View Full Version : Tidal energy.

30th Mar 2014, 17:09
I don't start many threads on here. :hmm:

Anyway, I didn't want to hijack the other electricity thread and this is a slightly different topic.

There has been a lot of discussion recently in regards of generating power and it got me thinking.

Locally in the Bay of St.Malo, we have fairly big tides, right in the SE corner in the vicinity of Mont St.Michel they experience tides of over 14.0 metres.
If we can take as an average throughout the Channel Islands to make things easier a tidal range of 10.0 metres.
In the past experts have looked at tidal flow, again locally this can easily reach 8 Kts + in certain areas, but you also need the engineering nous to anchor turbines and be able to gain access to service them. One local survey recently recorded sand waves 10 metres high moving through in a single tide. This has created problems which nobody can circumvent as yet.

This is where I was wondering if we have been tackling the problem from the wrong angle. With the range of tide we have, should we not be able to generate power from just using the vertical rise and fall of the tide. There are loads of gullies in amongst the cliffs on the four main islands where you could place large rectangular/any shape floats to pilings and with the correct gearing transfer the vertical rise and fall converted to energy ashore. In simple terms transfer the power of the rise and fall of 10.0 metres twice a day into energy.

There are numerous engineers on PPrune, and I'm probably missing something, but why has this route not been explored?:)

30th Mar 2014, 17:25
I'm thinking that the first explanation of some of the various methods here could be applicable for your shoreline and high tidal flow...

Tidal Power - How Tidal Power Plants Work (http://inventors.about.com/od/tstartinventions/a/tidal_power.htm)

But then you've also got to consider the production of electricity from generators that employ wave action on the surface.

30th Mar 2014, 17:40
I think you may be missing something; La Rance is the oldest tidal power station in the world.

Rance Tidal Power Station - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Rance_Tidal_Power_Station)

30th Mar 2014, 17:52
henry crun that explains very neatly why it hasn't been adopted. :ok:

I know the barrage at La Rance quite well as I've negotiated the locks there on numerous occasions. I've always found it a little disconcerting up river from there as they reserve the right to drop the water level by 2 metres in ten minutes for emergency electric generation. This stretch of the river is affected about nine miles before being safely locked in at Lyvet.

30th Mar 2014, 18:03
I did read recently about a proposed scheme in Swansea bay. It seems like a no-brainer to me - unlimited clean energy, enhanced sea defence to boot, plus fantastic in-shore recreational opportunities - sailing, windsurfing etc. You could also mount wind turbines along the length of the sea wall. If the inland sea silted up over time it could even open the way to reclamation.

30th Mar 2014, 18:33
I don't start many threads on here

You clearly like to make waves when you do, though.


Lightning Mate
30th Mar 2014, 18:53

30th Mar 2014, 19:48
as for waves...
2013 Perth Wave Energy Project Animation - YouTube

- well, one of the possibilities.

Little cloud
30th Mar 2014, 20:02
I'd have thought given the relatively warm waters around the Channel Islands and the specific heat capacity of seawater (4kJ per kg per degree Kelvin) that direct heat recovery could be very useful for district heating especially if the collector could be mounted in a location with a steady tidal current.

A commercial project in the relatively frigid waters of the Baltic:

Channel Island waters are around 10C at the moment. Combine that with an efficient industrial scale collector in a tidal stream with advanced refrigerant and heat pump and there's a lot of collectable heat.

30th Mar 2014, 20:54
BBC NEWS | UK | England | 'Hot rocks' found at cement plant (http://news.bbc.co.uk/1/hi/england/4096231.stm)

Harnessing hot rocks | In-depth | The Engineer (http://www.theengineer.co.uk/in-depth/analysis/harnessing-hot-rocks/1001460.article)

Cluff Geothermal signs agreement for project in Durham, England | Think GeoEnergy - Geothermal Energy News (http://thinkgeoenergy.com/archives/7192)

Outline planning permission was granted in 2009 to create Eastgate Renewable Energy Village, complete with homes, businesses and leisure facilities. Almost £2m was spent developing the scheme – dubbed eco-Disney – which was expected to create 350 jobs and reverse Weardale’s economic decline.
However, it was shelved after the government cut almost £1m funding to regional development agency One North East.

More at:- http://www.raeng.org.uk/events/pdf/david_manning.pdf

30th Mar 2014, 21:04
When I was in New Zealand a few years ago (superb place, just 1950s Britain!) I was told that the geothermal power station near Rotorua had led to the local geysers diminishing. Now what effect does taking energy from the tides have? Does anyone know?

