IEEE Power & Energy Magazine - November/December 2015 - 79

doors-©istockphoto.com/dliborzivotic, wind turbine photo courtesy of nrel

and energy from these generation sources has nearly zero
marginal cost.
Wind and PV generation, known as variable generation
(VG), are primarily energy sources because the "fuel" input
to these systems cannot be controlled. VG resources, however, can contribute a fraction of their nameplate capacity
toward planning reserves, and their connection to the power
system through inverter-based power electronics allows for a
fast, accurate control of their output.
The capabilities of wind and PV generation have evolved
significantly during the past decade, and these resources
can contribute to the economics and reliability of the power
system. As the penetration of VG increases relative to the
amount of conventional generation and peak demand, there
is potential for these operational capabilities to grow in value
and provide the types of services traditionally delivered by
conventional synchronous machines.
The range of services is divided into two main categories.
The first, system balance, concerns the operation of the power
system under normal conditions, when constantly changing
electric demand, potentially augmented by VG output variability, must be compensated by adjustments in net resource
output. Relevant topics include balancing net load (load
minus VG generation), regulation, and economic dispatch.
Although maintaining this balance often involves reliability-related aspects, such as maintaining the interconnection
november/december 2015

Wind and
Solar Power Are
Mainstays of a
Clean, Reliable,
Affordable Grid

frequency within prescribed limits, the primary concern is
the economic operation of the power system.
The second category includes services that are critical to
maintaining the operational security of the bulk power system during and after major disturbances. In this category, the
economics of power system operation take a backseat to reliability. Relevant issues include frequency response, system
inertia, and frequency and voltage ride-through capabilities.
VG was initially thought to increase the power system
operator's challenges in both of these categories. Technological advancements are now providing some power system
operators with additional tools to maximize the delivery of
renewable energy while reducing system operations cost and
enhancing system reliability and stability, in some ways even
better than conventional generators. (See "Wind Generation's
Evolving Dynamic Response Capability.") Numerous studies,
new advanced analysis tools, and the growing level of experience with VG on the power system are all showing that wind
and PVs are no longer constrained by many physical limitations. This article addresses frequently cited misperceptions
of wind and solar power by focusing on the capabilities that
modern wind turbines and PV systems can provide to both
the balance and security of the bulk power system. As such, it
provides an update to a 2009 article in this magazine, "Wind
Power Myths Debunked," by describing the recent development of advanced features of wind and PV power generation
ieee power & energy magazine

Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - November/December 2015