Validation Statistics for the PV_Forecast Service
31st July 2017
The PV_Forecast service uses statistical modelling techniques to forecast the generation of individual PV systems. The PV_Live National methodology is then applied to the forecast data in order to produce a forecast of the nationally-aggregated PV generation. Naturally, the error on the national forecast can be assessed by comparison with the PV_Live National results. For context, we also include a comparison with the National Grid’s own day-ahead forecast of embedded solar PV generation.
Here we consider a full year of historical simulated PV forecasts (hicasts) using the Sheffield Solar PV_Forecast methodology in order to evaluate and validate the performance of PV_Forecast. The PV_Forecast generation hicasts use real historical weather forecasts from MeteoGroup. The weather forecasts were initiated at 7am each day (GMT) and we considered the forecast error up to a 24 hour horizon (a.k.a lead time) i.e. up to the interval ending 7am the following day.
For benchmarking purposes we have included a comparison with the NG “day-ahead” forecast of nationally aggregated embedded PV generation, which is freely available to download from the Elexon BM Reports platform. This forecast is initiated by NG some time before the start of the day in question, and so the two forecasts are not technically equivalent since the NG day-ahead forecast of the midday generation has a longer lead time than the Sheffield Solar PV_Forecast. In future we will look to study how the forecast error in PV_Forecast changes with forecast lead time.
Figure 1; Typical hourly PV generation profiles for the PV_Forecast service alongside PV_LIve and the NG day-ahead forecast.
Figure 2; Forecast generation against PV_Live generation for PV_Forecast and NG Day-Ahead. Red lines show the linear fit and green lines show the line y=x.
Figure 3; Root Mean Square Error (RMSE) of PV_Forecast and NG Day-Ahead forecast by time of day.
Figure 4; Mean Absolute Percent Error (MAPE) by time for PV_Forecast and NG Day-Ahead during the months May to August (inclusive).