1. Physics and Engineering Questions of Importance in the Wind Energy Field  How much power is in the wind?  How much of this power can we extract?  How do we design devices to extract this energy?  What designs are already available, and what are their strengths and weaknesses?  What additional equipment do we need?  Where should we put these devices?  Can they ever pay for themselves? .....?

2. Total Wind Power  This power is measured in Watts = N-m/sec = Voltage-Amps  The power in the wind increases with the cube of the velocity!  It also increases linearly with the capture area, A.  Air Density, , doesn’t vary much in a fixed location, but it may vary several percent with altitude. –The air density in Flagstaff is only about 80% of that at sea level. –See next chart ρ = Air Density (Kg/m 3 ) A = Cross Section Area (m 2 ) V = Wind velocity (m/sec)

3. Air Density in kg/m 3 Z -50510152025303540 01.3161.2921.2691.2471.2251.2041.1841.1641.1451.127 1001.3001.2761.2541.2321.2111.1901.1701.1511.1331.115 2001.2831.260 1.2381.2171.1961.1761.1571.1381.1201.103 3001.2671.245 1.2231.2021.1821.1631.144 1.1261.1081.091 4001.2511.2301.2081.1881.1691.1501.1311.1131.0961.079 Z-10-505101520253035 5001.2581.2361.2141.194 1.1741.1551.1361.1181.101 1.084 6001.2421.2201.1991.1791.1601.1411.1231.1061.0891.072 7001.2261.2051.1851.1651.1461.1281.1101.0931.077 1.061 8001.2101.1901.1701.1511.1331.1151.0981.0811.0651.049 9001.1951.1751.1561.1381.1201.1021.0851.0691.0531.038 Z-15-10-5051015202530 10001.2001.1801.1611.1421.1241.1061.0891.0731.0571.042 11001.1841.1651.1461.1281.1111.0941.0771.0611.0451.030 12001.1691.1511.1321.1151.0971.0811.0651.0491.0341.019 13001.1541.1361.1181.1011.0841.0681.0521.0371.0221.008 14001.1401.1221.1051.0881.0721.0561.0401.0251.0110.997 Z-20-15-10-50510152025 15001.1431.1251.1081.0911.0751.0591.0431.0281.0141.000 16001.1281.1111.0941.0781.0621.0461.0311.0171.0030.989 17001.1141.0971.0811.0651.0491.0341.0191.0050.9910.978 18001.1001.0831.0671.0521.0371.0221.0080.9940.9800.967 19001.0861.0701.0541.0391.0241.0100.9960.9830.9690.957 Z-25-20-15-10-505101520 20001.0881.0721.0561.0411.0261.0120.9980.9850.9710.959 21001.0741.0581.0431.0281.0141.0000.9870.9730.9610.948 22001.0601.0451.0301.0161.0020.9880.9750.9620.9500.938 23001.0461.0311.0171.0030.9900.9770.9640.9510.9390.927 24001.0331.0181.0050.9910.9780.9650.9530.9410.9290.917 Elevation in meters Temp in ºC

4. Efficiency of your Wind Energy Device  Efficiency is the Output Power/Input Power

5. How much of the Total Wind Power can actually be converted to Mechanical Power?  We applied the 1 st law of thermodynamics – conservation of energy to find Wind Power.  We also must apply conservation of mass and conservation of momentum (Newton’s 2 nd law) to the system to determine how much of this power it is possible to retrieve.  After we do this we find….

6. Maximum Useable Power to the Power Contained in the Wind  Define a power Coefficient as:  This corresponds to 59.3%, or about 60%, and is an upper limit on wind turbine efficiency, usually called the Betz limit.