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pubblicazioni - Presentazione

The RSE Wind and Solar Forecast System

pubblicazioni - Presentazione

The RSE Wind and Solar Forecast System

RSE developed a wind and solar power forecast system (WSFS) based on a mesoscale meteorological model, such as LAMI (Italian suite of Lokal Modell) or RAMS, and some post processing algorithms. Both the models use the ECMWF meteorological forecast as boundary conditions until three days ahead.The RAMS forecasts are supplied with a resolution that usually is not able to take into account for the small topographic or land use features surrounding the wind farm. For this reason WSFS adopts both statistical approach (MOS), to reduce systematic errors, and more physical downscaling techniques, as diagnostic models (CALMET) or CFD models (WINDSYM). In these cases, the RAMS low-resolution (1-4 km) is enhanced by CALMET or WINDSYM till 100 m. Hourly wind and power measurements of several wind farm located in the south of Italy, in a complex topography situation, have been used as a benchmark. Several tests on the performances using different grid resolution have defined an optimal configuration that consist in a computational domain of two nested grids with a horizontal resolution of 12 x 12 km2 and 4 x 4 km2 respectively and a vertical step of 40 m near the ground. Only the outputs on the smaller grid are then post processed. In general our experience has defined the statistical downscaling technique to be the most successful in reduce systematic error, even if this approach requires enough long time series of wind or power measured data. If this is not the case, the other more physical approaches (CALMET or WINDSYM) constitutes a valid alternative as a post processing technique. We have also focused on the possibility of using the ensemble forecast system from ECMWF to estimate the hourly, three days ahead, power forecast accuracy. From this first analysis it seems that ensemble spread could be used as an indicator of the forecast’s accuracy at least for the first forecast time horizon. In fact low spreads often correspond to low forecast error.The WSFS solar forecast system is based on a physical post-processing, fed by the outputs of a numerical weather forecast model, such as LAMI or RAMS. The forecasted vertical distribution of pressure, temperature, humidity, water and ice cloud content, are used to evaluate global, direct and diffuse irradiance in atmosphere and at the surface. Datasets of ozone and atmospheric aerosols are continuously updated from satellite measurements. For low sun heights we are going to modify the scheme in order to take into account model variables on different cells along the slant ray pathWe have obtained global, diffuse, and direct normal irradiation data from monitoring stations in Milan, Casaccia (Rome), and in Catania (Sicily) for the last two years. We have investigated the performance of our post processing for different cloudiness conditions and sun heights. In clear sky and for all the sun heights the correlations between measurements and forecast are high. To evaluate the performance in cloudy conditions we have adopted different cloud schemes, using either NWP cloudiness or only liquid/ice water content or a diagnostic radiative cloudiness obtained from vertical humidity and its tunable thresholds.This work has been financed by the Research Fund for the Italian Electrical System under the Contract Agreement between RSE (formerly known as ERSE) and the Ministry of Economic Development – General Directorate for Nuclear Energy, Renewable Energy and Energy Efficiency stipulated on July 29, 2009 in compliance with the Decree of March 19, 2009.

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