Wind Energy

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Live Earth Talk – Nov. 11th,2009

Welcome to our program on the environment.

Live Earth Talk – Nov. 11th, 2009

Wind and the controversies of

Wind Power

Forces important in determining wind speed (and direction):

Pressure gradient force Coriolis force (not important for wind power discussion) Friction


The change in pressure measured across a given distance is called a "pressure gradient".

The pressure gradient results in a net force that is directed from high to low pressure and this force is called the "pressure gradient force".


The closer the isobars or height contours, the greater the PGF magnitude. Larger PGF result in stronger winds, so strong winds are associated with closely spaced contour lines.

PGF points at a right angle to the local isobar or height contour line. It also points from high pressure to low pressure (or high heights to low heights).


FRICTION The surface of the Earth exerts a frictional drag on the air blowing just above it. This friction can act to change the wind's direction and slow it down -- keeping it from blowing as fast as the wind aloft. The difference in terrain conditions directly affects how much friction is exerted.

For example, a calm ocean surface is pretty smooth, so the wind blowing over it does not move up, down, and around any features. By contrast, hills and forests force the wind to slow down and/or change direction much more.


The planetary boundary layer (PBL) the lowest part of the atmosphere its behavior is directly influenced by its contact with the planetary surface it responds to surface forcings in a timescale of an hour or less wind is turbulent and gusty within the PBL surface friction from vegetation and topography causes turbulent eddies and chaotic wind patterns to develop.


Above the PBL, the wind speed is much more uniform and stronger due to a marked decrease in friction Above the PBL the wind is approximately geostrophic (parallel to the isobars)


Above the PBL, the atmosphere is usually non turbulent, or only intermittently turbulent.

The PBL depth varies broadly: • at a given wind speed (i.e. at a given rate of the turbulence production), a PBL in wintertime Arctic could be as shallow as 50 m• a nocturnal PBL in mid-latitudes could be typically 300 m in thickness

• and a tropical PBL in the trade-wind zone could grow to its full theoretical depth of 2000 m.



An 'ideal' location for a wind turbine would have a near constant flow of non-turbulent wind throughout the year and would not suffer too many sudden powerful bursts of wind.


Power produced by a turbine is a function of:

Air densityCross sectional areaCube of the wind velocity

Rough Estimate of Electricity Produced at a site:

Annual Electricity = K Vm3 At T

K = 3.2 a factor depending on the turbineVm = mean wind speed m/sAt = area swept out by turbineT = Number of turbines


http://upload.wikimedia.org/wikipedia/en/b/b1/Windfarm_%2848%29.JPG

An average wind speed value for a given location does not alone indicate the amount of energy a wind turbine could produce there. To assess the climatology of wind speeds at a particular location, a probability distribution function is often fit to the observed data. Different locations will have different wind speed distributions.

Distribution of wind speed (red) and energy (blue) for all of 2002 at the Lee Ranch facility in Colorado. The histogram shows measured data, while the curve is the model distribution for the same average wind speed.

Because so much power is generated by higher wind speed, much of the average power available comes in short bursts. The 2002 Lee Ranch sample is telling; half of the energy available arrived in just 15% of the operating time.

As a general rule, wind generators are practical where the average wind speed is 10 mph (16 km/h or 4.5 m/s) or greater.


http://www.evac.ou.edu

At the end of 2008 the worldwide capacity of all wind turbines was more than 121 gigawatts, which represents around 1.5% of all electricity use in the world.

There is an inherent problem with wind power: It's not always there when you need it

A key issue in the application of wind energy to replace substantial amounts of other electrical production is intermittency


Variability in wind speed can present substantial challenges to incorporating large amounts of wind power into a grid system, since to maintain grid stability, energy supply and demand must remain in balance. While the negative effects of intermittency have to be considered in the economics of power generation, some argue that wind is unlikely to suffer momentary failure of large amounts of generation, which may be a concern with some traditional power plants, due to the distributed nature of generation. However, wind energy can still be a significant source of clean electrical production on a scale comparable to or greater than other technologies (e.g. hydropower)


The prospects for wind power could be greatly enhanced if cost-effective storage could be implemented.

• Some are utilizing new battery technology• A UK professor (Seamus Garvey - Nottingham University) proposes storing energy in flexible containers on the ocean floor• idea is to use Compressed Air Energy Storage (CAES)

• traditionally, CAES stows energy in a large underground reservoir• during peak energy hours, air is released, powering a turbine, which in turn produces electricity• currently only two CAES sites in the world -- in Huntorf, Germany and in McIntosh, Alabama

• Garvey proposes large, reinforced plastic bags at a depth of around 600 meters

• calculates that the bags would be able to store 25 megajoules of energy for every meter cubed• because turbines are typically in relatively shallow water, a series of pipes would be needed to connect turbines to plastic bags at depth

Offshore wind farms of the future – floating turbines?


Cost of wind power:

• Many critics argue that without substantial subsidies or tax credits, wind power is much more expensive than power generated by fossil fuels• Most major forms of electricity generation are capital intensive

• this means that they require substantial investments at project inception • but have low ongoing costs (generally for fuel and maintenance).

• This is particularly true for wind power• Figures for cost of wind energy per unit of production cited in various studies differ substantially.


