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[01:15.87Producing enough energy to meet our needs has become a seriousproblem.

[01:20.06Demand is rising rapidly, because of the world’s increasingpopulation and expanding industry.

[01:28.27Burning fossil fuels, like gas, coal and oil, seriously damagesthe environment and they’ll eventually run out.

[01:37.92For a number of years now, scientists have been working out how wecan derive energy from renewable sources, such as the sun and wind, withoutcausing pollution.

[01:50.55Today I’ll outline marine renewable energy – also called oceanenergy – which harnesses the movement of the oceans.

[02:00.57Marine renewable energy can be divided into three main categories:wave energy, tidal energy and ocean thermal energy conversion, and I’ll say afew words about each one.

[02:18.08First, wave energy.

[02:21.25Numerous devices have been invented to harvest wave energy, withnames such as Wave Dragon, the Penguin and Mighty Whale, and research is goingon to try and come up with a really efficient method.

[02:37.28This form of energy has plenty of potential, as the source isconstant, and there’s no danger of waves coming to a standstill.

[02:47.19Electricity can be generated using onshore systems, using areservoir, or offshore systems.

[02:56.43But the problem with ocean waves is that they’re erratic, with thewind making them travel in every direction.

[03:06.35This adds to the difficulty of creating efficient technology:ideally all the waves would travel smoothly and regularly along the samestraight line.

[03:18.99Another drawback is that sand and other sediment on the oceanfloor might be stopped from flowing normally, which can lead to environmentalproblems.

[03:35.42The second category of marine energy that I’ll mention is tidalenergy.

[03:40.97One major advantage of using the tide, rather than waves, as asource of energy is that it’s predictable: we know the exact times of high andlow tides for years to come.

[03:56.33For tidal energy to be effective, the difference between high andlow tides needs to be at least five metres, and this occurs naturally in onlyabout forty places on Earth.

[04:11.80But the right conditions can be created by constructing a tidallagoon, an area of sea water separated from the sea.

[04:22.87One current plan is to create a tidal lagoon on the coast ofWales.

[04:28.62This will be an area of water within a bay at Swansea, shelteredby a U-shaped breakwater, or dam, built out from the coast.

[04:39.70The breakwater will contain sixteen hydro turbines, and as thetide rises, water rushes through the breakwater, activating the turbines, whichturn a generator to produce electricity.

[04:55.70Then, for three hours as the tide goes out, the water is held backwithin the break water, increasing the difference in water level, until it’sseveral metres higher within the lagoon than in the open sea.

[05:10.91Then, in order to release the stored water, gates in thebreakwater are opened.

[05:17.69It pours powerfully out of the lagoon, driving the turbines in thebreakwater in the opposite direction and again generating thousands of megawattsof electricity.

[05:30.32As there are two high tides a day, this lagoon scheme wouldgenerate electricity four times a day, every day, for a total of around 14 hoursin every 24 – and enough electricity for over 150,000 homes.

[05:50.85This system has quite a lot in its favour: unlike solar and windenergy it doesn’t depend on the weather; the turbines are operated without theneed for fuel, so it doesn’t create any greenhouse gas emissions; and verylittle maintenance is needed.

[06:07.93It’s estimated that electricity generated in this way will berelatively cheap, and that manufacturing the components would create more than2,000 jobs, a big boost to the local economy.

[06:22.20On the other hand, there are fears that lagoons might harm bothfish and birds, for example by disturbing migration patterns, and causing abuild-up of silt, affecting local ecosystems.

[06:37.72There are other forms of tidal energy, but I’ll go on to the thirdcategory of marine energy: ocean thermal energy conversion.

[06:47.92This depends on there being a big difference in temperaturebetween surface water and the water a couple of kilometres below the surface,and this occurs in tropical coastal areas.

[07:02.52The idea is to bring cold water up to the surface using asubmerged pipe.

