1Reminders:Homework #7 due next WednesdayExtra Credit #4 due next WednesdayExam #2 next Friday (in class) – see details on web pageResearch Project #1 due October 31 in classWind PowerRight now it is only 0.11 QBtu of energy per year in the United States or 0.11% of our total current energy usage.Energy in the WindAbout 2% of incident solar energy at the top of the atmosphere is converted into “bulk” kinetic energy of moving air (i.e. wind).Real windmills are not heat engines, but they still have a maximum efficiency (due to physics). This maximum is around 60%. Real windmills today convert about 30% of the available wind energy into mechanical energy (turning blades) and then 90% of that is converted into electrical energy.How much energy is in ALL the wind over the United States?What is the solar energy incident?()WattsmmWatts152122103105.8350 ×=××Average Solar Constant x Area of USAJoulesondsWatts22715109)sec103()103( ×=×××If 2% of that is converted into kinetic energy in wind, then wehave 2 x 1021Joules per year or 2000 QBTU. If we account for the maximum efficiency 0.60 x 0.90 to convert to mechanical and then electrical, we get 1000 QBTUper year.We only use about 100 QBTU per year! Is this a plan?Area of face=AHow much KE crosses an area A (like a windmill) in a time t?←L→L= velocity x timeKinetic Energy of the WindSimple: A volume of wind has kinetic energy KE = ½ mv2.JoulesmvKE221=kgAvtmALmkgm )()()(33ρρ=×=Kinetic Energy in the Wind2333647.0293.12121mWattsvvvAtKE=×==ρJoulestAvvAvtKE3221)(21ρρ==Kinetic Energy hitting an area (of a windmill) per time.Notice that it depends on the velocity3!326.0 vmWatts=2Especially since the KE scales as velocity cubed, it pays to be in the highest wind area.This is a pretty modest size wind turbine.At least two stories tall and would power 3 typical US homes (if the wind keeps blowing at this nice speed).If the wind speed drops by a factor of 2 (22 MPH Æ 11 MPH), what happens to the Power Output?A) It increases by a factor of 2B) It decreases by a factor of 2C) It decreases by a factor of 4D) It decreases by a factor of 8E) It decreases down to zero.326.0 vmWatts=The Betz LimitIt is the flow of air over the blades and through the rotor areathat makes a wind turbine function. The wind turbine extracts energy by slowing the wind down. The theoretical maximum amount of energy in the wind that can be collected by a wind turbine's rotor is approximately 59% (Betz Limit). If the blades were 100% efficient, a wind turbine would not work because the air, having given up all its energy, would entirely stop.LimitWind Power ParametersWattsPmAmWattssmAP22505.121805.122/1805.059.0)/10(6.02223=×====×××=π326.0 vmWatts=Suppose wind speed is 10 meters/sec (22 MPH), the diameter ofwindmill is 4 meters, and the efficiency is 50% of maximumpossible value. How much power is generated?A: 10 WattsB: 250 WattsC: 2250 WattsD: 50,000 WattsE: 1,000,000 Watts59.0=EfficiencyMaxKinetic Energy per area per time of windBetz Limit maximum efficiency WindSource ® ProgramEffective January 1, 2007, the cost of buying one Windsourceblock (100 kWh) is a monthly Windsource Adjustment charge of $0.738. Residential Windsource customers must commit to purchasing clean, renewable wind energy for a minimum of one year.A typical Colorado residential customer uses about 600 kWh of electricity per month, so the 100% option would be a Windsource Adjustment charge of approximately $4.43 per month.Normally 600 kWh would cost ~ $60, so you pay an extra 7%.3$0.738Monthly Wind Energy Service Adjustment$0.116Less AQIR, per 100 kWh block:$2.973Less ECA, per 100 kWh block:$3.827Wind Energy Rate, per 100 kWh block:ECA = Electrical Commodity AdjustmentAQIR = Air Quality Improvement If Xcel does not have enough WindSource customers, then they have to charge an extra cost. They do this as a larger subtraction when they are close to full.Ponnequin Wind Facility Location: Northern Colorado, just south of the Wyoming border and east of I-25.Plant Description: 44 turbines.Power Production Capabilities: Up to 30 MegaWatts (MW).About The Facility: Xcel Energy owns Colorado's first commercial wind farm in the state. The wind farm currently has 44 turbines that can generate up to 30 megawatts of electricity; Xcel Energy owns and operates 37 of the turbines. One megawatt of wind power can serve the entire electricity needs of more than 300 customers. The power produced at Ponnequin is sold through Xcel Energy's Windsource® program.Peetz Table Wind Power Plant Location: Northeastern Colorado, near Peetz.Plant Description: 33 wind turbines.Power Production Capabilities: Up to 30 MegaWatts (MW).About The Facility: The Peetz Table Wind Power Plant is the second commercial wind farm in Colorado. The wind farm is located near Peetz in northeastern Colorado and can generate up to 30 MegaWatts of electricity for Xcel Energy's Windsource®program.Rated SpeedThe rated speed is the minimum wind speed at which the wind turbine will generate its designated rated power. For example, a "10 kilowatt" wind turbine may not generate 10 kilowatts until wind speeds reach 25 mph. Rated speed for most machines is in the range of 25 to 35 mph.Cut-out SpeedAt very high wind speeds, typically between 45 and 80 mph, most wind turbines cease power generation and shut down. The wind speed at which shut down occurs is called the cut-out speed. Having a cut-out speed is a safety feature which protects the wind turbine from damage. Due to these and other factors, typical wind facilities only generate 20% of their maximum quoted power capacity!What about birds?Toronto Hydro Energy Services Inc. and WindSharecommissioned a study on the bird mortality rate of the Exhibition Place Wind Turbine. Wind turbines in North America kill an average of 2 birds per year, per turbine. In comparison, house cats in Canada kill an estimated 140 million birds a
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