The wind doesn’t blow all the time. Why doesn’t this make wind power ineffective?

A common refrain by people who question wind power as an effective part of energy grids is that it doesn’t produce the same amount of power all of the time.

  • “On average, wind turbines are about 20% to 25% efficient”– Canadian Nuclear Association
  • “annual outputs of 15-30% of capacity” – National Wind Watch (a US anti-wind advocacy organization)
  • “On average, the wind developments already operating in Ontario achieve less than 20% of their capacity.” – Wind Concerns Ontario ( a Canadian anti-wind advocacy organization)

Short Answer

Wind turbines are cost effective forms of generation achieving 35%-47% capacity factors today that take into account the variability of the wind in specific sites along with their efficiency.  This is factored into the business cases for new generation.  New turbines aimed at specific wind conditions are much more efficient at capturing the wind than older wind turbines. As all forms of generation are more or less intermittent, this is just another form of energy to forecast, plan for and manage on a day-to-day basis and poses no particularly great challenges.

Long Answer

There are several related misunderstandings packed into these statements:

  1. That historical numbers are reflective of current industry experiences
  2. That wind energy only produces energy 25% of the time
  3. That this makes the lifecycle cost of energy uneconomic
  4. That this makes energy grids unmanageable
A couple of definitions are necessary before deconstructing these varied myths.

  • Faceplate Capacity:  Wind turbines are rated based on their faceplate capacity.  This faceplate number is the amount of energy that a wind turbine will create when it is operating at full capacity.  A 3 MW wind turbine could provide 3 megawatt-hours (MWh) of energy to the grid in one hour or 26,280 MWh in a year if it ran at full capacity the entire time.
  • Capacity Factor (CF): This is the projected or measured average of a wind turbines generation over a year (usually).  If the 3 MW wind turbine generates 7,900 MWh over the year, its capacity factor is 30% (7,900 / 26,280).  If it generates 10,500 MWh over the year, its capacity factor is 40% (10,500 / 26,280).
  • Lifecycle Cost of Energy (LCOE):  This is a moderately complex calculation that assesses the full cost of purchasing, installing, operating and decommissioning a form of generation, then divides that by the megawatt-hours it provides over its lifespan. This is the baseline by which different forms of generation can be compared on a level playing field.  The industry standard for LCOE’s is a 20-year lifespan as that is both commensurate with the lifespan of most new generation and does not artificially reduce the cost of decommissioning by pushing it so far out into the future that it becomes effectively irrelevant.

Taking the misunderstandings one by one:

1. Modern wind turbines achieve 35% – 47% average capacity factors in different wind categories

The wind turbines of 20 years ago were much less efficient and effective than modern wind turbines. In the best sites, they might have seen 30% as a good capacity factor.  Modern wind turbines are optimized for different wind conditions and now achieve 35% – 47% average capacity factors in different wind categories from very low wind sites to very high wind sites with new turbines installed in 2012. There are so many wind turbines being built and installed that significant differentiation in product lines makes sense and remains economic.

Screen Shot 2013-02-16 at 8.01.30 AM

[17]

Why are wind turbines better at catching the wind now?

  • Wind turbine height: the wind is stronger higher off of the ground and taller wind turbines can catch more of it.

    [3]

