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RERL Fact Sheet 1, Community Wind Technology Renewable Energy Research Laboratory, University of Massachusetts at Amherst Wind Power: Wind Technology Today Community Wind Power on the Community Scale Wind Power Fact Sheet # 1 RERL—MTC Community Wind Wind Power Technology for Fact Sheet Series Communities In collaboration with the Mas- sachusetts Technology Col- This introduction to wind power technology is We also recommend a visit to a modern wind laborative’s Renewable Energy meant to help communities begin considering or power installation – it will answer many of your Trust Fund, the Renewable planning wind power. It focuses on commercial initial questions, including size, noise levels, foot- Energy Research Lab (RERL) and medium-scale wind turbine technology avail- print, and local impact. Some possible field trips able in the United States. are listed on the back page. brings you this series of fact sheets about Wind Power on the community scale: Wind Power Today 1. Technology 2. Performance Wind power is a growing industry, and the technol- 3. Impacts & Issues ogy has changed considerably in recent decades. 4. Siting What would a typical commercial-scale* turbine 5. Resource Assessment installed today look like? 6. Wind Data • Design - 3 blades 7. Permitting - Tubular tower The focus of this series of fact • Hub-height - 164 - 262 ft (50 - 80 m) sheets is medium- • Diameter: - 154 - 262 ft (47 - 80 m) and commercial- • Power ratings available in the US: scale wind. - 660 kW - 1.8 MW * Other scales are discussed below. A wind turbine’s height is usually described as the height of the center of the rotor, or hub. Inside this Edition: Technology Size Ranges What do we mean here when we say “community-scale wind power”? Introduction p. 1 Windpower can be divided into three size ranges, • Diameter: 13 - 30 m (43 - 100 ft) Wind Power Today p. 1 which are used for different applications. The focus • Height: 35 - 50 m (115 - 164 ft) of this series of fact sheets is medium and commer- • Example: 597,000 kWh/year cial-scale wind power. The size is chosen differ- Size ranges p. 1 Commercial scale: 500 kW - 2 MW ently depending on the turbine’s purpose. Typical • Usually fed into the grid, not sized to a single Vocabulary p. 2 sizes in the three ranges available in the US are: Residential: below 30 kW load • Diameter: 47 - 90 m (155 - 300 ft) Power & Energy p. 3 • Choose a size based on electrical load • Diameter: 1 - 13 m (4 - 43 ft) • Height: 50 - 80 m (164 - 262 ft) Sources for Teachers & p. 4 • Height: 18 - 37 m (60 - 120 ft) • Example: 4,300,000 kWh/year For comparison, an average Massachusetts house- Kids • Example: 21,000 kWh/year hold uses 7,200 kWh/year Nearby Wind p. 4 Medium: 30 - 500 kW Example annual production is for comparison only. Based on sea- Installations • May be sized to a load. Typically used when level mean winds of 7m/s (15.6 mph); manufacturer’s data for the For More Info p. 4 there is a large electrical load. following turbines: Residential: Bergey XL-S (7.5kW); Medium: Fuhrländer FL 250 (250 kW); Commercial: GE 1.5 SL (1500 kW) . Page 2 Community Wind Power Fact Sheet #1 The Vocabulary of Wind Power Turbine: a turbine is a device that converts the Up-wind turbines: Modern commercial tur- kinetic energy of a moving fluid into rota- bines yaw themselves so the rotor is facing tional energy (engineers call both liquids and into the wind, i.e. upwind of the tower. gases “fluids” – i.e. things that flow). A Cut-in speed: the wind speed at which a wind wind turbine’s blades use aerodynamic lift turbine begins to generate electricity. Typi- and drag to capture some of the wind’s en- cally 4 m/s (9 mph) for commercial wind ergy and turn the generator’s shaft. turbines. The main parts of a typical wind turbine are: Cut-out wind speed: the - Rotor: a wind tur- high wind speed at which bine’s blades and the turbine must shut the hub to which down and turn perpen- they attach form dicular to the wind to the rotor. protect itself from being - Nacelle: the frame overpowered. Typically and housing at the 25 m/s (56 mph) top of the tower. It Variable-speed turbines: protects the gear- Some turbines incorpo- box and the gen- rate power electronics erator from that allow them to opti- weather, and helps mize their power output control the me- by varying their speed, chanical noise for instance, from 10 to level. 