Talk:Tidal power/Archive 1

message: This article states that, "In Europe,there are people that use Tide Mills and have been used for nearly 1,000 years, mainly for grinding corn."  The wikipedia article on maize isnt always true because people like me go in and change what is true about the story so dont trust anything that you find online for information becaue it begins, "Maize. . ., also known as corn, . . . was domesticated in Mesoamerica. It spread to the rest of the world after European contact with the Americas in the late 15th century and early 16th century. "  Corn could not have been ground in Europe for nearly 1,000 years. Delirium of disorder 19:04, 10 September 2006 (UTC)
replies: text: Maize is also known as "sweetcorn". Perhaps it is known as "corn" in US slang, but noone calls it that in the UK - on account of there being something quite different already called "corn". Perhaps the maize article should be changed. Fig 21:19, 10 September 2006 (UTC)
thread_title:  Corn 

message: Let's see some diagrams of machines that harness tidal power, eh?
Just wondering: the tides are caused by the moon, and the moon will never stop orbiting the earth, right?  So does that make tidal power perpetual motion, or am I overlooking something?
A: The tides slow the Earth's rotation down. So the source of the tidal power will be exhausted at the precise moment when the rotation speeds of the Earth around its axis and the moon around the Earth will coincide. Then the day should last more that a month now:). Harnessing the tidal power should not, IMHO, change anything in this natural process - just some part of the energy that now is dissipated as heat will be converted to electricity or whatever.
[[ Perpetual motion machines are more about entropy (second law and all that) than "energy".  "Energy" is related to entropy of course, but common use of the term "energy" (as in the "debate" about energy, or the "energy crisis") is more about the economics/practicality of harnessing various phenomena (mostly chemical) to do what we humans consider useful "work" (e.g. turn the wheels of a car).  In other words, there's plenty of "energy" to go about - if we could tap into the rest mass energy of a fistful of rocks, we'd be fine.  With "renewable" we mean tapping into processes in nature (rainfall, sunshine, wind, tides, geotherms) that are not noticeably affected by us tapping into them. --Psm 23:00, 29 July 2005 (UTC)
replies: text: Agreed Chris. This is out of place and lacks credibility here! It should be removed as it distracts from the main article.Tidalenergy 22:16, 13 August 2007 (UTC)
replies: text:  Agreed that it shouldnt be at the top of the article. I have moved it way down to a section by itself because the source of the energy is still of interest to some. Fig 09:22, 14 August 2007 (UTC)
thread_title:  Perpetual Motion Machines 

message: Why would the earth and moon decelerate in a vacum?  Surely after 4 billion years of decellerating would cause all sorts of problems! As the earth is decellerating in one direction, surely the tides would 'sit' on certain coast.
I was taught that the gravity due to the sun and moon on a side of the earth at any one time causes the sea to swell (cuasing the earth to appear elliptical), hence creating two tides per 24 hours.  If this is so then we are not taking energy out of the movement of the moon and sun, but out of these movements in the sea.
A: The earth and moon do theoretically slow down as they are moving in a constantly changing path. However you a correct, the decelleration of the earth has very little effect on the tides, more dominant forces include the Coriolis effect, energy form the sun, tidal resonance, funneling, atmospheric pressure, high & low pressure reigons...
To conclude to say that the root of tidal motion is due to the decelleration of the Earth and the Moons orbit is misleading - in some schools it would be termed "wrong".
:::Wikipedia says "The root source of the energy comes from the slow deceleration of the Earth's rotation. The Moon gains energy from this interaction and is slowly receding from the Earth."
:I don't think this is right.  Is the following argument correct?
::The moon is moving away from the earth and gaining potential energy. As angular momentum must be conserved the moon will also slow down, so as it moves out it will lose kinetic energy.  The Kinetic energy lost is greater than the potential energy gained, this energy is tranferred into tides on the earth.  The earth's rotation has nothing to do with it. Mike Young 15:18, 16 January 2007 (UTC)
replies: text: I dont know the proportion, no. I would imagine that is difficult to calculate. Off the top of my head, I seem to remember seeing that the day and month would stabilise at ~40 days. Regarding solar tides, everything that is happening in the earth-moon system is also happening to a very much smaller degree in the sun-earth system. But the sun will be long dead before that effect is noticeable! Fig 19:27, 17 January 2007 (UTC)
replies: text: This sublject matter I find a real head trip. Without reputable data and citations it is a moot point whether it has any menaing to the article and main page. Sometime in the far distant futrue whether a billion or trillion years this that or the other will happen does not wash with me ---- sorry. How about we keep the debate sane and in the present. Other wise it is a waste of time. Tidalenergy 22:21, 13 August 2007 (UTC)
thread_title:  Deceleration of the earths/moons orbit 

message: Someone might want to merge tidal harness with this article or visa versa as they appear to be talking about the same thing.--GD 10:28, 26 Sep 2004 (UTC)
replies: text: This sublject matter I find a real head trip. Without reputable data and citations it is a moot point whether it has any menaing to the article and main page. Sometime in the far distant futrue whether a billion or trillion years this that or the other will happen does not wash with me ---- sorry. How about we keep the debate sane and in the present. Other wise it is a waste of time. Tidalenergy 22:21, 13 August 2007 (UTC)

text: Not all tidal energy schemes suffer from high civil costs as do barrges. Tidal stream technologies currently being commercialised around the globe are being supported by investors as both more realistic then barrages, wind or solar. Shrouded turbines are predicted to further improve payback timelines as technology improves (see Kirke below). In the meantime MCT in the UK, Gorlov in Korea and Quantum in Canada to name a few that are moving ahead rapidly. Investors on the UK AIM (Alternative Investment Market) have supported this tidal stream industry with billions. They have obviously seen something after conducting their due diligence.Tidalenergy 22:31, 13 August 2007 (UTC)

text: I have Excel Spread sheets on tidal stream payback but as I am new here am not familiar with how to up load them.Tidalenergy 22:31, 13 August 2007 (UTC)

text: All very clever arguements to be sure. But I can't see this going anywhere but a head trip. VCan we keep this to science and engineering insrtead of the abstract that no can prove?Tidalenergy 22:35, 13 August 2007 (UTC)

text: Agreed. Lets keep the discussion in the realms of the real not at the bottom of the garden with the faries.Tidalenergy 22:35, 13 August 2007 (UTC)
thread_title:  Tidal harness 

message: I couldn't be more ignorant about the subject, so I'm hesitant to just delete the section, but the Tom and Wendy and the Random Clueless Person section is just vandalism, right?  --Bsteger 04:34, 25 February 2006 (UTC)
thread_title:  Tom and Wendy? 

