首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
Complete the notes below. Write ONE WORD ONLY for each answer. Hydropower Renewable—constant source (31) from natural
Complete the notes below. Write ONE WORD ONLY for each answer. Hydropower Renewable—constant source (31) from natural
admin
2012-01-16
66
问题
Complete the notes below.
Write ONE WORD ONLY for each answer.
Hydropower
Renewable—constant source (31) from natural hydrologic cyde
(32) —90% of hydro energy→electricity
Clean—no air or (33) pollution
(34) & curable—simple to operate
Flexible—can start
adapt quickly to meet demand→leads to (35) of power supply.
Welcome to our series on renewable resources. The topic today is hydropower. As you most probably know, ’hydro’ means water—so we are talking about using water to generate electricity. Of course, there are many ways to generate electricity but hydropower is important to the community, firstly and obviously, because it’s renewable. The earth’s hydrologic cycle of constant evaporation and transpiration provides a continual supply of water from rainfall and snowmelt. The second point to consider is its efficiency. Hydropower plants are able to convert approximately 90% of the energy from the falling water into electric energy whereas many fossil-fuelled plants lose more than half of the energy content of their fuel by way of waste heat and gases. For this reason they are very efficient.
Hydropower is also clean. It doesn’t emit harmful gases that contribute to air pollution, acid rain, and global warming. No trucks, trains or pipelines are needed to bring fuel to the site and there’s no noise pollution either. Furthermore, hydropower plant machinery is fairly simple and runs at slow speeds, which makes it reliable and durable. And, hydropower units are flexible also—they have the ability to start quickly and adjust rapidly to changes in demand for electricity, thus enabling them to meet peak loads. But this also allows them to serve as reserve capacity and bring more stability to the power system overall.
The dams that provide hydroelectric power also have other uses such as navigation, flood damage reduction, water supply, recreation, irrigation and low flow augmentation but it’s not the purpose of this talk to go into those details.
How do the hydropower plants work? Well, a dam is built across a river which captures water to form a reservoir and raises the water level to create ’head’. Think of ’head’ as the vertical distance that the water falls as it passes through the dam, in other words, the difference in water level between the reservoir behind the dam and the river below. Water from the reservoir flows through an intake gate into a penstock—this is kind of a narrow channel which leads to the turbine below. The force of the water causes the turbine to rotate rapidly which, in turn, drives the generator to spin and produce electricity. The electricity is carried the long distances from the powerhouse to substations on the outskirts of cities via power lines.
Can you build a hydropower unit on any river? Well, no, just having water in a river isn’t enough. A good dam site must have enough stream flow as well as enough head. A fast flowing river on the plains is probably not suitable because a dam couldn’t be built high enough to provide the head needed for efficient production of electricity. On the other hand, dams in arid high country may have plenty of head but insufficient stream flow. The perfect spot for a hydropower plant is where the right combination of stream flow and head exists.
What about the environment? Surely the construction of large dams has an environmental impact? Well, yes it does. Certainly dams and reservoirs are built to improve the lives of people living in towns, farming communities and cities. But there must be a balance between development and preserving the natural environment. Needless to say, the natural river environment is changed which leads to changes in river ecology and aquatic habitat. Sometimes, for example, dissolved oxygen levels below dams get so low in summer that there is a negative impact on aquatic life. These levels can be improved, however, by using special aerating turbines and/or injecting oxygen directly into the stream flow. In order to protect and improve the habitat for endangered and other species of birds, fish and water life, there needs to be a thorough review of operating plans to see if a better balance can be achieved.
Hydropower plant design and operation must not only meet the needs of consumers for electricity but work hand-in-hand with agencies whose concern is for the fish and wildlife, water quality and water supply.
选项
答案
reliable
解析
转载请注明原文地址:https://kaotiyun.com/show/TjAO777K
本试题收录于:
雅思听力题库雅思(IELTS)分类
0
雅思听力
雅思(IELTS)
相关试题推荐
Thepainterlamentedtheevanescenceofbeauty,eventhoughsheseemedinseveralofherworktohave(i)______itasitpasseda
Withinthecultureasawhole,thenaturalscienceshavebeensosuccessfulthattheword“scientific”isoftenusedin________
Naturalcausesnervestodieoffandmusclestoweaken,butregularexercisemuscleenlargesfibersandcan________thedecline
Intheearth20thcentury,somesmallmagazinesandtheinnovativegraphicsusedonthemcreatedthefaceofavant-garde.Avant-
Intheearth20thcentury,somesmallmagazinesandtheinnovativegraphicsusedonthemcreatedthefaceofavant-garde.Avant-
Themuseum’scompellingnewarchitecturalexhibitionlooksatelevenprojectsaroundtheworldthathavehadmajor(i)__________
Anumberofwriterswhooncegreatly(i)______theliterarycritichaverecentlyrecanted,substituting(ii)______fortheirfor
Massiveprojectilesstrikingmuchlargerbodiescreatevariouskindsofcraters,includingmulti-ringbasins–thelargestgeologi
WhyGirlsNeedtoSwitchontoComputingThegardeniscomingalongnicely.Flowersspringintobloomintheherbaceousborders;
A、hasnofees.B、haslowfees.C、avoidspayingfees.B
随机试题
不属于心源性哮喘与支气管哮喘的鉴别点是
委托代理人选定的转代理人亦即复代理人为()
下列关于牵张反射的叙述,错误的是
(2014年第87题)男性,75岁。因腹股沟斜疝嵌顿2天急诊手术。术中见疝囊内有大团小肠,仍有活力,并有少量淡黄色渗出液,松解疝环,将小肠还纳腹腔并作疝修补术。术后第2天,患者觉腹痛较前加重,T38.8℃,腹部压痛、反跳痛、肌紧张,WBC18×109/
心脏骤停后,要求尽可能在几分钟内给予除颤
A.维拉帕米B.利多卡因C.美托洛尔D.尼莫地平E.苯妥英钠急性心梗二级预防
在代理买卖证券过程中,证券公司对于证券买卖后形成的盈利有权参与分享;同样证券公司对于证券买卖后形成的损失需承担责任。()
社会主义协商民主就是在党的领导下,社会各个政党、阶层、团体、群众等,就共同关心或利益相关的问题,以适当方式进行协商,形成各方均可接受的方案,做出决策或决定,以实现整体的发展。发展社会主义协商民主有利于()。①我国发展西方主流民主形式②平衡整合社会各
下列选项中,能够引起不当得利之债发生的是()。
劳动力商品在使用价值上的特殊性在于
最新回复
(
0
)