But the tidal ranges there are poor, and that's what counts. West coast is very much better, and even there, sites are limited. Severn estuary is by far the best, Morecambe Bay and Solway firth are not too bad, and that's about all. But Morecambe and Solway have very close tide times (they're not far enough apart), so wouldn't help in smoothing out intermittency.
En el artículo , charles escribió:
/me makes note to watch The Secret Life of the National Grid again.
Note that harry doesn't understand boolean logic.
Big tides AND deep estuaries..
By way of a post script, I've now looked at results from La Rance near St. Malo in Brittany, and the world's largest tidal power station at Shiwa Lake in South Korea.
La Rance has a maximum capacity 240MW, and generates
540,000,000kWh/year, demonstrating just how much these people like to impress with their big numbers! It works out at an average rate of 61.6MW, giving a capacity factor of 25.7%Shiwa Lake is has a slightly bigger maximum capacity than La Rance, with a maximum capacity of 254MW. It is a one-way scheme, only generating on the flood tide, with water draining back out to sea through sluices. This is because it is part of a complex water management scheme. It generates 552.7GWh per annum, which equates to an average power output across the year of 63.1MW and a load factor of
24.8%. I'm a little surprised that Shiwa Lake does as well as it does, only generating on the flood tide. More atI came across an article with the intriguing title "Tidal giants - the world?s five biggest tidal power plants",
And thereby hangs the tale. If it was easy,and produced large amounts of cheap power it would have been done everywhere already.
Standard hydroelectricity never needed government subsidy to be profitable.
It is the myth of the renewable industry that public funding can eventually turn a sows ear into a silk purse. That somehow 1000 year old windmills, 100 year old photocells and 600 year old tidal barriers are 'new technology' can be developed to change the laws of physics and make them produce more than there is energy in the sun wind or tides.
Yes.
Always upsets a few vocal nimbyes.
Hmm.. big chunks of farmland now covered in arrays. (lot going up near Luton Airport currently) I have some South facing slopes and a convenient 11KV feeder but haven't bothered to follow the money.
I'm not sure I believe the oil/gas co interference with nuclear but I can believe govt. has allowed siren voices to cause delays in vital decisions.
In article , Chris Hogg writes
Unfortunately the timescales for correcting the mess are 10years +
When you are paid twice the going rate or more for whatever electricity you can produce, needed or not, its makes sense to farm subsidies instead of crops.
What you can see everywhere, from the internal politics of the Unions, UKIP and the Labour party, to the way the EU reacts and the way legislation always seems to benefit a narrow group of interests, is that infiltration especially over a long period, works wonders to subvert the democratic process.
Cue mass immigration. And the insistence on promoting unsuitable minorities to positions of power.
Infiltration on a huge scale.
PV might prove useful in the distant future. If it can be made very cheaply , like printed plastic film, and put onto roof tiles it may be worthwhile - but such technology is so far away from what we have today that we're not going to get there by funding today's PV. If you could print a PV roof for £50, and have it generate £50 a year of electricity that you use, and store by making the freezer colder. Figures for today's technology are utterly different of course.
Hydro AIUI does produce cheap electricity, there just isn't anywhere in the UK suitable for it.
As for wind... same story. Maybe one distant day, but the current designs a re never going to get there.
NT
I see the basic concepts of power density and intermittency have passed you by...
The radio active waste deaths doesn't enumerate fractions of deaths. ie lives shortened.
The depth is neither here nor there. Surface area and tidal range are what matters.
The Gibrat* ratio, k, is a quick and dirty way of assessing the viability of a particular tidal barrage scheme. It is calculated from the equation k = l/E, where l is the length of the barrage in metres, and E is an estimate of the power available**. E is calculated from E = 1.4 x R^2 x A where R is the mean tidal range in metres, and A is the impounded area in km^2 . The lower the better; good tidal barriers achieve figures less then 1.
So you can do your own estimates as to whether a particular location will be of any use as a tidal barrage.
