Wave Power -- swell !!

joule wrote on June 1, 2006

Wave energy happens to be a little side interest of mine in which I've dabbled a bit. While I recognize that it is even more location-specific than wind energy and will probably never become anything more than a niche in the total energy supply picture, I find it a fascinating subject nonetheless.

There are several categories of wave energy converters, each of which has its own set of pros and cons. In general, the whole trick to making a successful wave energy converter is i) to absorb as much of the wave's energy as possible in the smallest and/or least expensive mechanical embodiment, and ii) to make a wave energy converter capable of surviving the punishment of severe storm conditions.



It is in this last requirement where the Pelamis really excels. All wave energy converters need to have some form fixed 'reference' for the device to work against. In other words, if a float is just bobbing around freely, it is not absorbing any wave energy, but if the same float is tightly moored to the ocean floor, the foreces in the connection between the mooring and the float can be used to absorb energy, either through compressing air in a cylinder, or forcing hydraulic fluid through a turbine etc. However, during a severe storm tremendous stresses are set up between the mooring an the device. Many test devices have been smashed to pieces after encountering their first big storm.

The Pelamis, on the other hand, is very loosely moored on a very long mooring and does not rely on the connection between the mooring and itself to form that fixed reference. Rather, that reference is provided by the four connected segments of the Pelamis working against each other. When the foremost is at the crest of the wave, the aftmost is at the trough of the wave. This causes a relative movement between the segments, and energy is absorbed by hydraulic cylinders cleverly connected to the joints. In other words, through the hydraulic system, the Pelamis is trying to remain stiff while the wave action is trying to bend its segments relative to each other. Energy is absorbed in the process.

During a severe storm the hydraulic system is deactivated, and the segments then loosely follow the motions of the waves, with very little stress on the segment joints and the loose mooring. In effect, this design feature makes the Pelamis sort of 'invisible' to many of the undesireable effects of severe storms. As best I can tell, the Pelamis is probably the most storm-worthy design out there. The loose mooring also makes it quite suitable for offshore operations where the waves tend to be larger.

By the way, the Gulf of Mexico and tropical waters in general are relatively poor locations for wave power because the average size of the waves is rather small (occassional hurricanes notwithstanding). The west and north coasts of Ireland and Scotland, most of Norway, and parts of Portugal are also very good. As is the southern tip of South America and parts of Australia. Unfortunately, most of the best wave power locations are also relatively low-population areas.

By the way, near-shore breaking waves may look very dramatic but they don't have the power of the large steady and long-wave length waves that one encounters further offshore. Waves are also much more gradually sloped than they appear when viewed head on. A wave will typically have a wave length to height ratio of approximately 40 to 1. So a 6-ft high wave will have a wave length of typically 240 feet.

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Oilrig medic on June 2, 2006
The marine enviorment is so harsh, we have 4 guys on my drillship that are constantly painting scraping priming re painting. What materials is this serpent made of? Just a little scratch and it will begin degrading if its not stainless. As for hydraulics they require huge maintainence. I know little about wind but my impression was you can stick a windmill in the ground and plug it in. I really believe this can't be better than offshore wind. (are windmill mostly corrosion resistant?) If this thing breaks how do you fix it? at sea or is it retrieved and brought in? The boats fuel expense for once a year maintainence would cut into energy profit.


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joule on June 2, 2006

Oilrig Medic -

The current version of the Pelamis is made out of plain 'ol carbon steel, primed and painted, just like a ship. The construction is relatively simple, and not much different from normal non-pressurized tank construction. I'm sure it could be made out of fiber glass or other composites, but then you have a trade-off between low maintenance and high initial capital cost.

Yes, hydraulic motors do require maintenance, but so does every other mechanical device used in the extraction/production of energy. One positive maintenance feature, though, is that it does not have to be maintained or repaired in situ (a very difficult prospect in high wave areas), but rather can be just towed into port for routine maintenance or repairs and then towed back out. I believe the very first version that was installed off one of the islands in the Orkneys (which is one of the best wave energy locations in the world and therefore a rather harsh environment) ran for over 1,000 hour before some minor maintenance had to be performed. Not bad for a demo unit on its first try, I'd say.

At first glance, the Pelamis strikes me as a very well thought-out design that has pretty much solved the survivability problem. It does this largely by not fighting with the waves.

However, I have no idea what these things cost and what their life-cycle costs look like in relation to the amount of energy it can produce over its lifetime. Time will tell.

