@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.

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.

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.

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

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.

The Annapolis Royal Generating Station looks to have a better output per installed MW and a similar mean tidal range from ST's chart.

Posted By: renewablejohnThats what you get relying on ST's charts

Where is your data to show otherwise?

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.

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.

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.

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.

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.

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.