1、精選優質文檔-傾情為你奉上精選優質文檔-傾情為你奉上專心-專注-專業專心-專注-專業精選優質文檔-傾情為你奉上專心-專注-專業外文原文 Solar Tracking System: More Efficient Use of Solar Panels AbstractThis paper shows the potential system benefits of simple tracking solar system using a stepper motor and light sensor. This method is increasing power collection effi

2、ciency by developing a device that tracks the sun to keep the panel at a right angle to its rays. A solar tracking system is designed, implemented and experimentally tested. The design de tails and the experimental results are shown. Keywords Renewable Energy, Power Optimization. I. INTRODUCTION Ext

3、recting useable electricity from the sun was made possible by the discovery of the photoelectric mechanism and subsequent development of the solar cell a semi-conductive material that converts visible light into a direct current. By using solar arrays, a series of solar cells electrically connected,

4、 a DC voltage is generated which can be physically used on a load. Solar arrays or panels are being used increasingly as efficiencies reach higher levels, and are especially popular in remote areas where placement of electricity lines is not economically viable. This alternative power source is cont

5、inuously achieving greater popularity especially since the realisation of fossil fuels shortcomings. Renewable energy in the form of electricity has been in use to some degree as long as 75 or 100 years ago. Sources such as Solar, Wind, Hydro and Geo-thermal have all been utilised with varying level

6、s of success. The most widely used are hydro and wind power, with solar power being moderately used worldwide. This can be attributed to the relatively high cost of solar cells and their low conversion efficiency. Solar power is being heavily researched, and solar energy costs have now reached withi

7、n a few cents per kW/h of other forms of electricity generation, and will drop further with new technologies such as titanium-oxide cells. With a peak laboratory efficiency of 32% and average efficiency of 15-20%, it is necessary to recover as much energy as possible from a solar power system. This

8、includes reducing inverter losses, storage losses, and light gathering losses. Light gathering is dependent on the angle of incidence of the light source providing power (i.e. the sun) to the solar cells surface, and the closer to perpendicular, the greater the power 1-7. If a flat solar panel is mo

9、unted on level ground, it is obvious that over the course of the day the sunlight will have an angle of incidence close to 90 in the morning and the evening. At such an angle, the light gathering ability of the cell is essentially zero, resulting in no output. As the day progresses to midday, the an

10、gle of incidence approaches 0 , causing an steady increase in power until at the point where the light incident on the panel is completely perpendicular, and maximum power is achieved. As the day continues toward dusk, the reverse happens, and the increasing angle causes the power to decrease again

11、toward minimum again. From this background, we see the need to maintain the maximum power output from the panel by maintaining an angle of incidence as close to 0 as possible. By tilting the solar panel to continuously face the sun, this can be achieved. This process of sensing and following the pos

12、ition of the sun is known as Solar Tracking. It was resolved that real-time tracking would be necessary to follow the sun effectively, so that no external data would be required in operation. II. THE SENSING ELEMENT AND S IGNAL PROCESSING Many different methods have been proposed and used to track t

13、he position of the sun. The simplest of all uses an LDR a Light Dependent Resistor to detect light intensity changes on the surface of the resistor. Other methods, such as that published by Jeff Damm in Home Power 8, use two phototransistors covered with a small plate to act as a shield to sunlight,

14、 as shown in Fig. 1. Fig. 1 Alternative solar tracking method When morning arrives, the tracker is in state A from the previous day. The left phototransistor is turned on, causing a signal to turn the motor continuously until the shadow from the plate returns the tracker to state B. As the day slowl

15、y progresses, state C is reached shortly, turning on the right phototransistor. The motor turns until state B is reached again, and the cycle continues until the end of the day, or until the minimum detectable light level is reached. The problem with a design like this is that phototransistors have

16、a narrow range of sensitivity, once they have been set up in a circuit under set bias conditions. It was because of this fact that solar cells themselves were chosen to be the sensing devices. They provide an excellent mechanism in light intensity detection because they are sensitive to varying ligh

17、t and provide a near-linear voltage range that can be used to an advantage in determining the present declination or angle to the sun. As a result, a simple triangular set-up was proposed, with the two solar cells facing opposite directions, as shown in Fig. 2. In its rest position, the solar cells

18、both receive an equal amount of sunlight, as the angle of incidence, although not 90 , is equal in both cases as seen in Fig. 3. Fig. 2 Set-up of solar reference cells Fig. 3 Solar reference cells at rest position Fig. 4 Solar reference cells at a significant angle to the sun It can be seen in Fig.

