Naked Science Forum
Non Life Sciences => Technology => Topic started by: Mootle on 18/10/2012 18:49:09
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Hi Folks,
Thanks to all those who commented on my System Schematic animation.
Hopefully, the Scaled animation will go some way to answering the reservations which were raised:
http://www.youtube.com/watch?v=tjMYVVKE4ao&feature=youtu.be (http://www.youtube.com/watch?v=tjMYVVKE4ao&feature=youtu.be)
Please let me know if you have any further questions.
Many thanks,
Will
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£?
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Interesting presentation.
I'm not sure you need to have the flow of water for power generation. You could use the pull on the cable to turn your engine, with the "storage vessel" only being needed to save energy during off-peak times.
I like the idea of paired buoys.
[diagram=674_1]
which would naturally prevent buoy drift. And, would be a much simpler mechanism than what you proposed. The buoy pairs could generate electricity directly, or could be coupled with a third "storage" vessel for off-peak power storage.
The biggest issue for paired buoys as above would be to get the correct wavelength. By adding a dynamic couple in the middle, one should be able to dynamically adjust the wavelength.
The wavelength will also limit the size of the buoys.
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And here are the boys unpaired (I know it doesn't work with the US pronunciation of Bouy.)
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If the youtube animation is to scale then that's a tangle waiting to happen ...
[ Invalid Attachment ]
also see ... https://en.wikipedia.org/wiki/Biofouling
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Thinking of watching ocean waves the separation between waves never is quite constant. Nonetheless, the pairs of buoys above should generally prevent drift, and would be reasonably efficient.
Fouling, as well as corrosion is a big problem. However, the parts in constant motion (pulleys, spinning) might be kept free somewhat.
Another option would be to build an enclosed vessel that was designed to tilt (but not tip over) in the waves. Perhaps recycling some old ships or barge hulls. One could gain stability with a catamaran hull.
Choose a length the get the maximum tilting by the wave action without tipping.
A gyroscope could be used to provide a central plane from which one would generate energy from the deviation from level.
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The advantage of this is that there would be no critical moving parts that would be exposed to seawater.
Of course, one would not have a natural off-peak storage system as above, except, perhaps centrifugal energy storage in the gyroscope.
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One thing to keep in mind is that I believe the "near shore" waves are the most regular and intense.
In many situations, one might find the optimal location for surface based wave energy generator would be 50 to 100 yards offshore. This would have advantages of easy electrical connections and shallow water, but it would not be an "out of sight, out of mind" type of installation.
Does the edge of the continental shelf generate waves, much farther out?
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£?
Hi Bored Chemist,
I'm afraid the cost is still an unknown, although if you made it to the end of the animation a projected revenue is given for the Scaled Animation (SA). The series of the animations will include an estimation of the cost. Before any accurate costs can be ascertained I need to draw up a Statement of Requirements (SoR) for each of the main components. Once some funding is secured the SoR's would for the Design Substantiation Requirement (DSR) against which suppliers could quote their works and demonstrate compliance. In the meantime I will draw up a Rough Order Cost (ROC,) for the SA including detailed design, manufacture, construction, through life...
Cheers,
Will
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Interesting presentation.
I'm not sure you need to have the flow of water for power generation. You could use the pull on the cable to turn your engine, with the "storage vessel" only being needed to save energy during off-peak times.
I like the idea of paired buoys.
[diagram=674_1]
which would naturally prevent buoy drift. And, would be a much simpler mechanism than what you proposed. The buoy pairs could generate electricity directly, or could be coupled with a third "storage" vessel for off-peak power storage.
The biggest issue for paired buoys as above would be to get the correct wavelength. By adding a dynamic couple in the middle, one should be able to dynamically adjust the wavelength.
The wavelength will also limit the size of the buoys.
Hi CliffordK,
1. Electricity generation from the pulley motion, at certain parts of the cycle, is certainly a valid consideration. I haven't shown this in the Scaled Animation (SA) but it is likely to included in a detailed design as a means to improve the overall system efficiency.
