For more information see, "Wind turbines, flicker, and photosensitive epilepsy: Characterizing the flashing that may precipitate seizures and optimizing guidelines to prevent them," by Graham Harding, Pamela Harding, and Arnold Wilkins.
Wind turbines are known to produce shadow flicker by interruption of sunlight by the turbine blades. Known parameters of the seizure provoking effect of flicker, i.e., contrast, frequency, mark-space ratio, retinal area stimulated and percentage of visual cortex involved were applied to wind turbine features. The proportion of patients affected by viewing wind turbines expressed as distance in multiples of the hub height of the turbine showed that seizure risk does not decrease significantly until the distance exceeds 100 times the hub height.
Since risk does not diminish with viewing distance, flash frequency is therefore the critical factor and should be kept to a maximum of three per second, i.e., sixty revolutions per minute for a three-bladed turbine. On wind farms the shadows cast by one turbine on another should not be viewable by the public if the cumulative flash rate exceeds three per second. Turbine blades should not be reflective.
Doctors around the world as studying a condition called "Wind Turbine Syndrome". "Out of Kirby Mountain" reports that Dr. Nina Pierpont of Malone, N.Y., is one of those researchers. She testified about "Wind Turbine Syndrome" before the New York State Legislature Energy Committee. She stated:
Three doctors that I know of are studying the Wind Turbine Syndrome: myself, one in England, and one in Australia. We note the same sets of symptoms. The symptoms start when local turbines go into operation and resolve when the turbines are off or when the person is out of the area. The symptoms include:
1. Sleep problems: noise or physical sensations of pulsation or pressure make it hard to go to sleep and cause frequent awakening.
2. Headaches which are increased in frequency or severity.
3. Dizziness, unsteadiness, and nausea.
4. Exhaustion, anxiety, anger, irritability, and depression.
5. Problems with concentration and learning.
6. Tinnitus (ringing in the ears).
Not everyone near turbines has these symptoms. This does not mean people are making them up; it means there are differences among people in susceptibility. These differences are known as risk factors. Defining risk factors and the proportion of people who get symptoms is the role of epidemiologic studies. These studies are under way. Chronic sleep disturbance is the most common symptom. Exhaustion, mood problems, and problems with concentration and learning are natural outcomes of poor sleep.
Sensitivity to low frequency vibration is a risk factor. Contrary to assertions of the wind industry, some people feel disturbing amounts of vibration or pulsation from wind turbines, and can count in their bodies, especially their chests, the beats of the blades passing the towers, even when they can’t hear or see them. Sensitivity to low frequency vibration in the body or ears is highly variable in people, and hence poorly understood and the subject of much debate.
Another risk factor is a preexisting migraine disorder. Migraine is not just a bad headache; it’s a complex neurologic phenomenon which affects the visual, hearing, and balance systems, and can even affect motor control and consciousness itself. Many people with migraine disorder have increased sensitivity to noise and to motion -- they get carsick as youngsters, and seasick, and very sick on carnival rides. Migraine-associated vertigo (which is the spinning type of dizziness, often with nausea) is a described medical entity. Migraine occurs in 12% of Americans. It is a common, familial, inherited condition.
... Data from a number of studies and individual cases document that in rolling terrain, disturbing symptoms of the Wind Turbine Syndrome occur up to 1.2 miles from the closest turbine. In long Appalachian valleys, with turbines on ridge-tops, disturbing symptoms occur up to 1.5 miles away. In New Zealand, which is more mountainous, disturbing symptoms occur up to 1.9 miles away.
Windmills can be iced in the winter, and moving blades can throw large chunks of ice. See "RISK ANALYSIS OF ICE THROW FROM WIND TURBINES", by Henry Seifert, Annette Westerhellweg, and Jürgen Kröning.
Wind turbines are normally erected far away from houses, industry, etc., as the wind
conditions are not favourable in the vicinity of large obstacles. Furthermore, with regard to
acoustic noise emission and shadow flicker certain distances are required by national
regulations, when wind farms are planned in the neighbourhood of residential areas. Thus,
wind turbines should not cause risks as far as ice throw is concerned. However, the turbines
are erected close to roads or agricultural infrastructure in order to avoid long and expensive
access roads for erection and maintenance. This induces a risk for persons passing by the wind
turbines, cars passing the streets if ice fragments fall down from a turbine.
In addition to the health related problems and icing related falls, Paul Gipe reports that work related deaths associated with windmills have occurred. [url]http://www.wind-works.org/articles/BreathLife.html[/url]
it appears that the current mortality rate of wind energy of 0.15 deaths per TWh is roughly equivalent to that of mining, processing, and burning of coal to generate electricity according to some researchers. (This data doesn't include increases in mortality from the air pollution that results from burning coal.) Data from other researchers indicates that wind's mortality rate is about half that for the occupational mortality rate for coal.
Windmills also are hazardous to wildlife, especially insect eating bats.