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The water world
The British Isles is surrounded by water. Having tides, waves and water currents in the sea and with a relatively high rainfall to give full rivers most of the year, it is natural to see if water power can be used to solve our desperate energy situation. There are three main areas that are presently under investigation:
Wave energy
Tidal energy
and Hydro-power
Other specialist methods of energy production come from , for instance, Ocean Thermal Energy Conversion (OTEC) where the differential temperatures of deep and surface water ocean layers can be used as an energy source. Such systems are more likely to be suitable in equatorial regions of the world.
A comprehensive text on Renewal Energy Resources, with excellent sections on the above three topics, is listed below:
Wave energy
Through a combination of wind and tide, the sea is more often than not in a constant state of agitation and this energy can be harnessed for electricity generation. Serious work on wave power dates back to the Salter Duck in the mid 1970's but has only now been resurrected as the availability and cost of fossil fuels is causing concern. Work at Manchester is concentrating on a raft of floating concrete cylindars which bob up and down on a passing train of waves. An illustration is given below
At the present stage prototype models are being investigated in a wave tank at the Joule Centre at Manchester University to ascertain the optimum spacing and arrangement of bobbers and, in approximately a years time, field trials are planned to take place along the coast in North Wales. ( for information see the web site www.manchesterbobber.com )
Other examples of wave power are given below.
Pelamis Wave energy This installation looks like a giant snake wriggling on the surface of the sea. By having interconnected floating cylindars the relative motion can be harnessed through hydraulic couplers to produce mechanical energy to drive electrical generators. Power is transfered to shore by cables on the sea floor.
Press announcement 24th September 2008 The world's first commercial wave power project has been anounced today. The energy converters are semi-submerged cylindrical chambers connected by hinged joints. The relative movement of these chambers generates electrical energy which is taken ashore via cables. The installation is 3 miles off the southern Portuguese coast and the three promoters of the venture are Babcock and Brown, Energias de Portugal (EDP) and Pelamis Wave Power Ltd based in Edinburgh. More details on www.pelamiswave.com . An explanation and pictorial description is given in www.darvill.clara.net . From the home page choose "online material" on the left hand side. Click on Energy Resources and, again, on Wave Power and at the end the is a video presentation of the Pelamis wave machine.
Press reports in April 2009 have indicated that there are problems with the Pelamis installation off the coast of Portugal.
Searaiser The idea with this two chamber device is to use wave energy to pump water "UP HILL". Since waves only occur on the surface of the sea there is relative motion between an upper chamber floating on waves at the surface and a lower chamber (motionless) tethered to the sea bed. This relative motion can be used to pump water, say, to a reservoir on land . Microgeneration can then take place as the water returns to the sea www.thiet.org . The device is described in the Institute of Engineering and Technology - go to magazines, then Issue 20 of Engineering and Technology, the article is entitled "Push and Pull" on page 27.
Trident Energy Several devices on trial. Unfortunately, recent trial (22 September 2009) suffered a setback as the device capsized as it was being towed into position off the Suffolk coastline.
Tidal Power
Largely through gravitational attraction from the moon, ( tidal effect of the sun is 2.2 times less than that of the moon) the oceans around the earth bulge out along the Earth-Moon axis and, as the earth revolves, this bulge (tidal range) impinges on the shore line. In mid-ocean the tidal range is very modest, about half a metre, but estuaries magnify the tide many times so that the Tidal range in the Seven Estuary is about 10 m. Exploitation of tidal energy is beset by environmental objections that bird habitat, marshlands and hydrological coastal dynamics will all be severely altered, although an installation in La Rance in France has been operationg for decades.
An alterative method of harnessing tidal energy it to employ marine turbines as illustrated below:
With the steel tower attached to the sea bed, turbines are mounted on each side to revolve in both incoming and outgoing tides. With such an installation the environmental impact is minimal and the capital cost is a fraction of that necessary to construct a tidal barrage.
An installation like the above has been operating successfully in Strangford L., Northern Ireland for two years and sonar readings are taken to check if the turbines are disturbing marine life. So far there has been no obvious ill effects.
There are many other areas in the Irish sea that would provide equally good locations for tidal turbines as show on the map below:
The headlands of Angelsey and the Isle of Man have strong tidal currents marked by a red contour.
( visit the site www.marineturbines.com )
Hydro-power
This is without doubt the oldest of our energy sources from water power and water wheels were used in pre-industrial Britain to power many factories. Later electricity generation became the primary output from hydro-power so often any water energy source is synonymous with hydroelectric power.
We all know about the major projects in the world, the Three Gorges scheme in China, for instance, but there are a host of weirs up and down the country (remnants of our industrial heritage) and some of these are now being brought into use - www.newmillshydro.com - www.h2ope.org.uk- and many others. Such power sources will provide electricity for local needs and can be set up on a community basis.
Summary
In general terms the water world gives energy sources that are more predicable that those developed from wind or sunshine and are therefore more ameanable to networking into our national grid. Rights of ownership about land in estuaries or water flowing in rivers may pose some problems but there does appear to be exciting possibilities for this type of renewable resource.
It may be worth looking at the energy profiles of different countries to see how hydro-power is contributing to their total energy mix. If a Google search is carried out with " Energy from Earth trends" one usually can open a searchable database for each country. Although the data has not been updated since 1999, comparative figures will not have changed a great deal. For instance, Norway is a country where hydro-power contributes significantly to the energy mix as shown below:
Figures given for 1999 are - 14.8 Mtoe from fossil fuels, 10.4 Mtoe for hydro-power, 1.3 Mtoe renewable
Most of the electricity is produced from water power and, therefore, Norway is getting close to a 50:50 mix of renewable ( mainly hydroelectric) and fossil energy.
The UK in contrast is almost totally dependent on fossil fuels for its energy supply ( 200 Mtoe) with a very small amount of hydroelectricity ( 0.46 Mtoe ).
This page is just a taster for further reading into this important topic:
- as the tide ebbs and flows, as the waves beat our shores and as water flows from the mountains to the seas -
they are all part of the water world that contains usable energy and what we don't extract today we never shall, because it will be lost in the pages of history.
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