Short-Term Solar Irradiance Forecasting Using CNN-1D, LSTM and CNN-LSTM Deep Neural Networks: A Case Study with the Folsom (USA) Dataset

In this paper, solar irradiance short-term forecasts were performed considering time horizons ranging from 5 min to 30 min, under a 5 min timestep. Global Horizontal Irradiance (GHI) and Direct Normal Irradiance (DNI) were computed using Deep Neural Networks with One-Dimensional Convolution (CNN-1D), Long-Short Term Memory (LSTM) and CNN-LSTM layers on the benchmarking dataset FOLSOM, which is formed by predictors obtained by recursive functions on the clear sky index time series and statistical attributes extracted from images collected by a camera pointed to the zenith, characterizing endogenous and exogenous variables, respectively. To analyze the endogenous predictors influence on the accuracy of the networks, the performance was evaluated for the cases with and without them. This analysis is motivated, to our best knowledge, by the lack of works that cite the FOLSOM dataset using deep learning models, and it is necessary to verify the impact of the endogenous and exogenous predictors in the forecasts results for this specific approach. The accuracy of the networks was evaluated by the metrics Mean Absolute Error (MAE), Mean Bias Error (MBE), Root Mean Squared Error (RMSE), Relative root-mean-squared error (rRMSE), Determination Coefficient (R2) and Forecast Skill (s). The network architectures using isolated CNN-1D and LSTM layers generally performed better. The best accuracy was obtained by the CNN-1D network for a horizon of 10 min ahead reaching an RMSE of 36.24 W/m2, improving 11.15% on this error metric compared to the persistence model.