20 rpm. Other types vary -Tower: a steel struc- their speed little or not at ture, typically all. tubular, with a Variable blade pitch: ladder up the in- many turbines can change side for mainte- the angle of their blades nance access. to optimize performance. -Base or foundation: Horizontal axis: All com- made of concrete mercial-scale turbines reinforced with today have the rotor turn steel bars. Typi- around a horizontal axis. cally either a shal- Historically, vertical axis low flat disk or a turbines have been tested, deeper cylinder. such as the “Darrieus” egg-beater design, but have not been as efficient Diagram courtesyofJames Rowe Other useful terms are: or able to survive high winds. Yaw: commercial-scale turbines have a motor Penetration: The amount of wind energy in a to yaw, or turn the rotor to face into the given area of the grid, as a percentage of wind. At high wind-speeds, they yaw out of total production. In the US, wind penetration the wind to protect themselves. is under 1%. Northern Germany and parts of Denmark have penetrations of around 20% (2003 figures). Renewable Energy Research Laboratory, University of Massachusetts at Amherst Wind Technology Today Page 3 The Power & Energy in Wind The Power in Wind The Power from a Wind Turbine The first law of thermodynamics tells us that The power a turbine actually gets from the energy can neither be created nor destroyed, wind is: Energy but it can change forms. Anything that is in 3 P = Cp ½ U A motion – such as moving air – contains a form is the ability to change one- You can see that we have added two things to of energy we refer self or one's surroundings to as kinetic en- the original equation of the power in the wind: ergy. Slowing air Cp = the turbine’s power coefficient down reduces its = eta = the turbine’s mechanical & elec- kinetic energy and trical efficiencies. that energy has to go somewhere. Cp must be less than the Betz limit. In practice, Power Wind turbines it varies with wind speed, turbulence and oper- slow wind down and convert some of the en- ating characteristics; for example it could be is a rate of using or produc- ergy to mechanical and electrical energy. around 44% for a commercial-scale turbine, in ing energy. winds of 10 m/s. A typical overall efficiency, Kinetic energy is: , would be in the range of 90%. Power = energy / time 2 KE = ½ mU To estimate the power output of a given com- where m stands for mass (in kg) and U stands mercial turbine, we do not have to use the for velocity (in m/s). This allows us to calcu- power equation; rather we use power curves supplied by the manufacturer. late the amount of power in moving air. The Units of Measure power of the wind passing perpendicularly Wind Turbine Power Curve through a circular area is: 1,600 1,400 A kilowatt-hour (kWh) is a 3 P = ½ U A 1,200 unit of Energy 1,000 Where: 800 A kilowatt (kW) is a unit of P = the power of the wind (in Watts). 600 Power. So are watts, mega- Power (kW) Power 400 3 watts, and horsepower. = rho = the density of the air (in kg/m ) 200 (1.225 kg/m3 for dry air at sea level) - 0 5 10 15 20 25 30 U = the velocity of the wind measured in m/s Wind Speed (m/s) A = r2 = the area swept by the circular rotor, in square meters, and What does the power equation tell us? = pi = 3.1416... Even though we do not use the power equation r = the radius (half the diameter) of the to calculate power output of a particular tur- rotor (in meters) bine, the power equation tells us useful infor- mation about significant factors that determine Betz’s Limit on what we can extract what we can get from a wind turbine: A wind turbine slows air down, but it cannot U3 : The power available in the wind is propor- remove 100% of the air’s kinetic energy – tional to the cube of the wind speed. There obviously the air cannot stop completely, or is much more energy in high-speed winds else it would pile up behind the turbine. In than in slow winds. 1919 German physicist Albert Betz figured A : Power is proportional to the swept area, out that the upper limit to the amount of en- and to the square of the diameter. Dou- ergy you can capture from the wind is 16/27 bling the diameter quadruples the avail- or about 59%. In practice, all real wind tur- able power. bines extract less than this hypothetical maxi- mum. : Air density matters too. The lower density of warmer air, and air at higher altitudes somewhat reduces the power available in the wind. Renewable Energy Research Laboratory, University of Massachusetts at Amherst Page 4 Community Wind Power Fact Sheet #1 Renewable Sources for Teachers & Kids Energy Research Spirit Lake, Iowa, has 2 wind turbines on their Scholastic books offers wind energy activities for Laboratory school grounds.
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