message: can anyone provide a cite for this? would be very helpful to the article. Anlace 17:16, 8 June 2006 (UTC)
thread_title:  citation for mathematical modeling 

message: The article declares, "suitable locations are found in ... the former USSR." Why not just say Russia, or Eastern Europe? Seems a bit out of place. Trappleton 05:01, 11 August 2006 (UTC)
thread_title:  "Former USSR"? 

message: can someone have a look at Blue Energy Tidal power []. ? "The vertical axis turbine technology, which has been around since the 1920's, but held back for political reasons,?" However, i would like an advise on the statements made by this CA company, question is related to the naming of the article Blue energy. thanks. Mion 08:07, 8 October 2006 (UTC)
thread_title:  Blue energy 

message: I think that there is a form of vandalism on this page. It states "Wikipedia is not a reliable source dont use it==Dam==". I do not have the experience to fix it myself, so if someone else can do it that would be wonderful. Wikipedia is very helpful and all users know the risks. I don't think that comment is appropriate. Thank you very much. 70.240.204.149 00:08, 6 March 2007 (UTC)
thread_title:  Vandalism? 

message: Hello
Could you please add more info on this page thank you —The preceding unsigned comment was added by 124.186.4.37 (talk) 06:38, 23 March 2007 (UTC)
thread_title:  More information 

message: I've re-ordered the title headings to reflect the amount of written material in them and also the significance of each technology in the real world, and given then the correct names. I.e. I've renamed "Weir" to "Barrage" and put it first; renamed "Commercial attention is shifting to the new breed of eco friendly turbines" (which is a comment not a title) to "Tidal Stream"; and removed the text under "Tidal energy jet engine type turbine", since it was a) Clearly an advert; b) Clearly nonsense (How can the output of an 80% efficient turbine be increased by a factor of 3 or 4? A 320% efficient turbine?); and c) Clearly belongs under "Types of water turbines" in Water turbine if anywhere at all. Fig 13:08, 5 April 2007 (UTC)
replies: text: I have also made many POV removal edits, and inaccuracies and grammar fixes. Fig 13:31, 5 April 2007 (UTC)
thread_title:  Re-organisation, 5/4/7 

message: The template:renewable energy sources has been vandalized to change it to say "Energy development" instead of "Renewable energy" which is what it should say.  Nuclear power also needs to be deleted.  Very few people think that nuclear power is "renewable energy".  Template has been restored and protected for one week.199.125.109.108 07:17, 9 July 2007 (UTC)
thread_title:  Inappropriate template 

message: Someone keeps re-ordering the article to put Tidal Stream technology first. There is clearly some strange POV motive in this. The only tidal technology in large scale commercial use is barrage technology. Not only that, but the barrage section is many times larger than the stream section. It should clearly go at the top of the article. Please desist in re-ordering the items. Fig 15:27, 24 July 2007 (UTC)
replies: text: This appears to be user 210.9.237.1 - who also keeps deleting large sections of text on barrages, the tidal schemes table, and keeps adding spurious advertising information about tidal stream devices. I have put a warning on his/her talk page, and I notice other have also. It's a shame he/she wont come here to discuss his changes. Until then I will continue to revert his/her spurious changes if they are in this manner. Fig 09:25, 28 July 2007 (UTC)
thread_title:  persistent re-ordering 

message: One of the outstanding turbine inventions of the 20th century is that of the helical turbine invented and Patented by Professor Alexander Gorlov. In what has become know as the Gorlov helical turbine, it resembles a Darrieus cross flow turbine (Invented by Frenchman Georges Darrieus in 1923 aand patented in 1929) except that it is helically twisted, spiralling around the rotational axis. Patent infringement copies such as the turby have appeared on TV. Commercial trial have been underway in Canada along the west coast and in Korea in the Strait of Uldomok. Gorlov has claimed higher then ususal efficiencies of around 38% which is exceptional for a water turbine. Water turbines do not usually achieve efficiencies like their wing cousins due to what is believed the higher density of water. just think for a minute how you can spin freely in the air but stop very quickly if try to do the same underwater. The same heavy density of water that prevents you from turning freely in water also restricts the free steam water turbine. Fortuneatly when it comes to energy output the water turbine relies on the density of water (1025 kg per cubic meter) to produce power. (Added by User talk:210.9.237.1 on 8 Aug)
: This information is relevant, but probably not to the Tidal Power page. It is probably the case the the best location for this information is one of the following pages: Turbine, Water turbine, Wind turbine, Ducted fan, in particular Turbine#Types_of_turbines. Please read those, and links therein, and add this information in the most appropriate place, not forgetting to cite your references. Please note also that Wikipedia should not be used to place or promote original research - everything posted should be publicly available, and specific facts should be referenced (especially if they are new or controversial). Fig 11:10, 8 August 2007 (UTC)
replies: text:  Your bias shows through again. You say this is relevant without undestanding that the Gorlov Helical Turbine is suitable for free stream and has undergone testing in combination with shrouds (your pet hate). The fact that you denounce shrouds and acclaim Gorlov leaves one wondering if you have a handle on the discussion.
Response. Once again this is relevant as this technology is being used at a number of sites around the world as a device for generating energy from tides. And yet again it is NOT original research but a technology that has been proven. Tidalenergy 02:56, 9 August 2007 (UTC)
thread_title:  Professor Alexander Gorlov 

message: When it comes to the world of energy production from moving water and liquid flow there are two giants of the scientific world that have arguably contributed more then any. 
Betz who proved that the highest efficiency a water turbine is able to produce in free stream is 59.3%. That is to say that a turbine in free stream whether wind mill or water turbine no matter what the design (some are more efficient then others) is only able to harvest around 60% of the total energy available in the flow. Betz showed that if any more energy were to be taken from the flow the flow would stall and stop flowing.
: This is useful information. Please go to Water turbine or Hydropower to see where would be appropriate to add it. Please remember to add references to anything you do add. Fig 11:11, 8 August 2007 (UTC)
replies: text:  "Tidalenery" I see you have added this to the page anyway (even though I think it is more appropriate in Water turbine or Hydropower), can you add a proper reference for the figures you give, and also expand the text regarding the efficiency rate - At the moment you have the text saying that the shroud gives "3 times higher then the Betz Limit of 59.3%" i.e. 177.9% efficient, which is clearly impossible. Expand the text to explain how you are measuring that efficiency or I will delete it because it is misleading. Fig 15:44, 13 August 2007 (UTC)
replies: text:  In the article below by KIRKE --- PLEASE READ SHROUDED TURBINES ARE NOT SUBJECT TO THE BETZ LIMIT Read the article AGAIN, it states "when compared to the same turbine in free stream".....if that does not make sense, then you need to sit down have a good think about it. It does not say 177.9% it says 3-4 times the energy the turbine produces in free stream". But good to see you can add. In any event the article on Kirke states it for the record. You should avoid making comments based on your limited understanding. I tried to avoid this by posting the info but it appears you have not taken the time to read it. If it is still unclear ask! I will be most pleased to assist. In any event the bottom line is "shrouded turbine are NOT subject to the BETZ limit". Tidalenergy 22:01, 16 August 2007 (UTC)
replies: text: RE the above I can do a class on the topic and outline what appears to the Fig man as an extrodinary claim, that a shrouded turbine is not subject to the Betz Limit. I must confess in his defence, I have met many people who have had the same reaction. Imagine if I were to say that the Laws of Motion were out of date! So to it appears that on face value the ascertion about exceed the Betz limit is wrong.... What is actually happening is that two entirly different sets of rules apply. Betz is relative to open stream turbines, while shrouded turbines are subject to a set of different laws. So to are pressure turbines subject to a different set or laws then free stream, otherwise how could a pressure turbien be 99.9% efficient and thereby exceeding the Betz limit. What Mr. Fig has done is he has fallen into the trap of not comparing apples with apples. The free stream turbine is subject to the Betz Limit, while shrouded turbine are subject to another set of rules and the pressure turbine yet another ste of rules. So without a background in this field it is all too easy to become confused like Fig ---- I hope that helps to explain it! Tidalenergy 23:01, 16 August 2007 (UTC)