  • Mechanical efficiency: wind turbines have slowly evolved to eliminate unnecessary gearing and friction.  Many now have no gearboxes at all, significantly reducing complexity and gearing related losses. [4]
  • Specialization: Lower wind conditions get bigger blades and smaller generators.  Higher wind conditions get narrower blades and larger generators. [5], [19]
  • Aerodynamic improvements: The blades cut through the air better and generate more aerodynamic lift due to advances in their shape and changes to their shape through their length to accommodate different relative air speeds between tip and hub. [8]
  • Optimized maintenance: Well understood and costed best practices for maintaining specific wind turbines in specific conditions, ensure that they maintain the optimal balance, lubrication and uptime. [9]
  • Robustness: Wind turbines are now large scale machines with better tolerance for high-winds, icing and other realities of exposed structures. Wind turbine failure, while it makes for spectacular pictures and videos, is extremely rare. [14]
  • Wind modeling:  Understanding and modeling of wind conditions at specific sites is much more accurate now than 20 years ago.  This allows the right wind turbines to be selected and sited to maximize use of the wind resource in the specific location. [7]
  • Instrumentation and automation:  Wind turbines are heavily computerized today to adjust to maximize power output in different wind conditions.  In addition, they are connected through SCADA-interfaces to wind farm managers and grid operators who receive real-time updates on the state of the turbines, allowing much faster response in the event of problems.  This maximizes performance in the moment and minimizes downtime. [10]
  • Advanced materials: Materials for blades are being refined regularly, with stronger and lighter blades enabling increased robustness and increased efficiency. [2]
  • Advanced coatings: Manufacturers are now applying advanced coatings which deteriorate much more slowly on blades, especially the leading edge. This increases laminar flow and maintains aerodynamic efficiency for longer. [6]

This highlights another myth of wind energy: that no more efficiency gains are possible. There is tremendous ongoing innovation in wind power generation.

There are 240,000 wind turbines in operation in the world today.[21]  Many sites in the world are operating with very old wind turbines and are still profitably generating power. Wind turbines have been getting progressively bigger. The average wind turbine of 20 years ago was 600 KW; the average wind turbine in 2012 is 3 megawatts, six times bigger in terms of generating capacity. Wind power has roughly quadrupled in generating capacity since 2005 worldwide, dominantly with 1.5 MW + wind turbines.  Unless the capacity factor is adjusted for megawatts of generation, a simple historical average will give a low apparent capacity factor.  It’s also fairly easy to select locations, subsets of the data around low wind years and prove whatever you want about wind energy.

A corollary of this is that there are two multiplicative factors in wind generation: wind turbines are capturing more of the available energy AND they are several times larger. A modern 3 MW wind turbine is 5 times larger than the 600 KW wind turbine of 20 years ago, but it is also likely to have double the capacity factor.  That means that the modern wind turbine might reasonably generate 10 times as much power as the older wind turbine a fifth of its size. (10,512 MW vs 1,051 MW per year).

These advances, by the way, are why Holland’s experience is that wind turbines don’t stay in place for their entire 20-25 year possible lifespan.  On average, Holland has repowered wind sites (replaced older wind turbines with newer ones) after about 17 years to maximize wind generation and profits.

2. Wind turbines generate electricity 75%-85% of the time, not 25% of the time

The wind doesn’t blow at the optimum speed for the wind turbine’s design all of the time.  In a given site, the wind will usually blow sufficiently strongly for a wind turbine to generate electricity for 75%-85% of the year. For much of that time, the wind is lower than optimum and it is delivering less than its possible electricity to the grid. For some of the time it is operating at peak efficiency and is delivering its maximum.  The confusion arises when people mistake capacity factor with percentage hours of operation.

[11]

To do some simple conversion, 3.5 m/s is 12.6 KPH or 7.8 MPH.  Some low wind speed optimized turbines cut in at 3 m/s (10.8 KPH / 6.7 MPH). The wind turbines are selected based on the wind profiles at sites. Wind turbines will be generating power at much below their optimum wind speeds.

3.  Modern wind turbines produce electricity for 5-7 cents per KWh, have no negative externalities and create rural jobs 

This cost is in the same range as new nuclear, new hydro or new coal plants.  In the US, natural gas is artificially low at present, so wind is more expensive than natural gas, but with none of the negative externalities associated with fracking, particulate emissions or green-house gas emissions.

Wind energy has been reducing in cost by 14% for every doubling of capacity for the past 30 years.  That trend has been clear. [12] The LCOE is very important, as it provides levelized costing to allow different forms of generation to be assessed on the criteria of cost per MW or KW of generation.  This is not the only characteristic, but it is a very important one.  Other characteristics include annual energy provision profiles, consumer demand profiles, negative externalities [13] and job creation.

