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Author Topic: Wave power  (Read 3639 times)
George61
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« on: September 20, 2016, 09:55:54 PM »

I am very concerned about the slow progress in developing our wave power resources.
There are two basic approaches to utilising wave energy:
1, to convert it directly to electricity;
2, to convert it to stored potential energy in reservoirs and using this stored energy to generate electricity.
There are numerous suggested devices which use the first approach but using reservoirs would be far more efficient and is equivalent to building dams and reservoirs to capture the energy from rivers.
Wave pressure will force water to enter the reservoirs through one-way openings in their sides and exit through turbines to generate electricity. Water will enter if the pressure from the incoming wave is greater than the pressure inside the reservoir and so a head of water above sea level is created inside the reservoir. The hydrodynamic pressure of the wave enables the head of water to be higher than the amplitude of the wave.
The reservoirs store energy and smooth electricity output. They enable more electricity to be generated at times of peak demand .
The reservoirs can  be fixed to piles in shallow water or supported by floats in deep water. The bigger the reservoirs the better as more energy can be captured and stored and there would be less energy losses in heavy seas through overflowing.
The reservoir structure is able to survive the forces of heavy seas because of the weight of water inside the reservoir and because it is the stored water in the reservoir rather than the structure itself which absorbs the forces of the waves.
As the reservoirs block the forward motion of waves they are cost effective breakwaters which could be used for coastal protection.
The use of reservoirs is a far more efficient and cost effective way to capture wave energy than the innumerable designs which seek to capture wave energy directly without energy storage because they can capture and store more energy and they act as breakwaters.
With our greater use of intermittent renewable energy sources there is a great need for energy storage and the reservoirs would be an ideal solution to this problem.
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Allnightin
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« Reply #1 on: September 20, 2016, 11:13:35 PM »

I saw a report on this one on local TV quite a while back but haven't heard anything since

http://searaser.net/

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biff
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« Reply #2 on: September 20, 2016, 11:20:04 PM »

Hello George61 and welcome to the forum,
                                 Your,s seems a likely solution to the storage problem. It is possible that they are still out doing surveys. Not every place would be suitable and you would need a big difference between high tide and low tide, like you have on the Severn. Then you would need thousands of acres as well.
  It is certainly food for thought.
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knighty
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« Reply #3 on: September 21, 2016, 12:00:09 AM »

I don't think you'd be able to generate much of a head of water / high in the reservoir from normal waves on a normal day?
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RIT
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« Reply #4 on: September 21, 2016, 12:03:38 AM »

The basic idea of using wave pressure to force water 'up-hill' and then generate electricity from the potential energy difference is already used in a few small scale systems where the water directly drives a turbine.

The issue is that they is just very little energy available to be recovered per unit of water stored if the elevation/height is only that of how far the water can be forced uphill by wave pressure. Problems that the reservoirs you talk about would include the need cover vast amounts of sea, while supporting a varying weight as water flows in and out.  

The biggest issue is going to be the idea of such a system being a valid breakwater, such things are made from vast amounts of stone, such as the image below shows



Once you start building such a structure you end up going down the design route of building a lagoon behind the breakwater (which is where the image comes from). This then operates with the tides and while there is far less elevation the volume of water that can be stored is far greater.

A lot of information can be found here

     http://www.tidallagoonswanseabay.com/

As for the likely hood of the project going ahead it currently depends on the cost of the project and at the moment is is rather expensive.
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« Reply #5 on: September 21, 2016, 07:18:02 AM »

Hello George61 and welcome to the forum.
I am sure wave power in whatever form is a long term viable energy solution.
Regrettably I think the current government would rather frack or nuke, renewable is way down the to do list.
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« Reply #6 on: September 21, 2016, 08:51:39 AM »

Tidal power is predictable - stick that in your nuke and smoke it. Expensive, yes - but a lot cheaper than supporting banks.
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dhaslam
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« Reply #7 on: September 21, 2016, 11:28:23 AM »

