Just when you thought Guvmint energy policy was as daft as it could get . . .

[pressld2]

You may be right Mac, and I'm certainly no expert in these things. I'm just not aware of any reason why tidal generation shouldn't be as reliable as fossil fuel generation.

Not that I'm a big fan of tidal anyway, for the reasons Pauline gives. Of all the renewables the two that have the potential to do the most damage to wildlife are, in my view, tidal and biofuels. Although both can have a minimal impact on wildlife if done in the right place and on the right scale. And biofuels in the form of coppiced woodland even has the potential to be beneficial, with the same caveat - that it's in the right place and on the right scale.

Dave P.

[Lancashire Lad]

Originally Posted by muldonach

Sorry but whilst I can certainly accept that tidal generating output can be predicted to a fair degree in advance and that a degree of smoothing can be achieved by strategic positioning as described I think you are over-optimistic if you believe the output will be wholly predictable

Cheers
mac

Tidal flow is extremely consistent and predictable. The times of high and low water, slack current periods, spring & neap tides, seasonal current migration, tidal stratification, etc. etc. are all entirely predictable for any given location around our coastline. The amount of tidal flow is a just a function of the amount of water passing a given point at a given time. When all the variables are known, why should the calculation of the tidal flow be anything other than straight forward?

Standard deviation calculations can be included to provide assessments (or yet more predictions ) of the levels of uncertainties in power output for any given device at any given location.

Power output may not be able to be calculated "100% to the nth. degree", but it can certainly be predicted to within one or two percent - which is a whole lot more than a "fair degree". (Or to put it another way - it is orders of magnitude more predictable than that of wind turbines ).

The problem with tidal flow generation, is that the technology is not fully advanced, and as a consequence not very cost effective - but that will undoubtedly improve in years to come. - I'm convinced though, that of the presently available "sustainable" means of energy provision, tidal flow is the one that should be properly pursued as a long term major player.

I would repeat what I've said previously though, that it is not a case of "out of sight out of mind" with these things. Regardless of what might be best for the energy company, they absolutely must be located at such places that will have minimal impact on biodiversity. - The sub-sea habitat around our coast is a precious, species rich and finely balanced ecosystem - and we have to be absolutely certain that exploiting tidal energy is not done at its expense. (Although I would like to believe that these structures, over time, would become attractive to certain species and might indeed improve local biodiversity).

I would just add that like others, and from the same point of view of their potential adverse impact on local species and habitat, I'm wholly against tidal barriers. On that one I don't care what the protagonists might say, we can't know for certain what would happen until after they were built - at which time it would be too late. - I'm also against wave systems as I don't think they will ever be efficient, or cost effective enough when compared with other forms of generation.

Regards,
Mike.

[muldonach]

Originally Posted by Lancashire Lad

Tidal flow is extremely consistent and predictable. The times of high and low water, slack current periods, spring & neap tides, seasonal current migration, tidal stratification, etc. etc. are all entirely predictable for any given location around our coastline. The amount of tidal flow is a just a function of the amount of water passing a given point at a given time. When all the variables are known, why should the calculation of the tidal flow be anything other than straight forward?

.............

Regards,
Mike.

Sorry but that is exactly the point - tidal flow is consistent and predictable only up to a point, the tide at any given place on any given day may be somewhat different in both timing and strength to that predicted.

If you take the case of the Thames estuary which has real time tidal monitoring it is by no means unknown for the tide to be +/- 1.0m or even slightly more in variance to prediction.

It is a small point but tidal prediction is not the exact science that you seem to believe.


Regards
mac

[muldonach]

Originally Posted by pressld2

You may be right Mac, and I'm certainly no expert in these things. I'm just not aware of any reason why tidal generation shouldn't be as reliable as fossil fuel generation.

Not that I'm a big fan of tidal anyway, for the reasons Pauline gives. Of all the renewables the two that have the potential to do the most damage to wildlife are, in my view, tidal and biofuels. Although both can have a minimal impact on wildlife if done in the right place and on the right scale. And biofuels in the form of coppiced woodland even has the potential to be beneficial, with the same caveat - that it's in the right place and on the right scale.

Dave P.

I do agree that tidal power is reliable to the extent that it is at least always there to some degree and that it is at least predictable (if not precisely so).

One word of caution on biofuels - recently talking to a couple of forestry companies and I am told that if all the present proposals for woodfuel generation are implemented then the UK will be looking at an annual burn of some 24 million tonnes against a total timber harvest at the moment of 9 million tonnes annually.

Cheers
mac

[Lancashire Lad]

Originally Posted by muldonach

Sorry but that is exactly the point - tidal flow is consistent and predictable only up to a point, the tide at any given place on any given day may be somewhat different in both timing and strength to that predicted.

If you take the case of the Thames estuary which has real time tidal monitoring it is by no means unknown for the tide to be +/- 1.0m or even slightly more in variance to prediction.

It is a small point but tidal prediction is not the exact science that you seem to believe.


Regards
mac

I disagree. Tide heights in a tidal estuary such as the Thames are of no relevance to this since prior rainfall (affecting the volume of water going down river being stalled by incoming tide) would be one of the main determining factors on water height within the tidal reaches.

