Renewable energy refers to energy derived from natural resources that are constantly replenished and are virtually inexhaustible over human timescales. These resources include sunlight, wind, water (hydropower), geothermal heat, and biomass. Renewable energy technologies harness these resources to generate electricity, heat, or other forms of energy with minimal or no greenhouse gas emissions, making them environmentally sustainable alternatives to fossil fuels. Common examples of renewable energy sources include solar panels for solar energy, wind turbines for wind energy, and hydroelectric dams for hydropower.