Unintended consequences, anybody?

30th Mar 2014, 23:11
Now what effect does taking energy from the tides have?

Err, less coastal erosion? That said, any human intervention in tidal flows is likely to be negligible in the grand scale, given the amount of free-flowing water sloshing over our planet's surface.

31st Mar 2014, 02:46
Tidal systems extract energy from the Earth-Moon system. If you think about, it, the Moon is pulling the water round the planet, so if you impede that free movement, you're exerting a small drag on the Moon, slowing it down very slightly. However, it's very slight in the scheme of things, given the relative masses and the amount of energy in the system.

The bigger irony is that if we extracted enough energy from wind power, it would cause major climate change.

31st Mar 2014, 04:43
The bigger irony is that if we extracted enough energy from wind power, it would cause major climate change.
...and if you really went to town, you would stop the Earth rotating.


A A Gruntpuddock
31st Mar 2014, 05:12
Salter's duck - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Salter%27s_duck)

Salter?s Nodding Duck | Renewable energy (http://baonguyen1994.wordpress.com/introduction-to-wave-energy/ocean-wave-technologies/terminators/salters-nodding-duck/)

BBC News - Pentland Firth tidal turbine project given consent (http://www.bbc.co.uk/news/uk-scotland-24100811)

Just hope they are more reliable than bird shredders!

31st Mar 2014, 05:35
most water-constructions tend to get real nasty in the long run due to mud settling down somewhere unwanted. And the chain starts from there.

Tidal Power: Pros and Cons (http://www.triplepundit.com/2012/06/tidal-power-pros-cons/)

(P.S if the tidal energy slows down the Moon and wind energy the Earth, it should balance out? :ouch: )

31st Mar 2014, 07:54
Wasn't the likelihood of the silting up of the Bristol Docks one of the major factors in the Severn Barrage not going ahead?

Rather be Gardening
31st Mar 2014, 08:13
There's one project already underway in Ramsey Sound and another planned for St David's. :ok:

Crown Estate boost for tidal energy project (From Western Telegraph) (http://www.westerntelegraph.co.uk/news/9683930.Crown_Estate_boost_for_tidal_energy_project/)

31st Mar 2014, 08:34
Yes, we have a project underway locally. It has slipped time wise, the original plan was to have turbines in the water by 2012. I think the French are aiming to get some deployed by this year's end.

Home » Alderney Renewable Energy (http://www.are.gg/)

31st Mar 2014, 09:22
Alderney Renewable Energy

How long before the turbulent flow around these turbines under-cuts their foundations? Or are they designed to be re-deployable?

31st Mar 2014, 09:24
Silting up

Is this such a problem for coastal schemes? As I said above, deployment of a tidal barrage could be the first step in a land reclamation scheme.

31st Mar 2014, 09:29
I think one of the biggest problems to be overcome locally are the 'sand waves', it is rumoured that where the turbines were to be deployed these 'sand waves' up to 10 metres high can move through the area in a single tide.
If true they would certainly present an interesting engineering challenge.

Edit: deadpan I don't know. I think It was envisaged that there would be an on going maintenance programme.

Little cloud
31st Mar 2014, 09:43
This would appear to be the alternative to the seabed mounted tidal turbine, however it's still at the r and d stage.

Scotrenewables Tidal Power Ltd, leading the way in developing the tidal turbine concept. (http://www.scotrenewables.com/technology-development/the-concept)

31st Mar 2014, 10:20
Scottrenewables' insurers will be delighted when someone sails into one.

The problem with undersea turbines is that moving water has lots of momentum and little energy. This imposes huge forces (~rho x v-squared), but not much power density (~rho x v-cubed). Wind is much more favorable by comparison, producing lots more energy with relatively light forces.

Also, undersea construction and maintenance is very expensive.
A real underwater turbine is installed at Strangford Loch. Hebridean and Brittany-adjacent sites are possible.

The tidal power comes from the Moon's orbit, so the recession speed of the Moon increases a little. It's silting, and expense of construction and maintenance, that's the practical problem.

Wind turbines have almost no impact on either global temperature or Earth rotation. The energy in wind is produced by pressure gradients due to solar heating, not tides or Earth rotation. The Solar energy input to Earth is about 10-to-the-17 watts - that's 10-to-the-12 TWh per year, while human energy consumption is nearer 10-to-the-4 TWh per year.