1Producing enough energy to meet our needs has become a serious problem.
2Demand is rising rapidly,
3because of the world's increasing population and expanding industry.
4Burning fossil fuels, like gas, coal and oil,
5seriously damages the environment
6and they'll eventually run out.
7For a number of years now,
8scientists have been working out how we can derive energy from renewable sources,
9such as the sun and wind, without causing pollution.
10Today I'll outline marine renewable energy - also called ocean energy -
11which harnesses the movement of the oceans.
12Marine renewable energy can be divided into three main categories:
13wave energy, tidal energy and ocean thermal energy conversion,
14and I'll say a few words about each one.
15First, wave energy.
16Numerous devices have been invented to harvest wave energy,
17with names such as Wave Dragon, the Penguin and Mighty Whale,
18and research is going on to try and come up with a really efficient method.
19This form of energy has plenty of potential, as the source is constant,
20and there's no danger of waves coming to a standstill.
21Electricity can be generated using onshore systems,
22using a reservoir, or offshore systems.
23But the problem with ocean waves is that they're erratic,
24with the winds making them travel in every direction.
25This adds to the difficulty of creating efficient technology:
26ideally all the waves would travel smoothly and regularly along the same straight line.
27Another drawback is that sand and other sediment on the ocean floor
28might be stopped from flowing normally,
29which can lead to environmental problems.
30The second category of marine energy that I'll mention is tidal energy.
31One major advantage of using the tide, rather than waves, as a source of energy
32is that it's predictable:
33we know the exact times of high and low tides for years to come.
34For tidal energy to be effective,
35the difference between high and low tides needs to be at least five metres,
36and this occurs naturally in only about forty places on Earth.
37But the right conditions can be created by constructing a tidal lagoon,
38an area of sea water separated from the sea.
39One current plan is to create a tidal lagoon on the coast of Wales.
40This will be an area of water within a bay at Swansea,
41sheltered by a U-shaped breakwater, or dam, built out from the coast.
42The breakwater will contain sixteen hydro turbines,
43and as the tide rises, water rushes through the breakwater,
44activating the turbines, which turn a generator to produce electricity.
45Then, for three hours as the tide goes out,
46the water is held back within the breakwater,
47increasing the difference in water level,
48until it's several metres higher within the lagoon than in the open sea.
49Then, in order to release the stored water,
50gates in the breakwater are opened.
51It pours powerfully out of the lagoon,
52driving the turbines in the breakwater in the opposite direction
53and again generating thousands of megawatts of electricity.
54As there are two high tides a day,
55this lagoon scheme would generate electricity four times a day, every day,
56for a total of around 14 hours in every 24,
57and enough electricity for over 150,000 homes.
58This system has quite a lot in its favour:
59unlike solar and wind energy it doesn't depend on the weather;
60the turbines are operated without the need for fuel,
61so it doesn't create any greenhouse gas emissions;
62and very little maintenance is needed.
63It's estimated that electricity generated in this way will be relatively cheap,
64and that manufacturing the components would create more than 2,000 jobs,
65a big boost to the local economy.
66On the other hand,
67there are fears that lagoons might harm both fish and birds,
68for example by disturbing migration patterns,
69and causing a build-up of silt, affecting local ecosystems.
70There are other forms of tidal energy,
71but I'll go on to the third category of marine energy:
72ocean thermal energy conversion.
73This depends on there being a big difference in temperature
74between surface water and the water a couple of kilometres below the surface,
75and this occurs in tropical coastal areas.
76The idea is to bring cold water up to the surface using a submerged pipe.
77The concept dates back to 1881...