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Post by rsmith7 on Jan 20, 2014 16:13:21 GMT 1
Dear Prof Houlsby, www.bbc.co.uk/news/uk-scotland-north-east-orkney-shetland-25800448I came across this article and noted some errors. Leaving aside the standard unitary errors, the article failed to explain that the figures quoted were the possible average daily energy production. 1.9GWhrs/day is a very different figure from 1.9GW power potential. I'm sure you'd agree that 1.9GWhrs/day will not provide "half of Scotland's" energy. It also failed to say that in order to extract 1.9GWhrs/day, a dam - seven miles long and 280 feet high - would need to be installed. It would also be useful to point out in future that 1.9gwhrs/day equates to about one tenth of a day's output from an average sized conventional power station. Please find the attached tidal energy study summary I commissioned in the 90's. You are probably aware of the Carbon Trust's £2 million study that found the total average energy in the Pentland Firth to be 6GWhrs/day. I would be interested in your comments regarding the tens of millions currently being invested in tidal energy in Scotland. Kind regards, Robert Smith Dear Robert, First of all there is no error in the reported figures in the article - it was reported as 1.9GW, not 1.9GWhr/day, which is your changed interpretation. Your interpretation is incorrect. What was stated was 1.9GW, and this is the average power that we calculate as being available (of course this is a lot less than the peak power). If you want to convert to GWhr/day you need to multiply by 24 (the number of hours in the day), to get about 46 GWhr/day. That is indeed about half of Scotland's electricity consumption. It is also about twice what you get from a big coal or nuclear power station - but of course tidal comes with no CO2 emissions nor a nuclear waste disposal problem. To obtain that we would indeed need a very bid investment in tidal turbines, but emphatically not a "dam" 7 miles long and 280 feet high. There are much better ways of exploiting this resource by using tidal stream turbines. The great advantage is that the investment can be incremental - so that you get some power out with the very first small installation, more with the second etc. I am of course aware of the CT study and others, but our study probably uses the most advanced methods to date, and almost certainly leads to the most accurate figure. Of course this will be refined in due course, but it is unlikely that the conclusions will change by a huge amount. Thanks for your interest. I believe tidal power has the real potential to contribute to a truly sustainable energy mix for Scotland, and hope that, if developed with sensitivity to the environment, it could be a big success. I am not sure that the funds that are currently being spent on tidal projects is being spent wisely, but I have no doubt that it is worth investigating these options, and of course that involves some investment of funds. Yours Guy Houlsby |
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Post by rsmith7 on Jan 20, 2014 16:16:50 GMT 1
Dear Guy,
I'd be very interested to see your data and methodology that led to the figure 46GWhr/day. Is this figure averaged over a month? or year? *** Yes, this is the average over a spring/neap cycle, so you get about the same answer over a month or over a year*** Did you look at the study I had commissioned and attached to my last mail? It gave an average total daily figure of 10.9GWhrs. *** Have not had the chance to look at your figures in detail. Actually the difference between your 10.9 and our 46 GWhrs/day is not as big as some of the other variations that have been suggested. I doon't know how intensely you were proposing to develop, but our 46GWhrs/day is pretty near the theoretical maximum you could get. The practicable amount would be a lot less - and could indeed be down near the sort of value you quote***We had it checked by Southampton University and they agreed it was accurate. (error 5 - 10%) ***I'm not sure when that was - I think you said in the 1990's. The understanding of these issues has moved on in recent years, and I think we understand the physics much better now than we used to. I am pretty confident in our figure though***
Are you disputing the carbon trust's figure of 6GWhrs/day average?***No, again it depends on how intensely you develop the site, and they were assuming a much lower intensity***
Would you agree that in order to extract the maximum energy (30% probably) from the Pentland Firth, a dam would need to be built. ***No, I'd go with free stream tidal turbines***
What percentage of this maximum would be captured by an array of turbines across the extent of the stream? ***If you had enough turbines in theory you could get close to the 1.9GW
And at what cost? ***High, but I have to be honest that it is difficult to estimate at this stage.***
Kind regards,
Robert
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Post by rsmith7 on Jan 20, 2014 16:17:16 GMT 1
Robert -
Lots of questions! Easiest way is to interleave my answers below.