2. Twin buoys would reduce cost but as you have correctly observed the wavelength is variable / complex in nature which may make operation a bit hit and miss (given (2) P's need to rise together to pull the Storage Vessel (SV) down). The number of Pontoons (P) will be a matter for detailed design through Value Engineering (VE,) my initial scheme showed (6) P's per SV but simplified - there are many possible permutations. Triple buoys are shown to help account the variable wave vector, but detailed wave analysis will be needed to determine the optimum cost / system set up...
3. Dynamically altering the distance between P's would be desirable but in practice this would be very difficult to achieve. As it stands the ideal distance would be determined in detailed design using wave analysis from the target location. Once the Significant Wave Height (SWH) and associated wavelength is known the optimum distance would be set.
4. The wavelength is not likely to be a limiting factor as they will be much longer than shown in the SA.
Cheers,
Will
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If the youtube animation is to scale then that's a tangle waiting to happen ...
[ Invalid Attachment ]
also see ... https://en.wikipedia.org/wiki/Biofouling
Hi RD,
The system may be susceptible to tangles but this is only likely during Failure Mode (FM) due to the buoyancy forces involved. Failure Mode Effects Analysis (FMEA) will determine redundancy requirements but n+1 principles will be applied for system components such as hydraulic power packs, control circuits and the like which are needed to maintain cable tension.
In the event that the system does become tangled the system will enter into a fail safe mode. This will be an adaption to the Hibernation Mode referred to in the Scaled Animation (SA).
The spacing between systems can be adjusted if deemed necessary but at this stage I would say the ocean floor area for the screen shot you've taken of 2.4km x 2.4km is adequate. There are benefits to keep the systems closely spaced.
Underwater Substation Pods (USP's) akin to those shown here:
http://www.oceanpowertechnologies.com/technology.htm (http://www.oceanpowertechnologies.com/technology.htm)
will act as hubs for the Buoyancy Engines and transmission losses will be reduced by keeping cable lengths to a minimum...
Cheers,
Will
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Thinking of watching ocean waves the separation between waves never is quite constant. Nonetheless, the pairs of buoys above should generally prevent drift, and would be reasonably efficient.
Fouling, as well as corrosion is a big problem. However, the parts in constant motion (pulleys, spinning) might be kept free somewhat.
Another option would be to build an enclosed vessel that was designed to tilt (but not tip over) in the waves. Perhaps recycling some old ships or barge hulls. One could gain stability with a catamaran hull.
Choose a length the get the maximum tilting by the wave action without tipping.
A gyroscope could be used to provide a central plane from which one would generate energy from the deviation from level.
[ Invalid Attachment ]
The advantage of this is that there would be no critical moving parts that would be exposed to seawater.
Of course, one would not have a natural off-peak storage system as above, except, perhaps centrifugal energy storage in the gyroscope.
Hi CliffordK,
1. Fouling is a consideration.
a. The main body of the Pontoon (P) may be designed to promote marine growth. Floating coral reef's may help with Environmental Impact Assessments (EIA). These will impose addition loading and this will need to be factored into detailed designs.
b. The working parts such as the P pulley wheel assembly will be most susceptible to fouling. Over time they will need to be overhauled. The Construction Animation will show how this is achieved. However, in summary, assemblies such as pulley wheels and turbine assemblies are attached using remote activated jaws allowing them to be swapped out for spares. The equipment at the ocean floor will be subjected to much less marine foul loading and the corrosive effects of the sea water will be much reduced.
2. If I've interpreted correctly, your Gyroscope suggestion is already covered in other wave power solutions.
Cheers,
Will
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One thing to keep in mind is that I believe the "near shore" waves are the most regular and intense.
In many situations, one might find the optimal location for surface based wave energy generator would be 50 to 100 yards offshore. This would have advantages of easy electrical connections and shallow water, but it would not be an "out of sight, out of mind" type of installation.
Does the edge of the continental shelf generate waves, much farther out?
Hi CliffordK,
1. This system will work better with deep-water waves which tend to have longer wavelengths.
2. Ideal conditions would be deep water, good wave resource and close to land but realistically for the system to be viable it will have to cope with lengthy cable runs to land.