The big problem  with wave power is that  waves are  too small a lot of the time and at other times so large that they can break  floating devices into small pieces.    There are  large rocks on the Aran Islands cliffs, 80 metres above the sea,  that are said to have been put there by Atlantic storms.     Wind turbines in the ocean need to have flotation  devices well below the water surface  and have a narrow profile at water level, they can survive strong winds but the sea surface is much more damaging because of the weight of water.
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charlieb
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« Reply #8 on: September 21, 2016, 12:50:27 PM »

In fact plenty of device developers have gone for versions of your number 2 Goerge.  Not least Aquamarine, one of several to have gone under (sorry) with an idea that was never going to have been cost effective.

Simple problem is that there is not enough wave energy near-shore to make wave energy commercially viable.  (ie the waves are only big enough a tiny fraction of the time, as DH points out).  And also that the destructive forces near shore are amplified.  Imo wave devices will need to be far offshore to capture decent energy.  Bringing power back to shore  is MUCH more effective than bringing high pressure water back.     All at https://www.carbontrust.com/media/202649/ctc816-uk-wave-energy-resource.pdf if you can be bothered!
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smegal
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« Reply #9 on: September 21, 2016, 01:16:11 PM »

I am very concerned about the slow progress in developing our wave power resources.
There are two basic approaches to utilising wave energy:
1, to convert it directly to electricity;
2, to convert it to stored potential energy in reservoirs and using this stored energy to generate electricity.
There are numerous suggested devices which use the first approach but using reservoirs would be far more efficient and is equivalent to building dams and reservoirs to capture the energy from rivers.
Wave pressure will force water to enter the reservoirs through one-way openings in their sides and exit through turbines to generate electricity. Water will enter if the pressure from the incoming wave is greater than the pressure inside the reservoir and so a head of water above sea level is created inside the reservoir. The hydrodynamic pressure of the wave enables the head of water to be higher than the amplitude of the wave.
The reservoirs store energy and smooth electricity output. They enable more electricity to be generated at times of peak demand .
The reservoirs can  be fixed to piles in shallow water or supported by floats in deep water. The bigger the reservoirs the better as more energy can be captured and stored and there would be less energy losses in heavy seas through overflowing.
The reservoir structure is able to survive the forces of heavy seas because of the weight of water inside the reservoir and because it is the stored water in the reservoir rather than the structure itself which absorbs the forces of the waves.
As the reservoirs block the forward motion of waves they are cost effective breakwaters which could be used for coastal protection.
The use of reservoirs is a far more efficient and cost effective way to capture wave energy than the innumerable designs which seek to capture wave energy directly without energy storage because they can capture and store more energy and they act as breakwaters.
With our greater use of intermittent renewable energy sources there is a great need for energy storage and the reservoirs would be an ideal solution to this problem.


Like this?

http://www.wavedragon.net/index.php?option=com_content&task=view&id=6

I am dubious of this as the head for the turbine must be minimal.

Or this?



Unfortunately, these ideas have been around for quite a while, but wave power hasn't really gathered much traction.

As Charlie touched upon, a lot of wave energy devices seem to get damaged quite quickly. The sea really is quite hostile, especially on the moving parts used for energy capture.
« Last Edit: September 21, 2016, 01:18:45 PM by smegal » Logged

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pdf27
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« Reply #10 on: September 21, 2016, 01:32:19 PM »

Yeah, it's a combination of a very hostile environment and the fact that the energy density - particularly for any device which requires storage - is very low. It's certainly possible to build viable wave devices, but when you can build offshore wind for a third of the cost per MWh and much less technological stretch why bother?
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smegal
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« Reply #11 on: September 21, 2016, 03:06:43 PM »

Yeah, it's a combination of a very hostile environment and the fact that the energy density - particularly for any device which requires storage - is very low. It's certainly possible to build viable wave devices, but when you can build offshore wind for a third of the cost per MWh and much less technological stretch why bother?

Indeed.

Hopefully "they"'ll look into wave power in the future. It could be a pretty useful part of the energy mix.
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