Renewable energy is energy produced from sources that do not deplete or can be replenished within a human’s life time. The most common examples include wind, solar, geothermal, biomass, and hydropower. This is in contrast to non-renewable sources such as fossil fuels.
Most renewable energy is derived directly or indirectly from the sun. Sunlight can be captured directly using solar technologies. The sun’s heat drives winds, whose energy is captured with turbines. Plants also rely on the sun to grow and their stored energy can be utilized for bioenergy. 
Not all renewable energy sources rely on the sun. For example, geothermal energy utilizes the Earth’s internal heat, tidal energy relies on the gravitational pull of the moon, and hydropower relies 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 .
Renewable energy systems are a major topic when discussing the globe’s energy future for two main reasons:
- Renewable energy systems provide energy from sources that will never deplete.
- Renewable energy systems produce less greenhouse gas emissions than fossil fuel energy systems.
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.
It is important to note that the terms ‘renewable energy’, ‘green energy’ and ‘clean energy’ are not interchangeable in all cases; for example, a ‘clean’ coal plant is simply a coal plant with emissions reduction technology. The coal plant itself is still not a ‘renewable energy’ source. ‘Green energy’ is a subset of renewable energy, which boasts low or zero emissions and low environmental impacts to systems such as land and water.