[Meten upgrade composition] With the rapid development of science and economic, the Earth is now suffering from heavy energy consumption and pollution. Global warming is not just a term but we indeed face the extreme weather more frequently than 20 years ago. The main reason of global warming is the release of heat keeping gases which are well known CO2 and CH4. These gases mostly come from energy making by burning resources like oil which are called “Unrenewable resources”.

According to Figure 1, by the end of 2008, nearly 3/4 of the energy supply in the world comes from oil, coal, and natural gas. These products have become more expensive than two decades ago and the price is still growing year after year. Without other replaceable resources, countries will be ended as a result of fighting for energy. People in the world has realized this problem and started researches on eco-friendly, renewable energy which is normally termed “Green Energy” or “Green Power”. Large hydropower, biomass heating power, solar collector power and wind power are the four largest portions in renewable energy supply.

Figure Renewable energy Hydropower station uses water level to produce power. A dam is usually built to stop water in order that the water level can go higher. Hydropower does not contribute significant CO2 and “can be far less expensive than electricity generated from fossil fuels or nuclear energy” (Modern Usage, Hydropower, Wikipedia). And it is easy to save the power by stopping the water when power consumption is not high. Although hydropower contributes half of the whole renewable energy, the environmental impacts of the dam are considered more and more in recent years. The eco-system is changed; fishes disappear; a large number of people have to move to other places; historical heritages will keep underwater forever or will have to move higher; and researchers have found many disasters may have some relations with the big dam. Figure Three gorges dam Biomass heating power is an old and traditional way to produce power. When fire wood, it produces power. This kind of energy releases green house gases into air. Should it be green energy? Scientists have found that wood burning does not release any more CO2 than let it be rotten. It just releases what trees absorbed. This is so called carbon cycle. And the fire is the solar energy trees stored. Though wood burning is green, the way of transportation of wood does produce more greenhouse gas.

**Figure Wood burning ** Solar power is the most natural, costless, zero CO2 power. All of our energy initially comes from the sun. Two main methods are commonly used: solar cells generate electricity directly and solar heat to boil the water to steam then the steam drives the turbine to produce electricity. The first way can be used widely in housing power supply, car battery charging or even aerospace although it largely depends on the sunshine. The second way is more efficient and scientists have already found the way to store the power. The cost and unmovable are the main drawbacks of solar heat power. Figure Giant photovoltaic array Figure Solar heat power Wind power is growing rapidly with the capacity from 74GW in 2006 to 121GW in 2008 globally. European countries like Denmark, Spain, Portugal, and Germany had a ration of above 5% of energy from wind power. Not only can the wind power farm be built on the land, it also can be on the sea. The sea wind provides more stable and powerful wind than on the land. The main challenge is how to store the power because wind is not stable.

Figure Wind power These green sources are mainly used in large scale power stations to produce electricity. But cars cannot eat electricity directly and the process of saving the electricity to battery and releasing it to make car move is not mature; they need a kind of replacement. Scientists are making progress on a new kind of oil which is bio-fuel, so traditional engines can produce power directly from this oil without any modification. In development of this fuel, scientists must balance the total energy outcome and environmental cost. Figure Sugar cane can be used as a bio-fuel The sources of first generation of bio-fuel are corn, bean and cane which can use mature technology to make bio-fuel. But it will not last long because there’s no enough farms to satisfy the need which is growing by 10% every year. Scientists are also concerning about the whole carbon release from the beginning of the planting to the final product. The second generation bio-fuel is on the way, which mainly uses grasses to produce bio-fuel and could be more productive and environmentally friendly.

In conclusion, though classical oil resources are still occupying the main energy market, new green energy technologies are now taking fast lane. These technologies will finally give the earth a bright, clean future.