Wind power as an alternative to coal

From Global Energy Monitor
Renewable Energy Solution of the Month - Wind

Wind power is the conversion of wind energy into a useful form of energy, such as using wind turbines to make electricity, wind mills for mechanical power, wind pumps for pumping water or drainage, or sails to propel ships. At the end of 2009, worldwide nameplate capacity of wind-powered generators was 159.2 gigawatts (GW) and energy production was 340 terawatt hour (TWh), or about 2% of worldwide electricity usage.[1]

Between 2000 and 2010, world wind electric generating capacity increased from 17,000 megawatts to nearly 200,000 megawatts, with global wind capacity at 194.4 GW in 2010.[2]

Worldwide Usage

The worldwide use of wind energy is growing rapidly, with several countries having achieved relatively high levels of wind power penetration by 2008, such as 19% of stationary electricity production in Denmark[3], 13% in Portugal and Spain[4], and 7% in Germany and the Republic of Ireland.[5]

In 2008, wind machines in the United States generated a total of 52 billion kilowatthours, about 1.3% of total U.S. electricity generation. The world's largest wind farm, the Horse Hollow Wind Energy Center in Texas, has 421 wind turbines that generate enough electricity to power 220,000 homes per year.[6]

As of May 2009, eighty countries around the world are using wind power on a commercial basis.[7]

In 2010, Denmark ranked highest in terms of share of electricity supplied by wind, with 21 percent. Germany was second with 8 percent, although three north German states get 40 percent or more of their electricity from wind. In Iowa, enough wind turbines came online in the last few years to produce up to 20 percent of that state’s electricity. In terms of volume, the United States leads with 35,000 megawatts of wind generating capacity, followed by China and Germany with 26,000 megawatts each. The state of Texas is the leading generator of electricity from wind, with 9,700 megawatts of wind generating capacity online, an additional 370 megawatts under construction, and more under development. If all of the wind farms projected for 2025 are completed, Texas will have 38,000 megawatts of wind generating capacity — the equivalent of 38 coal-fired power plants, satisfying roughly 90 percent of the current residential electricity needs of the state’s 25 million people.[8]

Wind Energy

The Earth is unevenly heated by the sun, such that the poles receive less energy from the sun than the equator; along with this, dry land heats up (and cools down) more quickly than the seas do. The differential heating drives a global atmospheric convection system reaching from the Earth's surface to the stratosphere, which acts as a virtual ceiling. Most of the energy stored in these wind movements can be found at high altitudes where continuous wind speeds of over 160 km/h (99 mph) occur. Eventually, the wind energy is converted through friction into diffuse heat throughout the Earth's surface and the atmosphere.[6]

Wind Power and Electricity

Wind Turbines

Wind turbines use blades to collect the wind’s kinetic energy. The wind flows over the blades creating lift, like the effect on airplane wings, which causes them to turn. The blades are connected to a drive shaft that turns an electric generator to produce electricity. In a wind farm, individual turbines are interconnected with a medium voltage (often 34.5 kV), power collection system and communications network. At a substation, this medium-voltage electrical current is increased in voltage with a transformer for connection to the high voltage electric power transmission system.[6]

Wind Power and Grids

Small wind turbines can be used to power a single home or business, and may have a capacity of less than 100 kilowatts. Larger, commercial-sized turbines may have a capacity of 5 million watts, or 5 megawatts, and are often grouped together into wind farms that provide power to the electrical grid.[6] The surplus power produced by domestic microgenerators can, in some jurisdictions, be fed into the network and sold to the utility company, producing a retail credit for the microgenerators' owners to offset their energy costs.[9]

Wind power is non-dispatchable, meaning that for economic operation, all of the available output must be taken when it is available. Therefore other resources, such as hydropower and standard load management techniques, must be used to match supply with demand. The intermittency of wind seldom creates problems when using wind power to supply a low proportion of total demand.[10]