Guy
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Post by jonjel on Jan 20, 2014 16:28:03 GMT 1
Greetings Mr Smith. Nice to see you back here when bad weather keeps you on shore.
It is a tricky one. I think anyone with an axe to grind will manipulate figures, and I am not an expert on this.
My general view is that harnessing tidal power is no bad thing, and my reasoning is we know when it will be high water in Orkney on 21st September 3020, and the tidal range.
Therefore it should be possible to link large or small tidal stations around the coast to give continuous power, which can't really be said for any other power source, including those damned windmills. No, especially those windmills.
Everyone seems hell bent on turbines in the tidal flow. However if you moored a sectional hollow caisson - and lets think a mega sized one, and that had cable operated turbines on deck, the other end of the cable anchored to the sea bed then I think you might just start to get usable power. Low tech, but cheap compared with some of the crack-pot ideas I have seen.
And as for the green lobby. They would love it as it would be somewhere for the dear little birds to keep their feet dry.
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Post by rsmith7 on Jan 20, 2014 17:06:58 GMT 1
Thanks Guy, I'm still struggling to understand how an array of turbines could capture as much energy as a dam ... or anywhere close. Could you point me to your calculations that led to the figure of 46GWhrs/day? I would accept our figure could be out by as much as 20% ... at a push ... but by a factor of four? I cannot see that. In any case, for tidal energy conversion to be commercially viable it would need to be better by a factor of hundreds. The Carbon Trust's figure - like ours - was the total average potential energy. It wasn't dependent on the intensity of development. Sometimes some real world experience is valuable. I've fished lobster, mid channel, in the Pentland Firth for twenty years and I'm sure that if there was enough energy to power half of Scotland, my piffling little creels and thin, weakly rope wouldn't survive for ten minutes. Did you catch the news a couple of years ago about the girl that was the first person to swim the Pentland Firth? I planned the route and guided her across. She was a big strong girl; maybe we should connect her to the grid and save the country a fortune.  I should add that I'm not a vexed local trying to save his patch - if I thought tidal energy was viable, I'd have been involved long ago. That's why I commissioned the feasibility study long before tidal energy was fashionable. Kind regards, Robert |
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Post by rsmith7 on Jan 20, 2014 17:56:34 GMT 1
Hi Jonjel,
Been busy with other things indeed yet the bullshit keeps piling up. Our Island's council has just completed a new harbour specially for marine renewables.
You couldn't make it up....
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Post by mrsonde on Jan 21, 2014 3:54:16 GMT 1
Very good, Mr.Smith.
I'm not sure I quite get your caisson idea, Jonjel. Is it like the nodding ducks?
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Post by jonjel on Jan 22, 2014 13:52:58 GMT 1
Very good, Mr.Smith. I'm not sure I quite get your caisson idea, Jonjel. Is it like the nodding ducks? No Mrsonede Think in terms of Mulberry Harbour, but in theory up to several sq Km in size. Modern concrete technology means it has enormous lift on each tide in comparison to weight - they make ships from sprayed cement mixed with chopped strand, and moulds for boats etc. I once tried to break one up and gave up and it was only about 20mm thick. Although the 'lift' is only that of the tidal range the energy is pretty substantial. Connect some turbines on deck (easy to service) to cables anchored and there you might just have a low tech cheap solution. Be interested in wiser heads putting some maths on it. |
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Post by rsmith7 on Jan 22, 2014 15:29:57 GMT 1
Jonjel,
I get your idea about cable operated turbines. Wouldn't it be easier to fix the caisson to the sea bed and have it fill and empty through turbines? The potential energy would be similar and it would work on the ebb as well as the flood with less loss due to friction.
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Post by jonjel on Jan 24, 2014 15:34:53 GMT 1
Jonjel, I get your idea about cable operated turbines. Wouldn't it be easier to fix the caisson to the sea bed and have it fill and empty through turbines? The potential energy would be similar and it would work on the ebb as well as the flood with less loss due to friction. Mr Smith. Generating power on the ebb is simple. All you would need is another cable, but arrange it to run over a pulley on the deck and down to the turbine. The weight of the falling caisson would generate power on one cable and the rising caisson on another. Yes it may be completely crack pot, but I have seen anchor cables part on a rising tide because some fool did not put enough slack on, so there is power there. You just have to find a way of harvesting it. |
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Post by alancalverd on Jan 24, 2014 18:49:48 GMT 1
The only energy you can get from a float is its maximum potential energy mgh where m is the mass of the float g is g and h is the tidal range.
