TCASE 5: Ocean power I – Pelamis

The first four posts of the TCASE series were logically sequential — each post built on the conclusions of the previous one. Overall, I hope the TCASE will retain a sense of coherency, but at the same time, I don’t want to get too constrained in following a rigid structure. To be frank, I can’t plan the ‘storyline arc’ well enough at this stage to make that even half feasible, and besides, I want to the series to be responsive to topical debates (and keep each post to a digestible, bite-sized chunk of information).

So future offerings in TCASE will branch out to cover everything from examinations of different technologies/energy sources, case studies of actual real-world projects, evaluation of new policy decisions (such as Australia’s 2020 ERET), questions of build rates and constraints, cost/feasibility assessments, consideration of technology gaps and physical limitations, exposing spin and hype, limit analyses, thought experiments, etc. I certainly hope to continue to get ideas from the commenters on this blog, which collectively represent an enormous wealth of knowledge, experience and ideas. To me, this is a fine form of peer review and a great source of inspiration. Thanks BNC readers!

Today’s post offers a first look at ocean power — the mighty fist of Poseidon (mythologically and in reality) — harnessing the energy in waves (I’ll look at tidal energy separately). Wave power is a form of indirect solar energy — driven by fairly consistent oceanic winds, which whip up waves over hundreds or thousands of km of open ocean. This energy may be harnessed with the use of buoys, oscillating air columns, barrages and so on, with a conversion efficiency of ~30%. Waves are a linear energy resource — once you’ve tapped its energy, you need thousands more km of ocean to regenerate new waves, so the resource is measured in kW per linear metre (not metre-squared, like direct solar). Average annual wave power density range from 10-40 kW per metre in inshore regions to as much as 70 kW/m in highly energetic regions. Although it is somewhat more regular (‘available’) than wind (and with a higher power density), wave energy is not constant and will still require substantial back-up and/or energy storage. More technical documents here.

Carnegie corporation, an Australian wave power company, state that their CETO technology (which I will look at in detail in another post — it has some fascinating prospects) can generate 100 MW peak using an a 500 buoy system; so, 200 kW peak per undersea buoy. To date, however, the only commercially operating wave farm in the world is in Aguçadoura, Portugal, about a year ago — so let’s focus first on the energy potential of this technology.

The Aguçadoura wave farm has a peak capacity of 2.3 MW, and makes use of three linear snake-like ‘Pelamis‘ to convert the motion of the ocean surface waves into electricity. There are plans to add a further 25 Pelamis to increase its peak capacity to 21 MW. The Pelamis machines, moored 5 km offshore (too much energy is lost to bottom friction if they are placed in shallow water), are 150 m long, 3.5 m wide and weigh 700 tonnes. The are “… made up of connected sections which flex and bend relative to one another as waves run along the structure. This motion is resisted by hydraulic rams which pump high pressure oil through hydraulic motors which in turn drive electrical generators.”  The machines face into the principal direction of the waves. The Portuguese farm is currently supported by a specific feed-in tariff of €0.23/kWh.

It is stated in that a 30 MW offshore wave farm would consist of 40 x 750 kW Pelamis machines, arranged in a 3-row lattice with a front of 2.1 km and a depth of 600 m. At a nominal wave power of 55 kW/m (i.e. a farm placed along a high quality Atlantic coastal resource), a single 750 kW unit will apparently yield 2.7 GWh/yr, which gives it a capacity factor in ideal conditions of 41% (this is 12 MWe average power for the 40-Pelamis farm, or 5.9 MW/km). The annual output of an AP1000 nuclear reactor rated at 1,154 MWe and run at 92% capacity factor would be 9,300 GWh. So, going by the manufacturer’s data, we would need to deploy 3,450 Pelamis machines to generate the equivalent yearly energy of one AP1000, arranged in an array 0.6 km wide and extending along 180 km of high-energy coastline. (Note that these are projected, not measured figures — the real world is often tougher)

Or, to put it in the build-rate context of TCASE 4, the hypothetical limit analysis of  680 MWe/day equates to 116 km of linear wave farm to be deployed per day (70 km2 total area), using 770,000 tonnes of steel and an approximately equal weight of ballast. Not only would that be a huge length of coastline to industrialise and isolate from shipping traffic, but the logistics of transmission connection (each of the 2,210 units/day would need to be hooked up) and ongoing maintenance (in often rough ocean conditions) would also be challenging. It is not clear how long each unit would survive before requiring replacement, but other wave technology has claimed to last 20 years.

