Page 303 - Alternative Energy Systems in Building Design

BASICS OF WIND TURBINE OPERATION 277

There are also types of turbines that directly drive the generator and do not require
a gearbox. The amount of electricity that wind turbines generate depends on the tur-
bine’s capacity or power rating.
The electricity generated by a utility-scale wind turbine is normally collected and
fed into utility power lines, where it is mixed with electricity from other power plants
and delivered to utility customers.

ENERGY-GENERATION CAPACITY OF A WIND TURBINE
The ability to generate electricity is measured in watts. Watts are very small units, so the
terms kilowatt (kW, 1000 W), megawatt (MW, 1 million W), and gigawatt (pronounced
“gig-a-watt,” GW, 1 billion W) are used most commonly to describe the capacity of gen-
erating units such as wind turbines and other power plants. Electricity production and
consumption are measured most commonly in kilowatthours (kWh). A kilowatthour
means 1 kW (1000 W) of electricity produced or consumed for 1 hour. One 50-W light
bulb left on for 20 hours consumes 1 kWh of electricity (50 W × 20 hours = 1000 Wh =
1 kWh). The output of a wind turbine depends on the turbine’s size and the wind’s speed
through the rotor. Currently manufactured wind turbines have power ratings ranging
from 250 W to 1.8 MW.
For example, a 10-kW wind turbine, shown in Fig. 8.6, can generate about 10,000 kWh
annually at a site with wind speeds averaging 12 mi/h, equivalent to about the amount

Figure 8.6 Offshore wind turbine installation. Courtesy of AWEMA.