Interesting Facts, etc. (2/23/04)

Earth’s axial tilt = 23.5 degrees (23.45)             Earth-sun distance = 93 M miles = 92,955,820.5 miles = 149,597,892 km                   Earth Equatorial Radius = 6378137 m (WGS-77)            Summer Solstice: July 21; Winter Solstice: Dec 21; Equinoxes: Mar 21 & Sep 21

Wind Turbine Power, P = ρ/2·A· U3 watts, where ρ (rho) is 1.225 kg/m3, A is area = π r2 m2,
r= blade radius in m, U = wind speed in m/s.

P = 0.5 · ρ · A · Cp · U3 · Ng · Nb

where:
P = power in watts (746 watts = 1 hp) (1,000 watts = 1 kilowatt)
ρ = air density (about 1.225 kg/m3 at sea level, less higher up)
A = rotor swept area, exposed to the wind (m2)
Cp = Coefficient of performance (.593 {Betz limit} is the maximum theoretically possible, .35 for a good turbine design)
U = wind speed in meters/sec (20 mph = 9 m/s, or 2.24 mph = 1 m/s)
Ng = generator efficiency (50% for car alternator, 80% or possibly more for a permanent magnet generator or grid-connected induction generator)
Nb = gearbox/bearings efficiency (depends, could be as high as 95% if good)

(from AWEA, the American Wind Energy Association)

Average wind power density, P/m2 = 6.1x10-4 u3 watt/m2, where u is m/s

Locations:  Arctic Circle is 66.55º N; Big Blow, Texas is 31º N, 103.73º W; La Paz, Bolivia is 16.5 deg. S, 68.15 deg W; Colon, Panama is 9.7º N, 80º W; Cicely, Alaska is 66.55º N, 145º W; Florida Tech, Melbourne FL, 28.2º N, 80.6º W;  Panama City, Panama 8.97º N, 79.53º W;  Paris, France is 48.8º N, 2.33º E;

Area of sphere = 4 π r2            Volume of a sphere is 4/3 π r3                P=E*I=E2/R=I2R; E or V=IR

Typical computer/monitor power is 150 watts. “Standard” 40 W fluorescent ceiling lamps were/are being replaced by newer T8, 32 W  lamps.

The Link Building power meter (SE corner) indicates a typical weekday power load to be 60 kW, and nights/weekends, it is 35 kW.

A copy machine is on only during office hours (8 to 5) weekdays and usually draws 190 W.  When copying, it draws 900 W.

FPL charges $0.08/kWh for electricity (ignore demand charge and billing charge, taxes, etc.)

Melbourne FL, Dec. 24-hour radiation on a horizontal surface is 150 W/m2 and annual direct normal energy is 2.5 to 3.0 kWh/m2.

Air density is 1.225 kg/m3                Kinetic energy = 0.5 mu2 joules, where u is in m/s

K.E. also = p / (R·T), where p = pressure, T = Kelvin, and R = gas constant = 287.05 Joule/Kg/K for air

Snell’s Law: Angle of Incidence = Angle of reflection

altitude of the sun = 90º -latitude + sun declination [90-23.45 = 66.55 deg];
azimuth is the horizontal angle clockwise from north to a direction

derived from RE_MT.doc 040224FRL

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Miscellaneous/Interesting Facts.htm updated 040224

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