Abstract
In this paper, we propose a novel forecast method which addresses the difficulty in short-term solar irradiance forecasting that arises due to rapidly evolving environmental factors over short time periods. This involves the forecasting of Global Horizontal Irradiance (GHI) that combines prediction sky images with a Radiative Transfer Model (RTM). The prediction images (up to 10 min ahead) are produced by a non-local optical flow method, which is used to calculate the cloud motion for each pixel, with consecutive sky images at 1 min intervals. The Direct Normal Irradiance (DNI) and the diffuse radiation intensity field under clear sky and overcast conditions obtained from the RTM are then mapped to the sky images. Through combining the cloud locations on the prediction image with the corresponding instance of image-based DNI and diffuse radiation intensity fields, the GHI can be quantitatively forecasted for time horizons of 1–10 min ahead. The solar forecasts are evaluated in terms of root mean square error (RMSE) and mean absolute error (MAE) in relation to in-situ measurements and compared to the performance of the persistence model. The results of our experiment show that GHI forecasts using the proposed method perform better than the persistence model.
Highlights
The use of solar power as a renewable energy source has grown substantially over the last few decades
Solar irradiance forecasts have relied heavily upon information retrieved via satellites and from Numerical Weather Prediction (NWP) models
We found that when the sun was obstructed by the cloud, the Global Horizontal Irradiance (GHI) measured values changed with the cloud fraction and cloud optical depth
Summary
The use of solar power as a renewable energy source has grown substantially over the last few decades. The amount of solar irradiance that reaches the Earth’s surface can vary significantly over relatively short time periods, resulting in fluctuation and intermittence of power generation. It is crucial that we develop new techniques to accurately produce short-term forecasts of solar irradiance at the surface. 6-h period forecasts [3,4] Both NWP and satellite imagery lack the spatial and temporal resolutions necessary for providing detailed information regarding high frequency fluctuations of solar irradiance. To overcome this issue, ground-based sky imagers have been developed and deployed as a means of capturing local sky images with highly-refined spatial and temporal resolutions for intra-hour solar irradiance forecasts [5]
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