The Ninth International Conference on Electronic Measurement & InstrumentsICEMI’2009 All-Weather Automatic Solar Tracking Method Applied in Forest Fire Preventio Jing Xu1 Kaihua Wu2 Li Ma3 School of Automation, Hangzhou Dianzi University, Hangzhou 310018, China Email:
[email protected] Abstract – The monitoring equipment of forest fire prevention usually needs all-weather supply of electric power. But most of solar power systems applied in forest fire prevention use fixed-mounted solar panels. This problem results in low efficiency of electricity generation. Thus the area of solar panels has to increase to meet electricity demand of the equipment. An all-weather automatic solar tracking method was proposed, which combined the photoelectric detection and the solar trajectory tracking modes. The method used a sunlight intensity sensor to estimate weather conditions firstly. Then it utilized a solar position sensor and a solar trajectory algorithm to determine the changes of solar position. Finally, different tracking models were taken to track the sun in sunny, cloudy and rainy days. Through simulation experiments, this method could effectively reduce the impact of weather change and ensure to track the sun stably and accurately all weather. Keywords – automatic solar tracking, photoelectric detection, solar trajectory tracking. In Section IV, we will show the solar tracking software designed according to the proposed method; In Section V, the results of simulation experiments will be analysed. .AUTOMATIC SOLAR TRACKING METHOD The novel all-weather automatic solar tracking method combined the advantages of the photoelectric detection and the solar trajectory tracking modes: (1) Sunny days: Firstly, trajectory tracking mode is implemented; secondly, photoelectric tracking mode is used. (2) Cloudy days: Because photoelectric tracking mode is invalid, trajectory tracking mode is used only. (3) Rainy days: The solar light is too dark, so the tracking is suspended. .INTRODUCTION Forest fire prevention is an important application of solar power. At present, the solar panels of many solar power systems used to forest fire prevention are fixed-mounted. These systems have the disadvantage of low efficiency. Although some efficient solar power systems with tracking function are used, their tracking methods are not mature enough to guarantee themselves operating stably all-weather[1-2]. The common ways used to solar tracking are photoelectric detection and solar trajectory tracking modes. The former uses a photoelectric sensor to monitor the solar movement, and then it controls the mechanisms to track the sun. This mode has high sensitivity, but it is easy to be interfered by the weather and miscellaneous light. The latter controls the mechanisms of tracking by calculating the solar trajectory. This mode doesn't subject to environment, but it has accumulated error which can't be eliminated by it [3-5]. In view of this situation, an all-weather automatic solar tracking method applied in forest fire prevention was proposed. Solar power systems using this method can provide a reliable and efficient electric power for monitoring equipment of forest fire prevention. This paper will be structured as follows: In Section II, the idea of the all-weather solar tracking method will be explained; In Section III, the specific design and implementation of the proposed method will be described; Fig.1. Schematic diagram of all-weather automatic solar tracking system. The dashed part in Fig. 1 shows the schematic diagram of automatic solar tracking system. The trajectory tracking module calculates theoretical values of solar position (solar elevation angle and azimuth angle). The photoelectric detection module detects the signals of the solar position. The single-chip microcomputer (SCM) control module combines theoretical values and detected signals, and then drives two-dimensional mechanisms of tracking to track the sun. The photovoltaic power supply module can store and convert the electric power produced by the solar power system. Finally, it provides the power for forest fire monitoring equipment. .DESIGN AND IMPLEMENTATION A. Photoelectric detection tracking The photoelectric detection tracking was achieved by using the solar position sensor and sunlight intensity 1-805 _____________________________ 978-1-4244-3864-8/09/$25.00 ©2009 IEEE Photodiodes "A" and "C" respectively correspond with quadrants "A" and "C". (a) (b) 1) Horizontal coordinate system Horizontal coordinate system is a celestial coordinate system that uses local horizon circle as the fundamental plane. Circuit diagram of sunlight intensity detection. and zero in the south [7]. The value of "A" is positive when the sun is in the west of south.2. Schematic diagram of horizontal coordinate model 2) Calculate of solar elevation angle and azimuth angle In horizontal coordinate system. On the basis of the above sensor. 2). Using the solar trajectory. the distribution areas of the spot in four quadrants will change. the distribution areas of spot in four quadrants "A". solar elevation angle H and azimuth angle A for any location and any time on earth can be determined only by the current sun declination 1-806 . the SCM can control the mechanisms to produce the sun tracking. and the output signal of the four photodiodes will change accordingly. When the solar incidence angle is vertical. 