<script>on mouseUpput the short name of this card into xTempput char 2 to 6 of xTemp & ".mov" into Movie--put Movieif Movie is not empty then-- put "Animations:" & Movie into pMovieplayMovie Movie,"Animations:"end ifend mouseUp</script>
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<text><span class="style10">nergy (4 of 5) 2. Other Sources</span><span class="style7"></span><span class="style10">Water power</span><span class="style7">The average power in waves washing the North Atlantic coast of Europe is 50 kW per meter of wave front. Many ingenious techniques have been devised to harness this power, ranging from systems of rafts or floats known as 'ducks', rings of air bags known as 'clams', or columns in which water is forced up and down. Much effort has gone into the development of such techniques, but it has proved difficult to design structures capable of withstanding the force of the waves with- out excessive maintenance. It has become clear that wave power will not easily produce the hoped-for quantities of cheap energy.The power of running water has long been exploited by water mills - one of the most ancient means of harnessing the power of the elements. In some countries, </span><span class="style19">hydroelectric power</span><span class="style7">, or 'hydropower', is the most important source of energy. Hydropower provides 8% of Western Europe's energy, and worldwide it provides roughly as much energy as nuclear power. Major projects can be controversial as they may involve flooding environmentally sensitive areas. However, the latest design of low-head water turbines has reduced the necessary height difference (the 'head') between the turbine and the surface of the reservoir, so making it possible to build smaller barrages or even to place turbines directly into river beds.Tidal movements - ultimately derived from the Earth's rotation - are potentially a vast source of energy. Where tidal currents are funneled into river estuaries, there is an opportunity to harness this energy. There are currently six tidal power stations in the world, the biggest of them at the Rance Estuary in Brittany, France. Proposed tidal power schemes across the Severn Estuary in Britain and the Bay of Fundy in Canada would be much bigger.</span><span class="style10">Geothermal power</span><span class="style7">Just 30 km (19 mi) beneath our feet, the rock has a temperature of around 900 degC (1650 degF). This heat comes primarily from the gradual radioactive decay of elements within the Earth. Strictly speaking, this source of power is not renewable, but it is immense. There is enough heat in the top 10 km (6 mi) of the Earth's crust, at depths accessible with current drilling techniques, to supply all our energy needs for hundreds of years.In some parts of the world, including Iceland, the amount of geothermal heat reaching the surface is distinctly greater than elsewhere, and can be used directly as a means of domestic heating. In other countries, blocks of flats are heated by hot water from wells 2 to 3 km (1 to 2 mi) deep.The biggest reserves of geothermal heat, however, are to be found deeper still, at 6 km (4 mi) or so. As the rocks at this depth are dry, it is harder and more costly to get the heat out, because it is necessary to pump down water in order to bring the heat up. In an experimental project in Cornwall, England, three boreholes drilled to a depth of 2 km (1 1/4 mi) have been interconnected with a system of cracks, allowing water to be pumped from one borehole to another. There are plans to drill holes to three times this depth, but even at current depths the water returns to the surface hot enough to produce steam to drive turbines. Some estimates suggest that in Cornwall and other areas where the rocks are hotter at shallower depths, schemes of this kind could ultimately yield energy for Britain equivalent to 10 billion tons of coal.</span></text>
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<text>ΓÇó THE SUN AND THE SOLAR SYSTEMΓÇó ELECTRICITY IN ACTIONΓÇó THE FORMATION OF ROCKSΓÇó THE OCEANSΓÇó FORESTRYΓÇó ENERGY 1</text>
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<text><span class="style10">he tidal power station at La Rance in Brittany, France</span><span class="style7">, opened in 1966, consists of a barrage blocking the 750 m (2460 ft) wide estuary of the River Rance. The tidal waters are channeled through 24 tunnels in the barrage (seen in cross-section below). Each tunnel houses a reversible turbine generator that can operate efficiently both on the flood tide (when the water flow is from sea to basin) and on the ebb tide (from basin to sea). At high tide, the sluices are closed, trapping the water in the tidal basin. The water can then be released to turn the turbines when the tide is low but when demand for power is high. Each of the 24 turbines can generate up to 10 MW -the total output of the plant being sufficient to satisfy the needs of around a million consumers.</span></text>