Studies suggest the total amount of economically extractable power available from the wind is considerably more than present human power use from all sources.[11] An estimated 72 terawatt (TW) of wind power on the Earth potentially can be commercially viable, compared to about 15 TW average global power consumption from all sources in 2005, although not all the energy of the wind flowing past a given point can be recovered (see Betz' law).[12]

Distribution of wind speed

The strength of wind varies, and an average value for a given location does not alone indicate the amount of energy a wind turbine could produce there. To assess the frequency 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. Making wind power more consistent requires that various existing technologies and methods be extended, in particular the use of stronger inter-regional transmission lines to link widely distributed wind farms. Problems of variability are addressed by grid energy storage, batteries, pumped-storage hydroelectricity and energy demand management.[13]

Energy Capacity Factor

Since wind speed is not constant, a wind farm's annual energy production is a theoretical maxim, called the capacity factor. Unlike fueled generating plants, the capacity factor is determined by the inherent properties of wind. Typical capacity factors are 20–40%, with values at the upper end of the range in particularly favorable sites. For example, a 1 MW turbine with a capacity factor of 35% will not produce 8,760 MW·h in a year (1 × 24 × 365), but only 1 × 0.35 × 24 × 365 = 3,066 MW·h, averaging to 0.35 MW. Online data is available for some locations and the capacity factor can be calculated from the yearly output.[14]

According to a 2007 Stanford University study published in the Journal of Applied Meteorology and Climatology, interconnecting ten or more wind farms can allow an average of 33% of the total energy produced to be used as reliable, baseload electric power, as long as minimum criteria are met for wind speed and turbine height.[15]

In a 2008 study released by the U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy, the capacity factor achieved by the wind turbine fleet is shown to be increasing as the technology improves. The capacity factor achieved by new wind turbines in 2004 and 2005 reached 36%.[16]

Wind Power Density

Wind power density (WPD) is a calculation of the effective power of the wind at a particular location, indicating how much energy is available at the site for conversion by a wind turbine.[17] A map showing the distribution of wind power density is a first step in identifying possible locations for wind turbines. In the United States, the National Renewable Energy Laboratory classifies wind power density into ascending classes. The larger the WPD at a location, the higher it is rated by class. Wind power classes 3 (300–400 W/m2 at 50 m altitude) to 7 (800–2000 W/m2 at 50 m altitude) are generally considered suitable for wind power development. There are 625,000 km2 in the contiguous United States that have class 3 or higher wind resources and which are within 10 km of electric transmission lines. If this area is fully utilized for wind power, it would produce power at the average continuous equivalent rate of 734 GW. For comparison, in 2007 the US consumed electricity at an average rate of 474 GW,[18] from a total generating capacity of 1,088 GW.[19]

Wind Energy Penetration

Wind energy "penetration" refers to the fraction of energy produced by wind compared with the total available generation capacity. There is no generally accepted "maximum" level of wind penetration. The limit for a particular grid will depend on the existing generating plants, pricing mechanisms, capacity for storage or demand management, and other factors. At present, a few grid systems have penetration of wind energy above 5%: Denmark (values over 19%), Spain and Portugal (values over 11%), Germany and the Republic of Ireland (values over 6%). For instance, in the morning hours of November 8, 2009, wind energy produced covered more than half the electricity demand in Spain, setting a new record, and without problems for the network.[20] The Danish grid is heavily interconnected to the European electrical grid, and it has solved grid management problems by exporting almost half of its wind power to Norway. The correlation between electricity export and wind power production is very strong.[21].