Whilst I agree that height of a tide can be markedly affected by wind direction, long length waves, storms far out at sea, and other such varables which can't be predicted far in advance, such tide height and wave action would have no impact upon the output of tidal flow turbines provided that the turbines were located deep enough.

It wouldn't matter to a tidal turbine what the waves above were doing, or whether the height of water above it was 10m or 15m. - It is the flow that counts, and, regardless of whether due to exceptional circumstances, slack water was a few minutes late on a given day, the flow past the turbines would be highly predictable taken over sufficient timescale.

It is also the case that with tidal turbines deployed all around the coastline, the overall "percentage of total" power output at any given time of day would be very predictable indeed, as any one of these exceptional events would be far less likely to affect the whole system.

Regards,
Mike.

[muldonach]

Originally Posted by Lancashire Lad

I disagree. Tide heights in a tidal estuary such as the Thames are of no relevance to this since prior rainfall (affecting the volume of water going down river being stalled by incoming tide) would be one of the main determining factors on water height within the tidal reaches.

Whilst I agree that height of a tide can be markedly affected by wind direction, long length waves, storms far out at sea, and other such varables which can't be predicted far in advance, such tide height and wave action would have no impact upon the output of tidal flow turbines provided that the turbines were located deep enough.

It wouldn't matter to a tidal turbine what the waves above were doing, or whether the height of water above it was 10m or 15m. - It is the flow that counts, and, regardless of whether due to exceptional circumstances, slack water was a few minutes late on a given day, the flow past the turbines would be highly predictable taken over sufficient timescale.

It is also the case that with tidal turbines deployed all around the coastline, the overall "percentage of total" power output at any given time of day would be very predictable indeed, as any one of these exceptional events would be far less likely to affect the whole system.

Regards,
Mike.

Whatever else affects the rise of tide the volume of fresh water coming down a river is not one of them, I quoted the variance in the Thames because it is well known phenomenon and one that many visitors to the forum may be familiar with, the variation in tide extends right through the Thames Pilotage area as far as Sunk Head Towers etc. Similar variation (not necessarily of the same magnitude) is experienced in all tidal waters as far as I am aware.

I fully agree that with a tidal tubine it is the rate of flow that matters, however I am not sure where your focus on depth v flow rate comes from, the prime sites for tidal turbines that I am aware of are focused on the sounds on the west coast of scotland and the firths around the northern isles, these are all in relatively shallow water and tidal flows are to say the least variable.

The original phrase which I questioned was "constant reliable output" and I am sorry but I remain of the opinion that the output of any given turbine on any given day will be far from being predicable within one or two percentage points.

It is hardly feasible to site turbines all around the coastline since in general tidal streams on the eastern side of the UK north of the Yarmouth banks are not particularly strong. I am also of the opinion that the entire system may indeed be affected by a single event - a major storm surge or large high or low pressure system will affect the entire Uk although I do accept that these events can be modeled ahead of the actual event.

Again I fully accept that tidal power is more reliable and predictable than wind power - but i don't accept that it will provide a "constant reliable output".

cheers
mac

[Lancashire Lad]

Hi Mac,

I don’t imply any interrelationship between depth and flow rate. I was merely making the point that it doesn’t matter what height of water is above, provided turbines are deep enough such that the action of waves / wind etc. are not having any direct effect. (i.e. you don’t have to go very deep before even very strong wave action becomes undetectable).

Yes, obviously flow rates are significantly variable during any given cycle between low and high tide. – However, the data for a particular location, once obtained, will remain valid day-in day-out, other than for those times when abnormal (and non predictable) weather events manifest themselves.

With regard to the feasibility or otherwise, of locating turbines all around the coast - even if turbine arrays were restricted to locations such as your mention of Scotland’s west coast and northern isles, they would still be able to be deployed in areas comprising of all tide states from low to high water.

For example, a quick look at today’s tide tables reveals: -

High tide at Southend (Kintyre) 01:51am
High tide at Sound of Gigha 05:18am
High tide at Craignure 08:00am
High tide at Loch A’Bhraige 09:02am
High tide at Kyle of Durness 09:58am
High tide at Stromness 11:35am
High tide at Bur Wick 13:20pm

(NB: I'm not saying these places are prime locations for siting turbines, but merely to show that there is a full low/high tide spread around Scotland’s West & North coasts). - Deployed across the entire low/high tide range, some turbines would be producing full output, and some would be producing negligible to no output at any given time.

It is also worth noting that the power demanded from these turbine arrays would be based upon a percentage of their installed capacity. A calculated percentage which, given the various operating parameters would be fully achievable.

Therefore, a constant and reliable power output could easily be guaranteed.

I just don’t accept that major storm surge or low pressure would have any significant effect on the operation or output of such turbines. – With or without these events, there will still be two tide cycles per day, and it is the tide cycle which drives the turbines.


Regards,
Mike.

[STYRBJORN]

Also, climatic events such as low pressure co-inciding with a spring tide will increase the strength of the tide. Such events are much less likely to reduce the strength.