4.  Wind power does not make grids unmanageable and actually improves robustness of grids in some cases

Grid managers and energy experts know one inalienable truth: all forms of generation are intermittent, renewables just happen to be more so and their intermittency is well understood and typically more predictable.  In Ontario in 2002 or so, capacity factor for the nuclear fleet was in the 55-60% range. Nuclear industry estimates assert 89-90% average capacity factor world-wide in 2011, but external observers peg it at closer to 85%. As for coal, the US fleet experienced a range of 60% to 75% in 2000-2010.

In Europe and Australia, the ANEMOS system is in place providing high-accuracy forecasts of wind farm outputs on five minute, two hour, 40 hour, six day and two year timeframes.  Five minute forecasts are accurate to within 1-2% absolute of energy output.  This allows grid operators to have very accurate whole grid supply predictions in timeframes which allow them to respond with appropriate mitigations as the wind fluctuates in each wind farm.[20]

There’s an interesting example of the odd way that some people look at this in the moderately famous Ardrossan wind turbine fire of December 2011. One of a dozen 1.2 MW wind turbines caught fire in a massive wind storm that swept Scotland, taking its 1.2 MW out of generation.  The same wind storm knocked down transmission lines from the nearby Hunterston nuclear plant.  It was offline for 54 hours for a loss of 17,000 MWh to the grid. That’s about six years of generation capacity of the wind turbine. [14]

When an Australian 800 MW coal plant stopped delivering electricity to the grid recently, the wholesale price of power increased by a factor of 200 in minutes before returning to normal. This graph is leveled over 30 minutes so the peak price is masked, but the dramatic loss of power is readily apparent. As the linked article shows, loss of major generating assets is common and unpredictable, while loss of wind generation is common, but typically only a percentage of capacity and very predictable.

Grid managers have to maintain hot backup contingencies for failure of their largest single generation plants, typically coal, hydro or nuclear in the 1 GW range. Wind energy doesn’t rank as a grid management issue until you get into > 20% ranges, and even then it isn’t a particularly hard or sudden problem compared to dealing with a nuclear plant that suddenly isn’t there. [15]

The director of Energy Strategy for the UK National Grid is clear on this point:

The National Grid’s ability to predict where the wind is going to blow in a week, a day or an hour is crucial to this argument. A couple of years ago, the company launched a new wind forecasting system designed to help it plan for wind intermittency. On a day-to-day basis, says Smith, its accuracy is “phenomenally good” – getting it right 95 per cent of the time when it looks ahead 24 hours. He says:

In fact, Smith argues, wind is more predictable in some senses than conventional power sources like coal or gas. A traditional power station like a nuclear plant could “trip and fall off in a matter of milliseconds”, he says. Wind turbines may have to be shut off to protect them in high wind conditions, but these are easier to predict than a nuclear power station suddenly cutting out.[22]

Finally, in Brazil, wind energy is viewed favourably by the grid as the strongest and most reliable winds are in the time of year when their major hydro dams experience their lowest water levels. Note the high natural water flow in Dec-Mar and the significant dip in the natural water flow the rest of the year.  Note the very significant greater wind capacity at the same time.  This allows more water to be left behind the dams when water flow is low, preserving a key resource for optimum use.[16]

This is one of the reasons Brazil is building wind generation capacity rapidly, with one December 2011 energy auction seeing 0.97 GW of the 1.2 GW of generation requested going to wind energy bids.  Interestingly, Brazil has no special treatment of wind energy over other forms of energy in terms of tax treatment or subsidies and the wind bids averaged 5.5 cents USD / kWh.

The variability of wind is not a problem for economic, clean and effective wind energy. Those who say otherwise have an agenda other than effective energy sources and it is useful to figure out what it is.

