<P> Hydroelectricity is electric power generated by hydropower; the force of falling or flowing water . In 2015 hydropower generated 16.6% of the world's total electricity and 70% of all renewable electricity and is expected to increase about 3.1% each year for the next 25 years . </P> <P> Hydropower is produced in 150 countries, with the Asia - Pacific region generating 32 percent of global hydropower in 2010 . China is the largest hydroelectricity producer, with 721 terawatt - hours of production in 2010, representing around 17 percent of domestic electricity use . There are now three hydroelectricity plants larger than 10 GW: the Three Gorges Dam in China, Itaipu Dam across the Brazil / Paraguay border, and Guri Dam in Venezuela . </P> <P> The cost of hydroelectricity is relatively low, making it a competitive source of renewable electricity . The average cost of electricity from a hydro plant larger than 10 megawatts is 3 to 5 U.S. cents per kilowatt - hour . Hydro is also a flexible source of electricity since plants can be ramped up and down very quickly to adapt to changing energy demands . However, damming interrupts the flow of rivers and can harm local ecosystems, and building large dams and reservoirs often involves displacing people and wildlife . Once a hydroelectric complex is constructed, the project produces no direct waste, and has a considerably lower output level of the greenhouse gas carbon dioxide than fossil fuel powered energy plants . </P> <P> Wind power harnesses the power of the wind to propel the blades of wind turbines . These turbines cause the rotation of magnets, which creates electricity . Wind towers are usually built together on wind farms . There are offshore and onshore wind farms . Global wind power capacity has expanded rapidly to 336 GW in June 2014, and wind energy production was around 4% of total worldwide electricity usage, and growing rapidly . </P>

What are the main sources for producing electrical energy with particular reference to pakistan