Renewable EnergySources

Today petroleumprovides around 40%of the world's energy needs,mostly fuelling automobiles.Coalis

still used,mostly inpower stations,to cover one-quarter of our energy needs,but it is the least efficient,un-

healthiest and mostenvironmentally damaging fossil fuel.Natural gas reserves could plug some ofthe gap

from oil,butreserves of that will not last into the 22nd century either. Most expertspredict we will exhaust

easily accessiblereserves within 50 years.We could fast reach an energy crisis.We need torapidly develop

sustainablesolutions to fuel our future.Less-polluting renewable energy sources offer amore practical

long-term energysolution. They may benefit the world's poor too."Renewable"refers tothe fact that these

resources are notused faster than they can be replaced.

The Chinese andRomans used waterinills over 2, 000 years ago.But the first hydroelectric damwas built

in England in 1870.Hydroelectric poweris now the most common form of renewable energy,supplying around

20%of worldelectricity.China's Three Gorges Dam,which has just been completed,is thelargest ever. At

five times the sizeof the US's Hoover Dam,its 26 turbines will generate the equivalent energy of18 coal-

fired powerstations.It will satisfy 3%of China'sentire electricity demand.Surprisingly,some argue that hy-

droelectric damssignificantly contribute greenhouse gases.

In 2003,the firstcommercial power station to harness tidal currents in the open sea opened in Norway.

It is designed likewindmill,but others take the form of turbines.

As prices fall,windpower has become the fastest growing type of electricity generation一quadrupling

worldwide between1999 and 2005.Modern wind farms consist of turbines that generateelectricity.Though it

will be moreexpensive,there is more than enough wind to provide the world's entire energyneeds. Wind

farms come inonshore and offshore forms.They can often end up at spots of natural beauty,andare often un-

popular withresidents.And turbines are not totally benign一they can interfere with radar and leave a signifi-

cant ecologicalfootprint,altering climate and killing sea birds.Migrating birds may have moreluck avoiding

them.Scotland isbuilding Europe's largest wind farms,which will power 200,000 homes.The UK'sgoal is

to generateone-fifth of power from renewable sources,mainly wind,by 2020.But this maycause problems,

because wind isunreliable.Which of thefollowing statements is true of wind power?

A.Here is plenty ofwind to provide the world'S entire energy needs.

B.It is the mostrapidly growing type of electricity production.

C.It may not bereliable.

D.All of the above.