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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    • CommentAuthorMikel
    • CommentTimeMay 5th 2015
     
    @RJ,

    From the report page 18

    “Tidal engineering practice, based on the results of preliminary studies of tidal sites at various locations on the globe, usually allows an optimal annual energy production (AEP) for a single basin generating on the ebb flow of about one-third of the gross energy potential GEP."

    For the two pool system at Hayle the report suggests (page 19-20):



    "Ebb Generation. The incoming tide is allowed to flow into the pool and is trapped behind sluice gates at high tide. The water is held normally for 3 hours and then released through the turbine on the out going ebb tide to power. 2 output phases per 24 hours 50 minutes
    Flood Generation. The incoming tide is held back by sluice gates until sufficient water head is achieved then the water is allowed to pass from the turbine into the pool. 2 output phases per 24 hours 50 minutes.
    Combined or two way operation. By using a variable pitch turbine power can be extracted in both the ebb and flood cycles however efficiency is affected as the full head of water can not be utilised.


    The availability of two pools within the harbour system allows for a wider choice in operating regimes. A combined ebb/flood offers the following advantages


    Greater available production period. More useful as a base load generator. Opportunity to extract energy in the both directions while giving primacy to the most efficient or need for a secondary purpose
    Facility to increase the available head within the fill stage of the ebb selected pool by reverse running the turbine as a pump. This facility would be utilised when the energy release phase coincided with periods of high grid demand and an increased price for the energy exported to the grid beyond the commercial value of the energy to increase the available head.

    Initial research indicated that a utilising each pool as an individual asset with Copperhouse operating as an ebb and Carnsew as a flood pool would simplify the system and offer a longer time period of operation more commensurate with a base load generator.
    Discussions with Alan Travers of Buro Happold at an ING consultation day in Hayle, he expressed his concerns about the removal of energy from the tidal flow during the release of the Ebb generation Copperhouse pool. The reduction in energy would effect the sluicing capability required for the re development of the Harbour and the affect the proposed improvement to the navigation of the harbour channel.

    Reappraisal of the operating regime concluded that the operation of both pools in a dual mode ebb and flow generation would mitigate the loss of sluicing power. However additional systems work would be required to be undertaken covering the output, the souring effect of sluicing and it’s re-timing to produce the energy when it most needed by the grid. Two examples of differing operating regimes are illustrated at Annex B. The average single tidal cycle high to low water last 6 hours the hold in both ebb and flow would last 3 hours leaving 3 hours for the release and power generation phase. Therefore taking the;
    Optimal PE per tide = 12.56 MWh x 0.33 = 4.15 MWh acting over 3 hours requires a generating capacity of 1.38 MW, thus specifying a Turbine Generator of 1.5MW for each pool would be valid."

    Considering the caveats here for dual mode operation, it doesn't look like they expect to get double the output.
  1.  
    Mikel

    The report is actually showing its age. If the report was rewritten using current technology then dual mode operation would be used but using a turbine only in one direction similar to Sihwa Lake.
    • CommentAuthorMikel
    • CommentTimeMay 6th 2015
     
    Yes, the report is a few years old now. However, the sizes of the pools and tidal range won't have altered and hence neither will the turbine size of 1.5MW. For two turbines operating in dual mode for half a day, the maximum theoretical generation will be 1.5MW, which is 0.5% of Cornwall's electricity consumption.

    As a project, this has some advantages in that the pools exist (but need dredging) and the grid infrastructure is in place courtesy of the old coal-fired Hayle power station. Incidentally, that power station had a generating capacity of 70MW.
    •  
      CommentAuthorSteamyTea
    • CommentTimeMay 6th 2015 edited
     
    We could easily save 0.5% of our consumption. I would think that the natural loss of old lightbulds and TV will sort that out.
    There is also fridges, 10 years between models made a larger difference than I imagined.

    Did they not initially have use variable pitch and generation on both tides at La Rance, it was not as effective as one way generation.
    • CommentAuthorMikel
    • CommentTimeMay 6th 2015
     
    La Rance has been in for a long time, so I would expect they have worked out the optimal conditions there.

