| 摘要: | 本文透過長期（四個月）的戶外測試比較三種不同的追日偏差量測設備，包含PSD (position sensitive device)、CCD (charged diode device)和webcam，以直射日照和總日照的比例(Ir)和晴朗指數(Kt)來定義晴天和多雲，晴天和多雲的區別Ir和Kt分別為0.7和0.6以及0.3和0.4。結果顯示在晴天時（對應水平總日照GHI>700 W/m2），三台儀器量測的偏差角度約在0.2o~0.3o左右，三者解析追日偏差的能力相仿。而在多雲時（對應GHI<500 W/m2)），三台儀器會有差異，以8/12這天為例，PSD、CCD和webcam當日平均偏差角分別為0.23、0.46和0.49，此時的PSD平均偏差角明顯小於CCD和webcam，主要原因是在低日照時，光感測器會停止正常運作，使得追蹤器無法正常的追蹤太陽，隨著停止追日時間的長短，直接影響了追蹤器和太陽的偏差角度，當追蹤器和太陽的偏差角度較大時，PSD儀器無法接受到大量的直射日照來判斷太陽的位置，須等到追蹤器正常追日時，才能有效的判斷偏差角度，因此無法就此認定PSD比CCD和webcam可靠。
整體來說PSD採樣速度快(2~9 μs)，無需透過影像處理來判斷太陽質心位置，但是在低日照和多雲時無法有效判斷太陽質心位置，CCD和webcam則可以透過光學鏡頭和影像處理來提高尋找太陽質心位置的準確度，因為CCD可以更換不同的光學鏡頭因此拍攝的太陽影像清晰優於webcam，webcam的優點在於其成本低廉（約7000元），在日照條件好的時候也能穩定的判斷偏差角度。
此外透過PSD電壓值與DR01直射日照計做關聯分析，使得PSD在量測偏差角度同時也具備量測直射日照量之功能，PSD電壓轉換直射日照與DR01直射日照計在經過戶外實測時，證實其平均誤差皆小於4%，有一定的可靠性。
;In this study, through a long-term outdoor test comparison of three different measuring of offset devices for sun-tracking, including PSD (position sensitive device), CCD (charge-coupled diode) and webcam, the results show a clear day, the amount of the deviation angle of three instruments are measured at approximately 0.2o-0.3o around, but in cloudy, the three instruments will be a slight difference, this time the PSD will be significantly less than the average deviation angle CCD and webcam, but this does not mean that the PSD measurement instrument to the average deviation angle is small so than CCD and webcam reliable cause of this difference is due to the low sunshine PSD unable to effectively discriminating position of the sun.
Overall PSD sampling speed, image processing is not required to determine the sun through the centroid position, but in the low sunshine and cloudy when not effectively determine the centroid position of the sun, CCD and webcam is possible through the optical lens and image processing to improve Looking for the accuracy of the centroid position of the sun, while the CCD can be changed due to different optical lenses and therefore taken out of the sun than the superior image quality clear advantage webcam, webcam in good times its low cost , in sunlight conditions can also stabilize the judgment deviation angle.
In addition, through PSD voltage meter to do with DR01 pyrheliometer correlation analysis, making the PSD in measuring the deviation angle measurement but also have the function of the amount of direct normal irradiation, PSD voltage conversion direct normal irradiation and DR01 pyrheliometer when measured after outdoor confirmed the average percentage error are less than 4%, there is a certain reliability. |