In reality, no one is credibly imagining that wave power will be a majority component of a future sustainable energy mix, although a recent (highly speculative) paper suggested that 720,000 Pelamis-like units — 220 GWe average — could be deployed worldwide. Wave-power-poor areas, such as the coasts of the southeastern United States, northeastern South America, and southern Japan, where waves deliver only 10 to 20 kW/m, are unlikely to ever be exploited.

In a later TCASE post (not the next one), I will look more closely at the intriguing CETO electricity/desalination technology, consider some pitfalls, and speculate on its ultimate potential.

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  1. Interesting post! I’d wondered about how viable wave power was (actually, I’d hoped it was a big answer). I’ll be interested to see your 2nd post on CETO. I was thinking that wave would surely be better than wind because of the greater density of water, but it seems the difficulty in making use of diffuse power still remains challenging. Certainly using 180 km length of coastline to replace a single nuclear reactor is pretty compelling.

    I’ve just found your website and I think it is terrific, but there is a lot of material here to get through. You seem pretty pro-nuclear. Does this color your view of renewables? I guess I need to read more to find out. I’m not yet convinced that nuclear is necessary, and then there is still the problem of what to do about the nuclear waste. Also, if we run out of uranium soon, then we’re back to renewables pretty quickly. I dunno, I’d like to think nuclear was a useful option as the case for renewables is kinda weak, but it seems to be pushing it to me.

  2. Barry,

    The Aguçadoura wave farm HAD a peak capacity of 2.3 MW. The Australian bank, (Babcock and Brown was it?) owned 80% of the project and so when it went under the three Pelamis units were towed back into port at the beginning of this year.

    There haven’t been any other arrays put in the sea yet and according to Thomas (ed. Cruz, J, 2008, p 66,67) most studies or simulations of arrays have been concerned with point absorber types of up to 10 units (CETO is a form of point absorber). What effect an array 150 km on the side 7, 10 km etc out at sea would have no one can really state except that it may make a very effective marine park.

    its very early days in this sector (e.g. look at how many different devices are being designed, tested etc, on survivabilty the Pelamis people have spent a lot of time designing for extreme waves) I would’ve thought any suggestions of large arrays are just that and are just efforts to talk up what is a fledgling sector. Joao Cruz, one of the leading authorities in marine energy, suggests perhaps 10 – 25% of the wave resource is exploitable (2008, p1). So perhaps it will have a particular niche such as with coastal communities where running centralised power could be very expensive (unless you happen to be an Aluminium smelter near Portland).

  3. The Aguçadoura wave farm HAD a peak capacity of 2.3 MW. The Australian bank, (Babcock and Brown was it?) owned 80% of the project and so when it went under the three Pelamis units were towed back into port at the beginning of this year.

    Thanks for that update Jeremy. I knew Babcock & Brown were previously the owners, but I’d thought they’d managed to sell it on and keep the wave farm afloat (pardon the pun). That’s a shame that they towed them to shore — I would have loved to have seen some real-world operational data!

    I agree with your conclusion — after this review I cannot see wave power as ever being more than a niche application. I suspect it will be more useful for desalination than electricity generation, except perhaps for remote island communities where the dual role could be quite useful. Anyway, more on that when I look at the CETO technology.

  4. Alexander, did you notice that I cited that Jacobson study as the source of the claim for 720,000 Pelamis being possible?

    I’ve read the Sci Amer “lite” version and it’s all smoke and mirrors. The article is new, but the context are same old, same old. Sure, the resources are out there, globally — all that free energy. Shame harnessing it isn’t so easy. When I’ve read the technical version of the paper on which the Sci Amer conclusions were based, I will probably write up something here.