For La Rance, the barrage length is 750 metres, the mean tidal range
8.2 metres, the area 22 km^2, which gives a Gibrat Ratio k of 750/(1.4*8.2*8.2*22) = 0.36.For the Swansea Lagoon, the length is 9650 metres, mean tidal range
8.5 metres, area 11.5 km^2 so k = 9650/(1.4*8.5*8.5*11.5) = 8.3 , which is poor.** skemman.is/en/stream/get/1946/5676/16922/1/Bjarni_Jonsson_MASTER_Heild.pdf (can't tinyurl that).
*R. Gibrat was a pioneer in developing tidal power and was involved in the early designs of the La Rance tidal scheme in the 1940's.
The origin of Gibrat's formula is easily seen. Barriers are expensive, so the longer the barrier, the more expensive and less attractive the scheme. But barrier length per unit of energy available is a key factor. The potential energy of an elevated mass is mass x height. In a barrier scheme this is estimated from the volume of water, i.e. area x tidal range to give the mass, and tidal range to give the height. So barrier length per unit energy available is given by barrier length divided by the product of the square of the mean tidal range and the impounded area. The 1.4 is a correction factor, something to do with tidal movements but I can't immediately find an explanation.
The take-away from Gibrat's formula is that you want short barriers, a large tidal range and a large impounded area. This favors long estuaries with narrow mouths, rather than lagoons.
Some rough estimates, for example*,
The Wash: roughly 25 km square, so barrier length 25 km and 625 km^2 in area; mean tidal range ~5 metres. Hence Gibrat ratio =
25000/(1.4*5*5*625) = 1.1The Humber Estuary: barrier length (from tip of Spurn Head) ~6.5km; estuary length ~45 km; hence area (assume isosceles triangle) ~145 km^2; mean tidal range ~4 metres. Hence Gibrat ratio =
6500/(1.4*4*4*145) = 2.0The Firth of Forth: barrier length ~12.5 km; estuary length ~55 km; hence area (assume isosceles triangle) ~350 km^2; mean tidal range ~4 metres. Hence Gibrat ratio = 12500/(1.4*4*4*350) = 1.6
Although all three have better Gibrat ratios than the Swansea scheme, they're not below 1 so not marvellous. In addition, I've read that if the tidal range is below 5 metres, it's not worth considering for a tidal barrier.
*If anyone doesn't like my numbers, and they are only rough figures, don't whinge but your own calculations!
Sqaure root of two?
peak versus RMS?
Could be. I did see an explanation in my perusings but I can't find it now. How's your French?
Incidentally, if you Google for Gibrat ratio, you'll find many descriptions of how to calculate it along the lines 'The Gibrat ratio is the ratio of the length of the barrage in metres to the annual energy production in kilowatt hours'. They then quote La Rance at
0.36, Severn at 0.87 and Passamaquoddy in the Bay of Fundy at 0.92. But that has to be a nonsense. The length of the La Rance barrage is 750 metres, and the annual output is 540,000,000 kWh/y, which gives a Gibrat ratio just a teeny bit smaller that 0.36! OTOH the description that I gave earlier does give a value very close to 0.36, so I'd stick with that for future calculations. It's obvious that most people just quote an earlier source parrot-fashion, without thinking about it.
Welcome to the World That Socialism Built.
Actual thought is to hard for the Snowflake Generation... ...the sort of stuff we did for 'O' level would be cruel and unusual punishment in today's skools...
fair amount in Scotland, Beore "privatisation", there was the North of Scotland Hydro-Electric Board.
See
Also
Hydroelectric power is generally rainfall limited unless its on BIG rivers like the Victoria falls stuff or IIRC the Kariba dam.
However as it does usually involve building storage in the form of a reservoir, it actually is the one way to balance intermittent renewables, and nations that have lots of it use it as peak following technology, usually with nuclear baseload, to great effect. You can add a bit of wind or solar to that without it being too much of a problem, apart from the cost of course, until you reach the limits of it. IN graphical terms you shift its peak production to renewable lulls.
Until you get a rainless and windless patch.
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