Evidence shows that wind energy propelled boats on the Nile River as early as 5000 B.C. In China, simple windmills pumped water several centuries B.C. Millions of windmills were built in the United States as part of the development of the American West during the late 19th century. Most of the windmills pumped water for farms and ranches. The use of wind energy continued into the early 20th century with the development of small electric wind systems used to generate direct electric current. In the 1930s, grid power was extended to rural areas and replaced the small wind systems. Some farms and ranches still use windmills to pump water today.

The process by which the wind is turned into mechanical power or electricity is called "wind energy" or "wind power." Wind turbines are used to convert the wind's energy into mechanical power. That mechanical power can then be used for specific tasks (such as pumping water), or converted by a generator into electricity that powers homes, businesses, schools, etc.

Wind occurs as a result of the sun's uneven heating of the atmosphere over the earth's irregular surface, combined with the rotation of the earth. The shape of the earth's surface, as well as vegetation, and bodies of water, affect wind flow patterns. These wind flows can be collected by wind turbines and used to generate electricity.

The wind turns propeller blades on wind turbines, which power a generator that converts the motion to electric current. Modern wind technology takes advantage of recent advancements in materials, engineering, electronics, and aerodynamics development. Wind farms contain several turbines grouped together to create a single power plant that generates bulk electrical power. This electricity is transferred into the local utility grid and distributed to customers in the same way as energy generated by conventional power plants. 1

Clean, renewable forms of energy, such as wind power, are essential if we are to tackle climate change. They are also vital in ending the threat of nuclear power, which would leave a legacy of nuclear waste that will remain a threat to our health and the environment for hundreds of thousands of years.

It's clean. Wind power does not produce dangerous waste, nor does it contribute to global warming.

• It's abundant and reliable. The UK is the windiest country in Europe and the resource is much greater during the colder months of the year, when energy demand is at its highest. Wind power, in combination with a full range of renewable energy technologies, such as wave and solar, could meet all of our electricity needs. Technology is being developed to store wind power as hydrogen which can then be used to power fuel cells in power stations and in vehicles.
• It's affordable. The first offshore wind turbines in the UK are producing power more cheaply than our newest nuclear power station. The UK Government's figures show that all wind power will be cheaper than nuclear power by 2020.
• It works. Denmark already gets 20% of its electricity from wind power.
• It creates jobs. The wind industry could bring thousands of new jobs to the UK, many of them using offshore engineering skills used by the declining oil and gas industry. If offshore wind were developed to supply just 10% of the UK's electricity, then 36,000 jobs could be created.
• It's safe. Unlike nuclear power stations, wind turbines are unlikely terrorist targets.
• It's popular. Wind energy is one of the most popular energy technologies. Opinion surveys regularly show that just over eight out of ten people are in favour of wind energy, and less than one in ten (around 5%) are against it. 2

The biggest challenge to using wind energy as a source of electrical power is that the wind doesn't always blow when electricity is needed. Wind can't be stored, and not all wind can be used to generate electricity. Also, good sites for wind farms are often in remote locations that are far from cities, the typical areas of electricity demand. In addition, wind farms may compete with other land uses that may be seen as more valuable. However, wind turbines can be located on land that is also used for livestock grazing, or even farming. Other environmental issues include noise, visual, cultural land use, and fauna impacts.

Tidal

The world’s first commercial energy wave farm is being constructed off the shores of Portugal. This technology generates renewable electricity from ocean waves, using both tidal turbines and sails to capture the force of the tide, and may prove to be a valuable energy source for the 21st century. 3

Tides are caused by the gravitational attraction of the moon and the sun acting upon the oceans of the rotating earth. The relative motions of these bodies cause the surface of the oceans to be raised and lowered periodically, according to a number of interacting cycles. These include:

• a half day cycle, due to the rotation of the earth within the gravitational field of the moon
• a 14 day cycle, resulting from the gravitational field of the moon combining with that of the sun to give alternating spring (maximum) and neap (minimum) tides
• a half year cycle, due to the inclination of the moon's orbit to that of the earth, giving rise to maxima in the spring tides in March and September
• other cycles, such as those over 19 years and 1 600 years, arising from further complex gravitational interactions.

The range of a spring tide is commonly about twice that of a neap tide, whereas the longer period cycles impose smaller perturbations. In the open ocean, the maximum amplitude of the tides is about one metre. Tidal amplitudes are increased substantially towards the coast, particularly in estuaries. This is mainly caused by shelving of the sea bed and funnelling of the water by estuaries. In some cases the tidal range can be further amplified by reflection of the tidal wave by the coastline or resonance. This is a special effect that occurs in long, trumpet-shaped estuaries, when the length of the estuary is close to one quarter of the tidal wave length. These effects combine to give a mean spring tidal range of over 11 m in the Severn Estuary (UK). As a result of these various factors, the tidal range can vary substantially between different points on a coastline.

The amount of energy obtainable from a tidal energy scheme therefore varies with location and time. Output changes as the tide ebbs and floods each day; it can also vary by a factor of about four over a spring-neap cycle. Tidal energy is, however, highly predictable in both amount and timing.

The available energy is approximately proportional to the square of the tidal range. Extraction of energy from the tides is considered to be practical only at those sites where the energy is concentrated in the form of large tides and the geography provides suitable sites for tidal plant construction. Such sites are not commonplace but a considerable number have been identified in the UK, France, eastern Canada, the Pacific coast of Russia, Korea, China, Mexico and Chile. Other sites have been identified along the Patagonian coast of Argentina, Western Australia and western India.

Tidal energy can also be exploited directly from marine currents induced by the combined lunar and solar gravitational forces responsible for tides. These forces cause semi-diurnal movement in water in shallow seas, particularly where coastal morphology creates natural constrictions, for example around headlands or between islands. This phenomenon produces strong currents, or tidal streams, which are prevalent around the British Isles and many other parts of the world where there are similar conditions. These currents are particularly prevalent where there is a time difference in tidal cycles between two sections of coastal sea. The flow is cyclical, increasing in velocity and then decreasing before switching to the opposite direction. The kinetic energy within these currents could be converted to electricity, by placing free standing turbo-generating equipment in offshore areas. 4

Denmark leads the world in wind power – over 20 per cent of electricity consumption in this western, developed nation is covered by energy from wind turbines. This is the equivalent of 1.4 million Danish homes. Fiscally, the wind industry brings 3 billion euro a year to the Danish economy and employs over 20,000 people. 5

Notes

1. BBC News website, wind power, http://www.bbc.co.uk/climate/adaptation/wind_power.shtml
2. Yes2Wind For a Clean Energy Future, Why Wind?, http://www.yes2wind.com/whywind.html
3. P. Brown, ‘Global Warning: The last chance for change,’ Dakini Books NP (2006) p.308
4. World Energy Council, Tidal Energy,
http://www.worldenergy.org/wec-geis/publications/reports/ser/tide/tide.asp
5. P. Brown, ‘Global Warning: The last chance for change,’ Dakini Books NP (2006) p.30