Wind energy is non-polluting by nature. However, it does have some negative impacts on the environment. Wind farms consisting of hundreds of turbines take up significant amounts of land, and some people feel that these farms are eyesores. There are also issues around noise and "shadow flicker
" in the proximity of the turbines . However, the biggest environmental issue associated with wind turbines is risk to birds
from the moving blades.
The Altamont Pass Wind Farm
near San Francisco, California, developed in the 1980s, began a huge environmental outcry against wind farms and gave wind farms a bad reputation. At least 22,000 birds, including some 400 golden eagles, were found to have collided with wind turbines (or been electrocuted by power lines) there. The problem was that no one performed a migratory bird study before the 5,400-turbine facility was built. Such a study, required today, would have shown that the Altamont Pass is an important migration route and wintering area for raptors.
Modern turbines, with slower rotating blades, coupled with better locations for wind farms have been very successful in reducing bird fatalities. In the early 2000's, when the Altamont wind farm needed to renew its operating permits, the owners, utilities and environmentalists got together and spent two years negotiating a mutually acceptable solution
. This included shutting down the turbines during the winter migration (November - February) and permanently decommissioning the highest risk turbines, which were about 15% of the total. In 2006 the Buena Vista Wind Energy Project at Altamont replaced 179 turbines with 38 taller ones, avoiding ridge saddles between hills and other hotspots for raptor traffic. Since then, golden eagle fatalities at Buena Vista have dropped by 50% and other raptor deaths by 75%.
Following these initial changes, the various owners of the Altamont Pass Wind Farm have continued to make significant changes that have addressed its historical problem with bird fatalities. This includes shutting down older turbines and replacing turbines, with one new turbine replacing about 15 old ones while producing the same amount of power. Figure 1 illustrates the change in visual appearance after repowering.
These and other efforts around the world to make turbines safer for birds seem to be working. A 2003 study of 4,700 turbines located outside California found an average of 2.3 birds per year killed per turbine. That's a tiny number compared with the more than 4 million birds that collide annually with communication towers. In fact, bird fatalities from wind turbines are significantly lower than many human related "bird killers", as documented by the US Fish & Wildlife Service
and illustrated in Figure 2. Yet, there are still concerns that a number of particularly vulnerable groups, such as raptors, which are slow to reproduce and favor the wind corridors that are best suited for wind farms, are particularly vulnerable to getting killed by wind turbines.
The Royal Society for the Protection of Birds perhaps best sums up the situation with avian deaths from wind turbines when it says that it supports wind power
- not because windfarms pose a lower risk to birds than other energy sources - but because in its view climate change poses the "single greatest long-term threat" to bird species.