Sky-image based intra-hour solar forecasting using independent cloud-motion detection and ray-tracing techniques for cloud shadow and irradiance estimation




Nummikoski, Jaro Johannes

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Solar forecasting solutions provide utility companies with predictions of power output from large-scale solar installations or from distributed solar generation with a time scale ranging from the next few minutes up to several days ahead. These predictions decrease the risk associated with bidding renewable electricity to the regional grid. Increasing solar photovoltaic efficiency and decreasing manufacturing costs have driven solar electricity generation to become the fastest growing form of renewable electricity production. Adding solar generation in large quantities to the aging electricity grids of the world poses a problem due to the variability and intermittency of solar irradiance. The current state-of-the-art in solar forecasting is focused on the hour-ahead and day-ahead time horizons using publicly available satellite imagery or numerical weather prediction models. Conventional intra-hour forecasting methods are based on sky imagery and basic image processing and computer vision techniques.

This thesis discusses the architecture of an intra-hour forecasting tool and outlines the steps involved in taking a sky image and outputting a value of irradiance at specified intra-hour intervals. The thesis includes technical discussions on obstruction masking, geometric transformation, cloud-motion detection and ray tracing for irradiance estimation. The goal is to improve and enhance conventional techniques with innovative approaches to intra-hour solar forecasting. The forecasting tool provides predictions of irradiance and the associated uncertainty through the use of a novel irradiance estimation algorithm and a Monte Carlo simulation. The ray tracing procedure allows for multiple irradiance estimations to be made at spatially distributed points, providing a high-fidelity irradiance mapping of the area within the range of the sky imager. This map can be used to accurately estimate power output from large scale solar power plants or distributed solar generation sites.


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Cloud-motion, Intra-hour, Irradiance, Ray-Tracing, Sky image, Solar forecasting



Electrical and Computer Engineering