[M-ZZ39] Scientific, technical, and educational aspects of renewable energy

[MZZ39-P01] Cloud observation and solar irradiance estimation using all-sky imagers in Taiwan-II: A new concept of cloud recognition

*Shih-Sian Yang¹, Hsin-Chih Lai^1,2, Chen-Jeih Pan³, Li-Wei Lai¹, Yiwen Chen³, Hung-Chun Hou⁴, J.-H. Teng⁵ (1.Environmental Research and Information Center, Chang Jung Christian University, Taiwan, 2.Department of Green Energy and Environmental Resources, Chang Jung Christian University, Taiwan, 3.Department of Space Science and Engineering, National Central University, Taiwan, 4.Tohoku University, 5.Central Weather Administration, Taiwan)

Keywords:All-sky imager, Cloud cover, Solar irradiance, Solar power, Cloud optical thickness

This presentation is the follow-up to our former presentation at JpGU Meeting 2023, focusing on cloud recognition techniques. An all-sky imager (ASI) records all things, including the clear sky and clouds in the whole sky. After the imager takes an image, clouds within the image shall be recognized to count cloud cover and provide cloud information for any desired applications. The literature gives several methods and parameters to recognize the clear sky and clouds within an all-sky image. However, most criteria used in the literature are established in subjective ways and only applied to a specific ASI module. In the present study, we have conceived a new method for cloud recognition, which is named the ASI-COT method. COT, which stands for "cloud optical thickness," is a common parameter for meteorological satellite measuring, and it describes the attenuation of the light passing through clouds. Imitating the COT parameter of satellite observation, we have defined the ASI version of COT (hereafter, ASI-COT). ASI-COT is an objective parameter. It is defined according to a pyranometer accompanied by the ASI. The ASI-COT method can be applied to any ASI (any module and any place), though the corresponding criteria for cloud recognition at each ASI station may differ. A 10-level ASI-COT example will be demonstrated in this presentation, and its applications on solar irradiation estimation will be introduced as well.