Daily Clearness Index

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A. Ianetz - One of the best experts on this subject based on the ideXlab platform.

  • inter comparison of different models for estimating clear sky solar global radiation for the negev region of israel
    Energy Conversion and Management, 2007
    Co-Authors: A. Ianetz, Efim G. Evseev, V Lyubansky, Ilan Setter, Boris Kriheli, A I Kudish
    Abstract:

    Solar global radiation is a function of solar altitude, site altitude, albedo, atmospheric transparency and cloudiness, whereas solar global radiation on a clear day is defined such that it is a function of all the abovementioned parameters except cloudiness. Consequently, analysis of the relative magnitudes of solar global radiation and solar global radiation on a clear day provides a platform for studying the influence of cloudiness on solar global radiation. The Iqbal filter for determining the day type has been utilized to calculate the monthly average clear day solar global radiation at three sites in the Negev region of Israel. An inter-comparison between four models for estimating clear sky solar global radiation at the three sites was made. The relative accuracy of the four models was determined by comparing the monthly average Daily clear sky solar global radiation to that determined using the Iqbal filter. The analysis was performed on databases consisting of measurements made during the time interval of January 1991 to December 2004. The monthly average Daily clear sky solar global radiation determined by the Berlynd model was found to give the best agreement with that determined using the Iqbal filter. The Berlynd model was then utilized to calculate a Daily clear day Index, Kc, which is defined as the ratio of the Daily solar global radiation to the Daily clear day solar global radiation. It is suggested that this Index be used as an indication of the degree of cloudiness. Linear regression analysis was performed on the individual monthly databases for each site to determine the correlation between the Daily clear day Index and the Daily Clearness Index, KT.

  • Analysis of Daily Clearness Index, global and beam radiation for Beer Sheva, Israel: Partition according to day type and statistical analysis
    Energy Conversion and Management, 1996
    Co-Authors: Avraham I. Kudish, A. Ianetz
    Abstract:

    The magnitude of the Daily Clearness Index KT has been utilized to classify a day as either clear, partially cloudy or cloudy. The range of values for defining a day type was based upon a previous analysis of the Beer Sheva radiation database. These criteria were employed to partition the days according to type and the corresponding monthly average Daily values for the Clearness Index, global, normal incidence and horizontal beam radiation were calculated. A statistical analysis was performed on each of the monthly average Daily value subsets to help convey the shape of their respective distribution curves. The monthly average frequency of days according to type was also determined. Such an analysis of the solar radiation database for a particular site can be utilized to determine the relative merits of different types of solar energy conversion systems, e.g. concentrating vis-a-vis non-concentrating solar collector systems. The results of this analysis for Beer Sheva indicate that this region is very amenable to the utilization of non-concentrating solar energy conversion systems, since the combined frequency of both clear and partially cloudy days exceeds 80% annually. In addition, the Beer Sheva region is a prime candidate for the use of solar energy conversion systems utilizing concentrating collectors due to its relatively high frequency of clear days and the fact that the monthly average Daily values of the Clearness Index, even for partially cloudy days, are relatively high (KT > 0.50).

  • Analysis of the solar radiation data for Beer Sheva, Israel, and its environs
    Solar Energy, 1992
    Co-Authors: Avraham I. Kudish, A. Ianetz
    Abstract:

    Abstract The solar radiation climate of Beer Sheva, Israel, is reported upon in detail. The database utilized in this analysis consisted of global radiation on a horizontal surface, normal incidence beam radiation, and global radiation on a south-facing surface tilted at 40°. Monthly-average hourly and Daily values are reported for each of these three types of measured radiations, together with the calculated monthly-average Daily values for the components of the global radiation, viz. the horizontal beam and diffuse radiations. The monthly-average hourly and Daily Clearness Index values have also been calculated and analyzed. Monthly-average Daily frequency distributions of the Clearness Index values are reported for each month. The solar radiation climate of Beer Sheva has also been compared to those reported for a number of countries in this region. The annual-average Daily global radiation incident on a horizontal surface is 18.91 MJ/m2 and that for normal incidence beam radiation is 21.17 MJ/m2. The annual-average Daily fraction of the horizontal global radiation that is beam is 0.72. The annual-average Daily value for the Clearness Index is 0.587 and the average frequency of clear days annually is 58.6%. We conclude, based upon the above analysis, that Beer Sheva and its environs are characterized by relatively high, average-Daily irradiation rates, both global and beam, and a relatively high frequency of clear days.

Malcolm Mcculloch - One of the best experts on this subject based on the ideXlab platform.

  • Daily Clearness Index profiles and weather conditions studies for photovoltaic systems
    Energy Procedia, 2017
    Co-Authors: Chun Sing Lai, Loi Lei Lai, Malcolm Mcculloch
    Abstract:

    Abstract The increasing number of distributed photovoltaic (PV) systems connected to the power grid has made system planning and performance evaluation a challenging task. This is mainly due to the computational complexity, such as load flow analysis with large irradiance datasets collected from various locations of the installed PV farms. Solar irradiance data are known to possess the characteristic of high uncertainty, due to the random nature of cloud cover and atmospheric conditions. This paper presents the studies on the relationships of clustered Clearness Index profiles and the weather conditions obtained from the weather forecasting stations. Four years of solar irradiance and weather conditions data from two locations (Johannesburg and Kenya) were obtained and are used for the analysis. The preliminary study shows that the weather condition is related to the Daily Clearness Index profiles. This work will form the basis for estimating the Daily Clearness Index profile with weather conditions.

  • Daily Clearness Index Profiles Cluster Analysis for Photovoltaic System
    IEEE Transactions on Industrial Informatics, 2017
    Co-Authors: Chun Sing Lai, Youwei Jia, Malcolm Mcculloch
    Abstract:

    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.