Bear in mind that the Pelamis is not the only good design out there. But it seems to have gotten a good head start on the others.

Most of the wave energy development work is currently in the UK, Norway, and to a much lesser extent, Japan. I don't think there's all that much going on in the US at present, but it's been a while since I really looked.




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The key here is that if increased demand came from plug-in hybrids (PHEV), or pure electrical vehicles (EV), the % would increase (and probably faster than the rise in EV demand) because EV's provide storage that helps reduce the mismatch between intermittent wind production and general consumer demand - only very simple demand management would be required to have the EV's preferentially charge when electrical supply was high relative to demand. Thus, wind could supply all of the additional power needed by EV's.

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A 1MW Tidal Generator in Strangford Lough

During 2004-2007 the design, manufacture, installation and testing is planned of the first "full size" twin rotor system to be rated at 1MW. This will be grid-connected and will function with the flow in both directions - it will in fact be the prototype and test-bed for the commercial technology.

June 6th, 2007

Seagen Paul Taylor: Installation Of The World’s First Commercial Tidal Current Power System Confirmed. Marine Current Turbines has today (June 6th 2007) confirmed that installation of its SeaGen commercial tidal energy system will commence during the week of August 20th in Northern Ireland’s Strangford Lough. At 1.2MW capacity, SeaGen will be the world’s largest ever tidal current device by a significant margin, and will generate clean and sustainable electricity for approximately 1000 homes. It is also a world first in being a prototype for commercial technology to be replicated on a large scale over the next few years.

SeaGen ready for installation at Harland and Wolff, Belfast. One of the 16m rotors (above) and the complete crossarm with its twin 600kw rotors plus the superstructure (below)

The installation of SeaGen in Strangford Lough will be carried out by A2SEA A/S of Denmark, one of Europe’s leading offshore installation contractors. The SeaGen 1.2MW commercial demonstrator has been developed on the basis of results obtained from SeaFlow, the world’s first full-size tidal turbine installed by Marine Current Turbines off Lynmouth Devon in 2003. It has taken the subsequent four years for Marine Current Turbines to design and build SeaGen and secure the necessary environmental and planning consents.

SeaGen is a commercial demonstration project with permission to operate in Strangford Lough for a period of up to 5 years. It is intended as the prototype for commercial applications of the technology that will follow.

The A2SEA jack-up barge, “JUMPING JACK”, is planning to mobilize from Belfast’s Harland & Wolf shipyard, where SeaGen is already complete and waiting, to Strangford Lough on August 20th. It is expected that the drilling of a single pile into the seabed and the installation of the twin-turbine device will take 14 days, with commissioning and power generation to the local grid shortly afterwards.

Ebb and Flow

Nova Scotia Power owns and operates one of three tidal power plants in the world and the only one in the western hemisphere.

The Annapolis plant harnesses the tidal action of the Bay of Fundy, which boasts the world’s highest tides. The plant uses a head pond to capture the flow of the water and operate the plant, which can produce up to 20 megawatts daily.

New technologies are being created to capture the power of the tides, including the use of offshore floating tidal turbines and turbines that are anchored to the ocean floor. Nova Scotia Power is fostering their development.

Limpet -- (Land Installed Marine Powered Energy Transformer): A third of the energy requirements of the Isle of Islay, off the western coast of Scotland, are powered from one of these guys. Power is generated as waves enter the open cavity, concentrating and forcing air through a chamber on the top (or rear depending on the design) of the installation. The forced air turns a turbine, which turns a generator. Click here to see a great visual demonstration from Greenpeace.

Mighty Whale: This monster device is the latest incarnation of a long line of experimentation in ocean power technologies in Japan. A Mighty Whale prototype, complete with painted mouth and eyes, was launched in Japan in 1998, and has been the subject of open sea tests since. More info here and here.

As in every area of power generation, whether coal-fired, nuclear, wind or solar - energy storage issues are still a thorn in the energy industry’s side. Being able to feed Ocean Power into established power grids, with its generally more consistent generation, has the potential to supply a significant percentage of the energy needs - for those countries with appropriate westerly facing shorelines (e.g. west coasts of Scotland, northern Canada, the U.S. northwest and northeast seaboards, southern Africa, Australia and New Zealand in particular).

http://www.celsias.com/blog/2007/03/23/ocean-power-on-the-rise/