The power you can get from a turbine is proportional to the cube of the flow rate and the swept area of the rotor.
For a given mass of construction material, you will get a heck of a lot more energy per tide cycle from a turbine if you can restrict the water flow to maximise the tidal flow rate - at the limit, it depends not on the mass of the machine but on the mass of water that flows past it. Imagine an average tidal flow of 1 m/s (about 1.5 kt) across a square meter of turbine sweep. That's one tonne per second at 1 m/s. You would be hard pressed to find a vertical tidal range speed of 1 m/s anywhere.
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Post by mrsonde on Jan 24, 2014 20:06:46 GMT 1
Jonjel, I get your idea about cable operated turbines. Wouldn't it be easier to fix the caisson to the sea bed and have it fill and empty through turbines? The potential energy would be similar and it would work on the ebb as well as the flood with less loss due to friction. Yes, I thought that's what Jonjel meant. Either way, it would be more efficient to convert the linear lift into rotationary directly, wouldn't it? Like a traditional pump? And then you feed it directly into your dynamo. Still fairly feeble though. I can't see it as the future. I'm totally convinced splitting water using sunlight is the future. We're nearly there - a year or two at most, judging by current theoretical knowledge, and practical experiments. I've been working on a promising design myself for the past five years. I get enough hydrogen to fill a child's balloon in a couple of hours. Not adequate, of course - but I understand why, more or less. Given the right equipment, and time, neither of which unfortunately I can really afford at present, it would take less than a second, I'm fairly sure - the order of seconds, anyway. That's enough to drive a car, for example, if the sun is out, and for as long as it shone. The rest is down to the storage problem - which isn't really all that serious. |
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Post by jonjel on Jan 27, 2014 16:04:59 GMT 1
Interesting thoughts from both Alan and MrSonde.
You are of course right Alan, and it was just idle thoughts running through my now ancient head.
The Severn barrage idea is a similar concept and has been suggested and talked about since the 1930's but will probably never happen. It is alleged/claimed that it could produce 10% of the nations power requirements. Hmmm.
I wonder what it would have cost in 1935 compared to the estimates of several billion I have seen recently?
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Post by mrsonde on Jan 28, 2014 8:57:02 GMT 1
Have you ever seen a hydraulic ram pump working, Jonjel? My neighbour in the Auvergne used to run one to provide all the power for his home and farm, about 200 foot above the local river. He bought an old pre first world war ram pump for a song - still in perfect working order (of course - with only one moving part and a few rubber rings, there's nothing to go wrong.)Since seeing that miracle of engineering I've always wondered why a large modern design can't be used to generate hydroelectric power. As far as I can work out there is no reason why not - it's just an old piece of tech that's been forgotten about, since the advent of the steam engine. My neighbour used to use his to turn some comical Heath-Robinson contraption using a water-wheel connected to an artic alternator to charge a bank of batteries - mad, but it worked, for no expenditure at all. Completely free electricity, with the added bonus that he was off the water grid too (I surmise - he was Auvergnoise, something like a cross, stereotype wise, between a Scotsman* and a Scouser.)
Presumably a more direct design could be built deep beneath the level of every river, connected by a leit as in the old water-mills. Then a ram-pump returns the water to the river via another leit - no power expenditure at all. They make one hell of a racket, but as it would be deep underground that wouldn't be a problem. Barely any maintenance required - very simple design, minimal cost, applicable on every river, waterway, and coastline in the country. Far more efficient and much less cost than wind turbines, and totally, constantly, reliable.
Why do you think this isn't done?
* Apologies, mr.smith.
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Post by jonjel on Jan 28, 2014 10:05:44 GMT 1
I have indeed seen one mrsonde, a friend ran one in Wales, not for power but to get water to a higher level to give himself water in his cottage. As you say, ancient and very inefficient - I seem to recall that it only shoves about 10% of the water it uses to a higher level but Google and I don't get on!
But of course in this modern world if it aint high tech it is jeered at.
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