References
[1] Cost Of Wind Power Expected To Drop 12% By 2016, NAWindPower,  MAy 30, 2012, http://www.nawindpower.com/e107_plugins/content/content.php?content.9907
[2] Wind turbine blades: Glass vs. carbon fiber, Composites World, June 2012, http://www.compositesworld.com/articles/wind-turbine-blades-glass-vs-carbon-fiber
[3] Waarom alleen grote en kleine windturbines en niets daar tussenin?, EG Blog, August 16, 2010, http://emileglorieux.blogspot.com.br/2010/08/waarom-alleen-grote-en-kleine.html
[4] GE Grabs Gearless Wind Turbines, Technology Review, MIT, September 23, 2009, http://www.technologyreview.com/energy/23517/
[5] GE’s New 1.6-100 Wind Turbine Now In Circulation, NAWindPower, May 23, 2011, http://www.nawindpower.com/e107_plugins/content/content.php?content.7925
[6] 2012: Trends in coatings, Windpower Engineering & Development, June 1, 2012, http://www.windpowerengineering.com/design/materials/coatings-materials/2012-trends-in-coatings/
[7] 2012: Trends in simulation software, Windpower Engineering & Development, June 1, 2012, http://www.windpowerengineering.com/design/wind-power-software/2012-trends-in-simulation-software/
[8] Vestas hopes new blade technology will give it an edge, Recharge, May 8, 2012, http://www.rechargenews.com/business_area/innovation/article312729.ece
[9] 2012: Trends in operations & maintenance, Windpower Engineering & Development, May 31, 2012, http://www.windpowerengineering.com/maintenance/maintenance-operations/2012-trends-in-operations-maintenance/
[10] Wind Turbines Get Sensitive: National Instruments’ optical sensors give monstrous blades a self-protective touch, greentechmedia:, January 14, 2011, http://www.greentechmedia.com/articles/read/wind-turbines-get-sensitive/
[11] 14. Wind turbine power ouput variation with steady wind speed, WINDPOWER Program, http://www.wind-power-program.com/turbine_characteristics.htm
[12] How effective are wind turbines compared to other sources of energy?
[13] Governmental incentives for renewables are necessary and provide great value-for-money
[14] Wind farms causing fires? All smoke and no flame
[15] How much backup does a wind farm need? How does that compare to conventional generation?
[16] Wind / Hydro Complementary Seasonal Regimes in Brazil, DEWI Magazine #19, August 2012, http://www.dewi.de/dewi/fileadmin/pdf/publications/Magazin_19/13.pdf
[17] Recent Developments in the Levelized Cost of Energy from U.S. Wind Power Projects, Lawrence Berkeley National Laboratory and National Renewable Energy Laboratory, February 2012, http://eetd.lbl.gov/ea/ems/reports/wind-energy-costs-2-2012.pdf
[19] Suzlon announces new low-wind turbine with up to 29 percent increased output, Renewable Energy Magazine, June 7, 2012, http://www.renewableenergymagazine.com/article-wind-20765-48-Suzlon_announces_new_low_wind_turbine_with_up_to_29_percent_increased_output
[20] Australian Wind Energy Forecasting System (AWEFS) overview, Australian Energy Market Operator, July 2010, http://www.aemo.com.au/~/media/Files/Other/electricityops/0260-0007%20pdf.pdf
[21] Wind in Numbers, Global Wind Energy Council, http://www.gwec.net/global-figures/wind-in-numbers/
[
22] http://www.carbonbrief.org/blog/2013/03/interview-with-the-national-grid

10 comments

  1. Hello Barnard,

    First of all thanks a lot for this extensive and well documented blog on wind energy.

    A very interesting point is indeed that the average historical capacity factor is by no means representative for the newest generation of wind turbines.
    I did a quick calculation on the Danish master data register for wind turbine installed capacity and generation
    (see http://www.ens.dk/da-DK/Info/TalOgKort/Statistik_og_noegletal/Oversigt_over_energisektoren/Stamdataregister_vindmoeller/Sider/forside.aspx). The average capacity factor over the 1992-2012 period is 22%, while the 2011 and 2012 capacity factor was 28%. This confirms the increase in capacity factor.
    Furthermore – and this is important – if you take the “weighted average age”, this 28% capacity factor is achieved with an turbine base whose “weighted average” install date is 2001, so 11 years old technology!