1) Solar position sensor The proposed sensor is mainly constructed by a four-quadrant photoelectric detector and a cylinder with a loophole (see Fig. The move of the spot in the directions of x-axis and y-axis shows the changes of solar elevation angle and azimuth angle respectively. B. The photoelectric current of the cell is proportional to sunlight intensity. negative in the east of south. the detection circuit of solar position was designed. The circuit transfers the signal of sunlight intensity into voltage signal that could be sampled by the SCM. (a) Four-quadrant detector. The sunlight passes through the loophole and forms a spot in the surface of four-quadrant detector. 2) Sunlight intensity sensor ICEMI’2009 Sunlight intensity sensor is constructed by a silicon photoelectric cell and amplifiers. Fig. 5. 5). "H" is the angle between solar light of incidence and the horizon.The Ninth International Conference on Electronic Measurement & Instruments sensor. 3 only shows the detection circuit of solar azimuth angle. the solar position can be determined. Fig. 3. which are the detection circuit of solar elevation angle and azimuth angle. and then controls the mechanisms to track the sun. Fig. "A" is the angle between solar light of incidence projected on the ground and the south of the horizon. In this way. These voltage signals can be sampled by the SCM. The output voltage signals Ux and Uy are proportional to the changes of solar azimuth angle and elevation angle respectively. it's positive and gets the maximum at noon. 4. If the sun moves. The SCM transfers the voltage signals into angle signals by using the addition and subtraction algorithm of four-quadrant [6]. Fig. These diodes have good photoelectric consistency and each of them corresponds to a quadrant of Cartesian coordinate system. Fig. "B". (b) Cylinder with loophole. The four-quadrant detector consists of four photodiodes. It includes two absolutely symmetrical circuits. Both of the sensors were fixed on solar panels and parallel with the board of panels. the SCM judges the weather conditions in order to choose different tracking models. Schematic diagram of solar position sensor. According to the voltage signal. 4 shows the detection circuit of sunlight intensity. It utilizes solar elevation angle "H" and azimuth angle "A" to determine solar position (see Fig. "C" and "D" are equal. Circuit diagram of solar azimuth angle detection. This pattern can determine solar trajectory with the help of astronomical formulas. Solar trajectory tracking The solar trajectory tracking used solar elevation-azimuth angle pattern which based on horizontal coordinate system. Fig. Otherwise. Considering the solar power system applied in forest fire prevention doesn't require very high tracking accuracy. tracking the sun frequently in order to pursuit high power generation efficiency is not worth the candle. its latitude is 30°16'. two tracking conditions are judged firstly.The Ninth International Conference on Electronic Measurement & Instruments . Besides. They are mechanisms of tracking locating at benchmark position and current time between sunrise and sunset. Based on the above algorithm. Flow chart of solar tracking software. according to weather conditions. so as to reduce the accumulated error of solar trajectory tracking mode. The error of calculated values is within the range of ±0. Firstly. In the tracking cycle. The threshold values are set by the control system according to tracking accuracy. Similarly. . so the tracking times is about 60 times per day. so as to access to the tracking cycle rapidly. the tracking system will set the adjust values generated by photoelectric tracking module to zero. At the beginning of the program.1°. Secondly. The solar elevation angle and azimuth angle at start position can be calculated by solar trajectory algorithm. 7. Only if the two conditions are satisfied. In normal situation that is sunny weather. 9). it controls mechanisms of tracking to turn back to the benchmark position. So we determined 10 minutes as the value of time interval. the SCM calculates solar elevation angle H and azimuth angle A by using solar trajectory algorithm and controls mechanisms to implement the solar tracking. the program controls the mechanisms to move to the start position. motor M1 and motor M2 are tracking motors of the mechanisms. 6. the power consumption caused by frequent tracking can be avoided. At the same time. Fig. Besides. In this way. 6. C. in order to reduce the impact of climate changes on the tracking system. It is supposed that the system works 10 hours per day. Specific tracking is completed by the subroutines of solar trajectory tracking and photoelectric detection tracking (see Fig. which is the position of solar panels toward the local south and paralleling with the horizon. M1 can drive solar panels to turn in the horizontal plane in order to track the changes of azimuth angle. In Fig. certain power generation efficiency can also be guaranteed. 7. the software used to solar tracking is designed. its positive position is westward. the next tracking was enforced. Thus once tracking is completed. Combination of two tracking modes The closed-loop control system constructed by the two tracking modes is shown in Fig. they are sunny model. then compares h and a with the threshold values H0 and A0. According to approximate time of sunrise and sunset. the solar tracking system uses the two modes to complete once tracking together. The formulas * sin + cos * cos * cos ) ICEMI’2009 H = arcsin (sin When the sunlight intensity is weak. The program flow is shown in Fig. Schematic diagram of closed-loop control system for solar tracking. 