TIDAL RISE +FALL GENERATION

[scottishjohn]

any clues where to find more info 

like you do i was lying awake in bed and this idea appeared --probably been thought of a million times before

 a vessel in a tidal zone 

which goes up and down and that motion is converted to turn an alternator 

yes I know a serious gear box would be required --or if done with hydraulic rams -large diameter ones to then turn hydraulic motor connected to alternator 

If you have a 3-5000 Ton vessel that rises+falls  6-8 metres twice a day that must be a lot of power generated by the movement?

I use the word vessel as it could be a concrete tank inside an outer tank connected to the tide but not actually in the sea --and in theory  it cold be any size  

and even underground so something could be built on top of it

 

[Jeremy Harris]

There's quite a few such systems around, ranging from buoys with internal winches that drive generators as they are pulled up and down, though oscillating air column generators using submerged towers a bit like some oil platform ones,  to the far more powerful tidal barrage schemes like the one at Rance :https://en.wikipedia.org/wiki/Rance_Tidal_Power_Station

 

I believe there are still trial tidal flow generators, like this one that's been use up near Orkney, where the tidal flow rates are quite high: http://www.opusenergyblog.com/floating-tidal-turbine-off-orkney-islands-breaks-generation-records/

[scottishjohn]

yes i,ve seen that before --my thoughts are that anything that complicated in the sea will be very costly to maintain 

as anyone who has had a boat will know how the sea eats everything

something basically land based with only concrete things in the water should be very much cheaper to maintain 

and those cost are going to make big difference to viability long term and should have a life same as a dam --100years?

what i am suggesting could be virtually  made by any one with concrete re-enforced  shuttering experience- very low tech 

like building a simple multi storey  concrete building  or bridge 

I appreciate the out put will not be as much as turbine -

-but the cheaper costs could out weight that to make it viable ?

 

 

[SteamyTea]

Not tidal, but there was a land based wave generator based on Islay.

https://en.wikipedia.org/wiki/Islay_LIMPET

It was the turbine design I liked, simple and worked on both the in and out 'strokes'.

There was also a simple design that used a hydrofoil. As the tide went past, it lifted up or down, this was connect hydraulically to s generator on the land.

You could take a look at the WaveHub down here at Hayle.

They have not generated anything get, except a financial hole.

[Jilly]

No idea of the references, but the idea has been designed an calculated. The Uk has enough tidal power to be self sufficient in energy... and yet we are still building more nuclear power stations...

[scottishjohn]

i have seen the limpet as well --vnever thought it would be viable

but again complicated turbines and everything in close proximity to salt water or salt spray 

 and storms 

 

Edited September 20, 2019 by scottishjohn

[SteamyTea]

2 minutes ago, Jilly said:

The Uk has enough tidal power to be self sufficient in energy.

As always, it is not as simple as that.

One of the biggest problems is conservationists, they will stop almost all development because some bird or welk may vanish from an estuary.

[scottishjohn]

and of course making a barage to use tidal power is very expensive and long term --so private industry won,t do it and government  is same .but will waste on HS2 ,cos it fits inwith the westminster /London bubble

[Jeremy Harris]

13 minutes ago, Jilly said:

No idea of the references, but the idea has been designed an calculated. The Uk has enough tidal power to be self sufficient in energy... and yet we are still building more nuclear power stations...

 The really massive problem with tidal power, is that although we have locations where there is the potential for a lot of power generation, like the Severn Estuary, the interests of those keen on exploiting this large energy source have to be balanced against the interests of those keen to retain both shipping access and important tidal habitats. 

 

The same goes for other areas where there is a high tidal range that could be exploited.  The act of removing energy from a tidal stream has a direct and massive impact on the local environment somewhere - it's impossible to extract energy without that loss of energy appearing as an effect somewhere.  Even putting solar panels on the roof of a house reduces the heat into the house by ~20%, which then impacts on things that may grow on those surfaces, by altering the mean temperature range.

 

Arguing over the relative balance between the positive aspects of electricity generation, and the negative aspects of it is made all the more difficult because there are often somewhat irrational, but nonetheless strongly held, belief systems that come into play.  The same people that get sufficiently irate to mount mass protests about electricity generation schemes are often  the same ones that rely on the massive amount of electricity it takes to maintain the internet (currently the internet has an electricity demand that exceeds that of the UK as a whole, by a factor of about 8 to 10).

[scottishjohn]

ok -for you mathmatics gurus 

how much power would it take to raise 5000 tons by 8m--then allow say 70% efficiency transfer rate by hydraulics to drive alternator --how much power do you get  per rising tide.then you will also get somewhat less as the tide goes down-say 50% of the rising one 

 

 

Edited September 20, 2019 by scottishjohn

[Jeremy Harris]

1 minute ago, scottishjohn said:

ok -for you mathmatics gurus 

how much power would it take to raise 5000 tons by 8m--then allow say 70% efficiency transfer rate by hydraulics to drive alternator --how much power do you get  per tide?

 

 

 

Depends on time.  A mouse might be able to muster enough power to move this mass over a few lifetimes, an elephant would do it a lot quicker, as it's more powerful.

