Renewable energies, notably wind and solar, play crucial roles in achieving sustainable energy supplies for our society. While renewable energies are clean and do not rely on fossil fuels, they are also variable and uncertain in nature. Such variability and uncertainty pose great challenges on energy system operation with deep renewable energy penetration. We provide a variety of solutions for reliable and efficient integration of renewable energies. Exploiting statistical diversity among difference sources of renewables, efficient market mechanisms are developed for aggregation of renewable energies, and significant reduction of their variability and uncertainty is achieved. We also evaluate the benefit from energy storage in risk reduction of renewable energies.