text:  "Tidalenery", please stop attempting to add your own formatting to Wiki titles. The style guide for titles are set by the Wikipedia templates and should not be manually changed. Please also dont use the talk page as a reference - put in proper references to the main page, specifically addressing the point I raise in the paragraph above. Fig 09:11, 14 August 2007 (UTC)
replies: text: If Barrage and Tidal Stream mentioned at the top of the page are them main heading and Barrages is bold then so should Tidal Stream be bold or else un bold Barrages. Otherwise your formatting is wrong! Try to sit down and have a think before you say things! Tidalenergy 22:05, 16 August 2007 (UTC)

text: There is already extensive text at Bernoulli's principle. Please go there to see if you have anything to add. Please remember to add references to anything you do add. Fig 11:11, 8 August 2007 (UTC)
thread_title:  Betz Rule and Benoulli 

message: The user "Fig" person above has been dominating this section with his own bias toward the Severn Barrage. See the Severn Barrage page. There is clearly a conflict of interest that is not being disclosed by Fig when making comments here. I have been trying to restore credibility to the debate but he was instrumental in removing large amounts of my text I placed on the page and had me blocked over a minor infraction of a Wiki law that I had no idea existed as I was very new. Vandalism and then hypocrisy and bullying should not be allowed. The clear and credibile facts should be posted and where applicable discussed and debated. I appeal to the administrators to return this page to some sort of balance.Tidalenergy 11:58, 9 August 2007 (UTC)
thread_title:  Vandalism and Bias 

message: From a background in the industry almost every time tidal energy is mentioned the first thing people think of is harnessing the rise and fall of tides to generate electricity. However there is another component to the tides that people often over look, that of the tidal current that allows the rise and fall of tides to take place. There is a direct relationship with the height of a tide and the tidal current. The higher the tide height the faster the flow must be in order to make up the height of water.
While a lot has been said about barrages on this and other sites there appears to be little said about tidal stream technology and it’s application as an alternative to barrages. It can replace a barrage entirely without the high civil costs as has been suggested many times in the case of the Severn Barrage proposal and could do so without the cost to the environment that a barrage will cause.
Lets look at a hypothetical example. Given a tidal flow to a bay or river that is 100 meters wide and 10 meters deep and a flow of 1 meter per second we can work out how much energy is in the flow using the formula I posted on the main page.
Power  = Turbine efficiency x Area or size of the turbine x water mass or density x Velocity cubed
	
The typical turbine efficiency in water is around 20% which is much lower then for wind or hydro dams as the turbine needs to push against the density of the water. Some turbines have achieved higher efficiencies but let’s use this for the exercise. 
The area or the size of the turbine will have a direct bearing on how much energy produced. The bigger the turbine the more power. To keep it simple lets use 1 square meter.
The density of water is 1025 kg per cubic meter for sea water.
Velocity cubed or velocity x velocity x velocity. 
Therefore,
Power  = .20  x 1 x 1025 x 1 x 1 x 1(100 meters wide and 10 meters deep)
= 200 x 1000 
Or = 200,000 watts.
If the flow can be used. In reality it may be far less.
On the other hand if the velocity is more like what we can expect in real life, that is flows of 3 – 4 meters per second, then we have a very different picture due to the velocity cubed factor in the equation. 
When the velocity doubles the energy does not double it goes up 8 times. So 2 meters per second of flow in the example above would have,
Power 	= .20 x 1 x 1025 x 2 x 2 x 2 (100 meters wide and 10 meters deep)
= 1,600,000 watts
Or, if it were 3 meters per second
Power = .20 x 1 x 1025 x 3 x 3 x 3 (100 meters wide and 10 meters deep)
= 5,400,000 watts
Or if it were 4 meters per second
Power 	= .20 x 1 x 1025 x 2 x 2 x 2 (100 meters wide and 10 meters deep)
= 12,800,000 watts
It is not hard to see that for a very small cross-sectional area of flow the velocity ratchets up the available energy.
Now imagine if open stream turbines were to be arrayed across the Bristol Channel instead of the proposed Severn Barrage. How many turbines could be placed on the seabed where they could generate without the billion dollar disturbance to shipping and damage to the eco system. Seems like a no brainer to me. Tidalenergy 11:59, 9 August 2007 (UTC)
replies: text: As someone who has edited this page to put stream energy second, let me say quite clearly that I consider it has greater potential than the conventional barrage technology. However it is as yet an unproven technology at an industrial scale. There are many prototypes but few plants that are actually inputting to national electricity grids. So I think it right that the "non point of view" bias of Wikipedia put it second because barrage technology is the proven technique. But there still are about three pages given to stream energy in the article so why not try and improve those if you think they are wrong in some way? And as a sideline, one of the prototypes of stream energy is off the Devon coast which is in approaches to the Bristol channel.. Chris55 20:09, 10 August 2007 (UTC)
replies: text:  Thanks for the comments Chris, at least this time I am not blocked for editing. I would like to add there are a great many more then this one site. AND, far and away the greatest quantum of renewable energy available to an energy hungry world, is moving water, not rise and fall of tides that can use barrages. There are also a great number of tidal stream or moving water energy deployments then the one you have cited. As a new user to Wiki I seek assistance in adding the new info. Can you assist? Tidalenergy 10:09, 11 August 2007 (UTC)
replies: text:  Hey Chris, check out the heading below "Developments in ducted Turbines by Dr. Brian Kirke". He has a PhD in turbines design and is a retired engineer and is the former senior lecturer in enrgineering at Griffith University on the Gold Coast in Australia. He is considered the world leading specialist in water turbines. He agrees with your comments that it has more potential for an energy starved world. His recent work in Canada on commercial pilots has some remarkable implications that take the technology from the unproven. Regards Tidalenergy 02:19, 13 August 2007 (UTC)
thread_title:  Tidal energy 101 for dummies like me 

