Published by Barnard on Wind. View the original article.
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)
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.
There are several related misunderstandings packed into these statements:
- That historical numbers are reflective of current industry experiences
- That wind energy only produces energy 25% of the time
- That this makes the lifecycle cost of energy uneconomic
- That this makes energy grids unmanageable
- 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.
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.
- 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. 
- Specialization: Lower wind conditions get bigger blades and smaller generators. Higher wind conditions get narrower blades and larger generators. , 
- 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. 
- 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. 
- 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. 
- 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. 
- 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. 
- Advanced materials: Materials for blades are being refined regularly, with stronger and lighter blades enabling increased robustness and increased efficiency. 
- 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. 
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. 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.
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.  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  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.
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. 
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. 
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.
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.
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.
 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
 Wind turbine blades: Glass vs. carbon fiber, Composites World, June 2012, http://www.compositesworld.com/articles/wind-turbine-blades-glass-vs-carbon-fiber
 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
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 14. Wind turbine power ouput variation with steady wind speed, WINDPOWER Program, http://www.wind-power-program.com/turbine_characteristics.htm
 How effective are wind turbines compared to other sources of energy?
 Governmental incentives for renewables are necessary and provide great value-for-money
 Wind farms causing fires? All smoke and no flame
 How much backup does a wind farm need? How does that compare to conventional generation?
 Wind / Hydro Complementary Seasonal Regimes in Brazil, DEWI Magazine #19, August 2012, http://www.dewi.de/dewi/fileadmin/pdf/publications/Magazin_19/13.pdf
 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
 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
 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
 Wind in Numbers, Global Wind Energy Council, http://www.gwec.net/global-figures/wind-in-numbers/