  5. The industrial base load is the life blood of technological civilization; without it, we’d have a hideous global population crash, and then revert to pre-1750 conditions in which the economy is almost entirely subsistence farming and life is nasty, brutish, and short. The first question any energy proposal has to address is how to sustain an industrial base load equivalent to today’s — much higher than today’s actually, if we don’t want to condemn the Third World to perpetual poverty.

    In the real world, there are only three base load sources that matter: coal, oil, and nuclear (hydropower would be a fourth if it weren’t already maxed out). What they have in common is that they have very high power density for each power plant.

    Of these three, nuclear has the highest density, then oil, then coal. Both economic arguments and historical evidence tell us that you can’t have an industrial civilization without a fuel that has an energy density at least as high (and thus a cost per unit of energy as low as) coal. Higher density is better, because it means lower cost.

    Even though waves are in some ways more reliable than wind, this type of generation can’t always depend on lots of wave action, meaning it needs effective energy storing methods. On the other end, sometimes waves and weather can be far too harsh for wave energy devices to withstand. So they will need to be incredibly durable, which can drive up the price. But ultimately like wind and solar, it will never supply base load because like those others, it will never manage the energy density to suppy base load, and that is what makes this mode a waste of time.

  6. p.s. The two TCASE articles I am most keen to see would cover first geothermal and then demand management. The latter not so much in terms of efficiency but rather in terms of moving demand around during the day in order to flexibly match a variable supply. I think this analysis would be more tricky than the ones to date.

  7. Geothermal is like hydro economically speaking, and like hydro requires unusual geology.

    Both are limited resources because of this. The only place geothermal can work on a large scale is in Iceland, home of a full third of the world’s active volcanoes. As well it’s not as clean as it is made out to be. Accordingly, hydro and geothermal are not going to support any larger share of the industrial base load — the day-in, day-out demand for high-density power from all those factories and hospitals and server farms — and printing presses, and food-processing operations, and everything else.

    Yes, with technical advances, more could be brought on line, especially the so-called Hot Dry Rock type, but the other factor that will then emerge is that this is in essence mining heat as it won’t get replaced fast enough to make up the loss. But the bottom line is that it cannot be exploited as widely as it would need to be to serve as an energy backbone in most countries.

    We can’t bet the farm on something that first may not pan out, and secondly is unlikely to produce much more than a fraction of our energy needs.

  8. TerjeP,

    ” I wouldn’t be too quick to rule out geothermal”

    I’d put it in the same basket as the other non-hydro renewable energy resources – it’s another dream.

    The commercial geothermal plants that are operating around the world all use geothermal energy from volcanic areas. Australia has none of these. The hot rock system Australia is trying has not succeeded anywhere in the world since the first attempts in the 1970′s in USA, UK, Germany, Japan and other countries have all been running research projects. None are making much progress.

    The problem is similar to solar. The energy is diffuse. No one denies thare is a great deal of heat at depth. But to collect it we need to run water over a large surface area of fractures in the rock mass. The water does not cooperate. It takes the easiest path. It follows “channels”. So we cannot mine the heat that is in the rock mass. The modelling that is attracting the investors assumes planar fractures with water flow over the fracture surface. This is not what happens in practice. See this for more info:

    And, don’t be fooled by the publicity spin that Australia’s geothermal programs are ‘hot fractured rock’ rather then ‘hot dry rock’. The fundamental problem of channeling is the same.

    I am not saying we’ll get no power. Of course we will, but I seriously doubt it will ever supply a significant proportion of our electricity generation.

  9. Wind, solar, wave, ocean current, ocean thermal, geothernal are all distractions from what is the answer to our needs for energy security, health, and environmental needs. The answer is nuclear power. The real question for Australia should be: Do we want high cost nuclear power or low cost nuclear power? That is where we should focus our attention and our research resources.