    Wind technology is still evolving to capture more of these scale benefits. The largest offshore wind turbine is currently being installed on the Belgian coast near Ostend, it’s an Alstom 6MW Haliade 150 turbine. And more is certainly to come in terms of evolution. Each old turbine replaced with a newest generation will bump up the actual energy production and lowers the specific maintenance cost.

    This technology evolution and the relative advantages of wind energy technology is one of the main reasons that wind energy has a very bright future ahead, especially in those regions that only start adapting now!

    I only partially agree with your second statement misunderstanding, however.
    Of course, wind turbines generate electricity during much more than 25% of their time. However, with this statement people usually refer to the capacity factor, i.e. what is the fraction of available time (i.e. 8760 hours) that the turbine would be producing at “full power equivalent” (i.e. the faceplate power rating).
    This, 25% is a good actual value (but rising dramatically!!), depending on country (e.g. for 2012, Denmark is at 28%; for 2011 Germany is at 19%*)

    * Based on calculations from data in the Fraunhofer Wind energy report 2011 http://www.fraunhofer.de/content/dam/zv/de/forschungsthemen/energie/Windreport-2011-de.pdf

    I have to disagree with your opinion on point 3 “no negative externalities”

    Any negative side effect of a system on its environment or related systems is a negative externality.

    For coal, nuclear and gas these are all well known.
    There is direct pollution of the environment (particulates, sulphur, ashes…) and long-term effects related to greenhouse gas emission in the case of coal & gas. Also the very controversial fracking practices for gas create a number of new problems of which the extent is not even fully known and understood. Clearly the current US energy optimism and low gas prices will be tempered at some point.
    For nuclear there is the very low probability but extreme consequences of major incidents, and the nuclear waste issue that is nowhere near resolved. These externalities cannot be neglected.

    However, claiming that there are “no negative externalities” for wind energy is a wrong statement.
    I live in a densely populated country, Belgium, and nearly every new wind park is at least partly controversial for reasons of visual and noise pollution of the immediate environment, or for claiming portions of already very scarce rural areas. This stretches even to visual pollution of coastal areas in case of off-shore wind parks (Belgium only has 50kms of coastline). Furthermore, these parks will be erected in one of the busiest naval routes in the world (North Sea) with at least some probability of marine incidents sooner or later.
    Then there’s the impact on bird populations, especially since a lot of birds live near the seashores where conditions are favorable for wind turbines. Bird strikes do happen and lead to casualties. Nuclear power plants don’t strike birds from the sky.

    The biggest externality of wind power that has not been taking into account is the lack to produce on demand. This effectively externalizes the cost for the needed excess capacity.

    If we make abstraction of the environmental benefits and interconnection between areas for a moment, strictly speaking the only direct economical benefit that the wind turbine park is bringing, is saving the direct cost (i.e. only the fuel, the avoided direct cost of waste by not emitting & direct cost of equipment wear, NOT personnel or other infrastructure costs) of the gas or coal plant that is not needed to produce the instantaneous energy production of the wind turbine park.
    Of course, this is partially leveled by the geographic spread of the parks (“the wind always blows somewhere”), the interconnectivity between electricity grids (at an external cost!) and the presence of structural overcapacity (at an external cost!)
    Even if the ANEMOS system in use can accurately predict a windfall, somehow, somewhere, somebody must have “idle” capacity ready when needed!
    In the opposite case of “too much” instantaneous wind energy (e.g. production at maximum power output during the night), wind power is regularly dumped at near-0 cost, and sometimes wind operators even pay to dump it!
    Denmark regularly export excess energy to Sweden at “0″ cost, because they have easy to steer and very reactive hydro energy plants; they shut off part of their hydro power plants. Not only is that particular wind energy package loss-making, it’s less beneficial for the environment either since Sweden (mostly) cuts down their hydro energy output, substituting one for the other renewable energy source.