8. M2 can drive solar panels to turn in the style of pitching so as to track the changes of solar elevation angle. the mechanisms need not to track the sun again. 8 and Fig. So the feasibility of the algorithm was proved. its positive 1-807 . If the adjusting values are bigger than threshold values. Fig. three different models are selected to track the sun. the SCM uses photoelectric detection mode to get the adjusting values h and a of the current solar elevation angle and azimuth angle. the software can distinguish day and night. After a certain time.sin ) / (cos H * cos )) and the local latitude . . according to the date and time provided by the external clock. the SCM will control the mechanisms to track the sun further. Similarly. Taking Hangzhou as an example. cloudy model and rainy model.SOFTWARE DESIGN According to the all-weather automatic solar tracking method. a program was developed to calculate the theoretical values of solar elevation angle and azimuth angle. the hour angle are as follows: (1) A = arcos ((sin H * sin (2) The detailed calculation process can be found in references [8-10]. Delay time represents the interval of tracking circle. the setting of threshold values in photoelectric detection tracking is also used to prevent the frequent tracking. 63 54.2007C13062) and Zhejiang Province College Students Innovation Project.95 -49. So it is necessary to distinguish the two conditions to control the two motors easily.00 0. So the above research provides a good experimental basis for the application of this all-weather tracking method in the field of forest fire prevention.30 -55. As can be seen from the data. The X' and Y' axes represent the horizontal and vertical axes of the turntable respectively.98 -46.73 13. M1 always turns westward.87 -1. once tracking angles of the cycle are changing.98 -60.01 -1. the experimental system can track the sun stably and accurately. But the solar trajectory tracking mode had been proved on the experiment platform.98 3.65 41. To sum up.42 2.76 -1.82 -1. which are used to track the changes of solar azimuth angle and elevation angle.98 16.72 -58.98 2. and the corresponding tracking system had shown a good running state. Data of solar tracking experiments (Unit: degree).77 2. Because.12 -65.93 52. Some simulation experiments had been done by using the device and solar tracking software. when the mechanisms locate at benchmark position.20 3.72 -52. Solar position A 0 1 2 3 4 5 6 7 8 9 10 08:53 09:03 09:13 09:23 09:33 09:43 09:53 10:03 10:13 10:23 10:33 -69. the photoelectric detection tracking module has been designed.31 10. the position of mechanisms needs to be judged. M2 always turns downward. Otherwise. 9. The once tracking angles mean the volumes that the axes turned during one circle.65 39. 9.00 0. The subroutine of photoelectric detection tracking in Fig.34 H 37. . the all-weather solar automatic tracking method can effectively detect the weather conditions and take appropriate tracking model.90 -2.69 7.91 3. The authors would like to acknowledge Zhejiang Global Photovoltaic Technology Co. item number represents tracking circle.71 11.62 -1.63 43.60 18.05 22. By comparing the angle signals with threshold values.01 2. samples voltage signals and transfers them into angle signals.13 -1.49 47.00 0.29 14.98 3. Table1. Ltd for its support of the experimental solar panels. Flow chart of solar trajectory tracking subroutine. After a period of continuous operation. an experimental tracking device was designed.25 25. At present.93 2.95 6.14 Item number Current time Fig. The data was got from the solar tracking experiment depending on the trajectory tracking mode on March 30th in Hangzhou. it reflects the basic law of solar moving.58 2. It reduced the impact of weather change and accumulation errors on the tracking system.The Ninth International Conference on Electronic Measurement & Instruments position is downward.53 8.04 5. The interval of the circle is 10 minutes. Its simulation experiment is still in progress.07 19. The total tracking angles mean the total volumes that the axes turned since the beginning of the track.01 1.90 2. 8. 1-808 .26 2..36 49.03 -67.18 50.25 55. Table 1 shows the experimental data. ICEMI’2009 controller and a PC.31 16. the two motors take different movements to finish photoelectric detection tracking.EXPERIMENTAL RESULTS AND CONCLUSION Based on the hardware of a solar panel.84 9.00 1.58 45.44 -1.79 Once Total tracking tracking angles angles X' Y' X' Y' axis axis axis axis 0. Flow chart of photoelectric detection tracking subroutine. In Table 1.70 -1.53 13. a twodimensional electric turntable. In this subroutine of solar trajectory tracking.78 -43.91 -1. ACKNOWLEDGMENT Fig.11 -62. a dual-axis motion This work is supported by Zhejiang Science and Technology Project (NO. 69-72. Vol..“Calculation of ground photovoltaic systems by meteorological data”. 2007.1-3.. [1] ICEMI’2009 1-809 . 25. [8] Karabanov S. [9] Bingzhong Wang. [2] Douglas J. 2003. Dec. April. Vol. 2008. [7] Si-Yang Liu and Chun-Sheng Wu. Jan. pp. Vol. [6] Long-Ling Feng and Ren-Liang Deng. [3] Xiao-Nian Zheng and Qiao-Yang Huang. pp. Acta Energiae Solaris Sinic. Optics and Precision Engineering. 4. 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