Section 4

Section four.

You will hear part of a lecture on renewable energy that uses the power of the sea.

First you have some time to look at questions 31 to 40.

Now listen carefully and answer questions 31 to 40.

Producing enough energy to meet our needs has become a serious problem.

Demand is rising rapidly because of the world’s increasing population and expanding industry.

Burning fossil fuels like gas coal and oil seriously damages the environment, and they’ll eventually run out.

For a number of years now scientists have been working out how we can derive energy from renewable sources, such as the Sun and wind without causing pollution.

Today I’ll outline marine renewable energy also called ocean energy which harnesses the movement of the oceans.

Marine renewable energy can be divided into three main categories, wave energy, tidal energy, and ocean thermal energy conversion and I’ll say a few words about each one.

First wave energy, numerous devices have been invented to harvest wave energy with names such as wave dragon, the penguin, and mighty whale and research is going on to try and come up with a really efficient method.

This form of energy has plenty of potential as the source is constant and there’s no danger of waves coming to a standstill.

Electricity can be generated using onshore systems using a reservoir or offshore systems.

But the problem with ocean waves is that they’re erratic with the winds making them travel in every direction.

This adds to the difficulty of creating efficient technology, ideally all the waves would travel smoothly and regularly along the same straight line.

Another drawback is that sand and other sediment on the ocean floor might be stopped from flowing normally, which can lead to environmental problems.

The second category of marine energy that I’ll mention is tidal energy, one major advantage of using the tide rather than waves as a source of energy is that it’s predictable.

We know the exact times of high and low tides for years to come.

For tidal energy to be effective the difference between high and low tides needs to be at least 5 meters and this occurs naturally in only about 40 places on earth.

But the right conditions can be created by constructing a tidal lagoon an area of sea water separated from the sea.

One current plan is to create a tidal lagoon on the coast of Wales, this will be an area of water within a bay that Swansea sheltered by a u-shaped breakwater or dam built out from the coast.

The breakwater will contain 16 hydro turbines, and as the tide rises water rushes through the breakwater activating the turbines which turn a generator to produce electricity.

Then for three hours as the tide goes out, the water is held back within the breakwater increasing the difference in water level until it’s several meters higher within the lagoon than in the open sea.

Then in order to release the stored water, gates in the breakwater are opened, it pours powerfully out of the lagoon driving the turbines in the breakwater in the opposite direction and again generating thousands of megawatts of electricity.

As there are two high tides a day this Lagoon scheme would generate electricity four times a day every day for a total of around 14 hours in every 24.

And enough electricity for over a hundred and fifty thousand homes.

This system has quite a lot in its favour unlike solar and wind energy it doesn’t depend on the weather, the turbines are operated without the need for fuel so it doesn’t create any greenhouse gas emissions and very little maintenance is needed.

It’s estimated that electricity generated in this way will be relatively cheap and that manufacturing the components would create more than 2,000 jobs, a big boost to the local economy.

On the other hand there are fears that lagoons might harm both fish and birds for example, by disturbing migration patterns and causing a buildup of silt affecting local ecosystems.

There are other forms of tidal energy but I’ll go on to the third category of marine energy, ocean thermal energy conversion.

This depends on there being a big difference in temperature between surface water and the water a couple of kilometers below the surface, and this occurs in tropical coastal areas.

The idea is to bring cold water up to the surface using a submerged pipe, the concept dates back to 1881.

That is the end of section four, you now have half a minute to check your answers.

That is the end of the test.

In the IELTS test you would now have 10 minutes to transfer your answers to the answer sheet.