Renewable energy sources (RESs) such as solar, wind, and hydroelectric power play an increasingly significant role in the global energy landscape, offering sustainable alternatives to conventional fossil fuels. However, the intermittent and unpredictable nature of renewable energy generation poses challenges for effective integration into the power grid and reliable energy supply. In recent years, machine learning (ML) techniques have emerged as powerful tools for forecasting renewable energy (RE) generation, enabling improved planning, management, and grid integration strategies. This chapter provides a comprehensive survey of ML applications in renewable energy forecasting, covering various techniques, methodologies, and case studies across different RESs. It begins with an overview of traditional forecasting methods and their limitations, followed by an exploration of ML algorithms, including artificial neural networks, support vector machines, decision trees, and ensemble methods, among others, employed for RE prediction tasks. The chapter also discusses data preprocessing techniques, feature selection methods, and evaluation metrics commonly used in ML-based forecasting models. Furthermore, it presents a detailed analysis of case studies and real-world applications in solar, wind, and hydroelectric power forecasting, highlighting the strengths, limitations, and potential areas for future research in this field. Through this survey, researchers, practitioners, and policymakers gain insights into the current state-of-the-art in ML-based RE forecasting, paving the way for enhanced utilization and integration of RESs into the modern power grid.