19、4 that as the sun moves in the sky, assuming that the solar tracker has not yet moved, the angle of incidence of light to the reference panels will cause more light to fall on one cell than the other. This will obviously cause a voltage difference, where the cell that is facing the sun will have hig

20、her potential than the other. This phenomenon will result in a detectable signal at each cell, which can be processed by a suitable circuit. III. A PROTOTYPE SOLAR TRACKER The final stage involved coupling the circuitry to the motor and mounting it onto the bracket. The final product is seen complet

21、e in Fig. 5. It has a Solarex 9W solar array made of polycrystalline silicon mounted on the flanges, which was borrowed from the tech officers. Quite simply having two test subjects carried out testing. The first scenario involved removing the panel from the tracker and laying it in a flat orientati

22、on. The output was connected to a load that would dissipate 9W that would match the panels rating. 9W at 12V corresponds to a current of 0.75A, so by Ohms law; a load resistance was calculated as being 16 . A 15 50W resistor was the closest value found and was connected to the panel. The tracking de

23、vice still requires power, but a 12V battery that is connected in a charging arrangement with the solar panel supplies it. The voltage across and current through the load was monitored using two separate multimeters, and was recorded every half-hour on a clear day into an Ex cel spreadsheet. The rea

24、dings were taken on a span of days Fig. 5 A prototype solar tracker that possessed similar conditions including no cloud cover. The readings are shown below in a graph generated by Excel in Fig. 6. It is possible to calculate a percentage increase and an average increase by writing the appropriate c

25、alculations in excel. It was found that in this case, the fixed panel provided an average of 39% of its 9W, or 3.51W, calculated over a 12-hour period. By contrast, the tracked solar panel achieved an overall 71% output, or 6.3W over the same time frame. At the earlier and later hours, the power inc

26、rease over the fixed panel reached up to 400%. This amounts to an average 30% increase in power simply by maintaining the solar panel as perpendicular as possible to the sun. To ensure that power was not being wasted, the device itself was also monitored for current drawn to power itself. When the d

27、evice was at rest, an ammeter was placed in series with the battery. The total current at 12V was measured as only 4mA, which corresponded to a power dissipation of 48mW under no load. Fig. 6 Experimental results of power increase for tracked panel IV. D ISCUSSION A solar tracker was proposed, desig

28、ned and constructed. The final design was successful, in that it achieved an overall power collection efficiency increase from only 39% for a fixed panel to over 70% for the same panel on the tracking device. In terms of real value, this means that the overall cost of a system can be reduced signifi

29、cantly, considering that much more power can be suppl ied by the solar array coupled to a solar tracking device. By extracting more power from the same solar panel, the cost per watt is decreased, thereby rendering solar power much more cost-effective than previously achieved using fixed solar panel

30、s. The high outlay in a solar tracking system has been a factor that discouraged tracking as a means of increasing overall solar efficiency. Many commercial units cost in excess ofUS$2000 for a unit that can track the sun while bearing a panel of considerable weight. The device presented in this the

31、sis is capable of supporting a load of at least 8kg, the average weight of a 75W solar panel, owing to its simple construction and the high torque capabilities of the motor. The parts used for this device were also extremely low-cost, with the total value using parts found fromscrapsources being a t

32、otal of about A$30, including all electronic components and solar reference cells. The geared support was removed from an old security camera, the stepping motor from an old printer, and all other parts, excluding the 9W solar panel, were sourced from various scrap items. However, if all these parts

33、 would have to be purchased, the cost would be projected at no more than A$100. A single axis tracker such as the one made offers a great power increase over a fixed solar panel, but a two-axis tracker would provide more power still. This could be a subject for further development. Solar tracking is

34、 by far the easiest method to increase overall efficiency of a solar power system for use by domestic or commercial users. By utilising this simple design, it is possible for an individual to construct the device themselves. V. CONCLUSION A solar tracker is designed employing the new principle of us

35、ing small solar cells to function as self-adjusting light sensors, providing a variable indication of their relative angle to the sun by detecting their voltage output. By using this method, the solar tracker was successful in maintaining a solar array at a sufficiently perpendicular angle to the su

36、n. The power increase gained over a fixed horizontal array was in excess of 30%. REFERENCES 1 Fahrenburch, A. and Bube, R. 1983, Fundamentals of solar cells, Academic Press, New York. 2 Partain, L.D. 1995, Sollar Cells an d their applications, John Wiley & Sons. New York. 3 E Weise, R Klockner, R Kn

37、iel, Ma Sheng Hong, Qin Jian Ping, “Remote Power Supply Using Wind and Sola r energy a Sino-German Technical Cooperation Project”, Beijing International Conference on Wind Energy, Beijing, 1995 4 Wichert B, Lawrance W, Friese T, First Experiences with a Novel Predictive Control Strategy for PV-Diese