Conventional cable losses are a consideration and this is an active area of research:
http://www.columbussuperconductors.com/ (http://www.columbussuperconductors.com/)
3. A continental shelf would typically increase the wave height amplitude and reduce wave length for near shore waves. There are also likely to be remote effects but this would be subject to specifics. It is unlikely to be significant for this idea. Fortunately, there is a ready supply of wave data, so trawling through the telemetry should ID locations with good wave resource at the desired depth which don't interfere with shipping lanes.
Cheers,
PW
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Giant red sea snake, the 600ft machine (Pelamis' Vagr Atferd) oscillates on sea's surface (http://www.youtube.com/watch?v=F0mzrbfzUpM)
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.eaem.co.uk%2Fsites%2Fdefault%2Ffiles%2Fimagecache%2Flead_image_400%2FPelamis-in-Orkney4112.jpg&hash=5b1bcebb3a0d1fb5891443fc3d81a4e9)
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I like a few aspects of the design:
- It offers a way to store the energy for release during peak periods (always a challenge for electrical generation)
- It offers a way to protect the equipment from weather extremes, by hiding below sea level - many wave-power projects have been destroyed when storm-driven waves far exceeded the design power levels, and tore the equipment apart.
- The most complex part of the system is the turbine and associated electronics, which has a built-in mechanism to raise it to the surface for repairs, maintenance, de-fouling the turbine and fish-netting, etc.
Some challenges:
- Anchoring: The central float must have a buoyancy of thousands of tons. The pulleys must be attached to the seafloor to resist this static lift, plus the effects of the surface waves, tugging at the foundations.
- Wavelength: I think they described the floats as being 100m across. This means that they will only be able to extract energy from waves that have wavelengths of well over 200m.
- Undersea electricity transmission is a known technology. Learn from the earliest undersea optical fibre attempts: On the continental shelf, sharks are driven crazy by the electric field around the cable, and attack it furiously (leaving teeth embedded in the cable). So bury the cable, or shield it so there is no external electric field.
- If the turbine is in the float, then you need to get the electricity down to the seafloor. Flexible electric cables are possible (look at elevator lighting cables), but they are expensive, and need regular replacement. You also need a way to roll them up neatly and then unroll them, without getting tangled.
- 2km-long cables of the required strength are heavy, and have considerable "spring". I assume you have calculated that the wave motion would be reliably transmitted to the central float, rather than just stretching and releasing the cables?
So to some alternative suggestions:
- Moving the anchor points on the sea floor outwards slightly would splay the cables, and provide some horizontal stability to the floats, reducing the chance of tangles.
- The floats are all pancake-shaped: very stable on the surface, but the one rising and falling through the water column will lose a lot of energy to friction/viscosity. Something closer to a torpedo shape would have reduced frictional losses (but would be less stable when on the surface).
- The turbine intake makes up a very small fraction of the area of the rising float. A funnel shape above and below the turbine would direct water into the turbine with increased velocity, and reduced friction.
- To avoid flexible power lines to the seafloor, you could put the generator on the seafloor, perhaps attached to the drums of cable.[This solves the problem of turbine fouling, but makes it harder to repair the generator.]
- The device could be used as power storage device; during calm days with minimal wave power output, you could use cheaper off-peak electricity (1am-5am) to pull the float down to the seafloor, ready for the morning peak hour (6am-8am).
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Hi Evan,
Thanks for this, sorry I didn't get back to you sooner (for some reason I didn't get an email notification). Great comments, it's difficult to pitch the response at the right level, so feel free to follow up if I haven't gone into sufficient depth:
Challenges:
1. Anchoring: The central float must have a buoyancy of thousands of tons. The pulleys must be attached to the seafloor to resist this static lift, plus the effects of the surface waves, tugging at the foundations.
Correct, the anchoring is certainly a major challenge. I've been in discussions with a potential business partner and was delighted to find that they already have a system which could meet most of the anchorage requirements of the system shown in the animation. Unfortunately, their solution would need developing for use at the depth shown. I also have a solution in mind and plan to develop both lines in parallel.
2 Wavelength: I think they described the floats as being 100m across. This means that they will only be able to extract energy from waves that have wavelengths of well over 200m.
