# Wind energy

Wind energy is a form of solar energy.[1] Wind energy (or wind power) describes the process by which wind is used to generate electricity. Wind turbines convert the kinetic energy in the wind into mechanical power. A generator can convert mechanical power into electricity[2]. Mechanical power can also be utilized directly for specific tasks such as pumping water. The US DOE developed a short wind power animation that provides an overview of how a wind turbine works and describes the wind resources in the United States.

## Wind Energy Basics

Wind is caused by the uneven heating of the atmosphere by the sun, variations in the earth's surface, and rotation of the earth. Mountains, bodies of water, and vegetation all influence wind flow patterns[2], [3]. Wind turbines convert the energy in wind to electricity by rotating propeller-like blades around a rotor. The rotor turns the drive shaft, which turns an electric generator. Three key factors affect the amount of energy a turbine can harness from the wind: wind speed, air density, and swept area.[4]

### Equation for Wind Power

$P = {1\over2} \rho A V^3$

• Wind speed
The amount of energy in the wind varies with the cube of the wind speed, in other words, if the wind speed doubles, there is eight times more energy in the wind ($2^3 = 2 x 2 x 2 = 8$). Small changes in wind speed have a large impact on the amount of power available in the wind [5].
• Density of the air
The more dense the air, the more energy received by the turbine. Air density varies with elevation and temperature. Air is less dense at higher elevations than at sea level, and warm air is less dense than cold air. All else being equal, turbines will produce more power at lower elevations and in locations with cooler average temperatures[5].
• Swept area of the turbine
The larger the swept area (the size of the area through which the rotor spins), the more power the turbine can capture from the wind. Since swept area is $A = pi r^2$, where r = radius of the rotor, a small increase in blade length results in a larger increase in the power available to the turbine[5].

## DOE Wind Programs and Information

• DOE's Wind Energy Technologies Office works to improve the performance, lower the costs, and accelerate the deployment of innovative wind and water power technologies. Greater use of the nation's abundant wind and water resources for electric power generation will help stabilize energy costs, enhance energy security, and improve our environment[6].
• WINDExchange is a nationwide initiative designed to increase the use of wind energy across the United States by working with regional stakeholders. The WINDExchange program illustrates the Department of Energy's commitment to dramatically increase the use of wind energy in the United States. The WINDExchange website provides a wide range of wind-related information, including: State-by-state breakdowns of wind resource potential, success stories, installed wind capacity, news, events, and other resources, which are updated regularly[7].
• The National Wind Technology Center (NWTC) is the nation's premier wind energy technology research facility. The goal of the research conducted at NWTC is to help industry reduce the cost of energy so that wind can compete with traditional energy sources, providing a clean, renewable alternative for our nation's energy needs.

## Worldwide Installed Capacity

Country Total Capacity, end of 2014 (MW)[8] Total Capacity, June 2010 (MW)[9] Total Capacity, end of 2009 (MW)[10]
U.S. 65,900 36,300 35,159
China 114,600 33,800 25,853
Germany 40,000 26,400 25,813
Spain 23,000 19,500 18,748
India 22,500 12,100 10,827
France 9,300 5,000 4,775
U.K 12,200 4,600 4,340
Portugal 4,953 3,800 3,474
Denmark 4,883 3,700 3,408

### United States Installed Capacity

In the U.S., installed wind energy capacity has advanced significantly over the past ten years. As of the third quarter of 2017, the U.S. now has an installed wind capacity of 84,944 MW with over 29,634 MW of wind currently under construction or in advanced development—a 27% year-over-year increase, the highest since the American Wind Energy Association began tracking the categories.[11].

## Wind Farm Development

Siting a wind farm varies from one location to another, but there are some important matters for land owners to consider:[12]

1. Understand your wind resource
2. Evaluate distance from existing transmission lines
3. Determine benefits of and barriers to allowing your land to be developed
5. Identify reliable power purchaser or market
6. Address siting and project feasibility considerations
7. Understand wind energy’s economics
8. Obtain zoning and permitting expertise
9. Establish dialogue with turbine manufacturers and project developers
10. Secure agreement to meet O&M needs

## Necessary Services to Avail

Wind power project or WPP involves development through own resources and manpower or by availing the technical services from consultant organisations:[13]

1. SITE IDENTIFICATION: The process starts with regional overviews and precision GIS mapping, through which the specific opportunities are determined at a feasible site. This also involves mapping of project boundaries, turbine micro-siting and optimisation.
2. WIND RESOURCE ASSESSMENT: Accurate Wind Resource Assessment of a widely variable resource is the most critical feature for success of a WPP. Meso-Scale and then Micro-Scale Wind Power Density/Wind Speed Map is produced for the site location through input of accurate contour/terrain data. Ideal spot is selected to install Anemometry System. The recorded wind data is critically analyzed and formatted to represent wind characteristics. A preliminary wind resource assessment can be carried out by using the freely available Global Wind Atlas.
3. MICRO-SITING & ENERGY ESTIMATION: This constitutes the foundation of a Wind Power Project. Wind Resource data is formatted in terms of Speed and direction. The characteristic power of selected Wind Electric Generator (WEG) is formatted. Detailed Contour data at close interval is prepared indicating roughness and terrain features. WEG layout is optimised and Micro-siting Map is prepared using software and then estimated is energy generation.
4. DETAILED PROJECT REPORT: Once the site, make and rating of WEG and the selling option are finalized, detailed survey and field study is conducted. Comprehensive layout design is prepared with optimization of generation along with detailed design for approach road and grid evacuation. Detailed costing and financial analysis is carried out to establish overall viability.
5. PROJECT MANAGEMENT: Implementation and Management of Wind power project, WPP, calls for Multi-disciplinary activities related to Technical, Financial and Commercial aspects. Not only quality of works needs to be checked, it is equally important to ensure close co-ordination and monitoring for timely commissioning.
6. MONITORING: Energy generation with respect to wind resource, frequency and type of machine and system failures needs to be critically monitored and analyzed to optimize generation. Income from WPP can be optimized only if break down and failure of WEG and evacuation system is avoided particularly during the limited high wind months.
7. PERFORMANCE IMPROVEMENT: For the existing Wind Power projects also there is often need to ensure its performance improvement, which goes down with time. Critical analysis of monitoring reports along with on-site observations and in depth study immensely help in performance improvement through reduction in break-down time and interval losses. Due to seasonal availability of wind resource, generation increasing in cubic proportion of wind speed and overall low Plant Load Factor, parameter setting and operational/control logic needs to be site specific.
8. LENDER'S ENGINEERS: To meet the need of expert engineers to serve a project especially for a definite term or contract, where the task may not be managed with the available resources, the clients are provided Lenders Engineer’s services as per the requirements assessed mutually with the client. This involves serving through deputing or appointing suitable personnel and thus meeting the need of the project at a given point of time of various technical types.

## Land Requirements

The amount of land required for a wind farm varies considerably, and is particularly dependent on two key factors: the desired size of the wind farm (which can be defined either by installed capacity or the number of turbines) and the characteristics of the local terrain[14]. Typically, wind turbine spacing is determined by the rotor diameter and local wind conditions. Some estimates suggest spacing turbines between 5 and 10 rotor diameters apart. If prevailing winds are generally from the same direction, turbines may be installed 3 or 4 rotor diameters apart (in the direction perpendicular to the prevailing winds); under multi-directional wind conditions, spacing of between 5 and 7 rotor diameters is recommended[14].