Lecture 21 Chapter 12 Wind Energy

Outline History of wind power –Grinding wheat –Pumping water –Generating electricity Wind power for electricity –Fundamental principles –Horizontal axis (vertical blades) –Vertical axis (horizontal blades) Wind power used –World –U.S. Advantages & Disadvantages

History of Wind Power - World Indications that Babylon (now Middle East) and China had windmills around 1800 BC –Pumped water –Ground wheat Introduced into Europe around 12 th Century AD (1100 – 1199 AD) –Windmills in 1750 AD  Holland had 8,000  England had 10,000 –Use decreased with invention of steam engine

History of Wind Power - US Many windmills used in US to pump water on farms (still even today) 1000’s of windmills 1930’s and 1940’s produced 2-3 kW of electricity for remote farms (This decreased when government encouraged electrification through electrical wires from grid) Large 1.2 MW windmill operated at Grandpa’s Knob near Burlington, VT in 1940 –Very costly to build because not mass produced

Fig a, p. 408 Fig b, p. 408

History of Wind Power - US Windmill at Grandpa’s Knob –Had ft diameter blades weighing 8 tons each –Due to metal fatigue one blade broke, flying several hundred yards, never to operate again –Oil prices fell (oil found in Middle East); interest decreased in wind power

History of Wind Power - US Reemphasized after 1973 oil crisis –100 kW windmill built near Sandusky, OH in 1975 Designed for 18 mph winds –New blades are carbon fiber and fiberglass Lighter More durable 100 kW windmill Sandusky, OH 1975

History of Wind Power - US Public Utilities Regulatory Act (PURPA 1978) required utilities to purchase energy from qualified sources (such as wind)PURPA –Energy from wind increased dramatically in early 1980’s –Interest decreased in late 1980’s and early 1990’s Low oil prices Incentives from PURPA expired Significant growth in US in late 1990’s –15% growth in 1998 –38% growth in ,000 wind turbines in US each making 100 – 200 kW –90% in CA –73% of wind power (electricity) in US made in CA

Maximum power extracted from the wind is proportional to: –Cube of wind velocity (velocity 3 ) –Circular area covered (swept) by blades Power proportional to velocity 3 because: –Kinetic energy = ½ * *velocity 2 –m = mass flow rate, includes velocity –Therefore wind energy proportional to velocity 3 Placement of wind turbines very important –Increasing velocity from 5 to 15 mph leads to 3 3 or 27 times more possible energy –20 mph for 3 hours and 10 mph for 3 hours makes 2 times as much electricity as 15 mph for 6 hours Fundamentals of Wind Power

Betz Limit For Maximum Wind Turbine Power p. 406: P = 2.83x10 -4 D 2 v 3 (P in kW) for metric diameter and velocity P = 2.36x10 -6 D 2 v 3 (P in kW) for D=feet and v in mph

Fundamentals of Wind Power Residential wind energy system –AC power not directly made because rotor must always spin at same speed for AC power (not efficient) –Rotor may spin at any speed and make DC power If not connected to electrical grid, need storage (batteries) for days with no wind Commercial wind energy system –No batteries or DC load

Fundamentals of Wind Power Horizontal axis –Axis the blades spin on is horizontal; blades are vertical –Blades placed high off ground because more wind –Generator must be placed same height as the blades –2-3 blades more efficient in greater wind speed than many blades (better in low wind speed) A wind farm in a mountainous area in Galicia, Spain.

Fundamentals of Wind Power Vertical axis (Darrieus) –Axis blades spin on is vertical; blades are circular –Generator can be on ground –Difficult to build tall Does not take advantage of higher wind speeds up high Less frequently used 250 kW wind turbine at Altamont Pass, CA

Wind Power – World World countries have significantly increased their energy from wind because of: –High energy prices –Fuel security issues (Middle East conflicts) –Subsidies for renewable energy –Concern for the environment –Increasing turbine size has significantly decreased the cost per kW In 1981 – 25 kW model cost $2600 / kW In 1999 – 1000 kW model costs $800 / kW

Wind Power – World Countries with little land but much water (Denmark) are making offshore wind farms Wind has no obstructions in water Usually moderate breezes in the water Maintenance more expensive Longer electrical wires needed Near Copenhagen Denmark

Wind Power – US CA has local spots (mountain passes) good for wind power The Plain states have better overall potential (ND, SD, NE, KS, MT) CA closer to dense population to use electricity

Wind Power – US Note: In 2007, turbines in wind farms in CA generated 6,802 gigawatt- hours of electricity, about 2.3% of the state's gross system power.

U.S. Installed Capacity (MW)

Wind Power – Advantages Renewable source of energy After equipment is made no CO 2 or other pollutants emitted Price has substantially decreased (one of the cheapest forms of renewable energy) Augments solar energy well because days that are cloudy usually have wind

Wind Power – Disadvantages Ecological footprint –Compared to no previous development, wind farms need: Roads Foundations for wind turbines Clearing of trees (a distance of times the height of the wind turbine) Power lines –Pollution generated and energy used when making turbines, roads, concrete for the wind farm Energy used is (hopefully) produced back in around 6 months –Kills birds This is minimized during the planning stages by examining flight and migration patterns

Wind Power – Disadvantages Economic –Wind farms only able to compete with financial incentives (tax credits) –Maintenance of turbines, roads, new power lines is costly Visual –Not attractive to look at Maybe increase acceptability through community / citizen owned wind farms –Flicker of sun then shade when close to wind turbines

Wind Power – Disadvantages Noise –Feel subsonic thump when blade passes the tower Intermittent power –Need conventional power plants when no wind –Using excess wind turbine power, pump water into reservoir & use hydro power on calm days –If wind power becomes substantial it may cause large fluctuations in the electrical grid

Table 12-2, p As of April 30, 2009, wind power in the United States reached 28,635 MW megawatts (MW) of installed capacity, and the U.S. surpassed Germany as the country with the largest amount of wind power capacity installed by the end of 2008.

Growth in Global Wind Power Installed Capacity

Fig , p. 404 Altamont Pass, CA Tehachapi, CA

Table 12-3, p. 407

Fig , p. 409

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