 

If we assume that there is 12 hours to lift the 5,000 tonne mass 8 m,  and that the rate of lift is constant (it won't be for a tide, but this keeps things simpler) then the potential energy needed to achieve this is given by

Work done = 5,000,000 kg * 9.80665 m/s² * 8m = 392,266,000 J

Power over that 12 hour period = 392,266,000 J / (12 * 60 * 60) = 9,080.23 W

 

So very roughly, ignoring efficiency, the potential energy is about 392.266 MJ and the power over 12 hours would be about 9.08 kW.  Allowing for 70% efficiency, the mean power generated would be around 6.356 kW.

[scottishjohn]

thats the answer then --or close enough --even adding the falling tide that could add another 5kw --so 11-12 kw per tide or 24 kw per day 

24kw @5p per kw =£1

 not viable --end of

 

[Stones]

1 hour ago, JSHarris said:

There's quite a few such systems around, ranging from buoys with internal winches that drive generators as they are pulled up and down, though oscillating air column generators using submerged towers a bit like some oil platform ones,  to the far more powerful tidal barrage schemes like the one at Rance :https://en.wikipedia.org/wiki/Rance_Tidal_Power_Station

 

I believe there are still trial tidal flow generators, like this one that's been use up near Orkney, where the tidal flow rates are quite high: http://www.opusenergyblog.com/floating-tidal-turbine-off-orkney-islands-breaks-generation-records/

 

The European Marine Energy Centre is based up here - all kinds of tidal devices, systems and projects being trialled:

 

http://www.emec.org.uk/

 

38 minutes ago, SteamyTea said:

As always, it is not as simple as that.

One of the biggest problems is conservationists, they will stop almost all development because some bird or welk may vanish from an estuary.

 

Ongoing issues here with proposals to upgrade the grid to handle expected new renewable energy schemes - objections from those who want overhead cables buried, and in turn objections from those who think burying cables will damage wildlife habitat...

[SteamyTea]

28 minutes ago, Stones said:

objections from those who want overhead cables buried, and in turn objections from those who think burying cables will damage wildlife habitat...

And objections from government and end users who want cost to be low.

On a slightly off topic, but connected. Who sees the irony in this banner on the Humphrey Davy memorial in Penzance.

@JSHarris, you are not allowed to answer. Which may give others a clue.

[Jeremy Harris]

He went to the same school as my youngest brother.

[Simplysimon]

17 minutes ago, JSHarris said:

He went to the same school as my youngest brother.

you hide your age well!

[Temp]

4 hours ago, scottishjohn said:

If you have a 3-5000 Ton vessel that rises+falls  6-8 metres twice a day that must be a lot of power generated by the movement?

 

Perhaps not as much as you might expect...

 

3-5000 Ton is around 4.5 million kg.  If that was raised to a height of 8m it would store..

 

Energy = mass*height* gravity

= 4,500,000 * 8 * 9.8

=  353MJ of energy.

 

The stored energy would have to be used while the tide is going out allowing the vessel to descend turning a generator as it does so. That's 6 hours. If it was "discharged" at a continuous rate for 6 hours the max power output would be...

 

Power = Energy/time

= 353,000,000/(6*60*60)

= 16kW approx.

 

Obviously it could deliver more power for shorter periods - say 32kW for 3 hours or 64kW for 90 mins. In practice it would be a less as you can't capture and convert all the energy to electricity.

 

If you were thinking of using a real boat for this you would have some problems. The boat would need to be supported somehow when the tide goes out and the water disappears from underneath it. It can't float down as the tide goes out because that wouldn't allow you to capture the energy.

 

Tidal barriers like that proposed for the river seven work because the amount of water raised would be much larger. The real problem is that gravity is quite weak.

 

 

 

 

 

 

 

 

Edited September 20, 2019 by Temp

[SteamyTea]

18 minutes ago, Temp said:

Tidal barriers like that proposed for the river seven work because the amount of water raised would be much larger

Not that much larger, on average.  Just under 8 m at Weston-Super-Mare today.

They work because they are very large.  The proposed Severn Estuary barrage would make a lagoon 500 km², this would give a power range between 8W/m² (neap tide) and 30W/m² (spring tide).

Cheaper and more effective to put PV and battery storage somewhere.

 

[ProDave]

4 hours ago, JSHarris said:

If we assume that there is 12 hours to lift the 5,000 tonne mass 8 m,  and that the rate of lift is constant (it won't be for a tide, but this keeps things simpler) then the potential energy needed to achieve this is given by

Work done = 5,000,000 kg * 9.80665 m/s² * 8m = 392,266,000 J

Power over that 12 hour period = 392,266,000 J / (12 * 60 * 60) = 9,080.23 W

 

There are 2 tides in each (approximately) 24 hour period, so it will in fact only take 6 hours to raise the mass, but it will do that twice a day.

 

You should be able to extract power on both the up and the down "stroke" as well.

 

So the maths simply becomes how much energy does it take to raise and lower it x metres twice, and that is how much energy you can get in a day.  x being the tide height which varies here between 5 metres and 3 metres.  You would need to know the average tidal range for your location to work out the average energy.