Wind energy is another form of solar. The sun causes uneven heating across the earth’s surface, creating convection currents and pressure differences which result in air molecules flowing from high to low pressure regions. This is complicated by the earth’s rotation and the need to conserve angular momentum in the earth /ocean/atmosphere system. Add in the resultant Coriolis force and differences between upper and lower atmosphere and we get a very complex system dominated by westerlies and clockwise and anticlockwise moving highs and lows.
We collect a part of this energy by erecting windmills and converting the kinetic energy into electrical energy. Windmills can be onshore or offshore and either large scale (windfarms) or small scale home systems. It would appear to be a no brainer to collect as much of this energy as we can, using environmentally friendly methods, enduring materials and to levels that do not affect land use and weather patterns.
World wide wind generation has been increasing exponentially (a straight line on a log scale) going from 30 TWh (1 Terra Watt hour = 3600 Terra Joules) in 2000 to 520 TWh in 2012. It is currently at about 4% of worldwide electricity use (1.6% of total energy use). The largest wind farm in the world is the Gansu Wind farm in China generating 6000 MW from several thousand turbines. The next largest is the 1500 MW wind farm at Muppandal in India. Australia’s largest is the 420 MW plant at Macarthur in Victoria, closely followed by the South Australian Snowtown and Hallet Wind farms at 369 and 350 MW capacity. If the Ceres project on Yorke Peninsula proceeds it will be Australia’s largest at 600 MW.
Every 1000 MW (1GW) of wind energy has been calculated at approximately 4 MT (Million Tonnes) of CO2 that is not put into the atmosphere (compared to a standard coal fired system). As wind is not a consistent supply, it can be argued that coal or gas fired systems are still required as backup however. The cost of wind power is also caught up in this conundrum as it is often sold as the flexible portion of the energy requirement with coal (currently cheapest) as supplying the baseload.
The argument for:
Wind is an obvious renewable energy with low GHG output and as such should be promoted wherever possible. It also has the possibility of community involvement, earning money for local businesses and employment opportunities near wind farms and by owning smaller scale systems. In the Scandinavian countries it is common for local communities to form co-operatives to put in their own turbines.
All power supply systems require government support in their startup phases. Wind energy is no different and benefits from funding, low carbon legislation and local electricity infrastructure. Wind also benefits from a strong solar (and or hydro) business developed in association as the highs and lows of wind can be flattened out. It also requires a hydrocarbon backup power supply with the current technology, although this may be eventually be replaced by battery or other similar storage systems. The cleanest hydrocarbon support is natural gas (methane).
The argument against:
There are many anti arguments although they all seem somewhat contrived. Wind farms exist comfortably with most farming systems, have little environmental affect and are generally viewed as pleasant. They are even seen as tourist attractions. On the other hand some people find them an eyesore (visual pollution), creating industrial noise in rural landscapes and killing local and migrating birds.
There are also issues of rare earth requirements to make an efficient turbine and possible changes to local and global weather patterns.
General noise from modern windmills is minimal, said to be less than that made by a fridge at about 300m. Further technology enhancements are lowering this even further, particularly with blade length and design (from studies of owls flying with near zero noise).
Low frequency noise (infrasound) is the biggest problem but has proved to be the hardest to understand and study. Infrasound is defined as less than 20 hertz and is more felt than heard. Think of a subwoofer pulsing. It can make some people feel nauseous. High frequency sounds do not carry far but low frequencies do not dissipate their energy as easily. Some animals, including whales and elephants use infrasound for communication over very long distances (hundreds of kilometres in water and about 6 km on land).
Infrasound is produced naturally by surf, earthquakes, avalanches, tsunamis, weather events, iceberg calving etc. It is also created by humans from sonic booms, explosions, diesel engines, loud speakers and turbines. Some animals appear to respond to infrasound as part of an impending natural disaster (eg earthquakes).
Various experiments have shown that low frequency sound can cause a myriad of effects including anxiety, uneasiness, nervous fear, revulsion, chills down the spine and feelings of pressure. The resonant frequency of human eyeballs is about 18 hz and sounds at that frequency may cause odd sensations and ghost like sightings!
So it would appear that infrasound, even over large distances can cause humans and animals, anxiety and other related health effects. Some people are disturbed by surf noise, diesel engines, subwoofers and most likely wind turbines. Wind farm businesses need to take the problem seriously and do all they can to combat it. Noise cancelling equipment may also offer a solution for some.
Many environmental issues have been suggested by wind farm opponents. In general these have proved unfounded. A simple walk around a windfarm will show that there are no dead birds lying around and that farm animals generally ignore them. They do not appear to feel them as a natural disaster approaching!
Farmers can plant crops around them, they can be turned off in emergencies or during crop dusting activities (rare these days) and generally take up less good farmland than roads or golf courses. Most of the world seem to like the look of windfarms with only a few seeing them as visual pollution. They are less visually ( or otherwise) polluting than coal mines or fossil fuel power stations.
Rare earth magnets are the strongest permanent magnets that we currently have, and as such provide the most efficient method of building a turbine to create electrical energy from mechanical energy. Moving a wire between two poles of a magnet creates a current (Faraday’s Law). The better the magnet, the greater the conversion of mechanical to electrical energy.
A generator is essentially the opposite to an electric motor which also requires the best permanent magnets for the best efficiencies. With the growing businesses of wind power and electric vehicles the need for rare earth magnets is increasing drastically. Most batteries are Samarium – Cobalt or Neodymium – Iron-Boron with large amounts of Dysprosium also required for batteries that work at all required temperatures.
Exploring for, discovering, mining and processing these elements is a massive task and is potentially highly polluting. The toxic lake of waste material at Baotou, Mongolia (China) is testament to this. Rare earths are part of the lanthanide and actinide series of elements and require significant processing with acids to purify them. Remaining products can be radioactive and toxic. A quick look at Baotou on the internet will shock you!
Not all wind generators use rare earths in their turbines. They are very expensive. In South Australia, apparently only a few do.
A single wind turbine taking energy from the wind can be shown to affect the speed of rotation of the earth. While the effect is minimal, the effect of millions of turbines may not be. There is likely to be an upper limit to the number of turbines that can be used before the effects are measurable. Currently it is thought that slowing the earth’s rotation will add a heating effect.
While the effect is not a problem currently, more work needs to be done to ascertain the limits to wind generation. With the UK and others moving to offshore wind generation there may be a large scale increase in the number of turbines and perhaps a measurable effect!