    There seems to be a lot of rhetoric on tidal but the actual output figures are relatively small. 1.2MW for a tidal generator in a lough in Northern Ireland producing power for 1000 homes. That is probably only electricity for homes, not including heating and hot water.
    •  
      CommentAuthorSteamyTea
    • CommentTimeMay 6th 2015 edited
     
    Just had a quick look on the internet and this is what I have found.
    Seems that generation by installed capacity is going down, there is little correlation between mean tide heights and generation.
    There only seem to be 4 operational tidal barrage plants at the moment.
      Tidal 1.jpg
      Tidal 2.jpg
    • CommentAuthorbxman
    • CommentTimeMay 6th 2015
     
    Have a look at this strange Korean video advocating


    Hydrological Changing Double Current-typed Tidal Power Generation

    https://www.youtube.com/watch?feature=player_embedded&v=lnHwb8BKJzU


    It seems to suggest that it all a total No brain_er

    I am not that convinced but I would like to know what you think
    • CommentAuthorMikel
    • CommentTimeMay 6th 2015
     
    Bxman,

    The video refers to Sihwa which doesn't look exceptional according to ST graph.

    Here is another showing global tidal resources

    http://atlantisresourcesltd.com/marine-power/global-resources.html

    This suggests the UK is sitting on a large percentage of the global resource with potential global generating capacity ranging from 25-90GW. Not insignificant but we need much more than that.
    • CommentAuthorEd Davies
    • CommentTimeMay 6th 2015
     
    The use of sluices in that configuration is quite clever to allow both ebb and flow to go through the turbines in the same direction and to be able to use the same mechanisms to run the last bits of the ebb and flow through unrestricted. Still, the use of generation in both directions is not new - I think the Rance does it. The Sihwa plant is unusual in not doing so:

    http://en.wikipedia.org/wiki/Sihwa_Lake_Tidal_Power_Station

    “…power is generated on tidal inflows only and the outflow is sluiced away. This slightly unconventional and relatively inefficient approach has been chosen to balance a complex mix of existing land use, water use, conservation, environmental and power generation considerations.”

    So, yep, a rather strange video.

    Odd commentary as well, sounds like it's been translated by a machine (Google?) then read by a reasonably good English speaker who has no clue what it's about and how it ought to sound.
  2.  
    Posted By: MikelBxman,

    The video refers to Sihwa which doesn't look exceptional according to ST graph.

    Here is another showing global tidal resources

    http://atlantisresourcesltd.com/marine-power/global-resources.html" rel="nofollow" >http://atlantisresourcesltd.com/marine-power/global-resources.html

    This suggests the UK is sitting on a large percentage of the global resource with potential global generating capacity ranging from 25-90GW. Not insignificant but we need much more than that.


    How can you say Shiwa is not exceptional producing similar power outputs to tidal stations with tidal ranges nearly double the height. Normal hydro convention is that head height is paramount in power generation
    • CommentAuthorMikel
    • CommentTimeMay 6th 2015
     
    The Annapolis Royal Generating Station looks to have a better output per installed MW and a similar mean tidal range from ST's chart.
  3.  
    <blockquote><cite>Posted By: Mikel</cite>The Annapolis Royal Generating Station looks to have a better output per installed MW and a similar mean tidal range from ST's chart.</blockquote>

    Thats what you get relying on ST's charts. Actually Annapolis has some of the highest tides in the world upto 20 mtrs although at the moment there only half that.

    http://www.tide-forecast.com/locations/Annapolis-Royal-Annapolis-River-Nova-Scotia/tides/latest
    •  
      CommentAuthorSteamyTea
    • CommentTimeMay 6th 2015 edited
     
    Posted By: renewablejohnThats what you get relying on ST's charts
    Where is your data to show otherwise?
    • CommentAuthorMikel
    • CommentTimeMay 6th 2015
     
    The maximum tidal height for Annapolis is just over 9m with a mean tidal height of 6.4m. The mean tidal height for Sihwa is given as 5.6m.

    ST's chart is holding up so far.
  4.  
    Posted By: MikelThe maximum tidal height for Annapolis is just over 9m with a mean tidal height of 6.4m. The mean tidal height for Sihwa is given as 5.6m.

    ST's chart is holding up so far.


    You must be looking at a different chart as ST chart for Annapolis is definitely below the 6 line not above it.
    • CommentAuthorMikel
    • CommentTimeMay 6th 2015
     
    I got the Annapolis figure from http://www.thecanadianencyclopedia.ca/en/article/tidal-energy/
    I wanted to cross-check with ST's chart and your assertion of 20m.
    I cannot find any data that the Annapolis power facility operates over 20m tides. However, there are potential sites elsewhere in the Bay of Fundy.
  5.  
    Posted By: MikelI got the Annapolis figure fromhttp://www.thecanadianencyclopedia.ca/en/article/tidal-energy/" rel="nofollow" >http://www.thecanadianencyclopedia.ca/en/article/tidal-energy/
    I wanted to cross-check with ST's chart and your assertion of 20m.
    I cannot find any data that the Annapolis power facility operates over 20m tides. However, there are potential sites elsewhere in the Bay of Fundy.


