Observing Clouds from above and below - a chance for Redispatch 2.0?

Abstract

Balancing the power production and energy demand is a constant activity of electricity grid operators. Since October 2021, distribution system operators (DSO) in Germany have a completely new role in redispatch as they have now to collaborate more actively with transmission grid operators (TSO) in their daily operations. Important new tasks of the DSO in the Redispatch 2.0 are now the use of daily feed-in forecasts, ensuring the network effectiveness and calculating flexibility restrictions on grid node levels. For these tasks they need to know the photovoltaic power feed in the next minutes and hours. DLR’s high resolution hybrid irradiance forecast is currently based on the combination of a Meteosat satellite derived forecast (based on the Heliosat 3 method) and forecasts derived from the All Sky Imager (ASI) network Eye2Sky. DLR’s Eye2Sky is a cloud monitoring system covering roughly 110x100 km in north-west Germany. It is equipped with 38 all sky imagers, i.e. sky-facing fisheye cameras, ten solar irradiance measurement stations and two individual instruments for cloud height measurement (Ceilometer) distributed throughout the region. The system collects high-resolution information on solar irradiance , tracks the variability and provides forecasts for very short time scales. It has a spatial resolution 50 meters and the temporal resolution exceeds 1 minute. It can produce forecasts for up to one hour ahead depending on the prevailing cloud height and velocity. The data can inform about present and future weather (solar irradiance) conditions for the reliable operation of distribution grids, and economic operation of solar installations as well as for regional case studies. Outcomes of the Smart4RES project show that the hybrid forecast outperforms the RMSE of persistence and the individual input forecasts for all lead times (5min to 30min) for a first validation period of two months (July and August 2020). So, it is a promising candidate for assisting DSOs in their new tasks in Redispatch 2.0. Coupling cloud observations from above (satellite) and below (ground observations) combines the pros and cons of each observing system. We further analyze the cloud situation dependent accuracy of the forecast methods and assess the impact of the assumptions in satellite retrievals on their performances.