Avraham I. Kudish - One of the best experts on this subject based on the ideXlab platform.

  • Analysis of solar irradiation measurements at Beer Sheva, Israel from 1985 through 2013
    Energy Conversion and Management, 2015
    Co-Authors: Efim G. Evseev, Avraham I. Kudish
    Abstract:

    Abstract An in-depth analysis of the solar horizontal global, normal incidence beam and solar global incident on a south-facing surface tilted at 40° irradiation monitored at Beer Sheva from 1985 through 2013 has been performed. The horizontal beam irradiation, Daily Clearness Index, Daily beam Index and beam fraction of the horizontal global irradiation were determined from the measured parameters. A statistical analysis, which included average, median, standard deviation, maximum and minimum values and the coefficient of variation, was performed on the parameters under investigation. The monthly frequency distribution types were determined for the solar global, normal incidence beam and solar global incident on a south-facing surface tilted at 40° irradiation based upon their corresponding skewness and kurtosis values. In addition, typical meteorological years were developed for the solar horizontal global and normal incidence beam irradiation. Beer Sheva is characterized as a site with a high incidence of clear days with global irradiation consisting of a relatively high beam fraction. A relatively steep minimum in the annual average Daily normal incidence beam irradiation is observed from 1991 to 1993 and has been attributed to the eruption of Mt. Pinatubo, Philippines during June 1991. A time series analysis of the both individual monthly and annual average Daily global and normal incidence irradiation indicated a slight trend of solar brightening for this region during the time interval 1985 through 2013, but in most cases they were not statistically significant based upon their p values.

  • Analysis of Daily Clearness Index, global and beam radiation for Beer Sheva, Israel: Partition according to day type and statistical analysis
    Energy Conversion and Management, 1996
    Co-Authors: Avraham I. Kudish, A. Ianetz
    Abstract:

    The magnitude of the Daily Clearness Index KT has been utilized to classify a day as either clear, partially cloudy or cloudy. The range of values for defining a day type was based upon a previous analysis of the Beer Sheva radiation database. These criteria were employed to partition the days according to type and the corresponding monthly average Daily values for the Clearness Index, global, normal incidence and horizontal beam radiation were calculated. A statistical analysis was performed on each of the monthly average Daily value subsets to help convey the shape of their respective distribution curves. The monthly average frequency of days according to type was also determined. Such an analysis of the solar radiation database for a particular site can be utilized to determine the relative merits of different types of solar energy conversion systems, e.g. concentrating vis-a-vis non-concentrating solar collector systems. The results of this analysis for Beer Sheva indicate that this region is very amenable to the utilization of non-concentrating solar energy conversion systems, since the combined frequency of both clear and partially cloudy days exceeds 80% annually. In addition, the Beer Sheva region is a prime candidate for the use of solar energy conversion systems utilizing concentrating collectors due to its relatively high frequency of clear days and the fact that the monthly average Daily values of the Clearness Index, even for partially cloudy days, are relatively high (KT > 0.50).

  • Analysis of the solar radiation data for Beer Sheva, Israel, and its environs
    Solar Energy, 1992
    Co-Authors: Avraham I. Kudish, A. Ianetz
    Abstract:

    Abstract The solar radiation climate of Beer Sheva, Israel, is reported upon in detail. The database utilized in this analysis consisted of global radiation on a horizontal surface, normal incidence beam radiation, and global radiation on a south-facing surface tilted at 40°. Monthly-average hourly and Daily values are reported for each of these three types of measured radiations, together with the calculated monthly-average Daily values for the components of the global radiation, viz. the horizontal beam and diffuse radiations. The monthly-average hourly and Daily Clearness Index values have also been calculated and analyzed. Monthly-average Daily frequency distributions of the Clearness Index values are reported for each month. The solar radiation climate of Beer Sheva has also been compared to those reported for a number of countries in this region. The annual-average Daily global radiation incident on a horizontal surface is 18.91 MJ/m2 and that for normal incidence beam radiation is 21.17 MJ/m2. The annual-average Daily fraction of the horizontal global radiation that is beam is 0.72. The annual-average Daily value for the Clearness Index is 0.587 and the average frequency of clear days annually is 58.6%. We conclude, based upon the above analysis, that Beer Sheva and its environs are characterized by relatively high, average-Daily irradiation rates, both global and beam, and a relatively high frequency of clear days.

B. Holmgren - One of the best experts on this subject based on the ideXlab platform.

Chun Sing Lai - One of the best experts on this subject based on the ideXlab platform.

  • Daily Clearness Index profiles and weather conditions studies for photovoltaic systems
    Energy Procedia, 2017
    Co-Authors: Chun Sing Lai, Loi Lei Lai, Malcolm Mcculloch
    Abstract:

    Abstract The increasing number of distributed photovoltaic (PV) systems connected to the power grid has made system planning and performance evaluation a challenging task. This is mainly due to the computational complexity, such as load flow analysis with large irradiance datasets collected from various locations of the installed PV farms. Solar irradiance data are known to possess the characteristic of high uncertainty, due to the random nature of cloud cover and atmospheric conditions. This paper presents the studies on the relationships of clustered Clearness Index profiles and the weather conditions obtained from the weather forecasting stations. Four years of solar irradiance and weather conditions data from two locations (Johannesburg and Kenya) were obtained and are used for the analysis. The preliminary study shows that the weather condition is related to the Daily Clearness Index profiles. This work will form the basis for estimating the Daily Clearness Index profile with weather conditions.

  • Daily Clearness Index Profiles Cluster Analysis for Photovoltaic System
    IEEE Transactions on Industrial Informatics, 2017
    Co-Authors: Chun Sing Lai, Youwei Jia, Malcolm Mcculloch
    Abstract:

    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.