Daily Clearness Index Profiles Cluster Analysis for Photovoltaic System

Chun Sing Lai, Youwei Jia, Malcolm D. McCulloch, Zhao Xu

Research output: Journal article publicationJournal articleAcademic researchpeer-review

46 Citations (Scopus)


Due to various weather perturbation effects, the stochastic nature of real-life solar irradiance has been a major issue for solar photovoltaic (PV) system planning and performance evaluation. This paper aims to discover clearness index (CI) patterns and to construct centroids for the daily CI profiles. This will be useful in being able to provide a standardized methodology for PV system design and analysis. Four years of solar irradiance data collected from Johannesburg (26.21 S, 28.05 E), South Africa are used for the case study. The variation in CI could be significant in different seasons. In this paper, cluster analysis with Gaussian mixture models (GMM), K-Means with Euclidean distance (ED), K-Means with Manhattan distance, Fuzzy C-Means (FCM) with ED, and FCM with dynamic time warping (FCM DTW) are performed for the four seasons. A case study based on sizing a stand-alone solar PV and storage system with anaerobic digestion biogas power plants is used to examine the usefulness of the clustering results. It concludes that FCM DTW and GMM can determine the correct PV farm rated capacity with an acceptable energy storage capacity, with 36 and 46 rather than 1457 solar irradiance profiles, respectively.
Original languageEnglish
Article number7879846
Pages (from-to)2322-2332
Number of pages11
JournalIEEE Transactions on Industrial Informatics
Issue number5
Publication statusPublished - 1 Oct 2017


  • Clearness index
  • dynamic time warping (DTW)
  • fuzzy C-Means (FCM)
  • photovoltaic (PV) system

ASJC Scopus subject areas

  • Control and Systems Engineering
  • Information Systems
  • Computer Science Applications
  • Electrical and Electronic Engineering


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