[07:08.69The concept dates back to 1881, when…

出产满足的动力来满足咱们的需要已变成一个严峻的疑问。

因为世界人员的增加和工业的打开，需要正在灵敏增加。

燃烧化石燃料，如天然气、煤和石油，会严峻损坏环境，而且它们究竟都会耗尽。

多年来，科学家们一向在研讨如何在不构成污染的情况下从可再生本钱中获取动力，比方太阳和风。

今日，我将概述海洋可再生动力，也被称为海洋动力，它使用海洋的运动发生能量。

海洋可再生动力可分为波能、潮汐能和海洋热能变换三个首要品种，我将别离进行一些阐明。

首要，波能。

我们创造了许多设备来获取波能，这些设备的名字有“波涛龙”、“企鹅”和“巨鲸”等。我们也进行着研讨，企图找到一种真实有用的办法。

这种方法的能量有很大的潜力，因为它的来历是平稳的，没有波涛中止的风险。

电力可以使用陆上体系、水库或近海体系发生。

可是波涛的疑问是它们很不平稳，风让它们朝各个方向移动。

这给创造高效技能添加了难度：抱负的情况是，一切的波涛都沿着同一条直线平稳而有规则地行进。

另一个缺陷是，海底的沙和其他堆积物可以无法正常活动，这可致使使环境疑问。

我要说到的第二类海洋动力是潮汐能。

使用潮汐而不是波涛作为能量来历的一个首要利益是，它是可猜测的：咱们可以猜测将来几年潮汐涨落的切当时刻。

为了使潮汐能有用，涨潮和退潮之间的高度差至少需要五米，而在天然条件下在地球上只需大约四十个当方单合条件。

可是经过缔造潮汐泻湖–一个与海洋别离的海水区域，咱们可以创造这样的条件。

当前的一个方案是在威尔士海岸缔造一个潮汐泻湖。

这将是在斯旺西的海湾内的一个水域，它会受一个从海岸缔造的U形防波堤，或大坝的保护。

防波堤将包括16个

水轮机，当涨潮时，水冲过防波堤，激活了涡轮机，使发电机发电。

然后，在退潮的三个小时里，海水被挡在防波堤里，添加了水位的差异，直到它在泻湖里比在公海里高出几米。

然后，为了开释储存的水，防波堤的闸口被翻开。

水有力地从泻湖中涌出，向反方向推进防波堤的涡轮机，并再次发生数千兆瓦的电力。

因为每天有两次涨潮，这个泻湖方案将每天发电四次，每24小时中发电14小时，满足跨越150,000个家庭运用。

这个体系有许多利益：与太阳能和风能不一样，它不依靠于气候;涡轮机的运转不需要燃料，所以它不会发生任何温室气体排放;而且几乎不需要维护。

据估量，以这种方法发电的本钱相对较低，一起，制造这些部件将创造2000多个作业机缘，大大推进当地经济的打开。

另一方面，我们忧虑泻湖可以损害鱼类和鸟类，例如打乱迁徙方法，构成淤泥堆积，影响当地生态体系。

还有其它方法的潮汐能，但我会持续讲第三类海洋动力：海洋热能变换。

这种动力依靠于海平面海水与在海面以下几公里海水的无量温差，而这种情况发生在热带沿海区域。

这种办法是使用水下管道将冷水带到表面。

这个概念可以追溯到1881年，那时……

SECTION 4 Questions 31-40

Complete the notes below.

Write ONE WORD ONLY for each answer.

Marine renewable energy (ocean energy)

Introduction

More energy required because of growth in population and 31 ________

What’s needed:

· renewable energy sources

· methods that won’t create pollution

Wave energy

Advantage: waves provide a 32 ________ source of renewable energy

Electricity can be generated using offshore or onshore systems

Onshore systems may use a reservoir

Problems:

· waves can move in any 33 ________

· movement of sand etc. on the 34 ________ of the ocean may be affected

Tidal energy

Tides are more 35 ________ than waves

Planned tidal lagoon in Wales:

· will be created in a 36 ________ at Swansea

· breakwater (dam) containing 16 turbines

· rising tide forces water through turbines, generating electricity

· stored water is released through 37 ________ , driving the turbines in the reverse direction

Advantages:

· not dependent on weather

· no 38 ________ is required to make it work

· likely to create a number of 39 ________

Problem:

· may harm fish and birds, e.g. by affecting 40 ________ and building up silt

Ocean thermal energy conversion

Uses a difference in temperature between the surface and lower levels

Water brought to the surface in a pipe

31 industry

32 constant

33 direction

34 floor

35 predictable

36 bay

37 gates

38 fuel

39 jobs

40 migration