A wind turbine is a device that converts the kinetic energy of wind into electrical energy. As of 2020, hundreds of thousands of large turbines in installations known as wind farms were generating over 650 gigawatts of power, with 60 gigawatts added each year. Wind turbines are an increasingly important source of intermittent renewable energy, used in many countries to lower energy costs and reduce reliance on fossil fuels. One study claimed that, as of 2009, wind had the "lowest relative greenhouse gas emissions, the least water consumption demands, and the most favorable social impacts" compared to photovoltaic, hydro, geothermal, coal, and gas energy sources.