Hydro power
introduction
We have used running water as an energy source for thousands of years, mainly to grind corn.
The first house in the world to be lit by hydroelectricity was Cragside House, in Northumberland, England, in 1878. In 1882 on the Fox River, in the USA, hydroelectricity produced enough power to light two paper mills and ahouse.
Nowadays there are many hydro-electric power stations, providing around 20% of the world's electricity, The name comes from "hydro", the Greek word for water.
How it works
A dam is built to trap water, usually in a valley where there is an existing lake.
Water is allowed to flow through tunnels in the darn, to turn turbines and thus drive generators.Advantages
Once the dam is built, the energy is virtually free.No waste or pollution produced.
Much more reliable than wind, solar or wave power.
Water can be stored above the dam ready to cope with peaks in demand.
Hydro-electric power stations can increase to full power very quickly, unlike other power stations.Disadvantages
The dams are very expensive to build.
Building a large dam will flood a very large area upstream, causing problems for animals that used to live there.Finding a suitable site can be difficult--the impact on residents and the environment may be unacceptable.
Water quality and quantity downstream can be affected, which can have an impact on plant life.Is it renewable?
Hydro-electric power is renewable,
The Sun provides the water by evaporation from the sea, and will keep on doing so.
Nuclear power
Introduction
Nuclear power is generated using Uranium, which is a metal mined in various parts of the world.The first large-scale nuclear power station opened at Calder Hall in Cambria, England, in 1956.Some military ships and submarines have nuclear power plants for engines.
How it works
Nuclear power stations work in pretty much the same way as fossil fuel-burning stations, except that a "chain reaction" inside a nuclear reactor makes the heat instead.
The reactor uses Uranium rods as fuel, and the heat is generated by nuclear fission. Neutrons smash into the nu-cleus of the uranium atoms, which split roughly in half and release energy in the form of heat.
Carbon dioxide gas is pumped through the reactor to take the heat away, and the hot gas then heats water to make steam.
Advantages
Nuclear power costs about the same as coal, so it' s not expensive to make.
Does not produce smoke or carbon dioxide, so it does not contribute to the greenhouse effect.Produces huge amounts of energy from small amounts of fuel.
Produces small amounts of waste.Disadvantages
Although not much waste is produced, it is very, very dangerous.
It must be sealed up and buried for many years to allow the radioactivity to die away.Nuclear power is reliable, but a lot of money has to be spent on safety.
Is it renewable?
Nuclear energy from Uranium is not renewable.
Once we' ve dug up all the Earth' s uranium and used it, there isn' t any more.
Solar power
Introduction
We' ve used the Sun for drying clothes and food for thousands of years, but only recently have we been able to use it for generating power.
The Sun is 150 million kilometers away, and amazingly powerful.
Just the tiny fraction of the Sun' s energy that hits the Earth ( around a hundredth of a millionth of a percent) is enough to meet all our power needs many times over.
How it works
There are three main ways that we use the Sun' s energy:
Solar Cells (really called "photovoltaic" or "photoelectric" cells) that convert light directly into electricity.
In a sunny climate, you can get enough power to run a 100W light bulb from just one square meter of solar panel.This was originally developed in order to provide electricity for satellites, but these days many of us own calcu-lators powered by solar cells.
Solar water heating, where heat from the Sun is used to heat water in glass panels on your roof.This means you don' t need to use so much gas or electricity to heat your water at home.
Solar Furnaces use a huge array of mirrors to concentrate the Sun' s energy into a small space and produce very high temperatures.AdvantagesSolar energy is free--it needs no fuel and produces no waste or pollution.
In sunny countries, solar power can be used where there is no easy way to get electricity to a remote place.Handy for low-power uses such as solar powered garden lights and battery chargers.
Disadvantages
Doesn' t work at night.
Very expensive to build solar power stations.
Solar cells cost a great deal compared to the amount of electricity they' 11 produce in their lifetime.Can be unreliable unless you' re in a very sunny climate.
Is it renewable?
Solar power is renewable. The Sun will keep on shining anyway, so it makes sense to use it.
Wind power
Introduction
We' ve used the wind as an energy source for a long time. The Babylonians and Chinese were using wind pow-er to pump water for irrigating crops 4,000 years ago, and sailing boats were around long before that.
Wind power was used in the Middle Ages, in Europe, to grind corn, which is where the term "windmill" comes from.
How it works
The Sun heats our atmosphere unevenly, so some patches become warmer than others.
These warm patches of air rise, other air blows in to replace them--and we feel a wind blowing.
We can use the energy in the wind by building a tall tower, with a large propeller on the top. The wind blows the propeller round, which turns a generator to produce electricity.
The more towers, the more wind, and the larger the propellers, the more electricity we can make.
Advantages
Wind is free. wind farms need no fuel.
Produees no waste or greenhouse gases.
The land beneath can usually still be used for farming.Wind farms can be tourist attractions.
A good method of supplying energy to remote areas.Disadvantages
The wind is not always predictable--some days have no wind.
Suitable areas for wind farms are often near the coast, where land is expensive.Can kill birds--migrating flocks tend to like strong winds.
Can affect television reception if you live nearby.Is it renewable?
Wind power is renewable. Winds will keep on blowing; it makes sense to use them.
Section IV Writing
(40 minutes)
It is generally acknowledged that families are now not as close as they used to be. Give possible reasons and your commendations.
You should write no less than 250 words. Write your article on ANSWER SHEET 2.
THE END OF THE TEST
Section II Use of English(每小题1分。共计20分，权重l0%)
