The rapid growth of solar power generation and the variable nature of the solar resource pose challenges for our electricity grids. Forecasting future changes in the irradiance might help to cost-efficiently manage this variability both for photovoltaic and concentration solar plants as well as grids with high solar penetrations. So far, for shortest-term forecasts with lead times of a few minutes, all-sky imager based nowcasting systems are used. However, due to the complexity of dynamically changing 3d cloud shapes as well as certain geometrical effects such as self-occlusion or near-horizon saturation, all-sky imager based nowcasting systems exhibit inherent weaknesses. Here, we present a novel system to generate shortest-term solar forecasts, which is located at Plataforma Solar de Almería in southern Spain. This approach is based on downward-facing cameras (shadow cameras), taking images of the ground. From these images, spatially resolved irradiance maps are derived. By tracking cloud shadows, future irradiances are predicted. A demonstration system is achieved, which provides shortest-term forecasts for the next 2 min. To the best of our knowledge, this is the first time such a system is developed. We benchmark several possible algorithmic approaches on 16 days and compare the deviations to a state-of-the-art all-sky imager based nowcasting system on 22 days. The root-mean-squared deviation (RMSD) of this shadow camera based nowcasting system for direct normal irradiance (DNI) and 1-min temporal averages is 15.6 % for lead times of 2 min (MAD, DNI: 9.6 %). In comparison to an all-sky imager system, this is an improvement as the all-sky imager system only reaches 22.0 % RMSD and 14.8 % MAD (both DNI). This demonstrates the feasibility and attractiveness in terms of accuracy of the proposed concept.

中文翻译：

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用于短期预测的基于阴影相机的太阳能临近预报系统

太阳能发电的快速增长和太阳能资源的多变性给我们的电网带来了挑战。预测辐照度的未来变化可能有助于以具有成本效益的方式管理光伏和聚光太阳能发电厂以及具有高太阳能渗透率的电网的这种变化。到目前为止，对于提前几分钟的短期预测，使用了基于全天空成像仪的临近预报系统。然而，由于动态改变 3d 云形状的复杂性以及某些几何效应（如自遮挡或近视距饱和），基于全天成像仪的临近预报系统表现出固有的弱点。在这里，我们提出了一种新的系统来生成短期太阳预报，该系统位于西班牙南部的 Plataforma Solar de Almería。这种方法基于向下的相机（阴影相机），拍摄地面图像。从这些图像中，可以导出空间分辨的辐照度图。通过跟踪云影，可以预测未来的辐照度。实现了一个演示系统，它提供了接下来 2 分钟的最短预测。据我们所知，这是第一次开发这样的系统。我们在 16 天内对几种可能的算法方法进行了基准测试，并将偏差与 22 天的基于最先进的全天空成像仪的临近预报系统进行了比较。对于直接法向辐照度 (DNI) 和 1 分钟时间平均值，这种基于阴影相机的临近预报系统的均方根偏差 (RMSD) 为 15.6%，前置时间为 2 分钟（MAD，DNI：9.6%）。与全天成像系统相比，这是一项改进，因为全天空成像仪系统仅达到 22.0 % RMSD 和 14.8 % MAD（均为 DNI）。这证明了所提出概念在准确性方面的可行性和吸引力。