The power of the ocean

The following column was published in the Waikato Times on 19 January

Silent, invisible, predictable, sustainable. Those are the four words Crest Energy uses to describe its planned marine turbine power generation project in the Kaipara Harbour. Capturing the power of the tidal movement of the up to 8,000 million cubic metres of water which pass in and out of the harbour each day, the project may eventually contribute as much as 3% of New Zealand’s electricity supply. Assuming it gets under way, that is. However, that has just become more likely with the news that the Environment Court has delivered an interim decision in favour of consent, subject to a fine-tuning of consent conditions. Mainly the Court wants further monitoring work to satisfy concerns about possible interference with Maui’s dolphin and snappper fisheries.

Like wind, the ocean around New Zealand offers many promising sites of renewable electricity generation. None of us who have stood on a beach can doubt the power of the ocean.  Harnessing a little of it for our human purposes is now technically feasible and, if we ever face up to the real cost of fossil fuels, no doubt feasible economically as well. Ultimately in New Zealand wave power is the larger potential source, since our tidal range is not great.  But tidal flow offers significant opportunities in some places, as the Kaipara project makes apparent.  Cook Strait is one, and Neptune Power has consent to trial a turbine there, probably in the near future. They comment that the mass flow in Cook Strait makes it the most concentrated energy resource in New Zealand. Foveaux Strait is another site where tidal flow is very large and it is not fanciful to imagine the Bluff aluminium smelter powered from it.

The advantage of tidal power over wave is its predictability. Waves vary according to the weather. Nevertheless there are plenty of waves around New Zealand, and trials are under way to test their electricity generating capacity.  Last year the government made a grant of $760,000 to Wellington company Power Projects Ltd to enable deployment of a 20 kw device, building on their successful trialling of a smaller model. Surveys indicate that the potential from wave power is high in relation to New Zealand’s total electricity requirements.  A plus is that wave energy tends to peak in the winter season when power demand is at its greatest.

There are currently no fewer than 26 wave and tidal energy projects at various stages of development in New Zealand. That doesn’t mean that generation is imminent, but we should not be surprised if very rapid growth occurs as the technologies mature.  I’m in no position to predict how the various renewable energy options presented by New Zealand’s geography will sort themselves out, but between wind, marine and geothermal power there appears to be a wealth of resources. That could soon see us no longer reliant on the burning of fossil fuels which currently provides 34% of our electricity. Renewables should be well able to include supplying electrically-powered plug-in vehicles.

It would be nice to report that the government is enthusiastically driving the change to renewable energy.  In the case of marine energy it has, admittedly, provided $8 million over a period of four years to support selected projects. But it committed $20 million over three years to gather seismic data in support of oil and gas exploration, and has extended tax exemptions for offshore exploration.  The Minister of Energy reserves his greatest enthusiasm for when he speaks of the prospects for fossil fuel extraction and export over coming decades. In a rational world we’d be more interested in finding ways of leaving it in the ground, knowing, as we now do, the fearful prospects ahead if we keep burning the stuff. There’s still some priority-sorting needed at government level.

5 thoughts on “The power of the ocean”

  1. Gareth; off topic but a question. There are two ways to increase the fluid level in a vessel, increase the quantity of liquid or decrease the volume of the vessel. The usual source of a decrease is various dents and dings.

    Is anyone aware of any research on changes in the ocean basis which would influence the resulting sea level absent any change in volume of the liquid, either up or down? An example could be the spreading center moving at a marginally higher rate than subduction and causing compression ridge, or moving less and causing thinning and stretching. Both are observed in various places on land, so they may or may not be common on the sea floor.

    I don’t have a dog in this hunt and don’t have a preferred outcome, but since this site has more interest in sea level than any other I have seen I thought you may have some insights.


    1. You don’t have a dog, and I don’t have a ready answer (though I do have a dog). I would suspect that the amount of continental crust (ie the stuff that floats higher than the rest, that we live on, not the new sea floor created at ocean ridging) has to remain more or less the same over long time scales, and that should mean that as long as the amount of water is fixed, the sea level wouldn’t change too much. Continental crust that was dragged down in a subduction zone would tend to float back up over time, restoring whatever equilibrium exists. The timescales would be geological, though — multi-million year. Sea level cycles through the recent ice ages are undoubtedly related to the volumes of water locked up as ice (or not), and the changes are so large (160m ish from memory) that they would swamp any longer term small change from tectonics. But I’m no expert. If I find a good source, I’ll let you know.

  2. A recent draft paper utilizing GRACE satellite data (principally) sets out to chart weekly changes in mass of the Earth’s oceans. They address the issue of Terry’s “dents and dings”, although parts of it are Greek to me.

    A much easier read, dealing with solid Earth features, is here:

  3. Terry, why do you omit another obvious and very relevant way to increase the fluid level, i.e. heating the liquid?
    I suspect that you do indeed have a dog in this hunt, but it is one that prefers not to notice elephants in the room…

    “There are two ways to increase the fluid level in a vessel, increase the quantity of liquid or decrease the volume of the vessel… I don’t have a dog in this hunt”
    – Terry January 21, 2010 at 7:26 pm

  4. Apologies, lost two letters on keyboard, cant spell properly. Spell check fixes some.

    Rob, I was tinkin in terms of meter provin and te measurement vessel, were gravity and temp are applied as corrections. If te volume of te proving vessel canes ten all te oter stuff is meaningless. You are rit, sould ave mentioned it. Sorry.

    [H & G? – GR]

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