Intermittency and penetration limits

Electricity generated from wind power can be highly variable at several different timescales: from hour to hour, daily, and seasonally. Annual variation also exists, but is not as significant. Related to variability is the short-term (hourly or daily) predictability of wind plant output. Like other electricity sources, wind energy must be "scheduled". Pumped-storage hydroelectricity or other forms of grid energy storage can store energy developed by high-wind periods and release it when needed.[22]

In particular geographic regions, peak wind speeds may not coincide with peak demand for electrical power. In the US states of California and Texas, for example, hot days in summer may have low wind speed and high electrical demand due to air conditioning. Some utilities subsidize the purchase of geothermal heat pumps by their customers, to reduce electricity demand during the summer months by making air conditioning up to 70% more efficient.[23]

In the UK, demand for electricity is higher in winter than in summer, and so are wind speeds.[24] Solar power tends to be complementary to wind.[25] On daily to weekly timescales, high pressure areas tend to bring clear skies and low surface winds, whereas low pressure areas tend to be windier and cloudier. On seasonal timescales, solar energy typically peaks in summer, whereas in many areas wind energy is lower in summer and higher in winter.[26] Thus the intermittencies of wind and solar power tend to cancel each other somewhat. A demonstration project at the Massachusetts Maritime Academy showed the effect. The Institute for Solar Energy Supply Technology of the University of Kassel pilot-tested a combined power plant linking solar, wind, biogas and hydrostorage to provide load-following power around the clock, entirely from renewable sources.[27] Three 2009 reports on the wind variability in the UK generally agree that variability of wind needs to be taken into account, but it does not make the grid unmanageable; and the additional costs, which are modest, can be quantified.[28]

U.S. Wind Energy Proposals

Pickens Plan

Texas oilman T. Boone Pickens is the sponsor of a proposed 4,000 megawatt (MW) wind farm in Texas.[29] The Pickens Plan is a proposal put forward by Pickens to undertake a major exansion of wind power in the United States, mainly along the high-wind zone that runs from north to south through the Great Plains states. Pickens asserts that wind could provide 20 percent of U.S. electricity within the next ten years, offsetting natural gas consumption and thereby allowing natural gas to be used as a transportation fuel. The ultimate goal is to reduce U.S. oil imports. [30]

Google "Clean Energy 2030" Proposal

Google's "Clean Energy 2030" outlines a plan for weaning the U.S. off of coal and oil for electricity generation by 2030 (with some remaining use of natural gas as well as nuclear), and cutting oil use for cars by 44%.

To do so, the report recommends onshore and offshore wind could grow from 2008 levels of about 20 gigawatts (GW)[31] to 380 GW, generating 29% of 2030 electricity demand.

To support the feasibility of this increase, the google report points to the US Department of Energy (DOE) study "20% Wind Energy by 2030" that concluded the U.S. could deploy 300 GW of wind by 2030, and an earlier National Renewable Energy Laboratory study "20% Wind Energy by 2030: Increasing Wind Energy’s Contribution to U.S. Electricity Supply" that found up to about 600 GW of wind power by 2030 was feasible. These reports suggest google's target, 380 GW in 2030, is achievable.

The google report sees the biggest challenge as providing adequate transmission capacity to get the power to market. Extrapolating from the DOE study, about 20,000 miles of new transmission capacity would be required to support 300 GW of onshore wind and 80 GW of concentrating solar power generation. About 200,000 miles of high-voltage transmission now exist in the US.

To complement wind usage, google also recommends:

  • increasing solar energy, both photovoltaic (PV) and concentrating solar power (CSP), from 2010 levels of about 1 GW to 250 GW, generating 12% of demand;
  • increasing geothermal energy, both conventional and enhanced geothermal systems (EGS), from 2010 levels of 2.4 GW to 80 GW, generating 15% of demand.

The google report concludes that its proposed increases in wind, solar, and geothermal power, combined with modest projected expansion of other non-fossil energy sources such as nuclear (115 GW), hydro (78 GW), and biomass and municipal waste (23 GW), would meet about 90% of U.S. electricity demand by 2030.

