Energy is vital to any modern economy because it underpins human wellbeing and economic productivity. In recent years, a great deal of engineering research has focused on designing low-carbon, or “clean,” energy systems. A clean energy future will grant the rising global population access to reliable, affordable, and sustainable energy services without contributing to climate change. Transitioning our fuel mix away from coal and oil and toward natural gas and renewable energy will take time, as the energy industry progresses through a period of profound change. Effective government policies and considerable technological progress are being made in the transition from fossil fuels to ecologically sustainable energy systems, such that many studies support future energy systems based on 100% renewable energy.