Page 290 - Handbook of Energy Engineering Calculations

2
where A = cross-sectional area of stream, m or ft 2

The axial force on a turbine wheel operating at maximum efficiency where V e
= 1/3 V is given by
i

The axial forces are proportional to the square of the diameter of the
turbine wheel, which makes them difficult to cope with in extremely large-

diameter machines. There is thus an upper limit of diameter that must be
determined by design and economical considerations.

CHOICE OF WIND-ENERGY CONVERSION SYSTEM

Select a wind-energy conversion system to generate electric power at
constant speed and constant frequency in a sea-level area where winds
average 18 mi/h (29 km/h), a cut-in speed of 8 mi/h (13 km/h) is sought,
blades will be fully feathered (cut out) at wind speeds greater than 60 mi/h

(100 km/h), and the system must withstand maximum wind velocities of 150
mi/h (240 km/h). Determine typical costs which might be expected. The
maximum rotor diameter allowable for the site is 125 ft (38 m).

Calculation Procedure:

1. Determine the total available wind power
Figure 1 shows the total available power in a freely flowing windstream at
sea level for various wind speeds and cross-sectional areas of windstream.
Since the maximum blade diameter, given that a blade-type conversion
device will be used, is 125 ft (38 m), the area of the windstream will be A =

2
2
2
2
πd /4 = π (125) /4 = 12,271.9 ft (1140.1 m ). Entering Fig. 1 at this area and
projecting vertically to a wind speed of 18 mi/h (29 km/h), we see that the
total available power is 200 kW.