Operation of power systems - Wind Power Integration: Connection and System Operational Aspects - page 137

Chapter 5
Operation of power systems

5.1 Introduction

The connection of wind farms to distribution and transmission systems will have
a local effect on voltage levels and reactive power flows, as discussed in the
preceding chapters. The primary objective, however, of this network infrastructure
is to deliver active power economically and reliably from generation sources
to individual loads scattered across a national area. One of the underlying char-
acteristics of electricity supply, which profoundly affects the manner in which it is
engineered, is that electrical energy cannot be stored conveniently or economically.
The consequence of this statement is that, ignoring any losses incurred in the
electricity transmission network, there must be an instantaneous balance between
the electrical power generated and the system demand.
This chapter first examines how conventional generating units can be
scheduled and operated to cope with variations in the demand under both normal
and emergency conditions (Section 5.2). The inclusion of wind generation in this
task creates potential problems, as the power output of individual turbines is
subject to time varying weather patterns. Section 5.3 begins by presenting a status
report on how various countries are addressing the challenges (Section 5.3.1).
Then, taking the island of Ireland as an example, the variability of wind output on
different geographical scales and operational timeframes is examined in detail
(Section 5.3.2). Various key problems of wind power integration on a significant
scale, with some current solutions, are discussed in Sections 5.3.3-5.3.8. Wind
forecasting is a useful tool, in this respect, and its potential role is discussed
briefly here before being examined in detail in Chapter 6.
Finally, a number of alternative storage solutions, which can play a role in
maintaining the desired energy balance, are examined in Section 5.4, facilitating
further wind farm expansion. This section includes a discussion of how demand-side
management can provide some of the benefits of energy storage at minimal cost.

5.2 Load-frequency control

In addition to ensuring a continuous balance between electrical demand and the
combined output of the system generation, the system operator must also ensure
that network voltage levels and the system frequency remain within statutory limits.