38、l Hybrid Energy Systems, Solar99 5 Duryea S, Syed I, Lawrence W, An Automated Battery Management System for Photovoltaic Systems, International Journal of Renewable Energy Engineering, Vol 1, No 2, Aug 1999 6 Twidell J, Weir J, Renewable Energy Systems, Chapman and Hall, 1994 7 Centre for Resources

39、and Environmental Studies, ANU, Sustainable Energy Systems Pathways for Australian Energy Reforms, Cambridge University Press, 1994 8 Damm, J. Issue #17, June/July 1990. An active solar tracking system, HomeBrew Magazine. 太陽能跟蹤系統:更有效率地運用的太陽能電池板文摘本文展示了由使用步進電機和光傳感器來簡單跟蹤太陽的內部系統。通過改進跟蹤系統，在跟中太陽光的過程中，使得太陽

40、能電池板與太陽成一個直角。該文章包含了太陽能跟蹤系統的設計、實施和實驗測試。設計細節和實驗結果如下所示：關鍵詞：可再生能源，電力優化介紹光電機制的發現和之后太陽能電池材料一種把光轉換成直流電的半導體的發現使得從太陽中提取可用的電力成為可能。利用太陽能電池板獲得的直流電壓完全可以用來驅動太陽能電池板本身的運動。太陽能電池板或者面板的使用越來越普遍，特別是在那些電線不是怎么經濟可行的偏遠地區。 可再生能源正在不斷的發展，特別是隨著化石燃料的日益減少。可再生能源在一定程度上只使用了75到100年。例如太陽能、風能、水能和地熱能都在被利用并且取得了不同程度的成功。在太陽能能在全球范圍內使用的前提下，最

41、廣泛使用的卻是水能和風能。這可能是由于太陽能電池較高的成本和較低的轉換效率。通過對太陽能發電不斷的研究，如今太陽能發電的成本可以降低到每千瓦/小時幾美分的成本，并且隨著新技術如titanium-oxide細胞的發現將進一步下跌。實驗室最高效率32%，平均效率在15%20%,因此有必要從太陽能系統恢復更多能量。這包括降低逆變器的損失,存儲的損失,和光收集的損失。光收集是依賴光源的入射角(即太陽)與太陽能電池板的角度,角度越接近垂直、獲得的太陽能越大。如果一個平坦的太陽能板被安裝在水平地面,很明顯,在漫長的一天中陽光會有一個入射角接近90。在這樣的一個角度下,電池聚集光線的能力實質上是零,從而沒有

42、輸出。到正午的過程中，入射角越來越接近0，從而電能收集穩定增強，直到太陽與電池板完全垂直，轉化率才達到最大。 就在這一天繼續向黃昏走去時,相反的事情發生了,隨著角度的增大，轉化效率向最小值邁進。 從這一背景下,我們看到需要面板維持最大功率輸出，必須使入射角盡可能的接近0。通過傾斜太陽能板不斷面對太陽，這樣就可以實現上面那個要求。感覺和跟蹤太陽位置的過程被稱為太陽能跟蹤。為了更有效地跟隨太陽,實時跟蹤記錄是必要的,因此操作中不需要額外的數據 。 傳感元件和信號處理許多不同的方法已經被提出并且用來跟蹤太陽的位置。最簡單的是使用一個LDR用來檢測在電阻表面的光強度變化的感光電阻。其他的方法,如Jef

43、f Damm 公布在“Home Power”的論文所說,把覆蓋有一個小盤子的倆片光敏傳感器用來遮擋太陽光,如圖1所示.當窗體頂端當早晨來臨時，該設備在昨天結束運動的位子如圖一狀態A所示；左光敏晶體管是打開的，產生一個信號使得電機連續轉動，直到板上的陰影返回到狀態B；隨著時間的慢慢變化，不久之后達到狀態C，這樣就打開了右邊的光敏晶體管。接著電機轉動，直到再次達到B狀態，并循環下去，直到一天結束，或直至達到最小可探測光水平。 像這樣的設計存在一個問題，一旦光電晶體管被設置在偏置條件下，會降低它的敏感性。這實際上是因為太陽能電池本身被選為傳感裝置。他們提供了一個優良的光強度檢測機制 - 因為它們對不同的光線有不同的敏感度和能夠提供接近線性的電壓狀況，可以用來確定目前的太陽偏角或角度。因此一個簡單的帶有兩個方向相反的太陽能電池板的三角形模型被制造出來，如圖2所示 就如在圖3中所看到的情況一樣，太陽能電池板在其靜止位置時，雖然入射角并不是90，但是也同時接收等量太陽光。 圖4中可以看出，當太陽在天空移動時，假設該太陽能電池板沒有還沒有移動，由于光的入射角得變化，電池板的一邊會比另一邊獲得更多的太陽光。所以這