An Integrated Multi-Time-Scale Modeling for Solar Irradiance Forecasting Using Deep Learning

For short-term solar irradiance forecasting, the traditional point forecasting methods are rendered less useful due to the non-stationary characteristic of solar power. The amount of operating reserves required to maintain reliable operation of the electric grid rises due to the variability of solar energy. The higher the uncertainty in the generation, the greater the operating-reserve requirements, which translates to an increased cost of operation. In this research work, we propose a unified architecture for multi-time-scale predictions for intra-day solar irradiance forecasting using recurrent neural networks (RNN) and long-short-term memory networks (LSTMs). This paper also lays out a framework for extending this modeling approach to intra-hour forecasting horizons thus, making it a multi-time-horizon forecasting approach, capable of predicting intra-hour as well as intra-day solar irradiance. We develop an end-to-end pipeline to effectuate the proposed architecture. The performance of the prediction model is tested and validated by the methodical implementation. The robustness of the approach is demonstrated with case studies conducted for geographically scattered sites across the United States. The predictions demonstrate that our proposed unified architecture-based approach is effective for multi-time-scale solar forecasts and achieves a lower root-mean-square prediction error when benchmarked against the best-performing methods documented in the literature that use separate models for each time-scale during the day. Our proposed method results in a 71.5% reduction in the mean RMSE averaged across all the test sites compared to the ML-based best-performing method reported in the literature. Additionally, the proposed method enables multi-time-horizon forecasts with real-time inputs, which have a significant potential for practical industry applications in the evolving grid.Comment: 19 pages, 12 figures, 3 tables, under review for journal submissio

Space-Time High-Resolution Data of The Potential Insolation and Solar Duration for Montenegro

The assessment of the potential use of renewable energy resources requires reliable and precise data inputs for sustainable energy planning on a regional, national and local scale. In this study, we examine high spatial resolution grids of potential insolation and solar duration in order to determine the location of potential solar power plants in Montenegro. Grids with a 25-m spatial resolution of potential solar radiation and duration were produced based on observational records and publicly available high-resolution digital elevation model provided by the European Environment Agency. These results could be further used for the estimation and selection of a specific location for solar panels. With an average annual potential insolation of 1800 kWh/m² and solar duration of over 2000 h per year for most of its territory, Montenegro is one of the European countries with the highest potential for the development, production, and consumption of solar energy

SOLAR IRRADIANCE FORECASTING FOR TROPICAL REGIONS USING NOVEL STATISTICAL ANALYSIS AND MACHINE LEARNING

Ph.DDOCTOR OF PHILOSOPH

Spatio-temporal solar forecasting

Current and future photovoltaic (PV) deployment levels require accurate forecasting to ensure grid stability. Spatio-temporal solar forecasting is a recent solar forecasting approach that explores spatially distributed solar data sets, either irradiance or photovoltaic power output, modeling cloud advection patterns to improve forecasting accuracy. This thesis contributes to further understanding of the potential and limitations of this approach, for different spatial and temporal scales, using different data sources; and its sensitivity to prevailing local weather patterns. Three irradiance data sets with different spatial coverages (from meters to hundreds of kilometers) and time resolutions (from seconds to days) were investigated using linear autoregressive models with external inputs (ARX). Adding neighboring data led to accuracy gains up to 20-40 % for all datasets. Spatial patterns matching the local prevailing winds could be identified in the model coefficients and the achieved forecast skill whenever the forecast horizon was of the order of scale of the distance between sensors divided by cloud speed. For one of the sets, it was shown that the ARX model underperformed for non-prevailing winds. Thus, a regime-based approach driven by wind information is proposed, where specialized models are trained for different ranges of wind speed and wind direction. Although forecast skill improves by up to 55.2 % for individual regimes, the overall improvement is only of 4.3 %, as those winds have a low representation in the data. By converting the highest resolution irradiance data set to PV power, it was also shown that forecast accuracy is sensitive to module tilt and orientation. Results are shown to be correlated with the difference in tilt and orientation between systems, indicating that clear-sky normalization is not totally effective in removing the geometry dependence of solar irradiance. Thus, non-linear approaches, such as machine learning algorithms, should be tested for modelling the non-linearity introduced by the mounting diversity from neighboring systems in spatio-temporal forecasting

Renewable Energy Resource Assessment and Forecasting

In recent years, several projects and studies have been launched towards the development and use of new methodologies, in order to assess, monitor, and support clean forms of energy. Accurate estimation of the available energy potential is of primary importance, but is not always easy to achieve. The present Special Issue on ‘Renewable Energy Resource Assessment and Forecasting’ aims to provide a holistic approach to the above issues, by presenting multidisciplinary methodologies and tools that are able to support research projects and meet today’s technical, socio-economic, and decision-making needs. In particular, research papers, reviews, and case studies on the following subjects are presented: wind, wave and solar energy; biofuels; resource assessment of combined renewable energy forms; numerical models for renewable energy forecasting; integrated forecasted systems; energy for buildings; sustainable development; resource analysis tools and statistical models; extreme value analysis and forecasting for renewable energy resources

Deep Neural Network Regression and Sobol Sensitivity Analysis for Daily Solar Energy Prediction Given Weather Data

Solar energy forecasting plays an important role in both solar power plants and electricity grid. The effective forecasting is essential for efficient usage and management of the electricity grid, as well as for the solar energy trading. However, many of the existing models or algorithms are based on real physical laws, where tons of calculations, step-by-step modification, and many inputs are required. In this research, a novel deep Multi-layer Perceptron (MLP) based regression approach for predicting solar energy is proposed, in which the inputs are only ensemble weather forecasting data. The results demonstrate that our proposed deep Multi-layer Perceptron based regression approach for solar energy forecasting is efficient as well as accurate enough. A Sobol sensitivity analysis is performed over the trained model, determining the most important variables in the weather forecasting model data. The first-order and the total order Sobol sensitivity indices for quantifying feature importance, are calculated for each model input parameter. With using the process of feature removal, the result of Sobol sensitivity analysis is verified

State of the art of machine learning models in energy systems: A systematic review

Machine learning (ML) models have been widely used in the modeling, design and prediction in energy systems. During the past two decades, there has been a dramatic increase in the advancement and application of various types of ML models for energy systems. This paper presents the state of the art of ML models used in energy systems along with a novel taxonomy of models and applications. Through a novel methodology, ML models are identified and further classified according to the ML modeling technique, energy type, and application area. Furthermore, a comprehensive review of the literature leads to an assessment and performance evaluation of the ML models and their applications, and a discussion of the major challenges and opportunities for prospective research. This paper further concludes that there is an outstanding rise in the accuracy, robustness, precision and generalization ability of the ML models in energy systems using hybrid ML models. Hybridization is reported to be effective in the advancement of prediction models, particularly for renewable energy systems, e.g., solar energy, wind energy, and biofuels. Moreover, the energy demand prediction using hybrid models of ML have highly contributed to the energy efficiency and therefore energy governance and sustainability

Solar irradiance modeling and forecasting using novel statistical techniques

Ph.DDOCTOR OF PHILOSOPH