    I have to partially disagree with point 4 about the robustness of the grid.

    As the last point evokes, Denmark regularly relies on the availability of Swedish “on-off” capability of hydro plants to manage their production. Despite this, the large installed windbase concentrated in Northern Germany and Denmark has frequently lead to dangerously unstable situations that luckily didn’t result in huge blackouts yet. However, it’s putting a huge strain on the grid in the Northern Germany and Denmark region and beyond. This already lead to forced shutdown of heavy industry plants in Germany at moments (again, a serious external cost).
    End of 2011, Germany and Denmark together had about 33.000 MW of installed capacity. This means the equivalent of 33 (thirty-three!) 1GW plants that can go anywhere between 0 and 100% output in quite short time lapses. Even a 10% output variation means 3GW or the equivalent of 12 “steam and gas” 500MW power plants going from idle to full power!
    The electricity grid is historically not dimensioned to take these power surges. I don’t think that physical power trading between countries (see http://www.belpex.be/index.php?id=6) is helping to smooth the grid surges (it should be helping to lower energy cost though), especially because electricity producers and grid operators are fully independent (at least in large parts of Europe).

    This means that either areas with wind parks have to be better interconnected (updating the grid comes at an externalized cost of course!) with other areas to provide for the instantaneous shortage, or extra local spare capacity (different than wind) must be installed that can be rapidly ramped up when needed (again at an externalized cost).

    However, I am optimistic that other technical solutions will help changing all this.
    Much of the claims of coal and oil industry lobbyists are based on the premise that electricity demand must be fulfilled instantly at all times. What should happen (amongst others) is a serious evolution towards electricity demand management of the grid.
    Who cares if his washing machine starts at 10AM or 5PM, as long as he has freshly washed clothes by the next day? What if our portables, smart phones and pads could be temporarily switched off the grid or be charged at different rates? An average car usually commutes only about 4 hours per day (max.), and the move towards electric cars has already been initiated. What if the remaining 20 hours are used to dump electricity at the wind park’s convenience?
    Studying these micro-patterns and searching for flexibility in electricity use alone would probably solve the problem, at least for years to come.
    And also industry provides ways for energy buffering and management. Think about airco’s or cooling machines that use ice storage and make ice when electricity is available.

    Again, all of this comes at a cost, but I think this is the cost but more even the benefit of the advancement of society.

    1. Thank you for you’re extensive and informed comments, trizwiz.

      I agree, there are minor negative externalities related to amenity, but when compared to the negative externalities of fossil fuels — global warming, childhood asthma, significant mortality rate impacts — I believe I’m completely justified in being slightly hyperbolic and saying ‘no negative externalities’.

      As for birds, please read my just posted blog entry on bird and bat mortality for my research and opinion on this subject where numerous myths are also promoted by anti-wind lobbyists and the misinformed.

      Thanks again for your additional references and insights.

    2. Jens Stubbe · · Reply

      Hi you are dead wrong about bird mortality. It is a non issue and part of the anti wind scam.

      Any person who live in a town or own a house or a farm kills far more birds per person than an entire wind turbine regardless of size.

      The simple reason for this is that the land we humans use does not support the same population of birds and bats as land in the wild does.

      On average per wind turbine 4 birds among 130 species are killed every year and 4 bats among 17 species.

      This is not an issue at all and my former wife is the communication director of the Danish Bird Life organization so you have better believe it.

      Your belief that Denmark on occasion delivers free electricity to Sweden and you should add Norway too is a simple result of the order of merit system in the electricity market. On average however Denmark export electricity to Sweden, Norway and by the way also Germany for an average price per kWh than we buy electricity for and our export is growing.