Deep water waves are much greater than 200m. From my initial observations and calculations, if the system as shown in the animation was applied for an ocean depth of 250m rather than the 2km shown the wavelength would still be OK. This simplifies some of the engineering challenges but reduces the system output and thus the available revenue. At 250m depth the generation capacity would be in the range of 40MW for 1hr to 80MW for 1/2 hr. This would be repeated 5-6 times per day, taking into the other phases of the operation cycle. For the 9 system array over 20yrs a conservative revenue projection would be ca. £2.3b. This is much less that the £15b for a 2km application but this would have to be balanced against the reduced engineering costs.
3. Undersea electricity transmission is a known technology. Learn from the earliest undersea optical fibre attempts: On the continental shelf, sharks are driven crazy by the electric field around the cable, and attack it furiously (leaving teeth embedded in the cable). So bury the cable, or shield it so there is no external electric field.
Again, this is an active area of research. The Underwater Substation Pods (USP’s) and Superconductor Power Transmission Options are amongst the lines of interest, but I wasn’t aware of the optical fibre option:
http://www.oceanpowertechnologies.com/technology.htm (http://www.oceanpowertechnologies.com/technology.htm)
http://www.columbussuperconductors.com/ (http://www.columbussuperconductors.com/)
Burying the cables is unlikely to be a viable option and I’m not sure it would be such a marine issue for deep water application. However, reducing transmission losses has a direct benefit to revenues and is therefore worth development especially as the transmission lines will be long.
4. If the turbine is in the float, then you need to get the electricity down to the seafloor. Flexible electric cables are possible (look at elevator lighting cables), but they are expensive, and need regular replacement. You also need a way to roll them up neatly and then unroll them, without getting tangled.
The turbine and generator set is housed in the Storage Vessel (SV). The power transmission cable is not shown but I would anticipate this would be a trailing arrangement which runs off to the USP's located at a significant distance from the SV. The cable would be tethered to the ocean floor whilst allowing sufficient movement. Hopefully, this will become clearer in the Construction Animation.
5. 2km-long cables of the required strength are heavy, and have considerable "spring". I assume you have calculated that the wave motion would be reliably transmitted to the central float, rather than just stretching and releasing the cables?
This is another active research area. Traditional steel cables would probably break under their own weight. I would look to work with a specialist synthetic cable manufacturer, i.e., PVO is stronger than steel but much lighter. The correct properties of the cable are vital for the system to work.
Alternative suggestions:
6. Moving the anchor points on the sea floor outwards slightly would splay the cables, and provide some horizontal stability to the floats, reducing the chance of tangles.
The animation is not meant as a detailed design and whilst tangles (during failure mode,) is a consideration this is not the main driver for the setting out. The horizontal spacing would be optimised to suit the ocean depth as this is a significant function of the wave length. In much the same way as wind resources are monitored prior to a wind turbine development, the wave resources would be monitored prior to fixing the design. This is important as at least (2) of the (3) Pontoons are required to rise at once to effect SV descent.
7. The floats are all pancake-shaped: very stable on the surface, but the one rising and falling through the water column will lose a lot of energy to friction/viscosity. Something closer to a torpedo shape would have reduced frictional losses (but would be less stable when on the surface).
I have considered this but opted for commonality of construction methodology. Part of this was due to the modest descent / ascent velocity. Another factor is that increased SV height reduces the Turbine efficiency due to net head losses as the SV fills. The main challenge for the SV design is managing the crush pressure at depth.
8. The turbine intake makes up a very small fraction of the area of the rising float. A funnel shape above and below the turbine would direct water into the turbine with increased velocity, and reduced friction.
Managing the water flow is another active area of research. I plan to throttle the flow at the Sluice Valves and the pipe sizing shown will help reduce velocity and thus resistance. However, it is certainly worth optimising the turbine inlet in order to improve turbine efficiency and supplementing the inlet guides may well be a way to achieve this.
9. To avoid flexible power lines to the seafloor, you could put the generator on the seafloor, perhaps attached to the drums of cable.[This solves the problem of turbine fouling, but makes it harder to repair the generator.]
I'm not sure what you mean as the turbine and generator is usually hard linked with a common drive shaft (this is shown in the animation toward the end of the animation if you didn't quite make it that far).
