Page 295 - Handbook of Energy Engineering Calculations

providing efficient conversion of the energy of the wind; (2) the allowable
blade diameter, 125 ft (38 m), is suitable for the double-bladed design; (3) a
double-bladed rotor will operate well in the average wind speed, 18 mi/h (29
km/h), prevailing in the installation area; and (4) the double-bladed rotor is
well-suited for the constant-speed constant-frequency (CSCF) system desired

for this installation.

3. Compute the maximum electric power output of the wind machine
The power of the wind P is converted to mechanical power P by the wind
m
w
machine. In any wind machine, P = C P , where C = power coefficient.
p
m
w
p
The mechanical power is then converted to electric power by the generator.
Since there is an applicable efficiency for each of the systems, that is, C for
p
the aerodynamic system, η for the mechanical system (gears, usually), or η g
m
for the generator, the electric power generated is P = P η η .
e
w m g
In actual practice, the maximum electric power output in kilowatts of
horizontal-axis bladed wind machines geared to a 70 percent efficiency
3
2
6
electric generator can be quickly computed from P = 0.38 d V /10 , where d
e
= blade diameter, ft (m); V = maximum wind velocity, ft/s (m/s). For this
6
3
2
wind machine, P = (0.38) (125) (26.4) /l0 = 109.2 kW. This result agrees
e
closely with the actual machine on which the calculation procedure is based,
which has a rated output of 100 kW.