The simulation of cloud cover using  the diamond-square algorithm

Abstract

The method for simulation cloud cover of solar cells, solar panels or solar stations is presented. Modelling clear-sky index increments (i.e. changes in normalized surface irradiance over specified intervals of time) and their spatial autocorrelation structures is important for the reliable grid integration of photovoltaic power systems. In order to capture increment correlation structures under mixed sky conditions, I apply a fractal cloud model. Algorithm, based on method that Fournier proposed, was modified to generate fractal cloud for simulating surface horizontal irradiation variability. The modified algorithm allows us to get a "surface" of the fractal nature, which is a simulation model of the cloud. As the result, we have clouds represented as arrays of clear-sky indexes when algorithm done. Clear-sky index allows us to compute surface horizontal irradiance using only theoretical clear-sky global horizontal irradiation. Also it is shown, that the algorithm allows us to overcome the problem of obtaining sufficiently detailed for the needs of modeling cloud images of low-resolution source data. Parameters of the algorithm defined for the 10 step variant. As a random value was used an implementation of  a normally distributed value with the step coefficient. The coefficient was choose to reduce the magnitude of the random value at each iteration. We used the Hurst exponent that is directly related to fractal dimension. As the sources of data we proposed both photos from satellite and cloud cover, recorded at meteorological stations as integer number of oktas, which is the number of eights of the sky obscured by clouds. The image obtained from a satellite was proceeded. For the analysis  we need to get the clear sky surface global irradiation, that is the main problem of the algorithm. Aside from the solar-zenith angle, clear-sky irradiance is most influenced by aerosols, water vapor and ozone. Also we need to include ground elevation to get accurate value of clear sky irradiance. The resolution was increased 250 times, so we can use it for more detailed simulating. It thus helps to provide a variety of simulation model of solar power stations and even solar cells with information about surface horizontal irradiation variability. The ways for improvement of the simulation model of the cloud cover are proposed.  

Keywords

References

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Copyright (c) 2019 Роман Вікторович Сукач, Катерина Сергіївна Клен (Автор)