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Renewable Energy Sources Today petroleum provides around 40% of the worlds energy needs，mostly fuelling automobiles. Coal is still used，mostly in pover stations，to cover one-quarter of our energy needs，but it is the least efficient，unhealthiest and most environmentally damaging fossil fuel. Natural gas reserves could plug some of the gap from oil，but reserves of that will not last into the 22nd century either. Most experts predict we will exhaust easily accessible reserves within 50 years. We could fast reach an energy crisis. We need to rapidly develop sustainable solutions to fuel our future. Less-polluting renewable energy sources offer a more practical long-term energy solution. They may benefit the worlds poor too. Renewable refers to the fact that these resources are not used faster than they can be replaced. Hydroelectric power is now the most common form of renewable energy，supplying around 20% of world electricity. Chinas three gorges Dam，which has just been completed，is the largest ever. At five times the size of the USs Hoover Dam，its 26 turbines will generate the equivalent energy of 18 coal-fired power stations. It will satisfy 3% of Chinas entire electricity demand. In 2003，the first commercial power station to harness tidal currents in the open sea opened in Norway. It is designed like windmill，but others take the form of turbines. As prices fall，wind power has become the fastest growing type of electricity generationquadrupling worldwide between 1999 and 2005. Modern wind farms consist of turbines that generate electricity. Though it will be more expensive，there is more than enough wind to provide the worlds entire energy needs. Wind farms come in onshore and offshore forms. They can often end up at spots of natural beauty，and are often unpopular with residents. And turbines are not totally benignthey can interfere with radar and leave a significant ecological footprint，altering climate and lilling sea birds. Migrating birds may have more luck avoiding them. Scotland is building europes largest wind farm，which wil power 200，000 homes. The UKs goal is to generate onefifth of power from renewable sources，mainly wind，by 2020. But this may cause problems，because wind is unreliable. | 
