Renewable energy is energy produced from sources that do not deplete or can be replenished within a human’s lifetime. The most common examples include wind, solar, geothermal, biomass, and hydropower. Most renewable energy is derived directly or indirectly from the sun. Some other sources are geothermal energy utilizing the Earth’s internal heat, tidal energy relying on the gravitational pull of the moon, and hydropower relying on the flow of water. Renewable energy accounts for 13.5% of the world’s total energy supply, and 22% of the world's electricity.
While renewable energy systems are better for the environment and produce less emissions than conventional energy sources, many of these sources still face difficulties in being deployed at a large scale including, but not limited to, technological barriers, high start-up capital costs, and intermittency challenges.