Tidal Turbines (vaguely boaty)

[Nick]

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In response to a lack of general information on the state of play of tidal (turbine) electric generation in the UK we have created a new website:

TIDESTREAM

Feedback welcomed as usual . . .

[Olivepage]

Looks like an interesting site. 1MW is a substantial output for a turbine.

Is there any information on the duty cycle that these machines achieve. Clearly there will be zero o/p at slack water but for what percentage of time do they achieve say 75% of max or better.

On a related theme I remember a few years ago looking at the wave power scheme on Islay, the original small machine was working and they were starting to dig out the compression chamber for the bigger version.

Was it ever brought into service do you know?

[Olivepage]

Been looking at the various ideas for turbines. All very interesting, but is there a better way.

A generator works by moving a conductor in a magnetic field.

The earth has a magnetic field, and sea water is a conductor.

So is there a way to harness this potential natural generator.

Certainly submarine cables have had to be designed to allow for large voltages being generated along their length by this tidal effect.

I guess there will need to be some hard sums done to understand how much power could be generated by this effect, but the notion that you can provide useable power from nothing more than a length of wire is a tempting one.

[Telo]

I've heard it said that a barrage and turbine scheme would be ideal for the Cuan Sound. Could be all sorts of social benefits as well, not to speak of boat safety.

[Alcyone]

There was talk of putting one of these in Ramsey Sound in West Wales. As divers, this was very interesting, as clearly you had to give them a wide berth. The rumour is that they have a maximum tidal rate, and that the 4-8 knot range in Ramsey was outside that rate. I've only been through Cuan a couple of times, but the tidal rates seemed similar.

[Nick]

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The SeaGen unit in Strangford Lough, the only commerial unit currently in operation in UK waters, is operating in 4-8 knots of flow. The Race Rocks shrouded turbine installation operates in spring flow rates of 7 knots. The favoured sites are precisely those with this sort of tidal flow rate.

Tidal turbines turn very slowly, and generally present little or no danger to marine life or divers. SeaGen's rotors turn at 10 - 15 rpm.

[DaveS]

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Tidal turbines turn very slowly, and generally present little or no danger to marine life or divers. SeaGen's rotors turn at 10 - 15 rpm.

By my calculations a 16m diameter rotor turning at 15 rpm gives a tip velocity of about 12.5 m/s, i.e. about 25 knots. I'm not a diver, but I wouldn't have thought that getting hit by something solid going at that speed would be desirable.

OTOH could it give rise to a new game of underwater "chicken"? Grab a blade near the hub and gradually move outwards to see how far you can get before the increasing drag forces you to let go...

FWIW I'm a firm supporter of tidal stream generation for all the reasons given: predictability, avoidance of weather, and spreading of aggregate peaks through placement of devices in differently timed tides around the coast. I am currently involved with a small tidal generation project that I can't really talk about yet, and I have also developed my own outline design which is rather different from the various systems featured on the site. Like all developers I naturally believe that my design is much better than all the others! This line of thinking can, of course, get a bit out of hand. From the Marine Current Turbines site:

"For reference, MCT’s SeaGen system with 16m rotors has a swept area of 402 square meters. Most of the few competitors who have demonstrated systems in the sea have devices with rotor diameters in the order of 5 to 9m, which would be 15 to about 60 square meters."

Now, when I was at school the area of a circle was pi.D^2 / 4. Applying this, a 16m diameter circle has an area of 201 m^2, a 5m diameter circle an area of 19.6 m^2, and a 9m diameter circle an area of 63 m^2. Doesn't detract from the overall (correct) theme that big is good, but makes the ratios a bit more realistic.

[DaveS]

I've heard it said that a barrage and turbine scheme would be ideal for the Cuan Sound. Could be all sorts of social benefits as well, not to speak of boat safety.

AFAIK the project to replace the ferry with a barrage containing tidal turbines has been rejected, but that doesn't mean it won't re-emerge. There was much outcry at the time about blocking a useful shortcut passage (see, it's boaty, really) but if a (free) lock was incorporated in the design then boats could continue to use the Cuan without too much inconvenience.

[Ocklepoint]

Difficult to imagine a large infrastructure project like a lock on the "Cuan Barrage" being provided free to a relatively small number of yotties ( who are generally perceived as being tolerably well heeled")

That being said the locks on the Cardiff Bay Barrage are free. I think that that provision was put into the enabling legislation after pressure from two fairly large yacht clubs and a city council keen to promote yottie tourism.

I suspect that the free passage of a few norwegian lobsters and the odd brown crab up and down the Cuan Sound would be regarded as more important to the decision makers than that of the yotties

[Alcyone]

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The SeaGen unit in Strangford Lough, the only commerial unit currently in operation in UK waters, is operating in 4-8 knots of flow. The Race Rocks shrouded turbine installation operates in spring flow rates of 7 knots. The favoured sites are precisely those with this sort of tidal flow rate.

Tidal turbines turn very slowly, and generally present little or no danger to marine life or divers. SeaGen's rotors turn at 10 - 15 rpm.

We were told about them by the guys on the survey vessel, so large pinch of salt. They were very insistant that diving near them would be strictly off limits, however. I belive the idea has been shelved, which is a pity.

[ash]

"For reference, MCT’s SeaGen system with 16m rotors has a swept area of 402 square meters. Most of the few competitors who have demonstrated systems in the sea have devices with rotor diameters in the order of 5 to 9m, which would be 15 to about 60 square meters."

Now, when I was at school the area of a circle was pi.D^2 / 4. Applying this, a 16m diameter circle has an area of 201 m^2, a 5m diameter circle an area of 19.6 m^2, and a 9m diameter circle an area of 63 m^2. Doesn't detract from the overall (correct) theme that big is good, but makes the ratios a bit more realistic.

Your math calculations are excellent - just one little quibble





























There are two rotors




Ash

[JackJ]

That's a good site, long overdue, which you've created there young Nick. Free energy from the tides is a much better solution to our growing problem of oil dependency from unstable states than the useless idea of wind farms which is put forward by the global warming bores.
A boating question for you Nick, as you seem to be a bit of an expert on tidal power (and other things).
I take delivery of my new Squadron 68 in April (got a buyer for my little 52 at 400 which ain't bad) and wonder if there is such a thing as a drogue type electrical generator which I can throw off the stern while under way. I will be able to achieve 30 knots at close to top speed. How much electricity will it generate? Enough to power the onboard wine cooler perhaps (60 bottles of ordinary or 40 of Moet). Failrline don't know of such a device and don't recommend one of those little windmill type things as they spoil the lines of a beautiful boat.
Your advice very welcome.

[Alcyone]

Might be cheaper to fit an alternator.

[aquaplane]

got a buyer for my little 52 at 400 which ain't bad

Awwww Jack, you should have advertised on here, I'm sure you would have been offered more than 400 quid, MOBO's do depreciate fast don't they.

[DaveS]

There are two rotors
Ash

Ahh... Just so.

It's funny how the brain sometimes fails to make an obvious connection. I knew they used two rotors, and had noticed that their area number was exactly twice mine... Oh deary, deary me!

again.