit rotation capacity is large (over 20kW), the structure can be made simpler than ground tracking-type if tracking-type is applied to floating PV system, thus reducing malfunction risk and increasing efficiency[1-10].

The aim of this paper is to examine types of tracking-type systems for development of a tracking algorithm for maximum power generation in floating condition and to test the developed algorithm through application in the model.

2 Tracking Algorithm for Floating Photovoltaic System

2.1 Concept of Tracking Algorithm

Tracking the location of sun on the ground include the method of using optical sensor (passive), the method by astronomical calculations (active), and the method combining the two.

The sun tracking device using optical sensor involves operation of an actuator to operate the sun tracking system using the difference of radiation intensity detected through photo sensor. The sun tracking method using astronomical calculations involve using information of longitude and latitude of the tracking system installation location and performs calculation or computation by time so that it is in the optimal angle and linear direction with the sun at all times.

The sun tracker using optical sensor is operated by the sensor response characteristics, and thus has the weakness of not being able to make an accurate sun detection in an environment with diffusion such as under cloudy weather, and thus tracking accurate location with astronomical calculations is used to supplement.

As the sun location information is acquired by an astronomical method, it can track the sun even when the sun does not appear for a long period of time, and the malfunction by foreign substance can be limited within a certain range, so while there is the advantage of reducing errors in sun tracking, there is the weakness that the system initial position must be accurate.

On water surface, unlike on ground surface, the entire structure moves and rotates by wind or other environmental variables even if the mooring system is installed, so an error may occur to the azimuth angle[1-10].

In order to compensate for this error, GPS receiver and terrestrial magnetism sensor have to be used to compensate for the twisted angle and the algorithm minimizing the error from external disturbance on water surface has to be applied. Thus, tracking performance on water must be improved by a complex type that integrates optical sensor method and astronomical method. Therefore, the floating photovoltaic tracking method applied in this paper detects any variations in the direction of structure by wind and surface flow using sensor and corrects such variations. Program

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tracking (astronomical calculation) was selected as an auxiliary method to prevent dead operation in absence of the sun.

2.2 Azimuth Angle Tracking Algorithm for Floating Photovoltaic System

Manual Tracking Algorithm is a method for tracking position of the sun using photovoltaic sensor, as shown in Figure 1(a). It is a method that detects position of the sun for tracking. The sensor stops operating when the west limit switch is turned on (sunset) and moves to the position of the east limit switch for operation on the next day (sunrise).

Active Tracking Algorithm is an algorithm that tracks position of the sun by computing hourly azimuth angle based on astronomical position, as shown in Figure 1(b). It is operated so that current azimuth is the same as pre-entered astronomical azimuth.

(a) Manual Tracking Algorithm (b) Active Tracking Algorithm

Fig. 1. Tracking Algorithm Flow Chart

3 Algorithm Application Experiment

3.1 Tracking-type Algorithm Application Experiment

For development of the tracking-type algorithm, a scaled model similar to an actual structure was manufactured and launched on water to test with forward / reverse rotations using small motor.

Operation methods included manual rotation with forward / reverse rotation buttons, movement along the light using optical sensor (azimuth sensor), and movement for given time according to astronomical timer. Figure 2 shows the test of tracking-type floating photovoltaic model.

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Fig. 2. Test of Floating Photovoltaic Model

3.2 Forward and Reverse Rotation Test

The rotor is only operated when forward / reverse button is pushed, used for manual operation during emergency.

Fig.3. Forward and Reverse Rotation Control using the Control Panel

3.3 Manual Tracking Algorithm

Movement of the rotating structure along the light was experimented using an optical sensor (azimuth sensor). Since the model rotor could not sustain weight of the optical sensor, the sensor was attached outside the structure instead of the rotor for testing. (Optical sensors on an actual tracking-type floating photovoltaic system are installed on the module frame within the rotor.) An artificial sun was created using halogen lamp, which is equivalent to sunlight, and the lamp was moved to left / right of the optical sensor to test forward / reverse rotation of the rotor.

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Fig. 4. Solar Tracking Test

3.4 Active Tracking Algorithm

The model was moved for a given time according to the timer and tested to see if it comes to a stop. The experiment with the timer was conducted for development of astronomical tracking algorithm. Time and angle of forward / reverse rotation for small motor were calculated to rotate from the east to the west during the day, and it was automatically moved to the east once it arrived at the stop sensor on the west.

Fig. 5. Moving the East by the Limit-Sensor

4 Conclusion

On water surface, unlike on ground surface, the entire structure moves and rotates by wind or other environmental variables even if the mooring system is installed, so an error may occur to the azimuth angle.

In order to compensate for this error, GPS receiver and terrestrial magnetism sensor have to be used to compensate for the twisted angle and the algorithm minimizing the error from external disturbance on water surface has to be applied. Thus, tracking performance on water must be improved by a complex type that integrates optical sensor method and astronomical method. Thus, tracking

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performance on water must be improved by a complex type that integrates optical sensor method and astronomical method.

In this paper, manual / active tracking algorithms for floating photovoltaic system were demonstrated by model experiment.

Tracking performance can be improved in the future by adding an algorithm that sequentially rotates 1~2 structures to reduce the force inflicted on 4 rotating structures during tracking of azimuth angle and by considering time speed, time and angle of rotation during operation of actual motor.

Acknowledgments. This research was conducted under the financial support of the Ministry of Land, Infrastructure and Transport ’ s Construction Technology Innovation Program(Project number : 11technical renovation C-03, Development of ICT fusion technology for the commercialization of the floating PV system).

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