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Civil And Environmental Engineering
CEE 265
Phillip Savage

CEE 265 November 21, 2013 RECAP: Power Content of the Wind  Dependence on the cube of the wind speed  Important in choosing where to construct a wind turbine  Rotor efficiency indicates how much kinetic energy will be extracted by the turbine o Actual wind turbines can’t actually get all kinetic energy from wind o Based on limitation of generator  Wind speed distribution and average wind speed important for deciding turbine location  We also talked about capacity factor and effectiveness of turbine o Impossible to get high CF and EFF (the ideal) o Always a trade-off Cost of Wind Power  Triple bottom line: economics, performance, and social factors o Professor used baseball example  For wind turbine o Capital cost = cost of turbine rotor + blades + tower + electromechanical system o Capital cost (CC) increases as PR(rated power output) increases In-Class Problem 21.3: wind turbine energy payback time  Rate power of 2 MW running at 25% capacity o Required 100,000 kg of steel to make o Assume 40 kWh energy input to make each kg of steal  What is the payback period? o Embedded energy = (40 kWh/kg steel)*(1000,000 kg steal) = 4,000,000 kWh o Electricity production rate = (2 MW)*(1,000 kW/MW)*0.25 = 500 kW o Payback period = (4,000,000 kWh/500kW) = 8,000 hours  There are 8,760 hours in a year o So it takes almost an entire year to generate enough electrical energy to recover the energy used to build the turbine o The turbine might only last 25 years o So these are the sorts of things that a life cycle analysis helps us to understand Triple Bottom Line Aspects of Wind Power  Advantages: o Renewable energy source  fuel cost is nearly zero o Low operating cost o Low carbon emissions  footprint in assembly of course, but overall low  Disadvantages: o Large land use requirement o High capital cost  greater uncertainty because of availability of resources o Materials used in turbine assembly and their associated impacts o Noise issues o Aesthetic issues  they don’t look great in a backyard o How they effect animals in the ecosystem  kills birds Offshore Wind Farms and the Triple Bottom Line  Advantages: o Reduced land use intensity o Less obtrusive o Higher category winds  less turbulence  Disadvantages: o More expensive to build/operate o Undersea cable required for connecting to grid o Interference with waterways Key Points:  The power content of the wind is proportional to the cube of the wind speed  The recoverable kinetic energy from the wind is limited by the physics of Betz’s law  Large diameter turbines/large tower heights more cost–effective for wind energy capture  In selecting the rate power of a turbine, one must consider the capacity factor and effectiveness SOLAR ENERGY Sun emits enormous amount of energy across the electromagnetic spectrum  Sun’s spectrum almost matches a blackbody  Varies according to the season o Earth’s orbit is not quite elliptical o Also have a tilted axis o Means the regional variation of energy received depends on position on Earth also  Amount of insolation available depends on latitude, day, and cloud cover o Sun path diagrams and clear sky insolation tables are helpful o Solar noon = half way between sunrise and sunset on a given day o Spring and fall equinoxes are the only days that it perfectly rises in the East and sets in the West  Sun path diagram for Michigan at 40 N latitude o Shows the equinoxes are March 21 and September 21 o If you look at different altitude you would have different sun path diagram o Useful for trying to analyze shade effects when building something  Clear sky insolation table o Shows you how much insolation is available in watts per m by
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