message: Given time and debate here I would like to show there is no evidence that tidal schemes are being considered at these sites, or at least the majority of them. I declare an interest in all forms of tidal energy and do not make thses and any other statements to in any way defame those who have created the chart, but in the interests of full, complete and accurate information and the credibility of Wiki have initiated this work.
Srating with the first heading, it states
Argentina,  San Jose has a mean tidal range of 5.9 missing data on the basin size and estimated 6800 Megawatts of power.  
Starting with this site I can find no evidence of any tidal deployment under consideration.  There is talk about the tidal potential but NO evidence of any "scheme under consideration" as the heading suggests. Is there anyone out there who has any infomation about this site being under consideration? 
From the comments about the sute here it states that it has a mean tidal range of 5.9 meters (presumably meters) without quoting who measured this or whether is is blind freddy's best guess. The same goes for the number of megawatts. Is this the amount of energy that is capable from barrages or tidal stream? Again the numbers need closer scrutiny, is this the mean tidal range number or the peak. Even if it is the mean does it take into consideration that a tidal system will produce 42% of the energy available from the site if a barrage. As there are no velocity numbers no tidal stream potential can be estimated.
If this is to remain it needs to be qualified. It should include the size and shape of the basin as this will have a direct bearing on whether a barrage or tidal stream is best suited and include all measurements.
Finally, modelled numbers are at best, models and not measurements. Any data should include references. 
Next heading,
Australia Secure Bay a mean tidal range of 10.9 meters no numbers on the size of the catchment and no idea of the power. I have had a bit to say about this above as I live in that region and I can say that there is NO TIDAL SCHEME UNDER CONSIDERASTION at this location. There was one at Derby under consideration but was shelved due to concernc that the two tidal basind needed for the high water dam and the low water tail water dam would significantly destroy the wetlands ecosystems, AND the cost per megawatt of nearly AU$400 million (395 the last I heard) for 40 megawatts. This is 10 million per megawatt and out of the realms of investment without government coughing up. From the stance of the Environmental Protection Agency there it is highly unlikely that the site will never accomodate a scheme. This is sad as there is appeal for tidal stream turbine sto be arrayed at a fraction of the cost. However without definitive flow velocity data the probility is low.
The next heading is,
Canada. Cobequid 12.4 meter mean tide height a basin of 240 square kilometer and an energy potential of 5338.
I can not find any evidence of a "scheme under consideration" at this site. Whlile there may be significant potential thereis insufficient evidence to support the calim. 
Cumberland 10.9 meter mean tide height 90 kilometer basin and 1400 megawatts of potential. I can not find any evidence of a "scheme under consideration" at this site. Whlile there may be significant potential thereis insufficient evidence to support the calim. 
Shepody 10.0 mean tidal range a 115 square meter basin and 1.8 megawatt energy potential. I can not find any evidence of a "scheme under consideration" at this site. Whlile there may be significant potential thereis insufficient evidence to support the calim. 
Passamaquoddy 5.5 meter mean tidal height no data on the basin and no data on energy potential. I can not find any evidence of a "scheme under consideration" at this site. Whlile there may be significant potential thereis insufficient evidence to support the calim. 
Given the Canadian bat of Fundy experience and the dual problems of high civil cost and environmental issues there is little likelihood of any other barrages being built in this country. 
There is considerable interest of tidal stream schemes under cionsideration by the number of claims being lodged with the Canadian government for sites that hold potential with fast flowing water. The Canadian West Coast has the fastest ever recored naturally occurring water speed of 16 knots or about 8.5 meters per second.
It seems highly likely that the various turbines that have been trialed in Canada up till 2006, that there will be numerous tidal stream and run of river sites under full commercial development in 2007. 
As these schemes are tidal schemes they should either be included OR the chart deleted and a new section commenced that provideds information on these schemes.
The next heading is
India and Kutch with a 5.3 meter mean tide height and a 170 square meter basin and 900 megawatts of energy. 
Cambay 6.8 mean tide height a basin of 1970 square meters and a 7,000 megawatt energy potential.
I can not find any evidence other then the abstract of potential energy availability. I can find no evidence of any "power scheme under consideration"!
Time a space permitting I wish to complete this another time. Suffice to say that the chart has no credibility under its current format.
I say again, please do not leave this here without qualifications. 210.9.237.1 11:28, 11 August 2007 (UTC)
replies: text:  I would like to suggest another ammendment to the table if not remove it. There are a number of sites that are not suitable for barrages and vice versa for tidal stream. Why not include a break down of what is suitable at each site it it is to say. If not remove it and start again as it is misleading.210.9.237.1 09:04, 13 August 2007 (UTC)
thread_title:  Tidal schemes being considered chart "suggested ammmendments" 

