Civil Engineering Reference
In-Depth Information
FIGURE 12-4
Stand-alone wind power system with battery.
for winning. The energy balance analysis method for sizing the solar array
and battery is described later in this chapter.
12.3
Wind Stand-Alone
A simple stand-alone wind system using a constant speed generator is
shown in
Figure 12-4
.
It has many features similar to the pv stand-alone
system. For a small wind system supplying local loads, a permanent magnet
DC generator makes a wind system simple and easier to operate. The induc-
tion generator, on the other hand, gives AC power. The generator is self-
excited by shunt capacitors connected to the output terminals. The frequency
is controlled by controlling the turbine speed. The battery is charged by an
AC to DC rectifier and discharged through a DC to AC inverter.
The wind stand-alone power system is often used for powering farms
(
Figure 12-5
)
. In Germany, nearly half the wind systems installed on the
farms are owned either by individual farmers or by an association. The
performance of turbines under the “250 MW program” is monitored and
published by ISET, the Institute of Solar Energy and Technology at the
University of Kassel.
The performance reports are also available from the
German Wind Energy Institute. The reports list all installations, their per-
formance, and any technical problems.
The steady state performance of the electrical generator is determined by
the theory and analyses presented in Chapter 6. For example, Equations 6-
13 and 6-14 determine the rating of the capacitor needed to self-excite the
generator for the desired voltage and frequency. The power factor of the load
has a great effect on both the steady state and the transient performance of
the induction generator. The load power factor can be unity, lagging, or
leading depending on the load being resistive, inductive, or capacitive,
respectively. Most loads in the aggregate are inductive with a power factor
of about 0.9 lagging. Unlike in the synchronous generator, the induction
generator output current and the power factor for a given load are determined
1