  10. Recall that in a single week Australia’s redoubtable Energy Minister Martin Ferguson visited the Petratherm geothermal experiment and declared it would produce heaps of baseload power then flew to China to sign a $50bn LNG export deal. We’re in good hands.

    Apart from low steam/froth temperature, radioactive radon, lack of nearby transmission and the need to drill fresh holes HDR has an eerily familiar problem, since
    1) HDR geothermal
    2) underground coal gasification (per ABC Catalyst)
    3) the recalcitrant Montara gas rig blowout
    all have difficulty controlling the below surface plumbing.

  11. Dear sir,
    I just noticed this on the greens BLOG.

    Asking for climate scientists to ‘speak out’. I dearly hope you get to address the select council.

    “Greens, Coalition agree on ETS Senate Inquiry; Time for scientists to speak out
    Media Release | Spokesperson Christine Milne
    Tuesday 10th March 2009, 2:30pm
    in Climate Change & the Zero Carbon WorldEmissions TargetsEmissions TradingZero Carbon
    The Australian Greens are calling on Australia’s climate scientists to give evidence to a new Senate Inquiry into emissions trading that will be established today following agreement with the Opposition.

    Today’s release of the Government’s draft emissions trading legislation coincides with the opening of a global climate science congress in Copenhagen. The Senate Inquiry to be established following today’s agreement will give Australia’s scientists, including those who are attending that congress, the opportunity to report on the adequacy of the Rudd Government’s proposed emissions reduction target.

    “The Senate will now have an opportunity to properly examine the critical issues that surround the Government’s emissions trading plans,” said Australian Greens Deputy Leader, Senator Christine Milne.

    The Inquiry, to be conducted by a new Senate Select Committee on Climate Policy and reporting back on May 14, will examine the choice of emissions trading as a mechanism, the relative contributions of complementary measures to emissions reductions, the environmental effectiveness of the proposed targets and whether the scheme would appropriately transform the economy.

    “Climate change is not like so many other issues which can be negotiated and compromised when they come before the Parliament. You cannot negotiate with the laws of physics and chemistry.

    “Either Australia chooses to work towards a target that is scientifically valid and will help avoid climate catastrophe, or we choose to put ourselves at unacceptable risk.

    “Australia’s climate scientists have been remarkably reticent to publicly criticise what they have in private slammed as a totally unacceptable and inadequate target.

    “As the scientists well know, there is such a thing as being too late. Now is the time for them to come before the Senate and explain what a scientifically adequate target would be for Australia.

    “The Greens’ reading of the science tells us that Australia needs to work fast to build a net zero emissions economy, and certainly no later than 2050, with cuts of at least 40% below 1990 levels by 2020.

    “We believe that, if we aim for that transformation, we can achieve it, creating hundreds of thousands of new jobs along the way. If we do not try, we have no chance of success.”

    Terms of reference
    (1) That a select committee, to be known as the Select Committee on Climate Policy, be established to inquire into and report by 14 May 2009 on:
    a) The choice of emissions trading as the central policy to reduce Australia’s carbon pollution, taking into account the need to:
    i. reduce carbon pollution at the lowest economic cost;
    ii. put in place long-term incentives for investment in clean energy and low-emission technology; and
    iii. contribute to a global solution to climate change.
    b) The relative contributions to overall emission reduction targets from complementary measures such as renewable energy feed-in laws, energy efficiency and the protection or development of terrestrial carbon stores such as native forests and soils;
    c) Whether the government’s Carbon Pollution Reduction Scheme (CPRS) is environmentally effective, in particular with regard to the adequacy or otherwise of the Government’s 2020 and 2050 greenhouse gas emission reduction targets in avoiding dangerous climate change;
    d) An appropriate mechanism for determining what a fair and equitable contribution to the global emission reduction effort would be;
    e) Whether the design of the proposed scheme will send appropriate investment signals for green collar jobs, research and development, and the manufacturing and service industries, taking into account permit allocation, leakage, compensation mechanisms and additionality issues; and,
    f) Any related matter.