U.S. Wind Energy Projects

First U.S. Offshore Wind Farm Approved

In April 2010, the first U.S. offshore wind farm was approved, spanning 5 miles/8 km off the Massachusetts coast. The 130-turbine, 420-megawatt Cape Wind project will be in Horseshoe Shoal, Nantucket Sound, and will produce enough electricity to power 400,000 houses, or an estimated 75% of the area's electricity needs. The site is tucked between the mainland of the cape and the islands of Martha's Vineyard, an exclusive celebrity vacation destination, and Nantucket.[32]

The turbines, more than 400 feet high, will dot an area of about 24 square miles (62 square km), larger than Manhattan, and be visible low on the horizon from parts of Cape Cod. German conglomerate Siemens AG will provide the turbines. Construction is expected to begin in 2010, and power generation could begin by 2012.[32]

The project got final approval for its operating plans on April 19, 2011, and could start construction as early as fall 2012.[33]

There are other offshore wind projects already proposed for the East Coast and Great Lakes.[32]

Shepherds Flat Wind Farm in Oregon

On April 18, 2011, Google announced it would invest $100 million in the 845-megawatt Shepherds Flat Wind Farm in Oregon. Shepherds Flat, being built near Arlington, Ore., will be the world's largest turbine farm when completed. Other investors in the Oregon wind farm are General Electric, the nation's biggest turbine maker, and Sumitomo Corporation. Shepherds Flat is being developed by Caithness Energy, which has secured a $1.3 billion federal loan guarantee, as well as state incentives. Google's investment arm, Google Ventures, has put in tens of millions in various renewable projects.[34]

Reports Comparing Wind and Coal

Carbon Dioxide Emissions of Wind vs. Carbon Capture

A detailed report from Stanford University, released in December 2008, reviewed and ranked major energy solutions to global warming and energy security. The study showed that coal with carbon capture emits 60 times as much CO2 as wind energy per kilowatt-hour of electricity generated as wind.[35][36]

Costs and Benefits of Wind vs. Mountaintop Removal Mining

A 2008 report by Downstream Strategies "The Long-Term Economic Effects of Wind Versus Mountaintop Removal Coal on Coal River Mountain" examined the costs and benefits of mountaintop removal mining versus development of wind farms at Coal River Mountain in West Virginia. The report found considerable benefits for Raleigh County residents with wind farms. Among the report's findings:

  • When combining local externality costs with local earnings, the mountaintop removal mines actually cost the citizens of Raleigh County more than the income the mines provide, as the negative health effects from coal mining combined with the environmental impacts were costlier than mine earnings.
  • Developing wind resources on Coal River Mountain would provide net positive local economic benefits to the region, particularly when combined with development of a local wind turbine manufacturing industry. Even without considering externalities, the local industry wind scenario would provide more cumulative jobs than the mountaintop removal scenario.
  • Due to limited resources, the economic benefits from mountaintop removal mining would end after 17 years when the mining ends, but the costs would continue due to the health and environmental effects, while the benefits from the wind scenario would continue indefinitely.
  • The wind scenario would generate significantly more local taxes for Raleigh County than the mountaintop removal scenario. Only about $36,000 per year in coal severance taxes would be paid to Raleigh County by mountaintop removal mining on Coal River Mountain as compared to about $1.74 million in local property taxes a wind farm would generate each year. And while the severance taxes end when mining ends, the property taxes from the wind farm will continue into the future.
  • Despite the local economic benefits of pursuing the development of wind, a final decision rests with the landowners and the mining companies that are leasing the land. But there are governmental actions available that could shift the current emphasis on coal production to one that includes wind production, including a change in the regulatory or legal landscape in regard to surface coal mining, having the Governor use executive powers to rescind the Bee Tree Mine and Eagle Mine mining permits and prevent the further mining permits in the area from being approved, and having the state stimulate the creation of green jobs.

Bird death reports

  • Altamont
    • 4,700 bird deaths annually[37]; 10,000 bird deaths annually[38]
    • 576 MW
  • Backbone Mountain[37]
    • 4,000 bats
    • 126 MW
  • Wolf Island EcoPower
    • 1,962 birds and bats in 8 months (i.e. 2,943 annually)
    • 198 MW
  • Big Horn Wind Farm

Estimates of bird deaths from other causes.



