The International Energy Agency (IEA) examines various energy issues, including oil, gas, coal, renewable energy technologies, electricity markets, energy efficiency, access to energy, demand side management, and more. The IEA advocates policies to enhance the reliability, affordability, and sustainability of energy in its member countries, association countries, and beyond. This report analyzes how seasonal variations in both demand and supply affect electricity system operations in Europe, India, Indonesia, and Korea, and what sources will be used to manage them. The report is based on the IEA's work and any map included herein is without prejudice to the status of or sovereignty over any territory, delimitation of international frontiers and boundaries, and the name of any territory, city, or area.