IEEE Power & Energy Magazine - November/December 2019 - 26

Because of the variable nature of the resources,
systems with high VER penetrations are likely to have
much more generation capacity than peak demand.

40
20
EirGrid

KIUC

ERCOT

Xcel/CO

South
Australia

Energinet

SPP

Nonvariable Generation
Variable Renewables
Storage and Interconnections

figure 1. The (blue) installed capacity of nonvariable
generation, (orange) VERs, and (gray) storage and interconnections as a percentage of peak demand on each system.
This includes distributed VERs. SPP: Southwest Power Pool;
ERCOT: Electric Reliability Council of Texas.
ieee power & energy magazine

60
40

EirGrid

KIUC

100

ERCOT

100

120

Xcel/CO

120

140

South
Australia

140

160

Potential
Wind/PV Curtailed (%)

Wind/PV Penetration (Excluding Distributed
Energy Resources) and Curtailment
Wind/PV Penetration (%)

Installed Capacity
as % of Peak Demand

KIUC is the only electric service provider on the island of
Kauai in Hawai'i. Unlike the other regions mentioned in
this article, Kauai has no interconnection with its neighbors,
so balancing supply and demand is extremely challenging.
KIUC has long been a leader in solar integration, with

Installed Capacity as % of Peak Demand

160

Storage and Synchronous Condenser
Capability in Kauai

Energinet

180

Here we share system operators' secrets for successful
renewable integration. Some regions have unique techniques
for addressing the balancing challenge, such as using curtailed wind to provide a fast, accurate regulation service.
Others have developed mitigation options for high IBR
penetrations, such as running a gas turbine as a synchronous condenser. They all share a practical approach rooted
in innovative uses of existing infrastructure; a willingness
to develop new market services, incentives, or contractual
arrangements; the application of detailed studies and good
planning; and a readiness to adopt new practices.

SPP

slightly higher annual average VER levels (the orange
marker in the figure), but their instantaneous VER levels
are considerably higher. The length of the blue bars shows
that system operators must manage a range of operating
conditions: from zero VER output to VER output exceeding regional demand.
Figure 2 also shows the percentage of VER energy curtailment in 2018. In this article, curtailment is a broad
term for reducing VER output below its potential production; it may be enacted for various reasons, including
transmission congestion, provision of down-regulation
reserves, and system balancing during oversupply periods. The island system of EirGrid limits instantaneous
IBR penetration because of grid stability issues. In Denmark, wind turbines contribute to market-based downregulation on equal terms with other generators. The
island system KIUC uses various means to enhance flexibility, including energy-shifting battery storage, to hold
down curtailment.

Min Instantaneous Penetration Max Instantaneous Penetration
Average Annual Penetration Curtailment

figure 2. The (blue bars) minimum (min) to maximum (max)
instantaneous VER penetration as a percentage of demand
and (orange marker) the average annual VER penetration.
Min values are at or close to zero. This represents transmission-connected VERs, not distributed VERs, which would
further increase penetration levels. Green dots depict the
percentage of potential VER annual output that is curtailed.
november/december 2019

IEEE Power & Energy Magazine - November/December 2019

Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - November/December 2019