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  2. "March 21 News: Wind power surged from 17,000 MW to 194,000 MW in past decade; Google takes on climate science deniers" Climate Progress, March 21, 2011.
  3. "Danish Annual Energy Statistics 2007" (PDF) Danish Energy Authority, October 2008.
  4. "La demanda de energía eléctrica desciende un 4,6% en el 2009" Red Eléctrica de Espana, December 22, 2009
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  9. ["Home-made energy to prop up grid"] The Times, June 22, 2008.
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  12. "Mapping the global wind power resource" University of Delaware College of Earth, Ocean, and Environment, accessed March 2010
  13. Dr Gregor Czisch,"Optimal Solution: 100% Renewable HVDC Supergrid to save our climate" Claverton Energy Research Group, 2008 Conference Paper
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  15. Archer, C. L.; Jacobson, M. Z.,"Supplying Baseload Power and Reducing Transmission Requirements by Interconnecting Wind Farms", Journal of Applied Meteorology and Climatology (American Meteorological Society) 46 (11): 1701–1717 (2007).
  16. "20% Wind Energy by 2030" U.S. Department of Energy Report, May 2008
  17. "Basic Principles of Wind Resource Evaluation" American Wind Energy Association, accessed March 2010.
  18. "Net Generation by Energy Source: Total (All Sectors)", Energy Information Administration (EIA), Dept. of Energy (DOE), accessed March 2010.
  19. "Useful Thermal Output by Energy Source by Combined Heat and Power Producers", Energy Information Administration (EIA), Dept. of Energy (DOE), accessed March 2010.
  20. "Wind power produced more than half the electricity in Spain during the early morning hours" Red Eléctrica de Espana, November 8, 2009.
  21. V.C. Mason, "Wind power in Denmark" Dr V.C. Mason and Country Guardian, December 2008
  22. "Pumped Storage Hydroelectricity" Power Partners Resource Guide, accessed March 2010.
  23. "Geothermal Heat Pumps" Capital Electric Cooperative, accessed March 2010.
  24. David Dixon, Nuclear Engineer "Wind Generation's Performance during the July 2006 California Heat Storm", US DOE, Oakland Operations, August 9, 2006.
  25. Shelby Wood,"Wind + sun join forces at Washington power plan" The Oregonian, January 21, 2008.
  26. "Lake Erie Wind Resource Report, Cleveland Water Crib Monitoring Site, Two-Year Report Executive Summary" (PDF), Green Energy Ohio, January 10, 2008.
  27. "The Combined Power Plant: the first stage in providing 100% power from renewable energy", SolarServer, January 2008.
  28. Jo Abbess,"Wind Energy Variability and Intermittency in the UK : New Reports" Claverton Energy Research Group, August 17, 2009.
  29. "T. Boone Pickens kicking off the world's largest wind farm," Earth2Tech 4/14/08
  30. Pickens Plan website, accessed July 2008
  31. "2nd Quarter 2008 Market Report" American Wind Energy Association, July 2008.
  32. 32.0 32.1 32.2 Katharine Seelye, "U.S. Approves Wind Farm Off Cape Cod" New York Times, April 28, 2010.
  33. Jess Zimmerman, "Cape Wind approved: The U.S. could have offshore wind this year" Grist, April 19, 2011.
  34. Todd Woody, "Google invests $100 million in giant Oregon wind farm" Grist, April 11, 2011.
  35. "Review of solutions to global warming, air pollution, and energy security" Mark Z. Jacobson, Energy and Environmental Science, December 1, 2008.
  36. "How to Fix Global Warming and Gain Energy Security," Rachel's Democracy & Health News #990, December 18, 2008.
  37. 37.0 37.1 John Ritter, Wind turbines taking toll on birds of prey USA Today, January 4, 2005
  38. William M. Welch, Bird deaths present problems at wind farms," USA Today, September 22, 2010
  39. "Study: Wind farms = Bird Killers, DailyTech June 22, 2010

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