Worldwide every day,we devour the energy equivalent of about 200 million barrel of oil.Mot of the energy on Earth come from the Sun.In fact enough energy from the Sun hit the planet urface each minute to cover our need for an entire year,we jut need to find an efficient way to ue it.So far the energy in oil ha been cheaper and eaier to get at.But a upplie dwindle,thi will change,and we will need to cure our addiction to oil. Today petroleum,a mineral oil obtained from below the urface of the Earth and ued to produce petrol,dieel oil and variou other chemical ubtance,provide around 40% of the world energy need,motly fuelling automobile.The US conume n quarter of all oil,and generate a imilar proportion of greenhoue ga emiion. Mot expert predict we will exhaut eaily acceible reerve within 50 year,though opinion and etimate vary.We could fat reach an energy crii in the next few decade,when demand exceed upply.A conventional reerve become more difficult to acce,other uch a oil hale and tar and may be ued intead.Petrol could alo be obtained from coal.