Wind energy supporters argue that, once external costs and subsidies to other forms of electrical production are accounted for, wind energy is one of the most cost-effective forms of electrical production

• Most forms of energy production create some form of negative externality, i.e., costs that are not paid by the producer or consumer of the good. • For electric production, the most significant externality is pollution, which imposes costs on society in the form of increased health expenses, reduced agricultural productivity, and other problems. • Significantly, carbon dioxide produced when using fossil fuels for electricity production, may impose costs on society in the form of global warming.

• Other significant externalities can include national security expenditures to ensure access to fossil fuels, remediation of polluted sites, destruction of wild habitat, loss of scenery/tourism, etc.


In addition to saving on carbon dioxide emissions, production of energy from wind turbines does not produce sulfur dioxide, mercury, particulates, or any other type of air pollution, as do conventional fossil fuel power sources.

However, during manufacture of the wind turbine, steel, concrete, aluminum and other materials will have to be made and transported using energy-intensive processes, generally using fossil energy sources.


An estimated 2.3 million people worldwide currently work either directly in renewables, or indirectly in supplier industries:

solar thermal industry: at least 624,000 peoplewind power industry ~440,000solar PV industry 170,000biomass and biofuels sector more than 1 millionsmall-scale hydropower 39,000 Geothermal 25,000

Wind industry jobs in the U.S. jumped to 85,000 in 2008 (70% increase from 2007), according to a report released from the American Wind Energy Association.

The U.S. coal industry employs about 81,000 workers. (from a 2007 U.S. Department of Energy report but coal employment has remained steady in recent years though it's down by nearly 50% since 1986.)

Large-scale onshore and near-shore wind energy facilities can be controversial due to aesthetic reasons and impact on the local environment.

• Large-scale offshore wind farms are not visible from land• According to a comprehensive 8-year Danish Offshore Wind study on "Key Environmental Issues“, offshore wind farms have no discernible effect on aquatic species and no effect on migratory bird patterns or mortality rates.

Modern wind farms make use of large towers and blades, occupy large areas, and may be considered unsightly • They usually do not, however, interfere significantly with other uses, such as farming.

• The practice of farmers leasing their land out to companies building wind farms is common.

• In the U.S., farmers may receive annual lease payments of two thousand to five thousand dollars per turbine. • The land can still be used for farming and cattle grazing.

• Less than 1% of the land would be used for foundations and access roads, the other 99% could still be used for farming.


The impact of wind farms on wildlife—particularly migratory birds and bats—is hotly debated, and studies with contradictory conclusions have been published.

Two preliminary conclusions for wind developments seem to be supported: • The impact on wildlife is likely low compared to other forms of human and industrial activity

• studies show that the number of birds killed by wind turbines is negligible compared to the number that die as a result of other human activities such as traffic, hunting, power lines and high-rise buildings and especially the environmental impacts of using non-clean power sources. • For example, in the UK, where there are several hundred turbines, about one bird is killed per turbine per year; 10 million per year are killed by cars alone.• In the United States, onshore and near-shore turbines kill 70,000 birds per year, compared to 57 million killed by cars and 97.5 million killed by collisions with plate glass



• Another study suggests that migrating birds adapt to obstacles; those birds which don't modify their route and continue to fly through a wind farm are capable of avoiding the large offshore windmills, at least in the low-wind non-twilight conditions studied.

• In the UK, the Royal Society for the Protection of Birds (RSPB) concluded that "The available evidence suggests that appropriately positioned wind farms do not pose a significant hazard for birds."

• The study further notes that climate change poses a much more significant threat to wildlife, and therefore supports wind farms and other forms of renewable energy.

• However, negative impacts on certain populations of sensitive species are possible, and efforts to mitigate these effects should be considered in the planning phase. • In particular, the numbers of bats killed by existing onshore and near-shore facilities has troubled even industry personnel.• A study in 2004 estimated that over 2200 bats were killed by 63 onshore turbines in just six weeks at two sites in the eastern U.S.

• This study suggests some onshore and near-shore sites may be particularly hazardous to local bat populations and more research is urgently needed. • Migratory bat species appear to be particularly at risk, especially during key movement periods (spring and more importantly in fall). • Offshore wind sites 10 km or more from shore do not affect bat populations.


Wind Turbines vs. Radar• Large wind turbines have the potential to interfere with both commercial air traffic control and military radar• Wind towers, nacelles, and blades all reflect radar energy• Turbines have high reflectivity that can reduce radar sensitivity• Rotation of wind turbine blades causes Doppler reflections• Wind towers have a large “radar cross sectional area”• Some in U.S. military argue that wind farms add unreasonable national security risk• However, a very small percentage of proposed sites would create a significant hazard (i.e. risks outweigh benefits)•Department of Energy, FAA, and radar manufacturers are working together to develop mitigation strategies

www.windstop.org


Small wind systems

British Wind Energy Association has put together a guide for home wind power:

http://uk.oneworld.net/external/?url=http%3A%2F%2Fwww.bwea.com%2Fpdf%2Fbriefings%2Fsmallsystems.pdf

http://www.awea.org/

http://www.nrel.gov/wind/

Other useful websites on wind power:


Continue the discussion in Ning http://goapes.ning.com

Live Earth Talk - Sept. 9, 2009

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Presentation and Session Recording http://liveearthtalk.wikispaces.com


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Education

Wind Energy