Wind Turbines - Wind Energy: Renewable Energy and the Environment - page 93

FIGURE 5.20 Wind turbine with double rotor.
5.10 APPLICATIONS
The kinetic energy of the wind can be transformed into mechanical, electrical, and thermal energy.
Historically, the transformation was mechanical where the end use was grinding grain, powering
ships, and pumping water [14, 15].
The applications can be divided into wind-assist and stand-alone systems. In the wind-assist
system the wind turbine works in parallel with another source of energy to provide power. The
advantages of such systems are power is available on demand, generally there is no storage, and
there is better matching between the power sources and the load. Stand-alone systems will provide
power only when the wind is blowing and the power output is variable, unless a storage system is
connected to the wind turbine. Wind-diesel is an application where the wind turbine is primarily a
fuel saver, which is a wind-assist system. Another application, which is now emerging, is a hybrid
system for villages and telecommunications.
5.10.1 E LECTRICAL E NERGY
Most wind turbines are designed to provide electrical energy. In a wind-assist system, wind turbines
are connected to the utility line either directly through induction generators and synchronous gen-
erators or indirectly where variable-frequency alternators and DC generators are connected through
inverters. The utility line and generating capacity of the power station act as the storage system. For
stand-alone systems, battery storage is the most common option.
The U.S. Department of Agriculture (USDA), Bushland, Texas, and the Alternative Energy
Institute (AEI), West Texas A&M University, are evaluating stand-alone, electric-to-electric sys-
tems for pumping water [16]. The wind turbine generator is connected directly to an induction motor