Energy from the Oceans
| Event Name | Energy from the Oceans |
| Start Date | 17th Mar 2009 6:00pm |
| End Date | 17th Mar 2009 9:00pm |
| Duration | 3 hours |
| Description | Lecture by AbuBakr Bahaj Contact: Hilary Carrington Professor Bahaj is the Head of Sustainable Energy in the School of Civil Engineering and the Environment at Southampton University. Some time ago, at the personal behest of the Duke of Edinburgh, he gave the RSA Sigma President's Lecture on the subject of harnessing marine energy. He spoke to a full house, creating a great deal of excitement and interest in his subject. We are very fortunate that he has agreed to give a similar lecture in South Central Region, at his own University, thus giving Fellows in our region the chance to hear his ideas and expertise. We are grateful to Professor Bahaj for making available this link to the illustrations and tables used in this lecture. Professor Bahaj opened by reviewing the drivers for the quest for renewable sources of energy. The Government is a signatory to the Kyoto Protocol and has agreed to reduce CO2 emissions by 12.5% of 1990 levels by 2012 and by 60% by 2050. The Government has also set targets for electricity generation capacity from renewable sources of 10% by 2010 and 20% by 2020. Wind and water generation potential is estimated to be about 20% of UK demand. Other drivers are diminishing fossil fuel supplies, the requirement to maintain security of fuel and power supplies and the need to maintain the UK as an environment for technological and commercial development of renewable energy generators including the option of exporting the technology. Sources of renewable energy are sunlight, gravitational effects and geothermal heat. One hour of sunlight has sufficient energy to supply our needs for a whole year. Solar energy is converted by four processes, vegetatively through photosynthesis to produce plant growth and biofuels, kinetic energy which produces the wind and waves, latent heat or potential energy which produces rain, rivers and hydro power and sensible heat which can produce water heating for the home, radiation to power photovoltaic cells and ocean thermal energy and currents which can be harnessed to generate electricity and produce clean water. The gravitational effect of the moon – Lunar Gravity – produces the wave which we call tides and which results in tidal currents also called tidal streams. Geothermal energy captures the heat deep underground and uses it to heat water. Southampton, where this lecture was being given, has the only Geothermal Heating Plant in this country which is used to provide district heating for part of the centre of the city including the Civic Offices, which are known as the Civic Centre building. Currently Wind Power is the only established renewable power generation technology, which is accordingly described as a stable technology, but it has the disadvantage that it is very variable and its output is unpredictable. Surveys of potential wave power show that 80% of the wave power available to Europe lies off the United Kingdom and Irish coasts due the long fetch, the distance that a wave can travel before reaching land. However in a diagram of intensity of potential wave power, which is proportional to wave height, it was shown that the areas of greatest wave energy lie well off shore in deep water. This poses problems for the design and maintenance of installations to withstand the force of the sea, its aggressive nature and of bringing the electrical power ashore. One advantage of wave power is that it is greatest during the autumn, winter and spring months when demand for electricity is at its greatest but it is still a relatively unpredictable resource. There have been a number of attempts to develop wave power technologies over the past four decades with periodic spells of inactivity during periods of financial downturn. In 1975 there was a Government target for renewable energy generation capacity of 2000 megawatts. A variety of approaches have been tried without any becoming established as the proven technology. The Bristol Cylinder employed floats under the sea surface which rose and fell under the wave and generated power through hydraulic rams located in the anchorage to the sea bed. The Salter Duck was a series of floats whose cross-section was roughly tear-drop shaped which were fixed to an axial shaft about which they oscillated, generating power by means of a pendulum inside each float. Each float was large, about the size of a double decker bus, and to achieve a rated output of 2000 megawatts it would have required some 40 kilometres of arrays of floats. Several varieties of float have been tried which are anchored to the the sea bed and which generate power through the vertical movement of the float. Recently a device called the Pulamis http://www.pelamiswave.com/content.php?id=161 has been trialed in Scotland and in Portugal. It consists of a chain of four large cylindrical floats which is anchored at one end. This chain of floats moves relative to one another when following the profile of the waves. The relative movement of the joints drives hydraulic rams which in turn drive turbines. The latest development is the Anaconda http://www.soton.ac.uk/mediacentre/news/2008/jul/08_129.shtml which is a long flexible floating tube which also follows the profile of the waves but is of variable diameter causing a bulge to pass down the tube under the influence of the wave which in turn drives a hydraulic turbine. The Ocillating Water Column principle has been tried in a number of different devices both floating and shore based. The Mighty Whale is a Japanese example of a floating OWC device and the Limpet is a shore structure OWC. All of these rely on the action of waves to compress the air in a chamber which then drives a turbine. This turbine is usually a Wells turbine which continues to rotate in one direction when the airflow through it as the wave recedes. Attempts have been made to use natural coastal tapering channels of rock to funnel waves into turbines, of which