Was chatting to a Director of Neptune recently.

S(he) tells me that all the engineering problems have been solved, and also the potential for ‘bykill’.

They can equal NZ’s current generation capacity from turbines in Cook Strait alone.

Sounds like an idea worth looking into to me…

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The problem with wind is the rapid and unpredictable changes in output. Wave powered generation also has large changes in output power, but these are predictable a few days in advance and the output power changes much more slowly. This gives time for other generation to be started or stopped, making it much easier to handle.

New Zealand has some of the best wave and wind resources of any country – we should take advantage of this.

Trevor.

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There is still significant geothermal potential which could be exploited for generation, some of which is proceeding. Refer to

http://www.nzgeothermal.org.nz/elec_geo.html

On top of this, there is a large potential for low temperature geothermal energy to be used for water and space heating and some drying applications.

Trevor.

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Bj,
I had thought that it would be strongist in the canals since they are both the deepist and the most constrained. Though admitedly I dont know the depth effects of tidal flow.

http://www.niwa.co.nz/__data/assets/image/0003/50493/ocean3_large.jpg

http://www.niwa.co.nz/our-science/natural-hazards/research-projects/all/physical-hazards-affecting-coastal-margins-and-the-continental-shelf/news/cookmov

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12GW…. holy heck that’s even more than what I had heard. Obviously I doubt you’d ever get close to generating that amount, but 1-2 GW would certainly help things. Could help retire Huntly Power Station for example.

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Sapient

I don’t have the subscription, and I reckon Neptune can do the engineering. That sort of stuff is a specialized, difficult, full time job. If Neptune is doing pretty much what I expected them to do, I have to assume that they have some engineering staff and a reasonable knowledge of the situation. I would only look deeper into this if they weren’t doing what I expected.

Given that there is risk to the scheme from earthquakes, it makes sense to make the generation modules moored and buoyant.

The current will be strongest where it is most constrained.

Thanks Trevor

respectfully
BJ

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The wiki page is interesting:
http://en.wikipedia.org/wiki/Cook_Strait

The tidal flow through Cook Strait is unusual. On each side of the strait the tide is almost exactly out of phase, so high water on one side meets low water on the other. Strong currents result, with almost zero tidal height change in the centre of the strait. Although the tidal surge should flow in one direction for six hours and then the reverse direction for six hours, a particular surge might last eight or ten hours with the reverse surge enfeebled. In especially boisterous weather conditions the reverse surge can be negated, and the flow can remain in the same direction through three surge periods and longer. This is indicated on marine charts for the region

Neptune hopes to generate power from the unit by 2010. The company claims there is enough tidal movement in Cook Strait to generate 12 GW of power, more than one-and-a-half times New Zealand’s current requirements

http://www.niwa.co.nz/our-science/natural-hazards/research-projects/all/physical-hazards-affecting-coastal-margins-and-the-continental-shelf/news/m2mov

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I think the advantage of tidal is that it can be used to replace expensive baseload generation from diesel plants and (in the future) from coal & gas that I think will become more and more expensive once we put a price on carbon.

We will probably need to get used to paying more for electricity in the future than we do now – no matter what method we use to generate it. Hence the advantages of improving energy efficiency through insulation etc.

What potential is there in NZ for further geothermal generation?

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Another renewable resource to add to kahikatea’s list is generation from biomass. This could be implemented by burning charcoal at Huntley instead of coal (or perhaps a mixture), or by adding cogeneration at institutions that need a significant amount of low temperature heat such as hospitals and retirement homes.

Trevor

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The best return on investment for tidal flow power generation will be where the water flow rates are highest, which will be in areas of shallower water, such as on underwater ridge lines.

Plans I have seen from Neptune Power suggest bouyant generator modules which are moored using chains and which can be brought up to the surface for servicing by letting out the chains.

Tidal flow through Cook Strait peaks every 6 hours, so the generation troughs only last a few hours. A number of applications for electricity can cope with short periods without power, such as refrigeration units, so sensible demand management would allow a significant proportion of our power to be generated from tidal flow generation.

Trevor.

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BJ,
I just downloaded that study, rather large (lots of colourful pictures). From just a quick browse it looks like there are a good number of flats well away from cliffs and fairly deep. Though the canals where I suppose current based energy generation would be best look alittle risky. I havint read in enough depth to know the integrity of the slopes so I cant really make much of a risk judgement. I assume you dont have the subscriptions needed to download the PDF? I could send it if you desire, I doubt the journel snoops patrol this blog.

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It’s OK to consider building the tidal system in the strait. I am not saying it can’t be done. We put some damned big propellers on ships, and they turn and function for years and years.. the engineering to do that part is relatively well known and straightforward. Ships propellers are still made of bronze alloys. Sacrificial zinc is used to hold the worst corrosion at bay.