      The simple reason for this is that wind match consumption n northern Europe almost perfectly because in the winter time winds are stronger and air heavier, which coincides with the high demand for electricity for heating and the lack of water in hydro reservoirs, which are only filled again in the spring when the massive amounts of snow and ice in the mountains in Norway and Sweden melts.

      Your neighbors in Holland has discovered this and are establishing HVDC cables to Norway now.

      Iceland has offered PPA agreements for everyone who wants it provided the recipient pages the HVDC cable. The standard offering, which is of cause negotiable is little more than 4 US cents per kWh.

      As for the visual pollution and the noise problem there are no easy fixes for wind energy and you are also quite right that the Northsea one day or the other will see a catastrophic event involving an offshore wind turbine.

      Some good friends run the company that designed the security system for the Great Belt bridge and it was decided to disconnect the security system for a few hours when the complete software and hardware was changed – bang a coaster with a drunken crew hammered into the bridge with one fatality and damages enough to pay for decades of security systems.

      Ofshore wind turbines have no security systems at all and it is a given fact that collisions will take place due to the human factor if not some software or hardware glitch.

  2. “A modern 3 MW wind turbine is 5 times larger than the 600 KW wind turbine of 20 years ago, but it is also likely to have double the capacity factor. That means that the modern wind turbine might reasonably generate 10 times as much power as the older wind turbine a fifth of its size. (10,512 MW vs 1,051 MW per year).”

    Just questioning the accuracy of this statement. Surely it’s a square law thing so 5 times the size should be 25 times as much power?

    Otherwise, well written, a valuable resource, BERNIE.

    1. Thanks Bernie. I’ll return to this calculation and think it through once more.

      1. From your diagram comparing turbine power, diameter and height, the 5000kW is 124m diameter so 5 to1 ratio means compare against 25m size. You have 20m and 100kW, applying square law to this results in out put from 25m being 156kW. For 5 times larger, should be 25 times more power, 156 x 25 = 3900, a lot more than 5 times, even more than 5 squared times,

        BERNIE.

  3. […] For full references for each of these innovations, please see: The wind doesn’t blow all the time. Why doesn’t this make wind power ineffective? […]

  4. Hi Mike,
    What do you think about http://www.swayturbine.no/
    where a generator of great diameter (25m) allows a higher relative speed between stator and rotor, so a lighter generator, so maybe less neodyne of which extraction makes some problems, and longer blades? And also your advice about (passive or active?) magnet bearings allowing (?) higher speed than ball bearings? Thanks.

    1. Pierre, I’m reserving judgment on SWAY Turbine for now. I’m skeptical for a couple of reasons, but have insufficient insight to determine if it’s a non-starter or just a challenging departure from current technical approaches.

      To be clear, extending the diameter of the electrical generator is an understood approach to deal with high-torque, lower RPM generation, but has tradeoffs, specifically a lot more magnets, which SWAY do address in their literature and presentations.

      My points of skepticism are fairly straightforward:
      1. Enclosing the generation elements and other electronics in the hub provides significant protection from harsh offshore elements. They address this in part, but it’s unclear whether it’s addressed in full.
      2. They have been in development of this since 2004 and do not have a working prototype. They are seeking additional investment beyond what they have and industrial partners to align with. This indicates to me that the industry has spoken to a certain extent, and evaluations have not particularly favoured this iconoclastic approach. Whether that is innate conservatism or purely technical is impossible to tell of course.
      3. Virtually all of the press on this is press releases from the company itself. There is exactly one article in Windpower Monthly on the subject. It doesn’t get a lot of attention.
      4. There is no evidence that the principals participated in Upwind.eu which overcame barriers to 10 MW devices, or that they are involved in Innwind.eu, which is working on overcoming technical barriers to 20 MW devices.

      The industry has spoken on ball bearings vs magnetic bearings as well. Ball bearings work extremely well, are inexpensive, easy to maintain and just passively work. Magnetic bearings in theory provide lower friction in many conditions, but in the absence of electricity flowing do not work at all, and do provide a constant drain on net generation. Additional complexity of no net value is the obvious judgment.

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