message: Here it is again, the ducted or shrouded turbine report that was supplied by me yet mysteriously disappeared. Please make note of all the acknowledgements as they have bearing on this page and the credibility of emerging technologies such as shrouded turbines. Sorry I am unable to upload the pictures, tables and graphics as I am new to Wiki. It seems that the idea of a shroud here called a duct has been around for a very long time. Darrieus proposed in it 1923 for use with his "egg-beater" shaped cross-flow turbine. Read on.............
Dr. Brian Kirke. 
School of Engineering, Griffith University, PMB 50, Gold Coast Mail Centre, Qld 9726, Australia
Abstract
Unlike conventional hydro and tidal barrage installations, water current turbines in open flow can generate
power from flowing water with almost zero environmental impact, over a much wider range of sites than those
available for conventional tidal power generation. Recent developments in current turbine design are reviewed
and some potential advantages of ducted or “diffuser-augmented” current turbines are explored. These include
improved safety, protection from weed growth, increased power output and reduced turbine and gearbox size for
a given power output. 
Ducted turbines are not subject to the so-called Betz limit, which defines an upper limit of
59.3% of the incident kinetic energy that can be converted to shaft power by a single actuator disk turbine in
open flow. 
For ducted turbines the theoretical limit depends on,
(i) the pressure difference that can be created
between duct inlet and outlet, and 
(ii) the volumetric flow through the duct. These factors in turn depend on the
shape of the duct and the ratio of duct area to turbine area. 
Previous investigations by others have found a theoretical limit for a diffuser-augmented wind turbine of about 3.3 times the Betz limit, and a model diffuseraugmented wind turbine has extracted 4.25 times the power extracted by the same turbine without a diffuser. In the present study, similar principles applied to a water turbine have so far achieved an augmentation factor of 1.7 at an early stage of the investigation.
Keywords: Water-current turbines, ducted, diffuser-augmented.
1. Introduction: static head and current flow tidal power There are basically two methods of extracting energy from tidal flows. The conventional method is to place a barrage across an estuary with a large tidal range to create a static head or pressure difference, and operate a low head hydro-electric power plant with intermittent, reversing flow. The best known example of this approach, which has been treated in detail in
Baker [1], is the 240 MW installation in the Rance River Estuary in France, completed in 1966. An interesting variant has been proposed for Derby in Western Australia, where two adjacent tidal basins exist [2]. The proposal is to allow flow from the ocean into one estuary at high tide and out of the other at low tide, thereby creating a permanent difference in level between the two basins. A steady one-way flow could then be maintained through turbines in conduits connecting the estuaries. More efficient turbines can be used for one-way flow, and a steady flow overcomes one of the major drawbacks of most ambient energy sources, i.e.
intermittent availability. Pumped storage also becomes a possibility, whereby water is pumped back into the higher basin at off-peak periods for use during peak periods. However this scheme, like other proposals for large schemes based on static head, suffers from the drawbacks of expensive civil works, disruption to shipping and environmental concerns. 
The less well-known method of extracting energy from tidal and other flows is to convert the kinetic energy of moving water directly to mechanical shaft power without otherwise interrupting the natural flow, in a manner analogous to a wind turbine. This concept is not entirely new, having been investigated by Reading University in the UK in 1979 [3], by Davis in Canada [4] and by Hilton in Australia at about the same time [5]. It was in use in Africa on a small scale in the early 1980s to extract energy from river currents [3].
APPENDIX 3.1
tidal paper 16-08-03 2
But the idea of using current flow on a large scale is new. Even as recently as 1991 a complete book on tidal power made no mention of the concept [1]. It is only now that this concept is being explored for larger scale use [4, 6, 7, 8, 9, 10, 11].
Direct conversion of kinetic energy by a turbine in open flow harnesses less of the total available energy in a tidal flow in an estuary than could be extracted by damming the whole estuary. However direct conversion has several advantages:
1. The capital cost of civil works is eliminated.
2. Disruption to ecosystems and boating is minimised.
3. Ocean currents, wind-induced currents and river flows as well as tidal flows can be used.
There is no need for a large tidal rise and fall – for example the Messina strait between Sicily and the Italian mainland has 2.4 m/s currents with negligible rise and fall [11]. Hence a wider range of sites can be exploited, including rivers, straits between islands, sites off headlands and any other sites where there is frequent or constant strong flow.
There are also some potential problems with tidal or marine current turbines. These include,
1. Very large downstream drag forces, several times larger than those acting on a wind
turbine of similar power output, requiring strong anchorage.
2. Weed growth on blades, which could reduce their efficiency.
3. Corrosion.
4. Storm damage.
5. Possible danger to shipping and to swimmers in some areas.
However these problems should not be insurmountable, given the knowledge gained from some two centuries experience with ship propellers and several decades of experience with offshore oil platforms.
2. Recent developments in current flow turbine design.
Unlike wind turbine design, which is now a mature technology in which the axial flow propeller type turbine has emerged as the preferred design, water current turbine design is at an early stage of development.  Incremental improvements to wind turbine technology since the early 1980s has reduced the cost of grid-connected wind energy by a factor of about 5, to the point where it is now economically competitive with conventional fossil fuels in some areas. This process has not yet happened with water current energy conversion, and subsidies will be needed for research for some time to come.
The potential contribution of this form of energy is huge: it has been estimated that the UK
could obtain 20% of its electricity from tidal currents [12]. Several forms of turbine are being
investigated around the world and none has yet emerged as a clear winner. Some of the
various forms currently being evaluated are reviewed below.
2.1 Axial flow turbines.
Marine Current Turbines Ltd in Britain are pioneering the use of axial flow turbines. In 1994 they demonstrated a 10 kW axial flow turbine in Loch Linnhe in Scotland, and they are currently developing a 300 kW turbine for the Severn Estuary off Devon, England [7, 8, 9, 10]. This turbine is expected to resemble one or two conventional wind turbines, mounted on (tidal paper 16-08-03 3) a cantilever tower fixed to the ocean floor (Fig.1). Other small pontoon-mounted axial flow turbines have been built, for example by Teamwork Technology in the Netherlands [13] and by Swenson at the Northern Territory University in Darwin, Australia [14].
2.2 Cross flow turbines.
Turbines in which the direction of flow is across the axis of rotation are commonly referred to as “vertical axis” turbines, since their axis is usually vertical. However they are more accurately described as “cross flow” since their distinguishing feature is the fact that the direction of flow is across the axis of rotation, which may be horizontal. Davis conducted laboratory tests on a cross-flow water turbine in 1981-2 and constructed a prototype which produced 20 kW electrical power and an estimated 45 kW shaft power in 1983 [4]. More recently a 6 m diameter vertical axis turbine (Fig.2) has been installed in the Strait of Messina, between Sicily and the Italian mainland. It is expected to produce about 50 kW electrical in a 2.4 m/s current [11]. Gorlov and co-workers in the United States have tested models of a cross-flow turbine with helical blades and claim that its performance is superior to a conventional Darrieus cross flow turbine [15]. Gorlov has proposed large helical blade turbines to convert energy from the Gulf Stream. Salter [16] has proposed a large cross-flow turbine with 10 blades supported by rings top and bottom, driving ring-cam hydraulic pumps
to deliver 10 MW in a 4 m/s current. Fig.1. Open axial flow turbine concept [7]. Fig.2. Italian cross flow turbine [11]. 
3. Open and ducted turbines.
Like conventional hydropower turbines, installations such as the Rance River in France utilise the pressure difference created by a static head, i.e. the potential energy inherent in a difference in water surface elevation. In contrast, wind turbines and open water current turbines such as those shown in Figs. 1 and 2 utilise the kinetic energy of a moving fluid directly. Between these extremes, Darrieus [17] proposed placing turbines in ducts to augment the power extracted from a given sized turbine. Blue Energy Canada has proposed two variants on this theme: a single turbine can be placed in a duct in open flow without obstructing the free flow of water around the installation, or (tidal paper 16-08-03 4) alternatively their proposed “tidal fence” (Fig.3) forces all of the flow to pass through the turbines. They have proposed an ambitious scheme to build a tidal fence across a strait and use a large number of vertical axis turbines to produce up to 2200 MW [4, 12]. Recently, other organizations have also been investigating this concept. Ponta and Dutt [18] have tested
various profiles for a channelling device or duct to increase the available pressure drop and flow velocity through a cross-flow turbine. Teamwork Technology’s Tocardo turbine [19], Fig.4 is an example of a ducted axial flow turbine.
Fig.3. Tidal fence concept [4]. Fig.4. Ducted axial flow turbine [19].
4. Advantages of ducted turbines.
There are several practical advantages in placing the turbine in a duct. 
1. In areas where there is a danger of divers and/or floating debris being drawn into the turbine, a grid could be placed on the upstream opening, thus reducing danger to life and danger of damaging or clogging the turbine.
2. The duct shades the turbine itself from direct sunlight, and weed growth will thereby be reduced. Along with floating debris, this was one of the major problems experienced by Swenson in his work on tidal turbines in tropical waters near Darwin (Swenson, 1999).
3. A large duct made of low cost materials can be designed so the downstream side acts as a diffuser and reduces the downstream pressure, thereby increasing the available pressure drop, drawing in more flow and increasing the power output of a given sized turbine. Put another way, large flow area containing a large amount of energy is concentrated into a smaller area so that a smaller, lower cost turbine can be used for a given power output. Because a smaller turbine in a faster flow spins faster, the torque for a given power output is less and a smaller, lower cost gearbox can be used. This is a highly significant factor since flow velocities and hence turbine speeds are low and very large torque is required to produce useful amounts of power.
4. The duct eliminates tip losses on axial flow turbine blades, improving efficiency.
5. A rotating rim could be provided flush with the static duct, joining the blade tips of an axial flow turbine, with a belt or geared drive on its outside, thereby eliminating torque on the main turbine shaft.
6. This idea has been taken a step further in the Tocardo turbine, with magnets incorporated in the blades and stator windings in the duct so that the turbine rotor also functions as the (tidal paper 16-08-03 5) rotor of a permanent magnet generator, thereby eliminating gearing as well as torque on the main turbine shaft [20].
5. Principles of operation of ducted turbines.
Open turbines extract energy from the fluid by reducing the flow velocity with little or no pressure reduction as the fluid passes through the turbine rotor. The streamlines must therefore expand to maintain continuity (Fig.5) and they cannot expand indefinitely: hence there is a theoretical limit to the percentage of kinetic energy that can be extracted from the fluid. This limit has been shown by Betz [21] to be 16/27 or 59.3% for a single actuator disk (i.e. surface across which energy is extracted as the flow passes through it). Newman [22]
showed that the corresponding limit is 16/25 or 64% for a double actuator disk such as a
cross flow turbine.
But if a duct is provided around the turbine as in Fig.4, the flow boundaries are defined and streamline expansion is limited by the duct geometry. Energy is extracted primarily by a pressure drop, and in this way the turbine behaves more like an ultra-low head hydro turbine than like a conventional wind turbine. The maximum power available is the product of flow times available pressure drop. Radial flow along the blades of an axial flow turbine is prevented by a duct, and high conversion efficiencies up to about 90%, similar to those achieved by hydro turbines, should be achievable. Fig.5. Streamlines through turbine in open flow and DAWT [23]. The pressure drop available to a ducted turbine depends on the shape of the duct and the flow