What is different is that in this case, they want to couple what are essentially large propellers (working backwards) to generators that are immersed in water. On a ship, there is a shaft-alley and the engine-room is kept dry.

Building a space like THAT down there is feasible/expensive Hence my preference for hydraulics running to the surface and driving the generator sets. That makes the electrical parts more maintainable than they would be at 200-300 meters and simplifies the maintenance issues a bit.

I don’t think the system would be on the bottom.

http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V6M-4VM9KBY-5&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=954049979&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=879dc047a504202d277765464e1ae1f0

The only things on the bottom should be anchors or if the water isn’t real shallow, the legs of power platforms.

Maintaining the anchor chains and suspended propeller pods would be a big part of the maintenance. Keeping them dry internally… we know how to do that stuff. Submarines so it all the time.

Protecting the system from the odd whale will take some additional caging, Smaller fish won’t have a problem.

This is an engineering problem it is solvable. The expense of the maintenance means that this will not be CHEAP renewable power… and this is part of Owen’s consideration. The assumption that renewable=cheap isn’t valid.

One other thing, the nature of the ocean movement associated with the tide means that the N-S orientation of NZ is GOOD, not bad. It acts as a dam in the global flow. Bodies of water that are attached to the ocean at different points can have different timing for tides, even if separated by only a few NM of land.

http://www.linz.govt.nz/hydro/tidal-info/tidal-intro/nz-tides/index.aspx

Auckland-Manukau have a 3.5 HOUR difference in time of high tide. Which should suggest something to someone.

respectfully
BJ

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True, I am aware of the inefficency. But if we are generating excess to what we can resonably expect to use and in absence of use it woukd just be wasted then to utilise it inefficently is better than not utilising it at all. There are limits to how much we can expect people to shift their use patterns and the storage part is also relivant to wind generation. Both should be part of the soulution I think.

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One of the problems with storage of excess demand is that converting the electricity into the storage medium and then back out to electricity involves the loss of energy, compared to what BJ was pointing to with changing our use patterns.

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BJ,
Would non-rusting alloys or plastics not fit the job/ be too expensive? Could one use high-chromium alloys for the rotating joints and then coat the major components with rubber? Just something that occurs to me, I dont have the background to have any idea about its practicality.
I like the idea of using the batteries of electric cars as a sort of storage capacity or having them similar to hot water cylinders, decrease the amplitude. Could have excess go to pumped storage or the haber process for our non-electric vehicle fleet?

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One other thing about wind and tide… we can shift our work to match its rhythm sp as to use it better. Certainly not 100% but some things can be scheduled a bit differently to take advantage of the peaks and avoid the troughs. This would make the 9-5 into a 6 and 6 sort of shift, but it would avoid wasting available collectible energy.

respectfully
B J

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Owen – It isn’t necessary for the generators to actually create electricity down there, all they have to do is extract energy. Something hydraulic perhaps. Which would be my preferred solution as the point about electricity and salt water is IMHO, well taken. People who want to generate power out of wind and wave at SEA have to reckon with rust.

I spent enough time at sea to have a powerful appreciation of the power of rust.

Most tidal generation isn’t deep-water. Cook strait is a special case, it is using the two islands themselves as a dam, and the flow through the strait is pronounced and reliable and can be harnessed at depth.

I don’t like the likely costs of maintenance though. Probably would have to have the equivalent of a small drill-rig out there in the middle of the strait, just to keep the whole thing running reliably.

BJ

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How deep is Cook Strait? I would guess the tidal tubines would be hundreds of metres below the ships.

From memory its 535 m at its deepest, I think NIWA has some good maps on their site…

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15% of our peak load is about 25% of our average load, as our peaks are around 50% higher than our average. If we can even out our peaks and troughs then we will be able to use more of the wind generation when it is blowing. Good demand management will help with this, including such tricks as freezing water during off-peak times and using the ice for cooling at peak times instead of running air conditioning pumps.

We can also improve the utilisation of wind by taking advantage of spatial diversity – spreading out our wind farms so their peaks and troughs don’t coincide.

If that is not enough, we can use energy storage such as pumped hydro storage or on a smaller scale vanadium redox flow batteries, such as the ones they use on Kings Island. If battery electric vehicles become common, we may also be able to use some of their capacity to even out the supply and demand.

Trevor.

PS: You could add solar to kahikatea’s list, but don’t expect much since we are in the land of the long white cloud.

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Re: decommissioning US dams: Most have been old and small (i.e., of no use and in some instances dangerous). It would be more instructive to know what level of net societal uses (and what types) have been lost/gained through decommissioning.

Re: nuclear energy: I’m not aware of any nation that has solved the waste stream problem. Aside from perhaps Iran and North Korea. MIT’s “Future of Nuclear Power” report is relevant here.

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