Using Artificial Intelligence on environmental data from Internet of Things for estimating solar radiation: Comprehensive analysis

Solar radiation measurements are highly important for achieving energy efficiency in smart buildings as well as solar energy production. They are commonly acquired with pyranometer sensor device. However, due to its high initial and maintenance costs it is not densely deployed in the field. Consequently, it provides only limited coverage as a data source for solar radiation. Hence, theoretical, empirical and/or data-driven models are utilized to estimate solar radiation in areas without pyranometers using only data from meteorological sensor stations, which on the other hand are widely available and obtained from sustainable sensor networks. In this paper, end to end process is described for building hybrid models for solar radiation using Artificial Intelligence (AI), or more specifically Machine Learning (ML) methods, after which a detailed analysis is performed on (1) the accuracy of the models regards to their parameters and input features, (2) the sustainability of the models in the real world, and finally (3) their feasibility in (near) real-time monitoring. The results are expressed with relative root mean squared error (RRMSE) and they show that hybrid models outperform model- and data-driven ones, with artificial neural network giving the best results (RRMSE = 0.0393). Additionally, the models can be enhanced by performing an informed feature selection, where a posteriori selection proves to be better than a priori selection (RRMSE = 0.0371). Further investigation shows that randomly selected input data gives faster model convergence as expected. However, sequential input data can match it if model training starts with autumn or spring data when weather exhibits sufficient variety. When applied on different times scales, all models perform best on 3h scale rather than daily, where random forest (RRMSE = 0.0275) outperforms neural network (RRMSE = 0.0315). However, for (near) real time usage the models perform almost the same as for daily, with RRMSE of 0.0469 for 1min scale with neural network. This demonstrates the feasibility of the hybrid models in Internet of Things (IoT) applications, which commonly require at least hourly intervals for solar radiation. (C) 2020 Elsevier Ltd. All rights reserved.