*2.2. Drag Factors*

Harnessing energy from renewable sources can have some negative environmental consequences. Indeed, the United Kingdom's Sustainable Development Commission was criticized for its failure to minimise the negative environmental consequences of wind energy such as noise, visual intrusion in sensitive landscapes, and bird strikes. The fair balancing of the advantages and disadvantages of harnessing wind energy in specific situations should be evaluated and after which wind energy should be utilised [15]. Wind farms also have a poor reputation; for example, it was reported that 40,000 birds in a year ran into wind turbine blades in the United States [16]. The modern type of wind turbine whose height is 125 m is almost as high as the London Eye, whose height is 135 m. After 16 years of litigation, relentless opposition from industrialists, and financial and political setbacks made a plan to build a wind farm in Cape Cod, Massachusetts, fail. The wind farm could have provided clean energy to 200,000 homes on Cape Cod and would have helped develop wind farms to nearby regions [17]. Financial viability also affects the development of wind energy, as, for example, the credit crunch drastically affected wind-energy projects in the United States during the Global Financial Crisis in 2008 [18].

In addition, the large-scale deployment of wind turbines appears to reduce wind speed and, in turn, lower turbine efficiency. The reduced wind speed eventually leads to set low generation limits [19].

Wind energy, especially onshore wind, is a mature technology that has achieved a certain level of reliability. However, the reliability, or load factor, is affected negatively by the age of the wind turbines. In the United Kingdom, the normalised load factor declined from about 24 percent during peak (i.e., age 1 year) to 15 percent at age 10 years, and 11 percent at age 15 years. The normalised load factor for Danish wind farms showed a similar decline—from 22 percent at age 1 year to 18 percent at age 15 years. Offshore Danish wind farms exhibited huge declines in their normalised load factors—from 39 percent at their peak to 15 percent at age 10 years [20].