through and around it. If the duct is designed as a diffuser it will draw more fluid through it and will also increase the available pressure drop across the turbine by recovering some of the velocity head downstream as pressure head. The turbine then becomes “diffuseraugmented.” Considerable work has been done on diffuser-augmented wind turbine design, but the concept has not so far been systematically applied to water turbines, with the possible exception of Blue Energy. Their web page [4] refer to tests in a laboratory flume in Ottawa in 1981-2 from which they estimated that an augmentation factor up to about 5 could be (tidal paper 16-08-03 6)
achieved in a ducted cross-flow water turbine. However they have not discussed the diffuser concept nor published any experimental data in the literature. Riegler [23] showed that the theoretical maximum power coefficient for a diffuseraugmented turbine based on turbine area is 1.96, i.e. 3.3 times higher than the Betz limit. This is possible because flow is drawn in from a greater area upstream than that intercepted by the
same sized turbine in open flow. After much experimentation with wind tunnel models, Gilbert and Foreman [24] reported a power augmentation factor of 4.25 for a turbine with a diffuser, i.e. it produced 4.25 times as
much power as the same turbine in open flow. They used slots (Fig.6) to draw in high energy flow from outside the diffuser for boundary layer control and were able to achieve this result with a short, wide angle diffuser, a much more economical arrangement than the long diffusers studied by a number of other investigators. Fig.6. Short, wide angle diffuser with slots for boundary layer control [27]. Their measured augmentation factor of 4.25 is not inconsistent with Riegler’s theoretical finding because the turbine they used had untwisted blades of low aspect ratio and its performance in open flow would have been well below the Betz limit. It has been strongly argued by Dörner [25], with some justification, that the additional cost of
a diffuser on a wind turbine will far outweigh the advantages. Wind turbines must be designed to survive wind forces many times higher than those at which they develop their rated power output. They normally do this by feathering either the complete turbine rotor or the blades to reduce the area presented to the wind. This cannot be done with a diffuser, which presents a large area to the wind whatever its orientation. Further, an axial flow wind turbine must normally be made to yaw to follow rapid changes in wind direction, so that the
diffuser must be made not only very strong, but also light to minimise its inertia. Even so, Vortec in New Zealand raised enough capital to construct a 7 m diameter turbine based on the findings of Foreman and Gilbert before going into liquidation. (tidal paper 16-08-03 7) In contrast to wind turbines, the maximum loads on a marine current turbine can be accurately predicted and are in the same order as normal operating loads. Further, a marine current turbine duct can be made neutrally buoyant so that its weight need not be supported
by a tower. It can be used to support the turbine and can be moored so that it orients itself into the current like a boat at anchor. It can therefore be argued that Dörner’s criticisms are not applicable to marine current turbines.
6. Experimental work.
Experimental work is being undertaken in conjunction with Tidal Energy Pty Ltd of Palm Beach, Queensland, in several stages:
(i) model performance testing in a flume
(ii) flow visualisation on a flow table
(iii) model performance testing in a tow tank
(iv) prototype testing under a motor-driven pontoon in still water
(v) prototype testing under a moored pontoon in a current.
In 1999 a 0.2 x 0.4 m cross flow turbine was tested in two ducts of parabolic profile in a flume at the Queensland Government Hydraulics Laboratories at Deagon in Brisbane. Because very small Darrieus turbines do not generally self-start 26, a Savonius rotor was used. The aim was to assess the augmentation factor rather than to demonstrate maximum overall efficiency, and the characteristics of Savonius rotors are well known. Although these tests indicated some augmentation it was difficult to quantify the effect as the turbine was not
tested without a duct and bearing friction was significant.
Flow table tests were subsequently conducted on various two-dimensional duct profiles to visualise qualitatively the effect of the profile on the flow pattern. In particular we were interested in the possibility of enhancing the boundary layer control effect demonstrated by Foreman and Gilbert [27], by using flaps or slats of aerofoil profile. These tests showed clearly how the duct draws in the upstream flow (Fig.7).
Fig.7. Flow table dye traces showing flow drawn in upstream (on left). However the Reynolds numbers were low and flow was laminar. It is well-known that aerofoils perform poorly in laminar flow, and the diffuser effect of the downstream part of the (tidal paper 16-08-03 8) duct is similar to the action of a wing section in that it must deflect the flow. Consequently these tests did not conclusively demonstrate diffuser action. In fact two diffuser profiles based on those shown in Foreman and Gilbert’s patent specification completely failed to
demonstrate diffuser action. Tow tests were then conducted on a 280 mm diameter axial flow turbine to compare the power and efficiency of the bare turbine with that of the turbine in various types of duct. Since the aim was to compare the performance of the bare turbine with that of the same turbine in a duct, the exact dimensions of the turbine were not important. The impeller of a desk fan was used as a turbine. A slatted duct of rectangular section was used as it is easier to construct than one of circular section, and a transition duct was used between the circular shroud around the turbine and the rectangular diffuser portion. Results plotted in Fig.8 show approximately 70% increase in output with a slotted diffuser.
Comparison of open and ducted turbine efficiency
0
10
20
30
40
50
60
50 60 70 80 90 100 110 120 130
RPM
efficiency, %
ducted
open
Fig. 8. Performance of model axial flow turbine with and without diffuser.
A 1.2 m diameter Darrieus turbine was then constructed with 3 straight, 1.2 m long fibreglass blades of 100 mm chord length and FX 63-137 section. This section was selected as it gives a good combination of structural strength and high lift to drag ratio at low Reynolds numbers (Selig et al, 1995). The chord length was a compromise between the need for low solidity to give good overall turbine performance and the need for a large enough chord length to give mechanical strength and high enough Reynolds number to give reasonable performance. A discussion of these conflicting requirements for small Darrieus turbines is given in Kirke
(1998). The number of blades was subsequently increased to 4 and blades were allowed to pitch, initially through ± 5° and then through ± 10°, to give more even torque. Unlike a wind turbine, the inertia of the rotor is not enough to even out torque fluctuations as the turbine rotates. The turbine was tested initially without a duct, and then a duct was added, as shown in Fig.9. The duct has flat top and bottom faces, with aerofoil section slats on the sides. As expected, overall performance was low due to low blade chord Reynolds numbers, but the significant finding was that the performance increased by a factor of about 3 when the duct was added, as shown in Fig.10. The performance of the turbine itself can be expected to increase with increased size and blade chord Reynolds number, and the threefold increase due to the duct can be expected to remain. (tidal paper 16-08-03 9)
Fig.9. Ducted turbine mounted on motorised barge, lifted partly out of the water to show
construction.
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.8 1 1.2 1.4 1.6 1.8 2 2.2
tipspeed ratio
peformance coefficient Cp
5 deg pitch open
10 deg pitch open
10 deg pitch ducted
Fig.10. Performance of open and ducted straight blade Darrieus turbine.
Conclusions.
Water current turbines, which operate in a manner analogous to a wind turbine, are a relatively new technology which can generate power from flowing water with very little environmental impact. A duct placed around the turbine has several potential advantages. The maximum efficiency of energy conversion by ducted turbines is not subject to the Betz limit of 59.3%. A turbine in a suitably shaped duct can be expected to generate about three times more power than can an open turbine of similar swept area. Besides these theoretical (tidal paper 16-08-03 10) advantages, a duct has several major practical advantages, including improved safety, protection from weed growth, increased power output and reduced turbine and gearbox size for a given power output. Unlike “diffuser augmented” wind turbines, ducted turbines in water do not need to be supported by a tower with a yawing mechanism. The duct can be constructed of low cost, heavy material such as concrete or structural steel. It is concluded that the ducted tidal current turbine is an attractive option for further development.
Acknowledgements.
The author would like to thank the following people and organizations for their help in this
work: The Gold Coast City Council for financial support through the Griffith Centre for
Coastal Management Queensland, Australia, Mr Leo Lazauskas of the University of
Adelaide, Professor Domenico Coiro of the University of Naples, and Professor Rodger
Tomlinson of the Griffith Centre for Coastal Management and Ms Helena Eriksson, a former
student of Griffith University.
References.
1. Baker, A.C. Tidal Power. Peter Peregrinus Ltd, 1991.
2. Derby Hydro Power. Hydro Electric Proposal, Double Basin Tidal Plant, Doctor’s
Creek, Derby. Promotional material, Derby Hydro Power Pty Ltd., West Perth, WA
(undated).
3. Garman, P. Water current turbines: a fieldworker's guide. IT Publications, London,
1986.
4. Blue Energy Canada. http://www.bluenergy.com. Accessed 6 March 1999, 30 Sept
2002.
5. Hilton, D.J. A vertical axis water turbine for extracting energy from rivers and tidal
currents. Proc. 1st Internat Conf on Technology for Development, IE Aust/ADAB et al,
Canberra, 24-28 Nov. 1980, pp.138-141.
6. Pearce, F. Catching the Tide. New Scientist, 20 June, 1998, pp.38-41.
7. Fraenkel, P.L., Clutterbuck, P., Stjernstrom, B. and Bard, J. SEAFLOW: preparing for
the world's first pilot project for the exploitation of marine currents at a commercial scale.
Proc. 3rd European Wave Energy Conf. Patras, Sept-Oct 1998.
8. Fraenkel, P.L. Tidal currents: a major new source of power for the millennium.
Sustainable Development International No.1, 1999, pp.107-112. ICG Publishing.
http://www.sustdev.org .
9. Fraenkel, P.L. Marine currents: a promising large clean energy source. Proc. I.Mech
Eng Conf. “Power Generation by Renewables,” London, 15-16 May, 2000.
tidal paper 16-08-03 11
10. Fraenkel, P.L. (2002). Power from marine currents. Proc. Inst. Mech. Eng, J.Power
and Energy 216(A1), 2002, p.1-14.
11. Coiro, D. Dept of Aeronautical Eng, University of Naples. Pers. Comm, 2001.
12. Open University, UK. Tidal current power update. Http://eeruwww.
open.ac.uk/natta/techupdates.html. (Accessed 12 April, 2001).
13. Van Breugel, H., and Schaap, P. New developments in the field of simple and
sustainable energy generation. Sustainable Developments International, 1, 1999, p.113-
115. ICG Publishing. http://www.sustdev.org .
14. Swenson, J. Tidal power project: report on the evaluation of an axial flow, lift type
turbine. Centre for Energy research, Northern Territory University, 1999.
15. Gorban, A.N., Gorlov, A.M. and Silantyev, V.M. Limits of the turbine efficiency for
free fluid flow. J. Energy Res. Technology, Vol.123, 2001, p.311-317.
16. Salter, S.H. Proposal for a large, vertical-axis tidal-stream generator with ring-cam
hydraulics. Proc 3rd European Wave Energy Conf, Patras, Greece, 30 Sept-2 Oct, 1998.
http://www.mech.ed.ac.uk/research/wavepower. Accessed 25 April 2002.
17. Darrieus, G.J.M. Turbine having its rotating shaft transverse to the flow of the
current. US Patent No. 1,835,018, 1931.
18. Ponta, F. and Dutt, G.S. An improved vertical axis water-current turbine incorporating
a channelling device. Renewable Energy 20, 2000, p.223-241.
19. Tocardo. Inrichting voor het opwekken van energie uit de stromende beweging van
een fluïdum. Nertherlands Patent No.9400050, 1994.
20. Gardner, F. Teamwork Technology, Antwerp, Netherlands, pers comm, 8 Sept 1999.
21. Betz, A. Das Maximum der theoretisch möglichen Ausnützung des Windes durch
Windmotoren. Zeitscrift für das gesamte Turbinenwesen, Heft 26, Sept.26, 1920.
22. Newman, B.G. Actuator-disk theory for vertical-axis wind turbines. J. Wind Eng. And
Industrial Aerodynamics, 15/3, 1983, p.347-355.
23. Riegler, G. Principles of energy extraction from a free stream by means of wind
turbines. Wind Engineering 7/2, 1983, p.115-126.
24. Gilbert, B.L. and Foreman, K.M. Experiments with a diffuser-augmented model wind
turbine. J. Energy Resources Technology, Trans ASME, vol.105, March 1983, p.46-53.
25. Dörner,.H.H. Concentrating windsystems – sense or nonsense? University of
Stuttgart. http://www.ifb.uni-stuttgart.de/~doerner/diffuser.html. Accessed 30 March
2002.
tidal paper 16-08-03 12
26. Kirke, B.K. Evaluation of self-starting vertical axis wind turbines for stand-alone
applications. PhD Thesis, Griffith University, 1998.
27. Gilbert, B.L. and Foreman, K.M. Experimental Demonstration of the Diffuser-
Augmented Wind Turbine Concept. J. Energy Vol.3, No.4, 1979, p.235-240.
28. Foreman, K.M., and Gilbert, B.L. Technical Development of the Diffuser Augmented
Wind Turbine (DAWT) Concept. Wind Engineering 3/3, 1979, p.153-166.
Happy researching Tidalenergy 00:53, 12 August 2007 (UTC)
thread_title:  Developments in ducted water current turbines by Kirke 