the Norwegian TapChan is an example but any debris which enters the channel eventually enters or blocks the turbine. None of the earlier attempts at wave power generation have progressed beyond the prototype stage. Tidal power has been the subject of a lot research and computer modelling to analyse and predict the potential available. Using these models useable tidal current flows have been identified around the coast of the United Kingdom at a number of sites including Portland Bill, the Severn Estuary and the Pentland Firth. It has been estimated that the Pentland Firth has the potential to supply 10% of the UK’s power needs. Water is some 800 times more dense than air which means that a 20 metre diameter water turbine can deliver as much power as a 55 metre diameter wind turbine. Tidal stream velocities of between 2.2 and 2.5 metres per second are equivalent to wind speeds of 15 metres per second in term of the power they contain and these levels of tidal stream are found in a significant number of locations around our coasts. However the forces on turbines and the structures that house them can be very great, requiring expensive civil and structural engineering solutions whose cost escallates rapidly as the current speeds rise. Models of power available against the force acting show that tidal current maxima of 2.2 m/sec is considerably more economic than 2.5 m/sec because at 2.5m/sec the increase in available power is significantly less proportionately than the increase in the force to be resisted by the structures. Hence the infrastructure costs rise at a faster rate than the power available. A number of tidal gauges in the sea around Portland Bill in Dorset have produced data which was displayed as a coloured rolling diagram showing the strength and direction of the tidal stream every 15 minutes throughout the day. From these and other measurements, computer models have been developed which allow the power available to be calculated for the whole of a tide cycle and for periods upto 16 or 18 years into the future due to the long established knowledge which permits the prediction of the time and height of tides and results in mariners tide tables and tidal stream atlases. In this ability to predict future power availablity lies one of the strengths of tidal power in that it allows developers / investors in this form of power generation to calculate the return on their investment with considerable certainty, unlike all other forms of renewable energy generation, with the exception of photovoltaic cells (PVs). Now the race is on to produce practical tidal power devices. One example is the Marine Current Turbines ltd, SeaGen 1.2 megawatt device, (http://www.seageneration.co.uk/ ) which has two horizontal axis turbines (similar to current wind turbines) mounted on a single column in a tidal stream which can be adjusted to generate on both incoming and outgoing tides and which can be raised above sea level for maintenance . Mounting two turbines on one column reduces the infrastructure cost per turbine. This device is installed in the entrance to Strangford Lough in Northern Ireland and is a development of the SeaFlow device which has been tested off Lynmouth in Devon for several years. Another device is the Lunar Energy device http://www.lunarenergy.co.uk/ is a a shrouded turbine similar in appearance to an aircraft jet engine which sits on the seabed. The shroud or outer casing funnels the tidal stream into the turbine increasing the water speed across the turbine and increasing its efficiency. Research is now being done into the spacing between turbines, both along side one another and down stream, to maintain optimal performance. Currently the total generation costs of wave and tidal power are between 18p and over 40p per unit compared with 2.5p – 3.5 p for conventional power stations. Water powered generation will not be subject to fuel cost increases over the working life of the devices, so cost inflation of fossil fuels should erode the differential but at present these renewable energy devices cannot compete on cost with conventional fossil fuelled generation. However little value is being placed on CO2 reduction or the security of energy supplied by wave or tidal power. That which has been given to wind power is progressively being reduced. Renewable Obligation Certificates (ROCs) only contribute to covering part of the cost differential. Currently water power is not a stable technology and is at a similar state of development to that of wind power two or three decades ago. Until an industry standard technology for wave and / or tidal generation emerges the economies of scale which come from installed capacities of a similar order to that of wind power, ie: something in excess of 1 – 2 gigawatt, are unlikely to make substantial reductions in generated cost. Currently therefore wave and tidal power are not viable but improvements in design, volume installation and considerations of diminishing fossil fuel reserves and energy security should make it a practical proposition in the coming years, provided that resources are made available for research and development at a sufficient rate to keep ahead of our competitor nations. There is a danger that the change of government in the United States and the anticipated change of US policy, from being in denial about global warming to making available resources vastly greater than can be provided by the United Kingdom, will result in us being left behind or being swamped by an industry standard set and manufactured by the United States and its industries. Groups involved in development of these technologies currently are also concerned that in order to receive funding they have to make public any data that they obtain about the performance of their devices, in effect giving away any competitive advantage to their competitors of whatever nationality.
In researching this report the following link from a 2005 report illustrates a number of the wave generation devices that have been mentioned above |
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