IEEE Power & Energy Magazine - November/December 2021 - 94

Reduction in transient stability margins, controllable reactive
power resources, and voltage-dip-induced frequency dips
add to operational challenges.
(typically, intraday and day ahead). Voltage management
has become more challenging due to the reduction
of available reactive power resources. This is the
result of the displacement of conventional plants and
dispersed location of wind farms with different capability
characteristics, combined with the increasing
installation of high-voltage cables.
Need for a New Suite
of Reliability Services
An alternative to the out-of-market commitment of synchronous
generators to provide reliability services is to develop
new market products for these services that market participants
can competitively provide. The increasing levels of
VRE create a need for both new/modified reliability services
and VRE to help provide the services.
In Ireland and Northern Ireland, a suite of system services
was developed to encourage investment in service
provision capability and help to mitigate technical scarcities
associated with operating the transmission system up
to 75% SNSP. Seven new services were introduced: three
ramping margin (RM) services (RM1, RM3, and RM8)
over various time horizons out to 16 h; the fast frequency
response (FFR) and synchronous inertial response, devised
to address frequency stability by mitigating the RoCoF;
and the dynamic reactive response and fast postfault active
power recovery services to respond to voltage disturbances.
A qualification system is in place to procure a total of 14
services altogether.
To date, all except the dynamic reactive response and
fast postfault active power recovery have been procured
by EirGrid and SONI. A key trend observed is that each
procurement round results in an increased percentage of
overall system service capability provided by nonsynchronous
technologies.
Being an electrical island system, ERCOT requires all
generators, including VRE generation resources, to provide
primary frequency response with 17-mHz deadband and 5%
droop. The capability has to be enabled whenever a resource
is online, but the capacity reservation for the provision of the
primary frequency response is not required unless a plant is
providing ancillary services.
ERCOT introduced the FFR as a part of the frequency
containment reserve. FFR resources should respond within
0.25 s to a frequency trigger of 59.85 Hz and sustain for at
least 15 min. The first-phase system changes for the FFR were
implemented in 2020, and more comprehensive upgrades
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were to be completed before June 2021. A new ERCOT contingency
reserve service, a 10-min ramping product, will be
implemented in 2024 to restore the fast-acting responsive
reserve and help maintain system balance if needed.
The FFR was also introduced in the Nordic power system
in 2020. In Denmark, Energinet focused on providing
market-based solutions to support reliability via increased
flexibility, providing appropriate incentives to deliver the
needed balancing or ancillary services. The actions foreseen
or already implemented are 1) flexible settlement, with
electricity meters delivering hourly data; 2) the implementation
of an aggregator role in the market; 3) demand flexibility;
4) increased price caps; and 5) market coupling of
reserve markets.
In China, several new requirements to the technical capability
of wind and solar power plants were added to the new
Guide on Security and Stability for Power System's added
requirements to the technical capability of wind and solar
power plants, e.g., the ability to provide inertia and primary
frequency control. The electricity market in China is still
under development, with eight spot electricity market pilots
ongoing. VRE participation in the spot market is encouraged
and expected to become the trend of the future.
Resource Adequacy Becomes
More Challenging
Increasing levels of VRE fundamentally change the resource
adequacy challenge of how we plan and meet the security of
the supply. As shown in the statistics for wind/solar and electric
load in China, during the summer and winter high-electric-demand
periods, the output of VRE is generally below
15% of its capacity for 60% of the time. During the cold
wave in Hunan Province in the winter of 2020, the electric
load was historically high due to heating loads, while more
than 80% of wind turbines were frozen and unable to serve
the grid. The output of wind was less than 2% of its capacity,
contributing little to resource adequacy.
After 2025, Denmark expects more challenging resource
adequacy situations and related increases in electricity
prices. The means to address adequacy issues include market-based
solutions offering long-term flexibility, massive
installations of renewable resources, and investments in the
electricity network and interconnections. The decarbonization
of other sectors is expected to increase electricity
demand significantly. However, the pathway of how to reach
the country's 2030 70% greenhouse gas reduction target has
not been decided yet.
november/december 2021
IEEE Power & Energy Magazine - November/December 2021

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