message: As everyone can see from the Kirke report the shrouded turbine has an impressive CV (not my POV Fig man). I have made a few minor amendments to the Shrouded Turbine article on the main page as there were serious errors in it. The Energy Clac heading has also been updated to reflect the shrouded turbines ability to exceed the Betz Limit. Also the person who changed the efficiency of the shrouded turbine and made it equal to the area of the duct, please re read Kirke above. The shrouded turbine has a capture area "greater" then the area of the shroud or duct. It achieves this by a low pressure or sub atmosphere behind the turbine so that literally sucks flow across the trubine from outside the sweep area of the turbine. Kirke and others explain it better then I. I have some great CFD graphics that nail the issue down for those like me who are visual learners ( a picture says a thousand words). I can make it available to place it on the page but I need some help as I am new to Wiki. Anyone out there want to lend a hand?
In any event Kirke wrote above,
A large duct made of low cost materials can be designed so the downstream side acts as a diffuser and reduces the downstream pressure, thereby increasing the available pressure drop, drawing in more flow and increasing the power output of a given sized turbine. Put another way, large flow area containing a large amount of energy is concentrated into a smaller area so that a smaller, lower cost turbine can be used for a given power output. Because a smaller turbine in a faster flow spins faster, the torque for a given power output is less and a smaller, lower cost gearbox can be used. This is a highly significant factor since flow velocities and hence turbine speeds are low and very large torque is required to produce useful amounts of power.
Please take the time to research these and read up and become familiar with them as they are essential if you are going to edit this page.Tidalenergy 01:37, 12 August 2007 (UTC)
thread_title:  Shrouded update and Energy Calc's deleted comments 

