That wind is generated by the fact that the air at the equator is warmer than at the poles. That hotter air rises and spreads out. Thanks to the rotation of the earth (the Coriolis effect) it tends not to go all the way to the pole and instead to move in largeish circles.

Local conditions, altitude, the flatness or ruggedness of the ground all have an impact on wind conditions at any given site. In general, wind near the ground suffers from turbulence, irregular patterns, and its energy is diseprsed by obstacles. as you go higher in altitude, it becomes more regular and steady, and is much easier to transform into usable energy.

The way to do it is to convert mechanical energy into electricity. The mechanical energy in wind is captured as mechanical energy by the blades of the wind turbine, which lead the rotor.

To convert that torque into electricity, a generator is needed, usually located in side the nacelle of the wind turbine. Electricity is then transformed into medium or high voltage current and sent into the grid.

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Today's turbines are typically 60-80 meters high, with blades 30 to 40 meters long:

Such turbines now have a capacity of 1.5 to 3 megawatts (MW), and typically generate 3-10 million kWh (or TWh) depending on the wind conditions. A big wind farm in the USA can include up to 100 turbines (150 MW) and generate, say, 500 TWh per year, enough to fulfill the needs of 45,000 families.

As a comparison, a typical coal-fired power plant will have a capacity of 600 MW and generate close to 5,000 TWh.

As the exemple above shows, wind farms generate fewer kWhs per MW, i.e. they have a lower availability factor, which is caused by the variability of the wind: it does not blow all the time, and it does not blow all the time at speeds enough to generate the maximum capacity of the turbine. Availability typically ranges from 20-30% for onshore windfarms to close to 50% for offshore projects or a few exceptional onshore locations. The good news is that wind tends to be available at the time of the day when we need it most, i.e. during the day and in the evening. But it's not available on demand.

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Let's go through the main advantages and potential drawbacks of windpower.

Advantages

• it requires no fuel. Once build, it produces endlessly (well, at least for the lifetime of the equipment, typically 20-25 years) renewable energy and requires no additional input. That lowers its cost of production, eliminates the price risk on such additional inputs and does away with the political risks associated with imports of valuable commodities, and the realpolitik that goes along with these;

• it creates more jobs. Windpower is actually the energy source that creates the most jobs per kWh. 10 MW generate about 4 full time jobs, of which 2 will necessarily be located in the community that hosts the wind farm. Windfarm construction generates good industrial jobs in the mechanical, electrical equipement and financial industries (as all the investment needs to be done at the beginning, the financing costs are a vital part ofthe package). Today, the main manufacturers are based in Europe, but they are investing in facilities in the US a s demand here increases.

  

• it is becoming quite price-competitive

  

  the graph above, from the Economist last year, does not fully reflect the nasty increases in gas and coal prices, and suggests that wind power is pretty much price competitive compared to alternatives. It still requires some minimal public support to be financed today, as banks are not quite ready yet to bet on $60+ oil over 20 years yet, but this may soon no longer be required;

• it generates no carbon emissions. In today's world, not contributing to global warming is no longer an irrelevant argument. Wind power is the only power source (with nuclear, which has other issues to deal with) to not make that problem worse.
  

Against that, wind power has a number of real or perceived drawbacks.

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Potential drawbacks of wind power

• it is intermittent. As discussed above, wind power cannot be produced on demand and is subject to the vagaries of wind speeds. This can be a handicap in some cases it would not do, for instance, as the sole power source for a hospital), and it excludes, for now, the hypothesis that wind power can contribute the majority of our power needs. But in practice, experience demonstrates that electricity networks can tolerate with almost no adjustment up to 10% of power coming from wind, and around 20% with some minor effort. We're still very far from these levels in most places (the USA in aggregate are still below 1%), so let's build capacity before we worry about that particular issue; In particular, the argument brandied around by some that building windfarms does not eliminate the need to build polluting plants, to be available as back up, is absolutely bunk.

• it is ugly. This is the most contentious issue, as the numerous - and highly polemical - diaries about the offshore project on Cape Cod have shown. To a large extent, it is subjective, so there never will be a satisfactory reply to all. What can reasonably be said is that it is probably wise to avoid some sites of particular beauty. Studies in Scotland have shown that there was more acceptance of windfarms by their direct neighbors than by people a few miles away, which suggests that on the gorund work to educate and convince the locals prior to construction stand a good chance of allaying the legitimate fears of being invaded by massive towers.

• it kills birds. This has been given some credence by the sad case of the Altamont Pass windfarms, where a combination of a poor location (in a migratory path), lattice structure (inciting birds to rest on the wind turbines) and small and fast turning blades created a nasty mix and led to too many raptors being killed. But with modern turbines (which rotate much more slowly), and provided that sensitive sites are avoided, the issue is really marginal. (See this diary for a specific discussion of bird issues, including the point of view of bird protection NGOs)

  Wind farms cause a negligible fraction (less than 0.01%) of all man-caused bird fatalities:

  

• it is noisy. This may have been true of some of the older turbines, but it no longer the case. I have personally been around wind turbines and you can barely hear a hum.

• it takes a lot of land. This is both true and untrue. It is true that a wind farm requires a lot of land, as big windfarms typically need to be spaced almost 500 meters from one another in order not to disturb their ability to capture wind energy. But the footprint of the wind turbines is actually very small, and the land around them can still be used. In rural settings, the impact on farmland is practically nil (the dirt road to get to each turbine, and a few yards around each) and farmers can still use it as before (and they get a really decent chunk of income from granting the land rights). In urban areas, it is obviously harder to build large scale windfarms, but small numbers can easily be built on or around industrial plants, port facilities, or along road or railways.

• it costs taxpayers' money. It does, and it still needs that support (although, as explained above, less and less). Butthe big difference between wind and other power sources is that most subsidies for wind are explicit and visible, whereas subsidies for other energy sources are more discreet. Tax breaks for oil&gas companies, public insurance of nuclear power plants, and, the most important, the lack of payment for the environmental damage caused by the extraction, transport and burning of valuable (and yet dirty andf/or carbon rich) natural resources. and we won't even mention the cost of the Pentagon budget, a hefty chunk of which goes to protect energy imports. So subsidies for wind are actually fairly small, well identified, and correspond to a real public necessity. (And they make bankers like me more comfortable to finance wind farms...)

  
  

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Altogether, I think it can reasonably be said that the advantages far outweigh the disadvantages. There is not one single "magic bullet" solution to the current energy crisis, but wind is certainly one of the best options already available, and it needs to be deployed on a larger scale. The good news is that the industry is currently booming in the USA, after years of ups and downs linked to a chaotic renewal process for the main support mechanism, the PTC.

Energize America strongly supports the development of wind power (via a simple extension of the PTC) and expects that 200,000 MW can be built by 2020, creating more than 50,000 highly qualified jobs in the process.

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Some links

My diaries on the topic
Energy - some good news (for once)
Don Quixote meets Wall Street - financing wind farms
The future of power generation
Wind power: birds, landscapes and availability (I)
comment on PTC
Something to take your mind off indictments: Windfarm blogging
Wind power now CHEAPER for US retail consumers
USA to become world leader in wind power in 2005
2005 was a great year for wind power worldwide

On birds
American Bird Conservancy
Audubon Society

Professional organisations and sites
Danish wind power association (with a great intorduction to all parameters of wind power, starting here
American Wind Power Association
European Wind Power Association (with a great library of detailed studies)
Windfarm pictures (including construction) by Gunnar Britse