    If you actually look at what I said not what you think I said the comment was upto not over 20m tides with the actual figures half that even including the live data feed to the nearest tide station.

    http://www.annapolis-valley-vacation.com/tidal-power-plant.html

    The local tourist office above gives a bit more detail of normal running heights.
    • CommentAuthorMikel
    • CommentTimeMay 7th 2015
     
    I cannot find any reference to tides of 20 metres in the Bay of Fundy. 16.3 meters is quoted for the extreme range.

    For Annapolis the maximum tide is quoted at over 9 metres.

    You have not provided any evidence to refute ST's figures.
    •  
      CommentAuthorSteamyTea
    • CommentTimeMay 7th 2015
     
    If I change it to 6.4 m, will it make any difference to the output. The main points are that the ratios are pretty similar, there does not seem to be any significant improvements over the last 40 years or so.

    Tidal, like any hydro scheme, is very limited by geography, not as if we can barrage every western estuary and port. It is also not environmentally benign.

    I like big civil engineering projects and would like to see the Seven produce some power, be even better of they built a huge lagoon off Perranporth (would stop the next very large storm taking the rest of the beach away, may kill the surfing though), but there really is a limit to what can be done, and it is a low limit.
  6.  
    Posted By: MikelI cannot find any reference to tides of 20 metres in the Bay of Fundy. 16.3 meters is quoted for the extreme range.

    For Annapolis the maximum tide is quoted at over 9 metres.

    You have not provided any evidence to refute ST's figures.


    Mikel

    Record tide for Bay of Fundy recorded at 21.6 mtrs Oct 4-5 1869

    As for evidence what more do you require I linked direct to the live data. From that site Spring Tide 9.27 current lunar low 7.92 then adjust for the lowest tide 1.05 to give mid tide value of (8.22+6.87)/2 ie 7.54
  7.  
    Posted By: SteamyTeaIf I change it to 6.4 m, will it make any difference to the output. The main points are that the ratios are pretty similar, there does not seem to be any significant improvements over the last 40 years or so.



    If you did change it to 6.4 it will show the significant improvement in low head turbine design over the last 40 years whereby sites that where once termed uneconomic through lack of tidal head have now become economic.
    • CommentAuthorMikel
    • CommentTimeMay 7th 2015
     
    Got it. Thank you.

    However, you omitted to mention the presence of a cyclone with high winds and extreme low pressure, making the conditions exceptional.

    Your Annapolis data is over one month and not annual.
  8.  
    Posted By: MikelGot it. Thank you.

    However, you omitted to mention the presence of a cyclone with high winds and extreme low pressure, making the conditions exceptional.

    Your Annapolis data is over one month and not annual.


    Would you design your sea defences based on 16.3 mtrs if you new historically you had a tide of 21.6 mtrs. With rising sea levels tides are likely to be affected.

    I accept the data is only over 1 month but thats the lunar cycle as you can see the tides are now increasing again.
    •  
      CommentAuthorSteamyTea
    • CommentTimeMay 7th 2015 edited
     
    Posted By: renewablejohnIf you did change it to 6.4 it will show the significant improvement in low head turbine design over the last 40 years whereby sites that where once termed uneconomic through lack of tidal head have now become economic.
    Explain that a bit more. It would not change the second chart at all, the commissioning date and generation ratios.

    Biggest problem here is that there is just a handful of sites. I think there is one in Russia as well.
    • CommentAuthorMikel
    • CommentTimeMay 7th 2015
     
    no, I would not design my sea defenses at less than a historical tide height but we are not talking of sea defenses here.

    I would be specifying my turbine to cope with an average maximum and then design in a factor to cope with higher loads and possibly a cut out at extreme load. I would be basing the investment case on average load and not the exceptional case.
  9.  
    Posted By: Mikelno, I would not design my sea defenses at less than a historical tide height but we are not talking of sea defenses here.

    I would be specifying my turbine to cope with an average maximum and then design in a factor to cope with higher loads and possibly a cut out at extreme load. I would be basing the investment case on average load and not the exceptional case.


    Obviously thats where we differ. My steam plant has 100% redundancy ie 2 engines but only 1 running and one on standby. May be overkill but does allow dual operation if peak energy pricing makes generation worthwhile.
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