10. The device could be used as power storage device; during calm days with minimal wave power output, you could use cheaper off-peak electricity (1am-5am) to pull the float down to the seafloor, ready for the morning peak hour (6am-8am).
I hadn't considered this option but I’ll certainly take a look at this to see if the Business Case can be improved.
Cheers,
Will
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9. To avoid flexible power lines to the seafloor, you could put the generator on the seafloor, perhaps attached to the drums of cable.[This solves the problem of turbine fouling, but makes it harder to repair the generator.]
I'm not sure what you mean as the turbine and generator is usually hard linked with a common drive shaft (this is shown in the animation toward the end of the animation if you didn't quite make it that far).
The suggestion here was to use the lift of the rising float to rotate the drum cables on the sea floor, which are hard-linked via a drive shaft to a generator on the sea floor.
In this scenario, there would not be a need for any turbine, so you would not need fish-netting in the rising float, so less maintenance.
The rising float would have the same mechanical structure as the surface floats.
[This was just a random thought on how to retain some of the advantages of the design, and bypass some of the challenges...
There are pros and cons for each method...]
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Hi evan_au,
I see what you meant now, thanks. I don't think this method would be suitable as a primary generation method as the generation profile would be intermittent. However, the incorporation of generators into the cable drums has been considered in order to increase the overall system efficiency.
Furthermore, cable drum, generator set repairs may be achieved by remote decoupling using the hydraulic jaw arrangement.
Cheers,
Will
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A cable strung between the ocean floor and a bobbing buoy, as well as the challenges of underwater pump/generators ... may share issues with designs we've discussed before:
Does deep ocean have potential energy due to pressure? (http://www.thenakedscientists.com/forum/index.php?topic=36659)
and, to a lesser extent
How much work in the form of pressure is there at the bottom of the deep ocean? (http://www.thenakedscientists.com/forum/index.php?topic=31433)
Perhaps this design could also integrate storage into the equation, with a second larger float on a common cable which can be raised or lowered as necessary.
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Hi Peppercorn
Storage is already a key element of the system, energy is stored each time the Storage Vessel descends. Once at the desired depth the power generation can be geared to suit the demand. The peak output of such the array shown in the Scaled Animation is equivalent to a conventional power station (albeit for a limited duration).
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Storage is already a key element of the system, energy is stored each time the Storage Vessel descends. Once at the desired depth the power generation can be geared to suit the demand. The peak output of such the array shown in the Scaled Animation is equivalent to a conventional power station (albeit for a limited duration).
Ahhh .... helps if one watches the video prior to comment.
My biggest concern about the system is the number of control and storage elements that appear to be deep below the waves.
Is there a means to hold on to the principle design whilst moving elements such as generator(s) to the sea's surface instead?... I'm just thinking that offshore wind-turbines seem to suffer a high number of failures (compared with their landlubber counterparts) due mainly to salt water and they're above the sea.
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The Scaled Animation shows:
1. Hibernation Mode, this submerges the Pontoons below the surface when the ocean gets too rough for system operation. This is a bit like rotating wind turbine blades to unload them when the wind gets too strong. The equipment could be designed to operate in high winds but this would significantly increase the cost whilst only marginally increasing revenue. The same Value Engineering process would apply to the Buoyancy Engine.
2. Remote Controlled Hydraulic Jaws, these can be use to release all Pulley Assemblies and key items of equipment in order that they can be raised to the surface and loaded on a transporter. Spare parts would be swapped out at the same time to allow operations to continue whilst repairs can be carried out on land. This will be shown in the Construction Animation.
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£?
Hi Bored Chemist,
Sorry it's taken a while to come back on this. I continue to work towards the specific business case but that's still a little way off at the moment. However, I came across the following:
http://webarchive.nationalarchives.gov.uk/20121205174605/http:/decc.gov.uk/assets/decc/what%20we%20do/uk%20energy%20supply/energy%20mix/renewable%20energy/explained/wave_tidal/798-cost-of-and-finacial-support-for-wave-tidal-strea.pdf
Figure 2 collates the CapEx / OpEx figures for similar projects. Based on these figures I remain optimistic that there will be a very strong business case.
Cheers,
Will