message: These were in the wrong place. I moved them up under barrages where they belong.210.9.237.1 04:01, 12 August 2007 (UTC)
thread_title:  Energy calculations & Economics 

message: The energy of the tide wave contains two components, namely, potential and kinetic. The potential energy is the work done in lifting the mass of water above the ocean surface. This energy can be calculated as:
E = ρgA ∫zdz = 0.5goAh2
where E is the energy, g is acceleration of gravity,ρ is the seawater density, which equals its mass per unit volume, A is the sea area under consideration, z is a vertical coordinate of the ocean surface and h is the tide amplitude. Taking an average (ρg)10.15kNm-3  for seawater, one can obtain
for a tide cycle per square meter of ocean surface:
E 1.4h2, watt-hour
or
E 510.4h2, kilojoule.
The kinetic energy T of the water mass m is its capacity to do work by virtue of its velocity V. It is
deRned by T=0.5mV2. The total tide energy equals the sum of its potential and kinetic energy components. Knowledge of the potential energy of the tide is important for designing conventional tidal power
plants using water dams for creating artiRcial upstream water heads. Such power plants exploit the
potential energy of vertical rise and fall of the water. In contrast, the kinetic energy of the tide has to be
known in order to design Soating or other types of tidal power plants which harness energy from tidal
currents or horizontal water Sows induced by tides. They do not involve installation of water dams.
Can someone load this on the main page. I tried and it came up with an error.........210.9.237.1 09:37, 13 August 2007 (UTC)
thread_title:  Mathemetical model for tidal barrgae power 

message: There should be a simple explaination of what tidal resonance is to supplemental tidal barrages as it is mentioned more then a few times. Tidalenergy 22:41, 13 August 2007 (UTC)
thread_title:  Tidal resonance 

message: Tidal energy has an efficiency of 80% in converting the potential energy of the water into electricity [citation needed], which is efficient compared to other energy resources such as solar power or fossil fuel power plants.
:I have serious misgivings with this quote. It is unsupported for and and two I have not found any data to support that tidal barrage power being capable of more then 42% efficient. That is only 42% of the peak head is able to be converted into energy. The peak may be 10 meters but the tide needs todrop sufficiently before the turbine develop head to generate. The before the basin empties and while the generator/s are still running the tide turns and begins to reduse the head in the basin. The end result is about 42% of the peak high tide. Then there is the spring and neap cycle that effects the amount of head captured in the basin over a lunar cycle. 
This needs to be deleted or revised and citations added. Perhaps Rance has numbers that can be referenced? Tidalenergy 22:49, 13 August 2007 (UTC)
thread_title:  Energy Efficiencies 

message: In the article above by KIRKE --- PLEASE READ SHROUDED TURBINES ARE NOT SUBJECT TO THE BETZ LIMIT Tidalenergy 22:43, 16 August 2007 (UTC)
thread_title:  Shrouded Turbine are not subject to the Betz Limit