    (2) That the committee consist of 10 senators, 4 nominated by the Leader of the Opposition in the Senate, 4 nominated by the Leader of the Government in the Senate, 1 nominated by the Leader of the Australian Greens and 1 nominated by the independent senators.
    (3) That:
    a) participating members may be appointed to the committee on the nomination of the Leader of the Government in the Senate, the Leader of the Opposition in the Senate or any minority party or independent senator;
    b) participating members may participate in hearings of evidence and deliberations of the committee, and have all the rights of members of the committee, but may not vote on any questions before the committee; and
    c) a participating member shall be taken to be a member of the committee for the purpose of forming a quorum of the committee if a majority of members of the committee is not present.

    (4) That the committee may proceed to the dispatch of business notwithstanding that all members have not been duly nominated and appointed and notwithstanding any vacancy.
    (5) That the committee elect as chair one of the members nominated by the Leader of the Opposition in the Senate and, as deputy chair, a member nominated by the Australian Greens.
    (6) That the deputy chair shall act as chair when the chair is absent from a meeting of the committee or the position of chair is temporarily vacant.
    (7) That the chair, or the deputy chair when acting as chair, may appoint another member of the committee to act as chair during the temporary absence of both the chair and the deputy chair at a meeting of the committee.
    (8) That, in the event of an equally divided vote, the chair, or the deputy chair when acting as chair, has a casting vote.
    (9) That the committee have power to appoint subcommittees consisting of 3 or more of its members, and to refer to any such subcommittee any of the matters which the committee is empowered to examine.
    (10) That the committee and any subcommittee have power to send for and examine persons and documents, to move from place to place, to sit in public or in private, notwithstanding any prorogation of the Parliament or dissolution of the House of Representatives, and have leave to report from time to time its proceedings, the evidence taken and such interim recommendations as it may deem fit.
    (11) That the committee be provided with all necessary staff, facilities and resources and be empowered to appoint persons with specialist knowledge for the purposes of the committee with the approval of the President.
    (12) That the committee be empowered to print from day to day such papers and evidence as may be ordered by it, and a daily Hansard be published of such proceedings as take place in public.”


  12. Barry

    You say:

    “In reality, no one is credibly imagining that wave power will be a majority component of a future sustainable energy mix, although a recent (highly speculative) paper suggested that 720,000 Pelamis-like units — 220 GWe average — could be deployed worldwide.”

    This of similar magnitude to the current output of nuclear power plants wordwide and about half that of hydroelectricty worldwide, and this estimate is relatively conservative in relation to the resource.

    You are also not comparing apples and oranges. Comparing current Pelamis technology with next generation nuclear technology is bit like comparing the Wright brothers with Concorde. One technology has had £40m investment, the other >£200,000m. The theoretical energy capture from a point absorber such as Pelamis is many times greater than that currently being achieved, the figures you quote are based on wave capture widths already demonstrated.

    You extrapolate from a wave farm 16MWe wave farm to a 1000MWe wave farm and say it will be 180km long occupying an area of 100km2. However I think it should be emphasised that, like a wind farm only a fraction of this area will be the footprint occupied by machines. In fact the area density (MW/km2) is 4-5 times greater than for wind, and of course there is a lot more sea out there than land, so this isn’t necessarily the constraint you imagine, particularly if it is economically to add more rows of machines to the farm….

    The real point here is that extrapolation is a dangerous game… The amount of steel cited is not particularly large and can be compared to the thousands of km of pipelines already installed for the oil and gas industry.

    The issue is also not renewables versus nuclear….

  13. Pingback: The problem with ‘Generating the Future: UK energy systems fit for 2050′ « BraveNewClimate

  14. Martin

    You are quite correct – the machines are tied up at a quayside. The fact that the project is no longer operating has been well reported following the collapse of Babcock and Brown who were the owner of this project and responsible for operating it. The start of this article incorrectly assumed that the project was still operating (as Jeremy C has corrected above the day after this was written). It’s certainly unfortunate but I don’t see anyone being untruthful.

  15. Pingback: Orkney waters unsuitable for marine renewables? | The Digital Glebe

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