IEEE Electrification - September 2022 - 68

technologies can be used. In general, these technologies
can belong to one of the following groups (or more than to
one group as shown in Table 2):
x Group 1: Energy spilling technology. During high RE
penetration (instantaneous renewable generation
exceeds the electrical demand), the excess of generation
is spilled and cannot be recovered. Technologies
of this group enable integration of RE sources and stable
operation of the system.
x Group 2: Provider of ancillary services. Instead of
engaging in energy production or consumption, the
technology is connected to the grid to provide system
TABLE 2. The classification of enabling
technologies.
Enabling Technology
Supercapacitor
Flywheel
SMES
High-power battery
High-energy battery
Pumped hydro energy
storage
CAES
Hydrogen energy storage
Thermal storage
Dump loads
Inverter-based PV and
wind generation capable
of operating below
maximum power point
Low-load diesel engine
Variable-load diesel engine
Access-oriented storage
Group 1
(Energy
Spilling)
Group 2
(Ancillary
Service)
ü
ü
ü
ü
ü
ü
ü
Group 3
(Energy
Shifting)
stability and reliability needs (frequency and voltage
support, inertial, reserves, and so on.)
x Group 3: Energy shifting technology. During high
renewable penetration, excess of RE in the grid can
be utilized by enabling technology. Later, under low/
zero renewable generation, the equivalent amount
of energy can be recovered back to the grid. Technologies
of this group allow increasing RE penetration.
When increasing the installed capacity of intermittent
generation, the system might face the problem of insufficient
downwards reserves-the system capability to
reduce generation and to match it with the electricity
demand. This can result in the frequency escalation and
system deviation from the stable operating state.
One approach to improve the system stability is to
ü
ü
ü
ü
ü
ü
ü
ü
ü
ü
ü
ü
ü
Capacity-oriented storage
Synthetic storage
Demand
RE
Spill
RE
Conven.
Generation
00:00
12:00
Time (h)
Figure 5. RE spillage. Conven.: conventional.
68
IEEE Electrification Magazine / SEPTEMBER 2022
24:00
operate wind and solar generation units in a manner similar
to conventional power plants, i.e., using droop controllers.
Deloading techniques applied for wind turbines can
provide primary frequency response using the speed and
pitch controllers. The same can be achieved using maximum
power point tracking for photovoltaic (PV) units.
Wind turbines can also emulate inertial response. This
approach enables the installation of significant renewable
capacities, however, resulting in significant spillage of RE.
In addition, such an approach complicates control strategies
and demands highly qualified personnel.
Another approach is to utilize variable resister banks,
called dump loads, which spill surplus system energy and
provide the balance between generation and consumption.
Utilization of dump loads offers simplicity and is
well-received in many practical applications (e.g., King
Island, Flinders Island). An illustration of RE spillage under
high instantaneous RE generation (greater than the system
load) and conventional generation operating at the
low load limit is presented in Figure 5.
Both de-loading and dump load techniques can provide
system ancillary services (i.e., providing synthetic
storage), converting excess RE into fast-response grid-connected
reserve and acting as a regulator of system frequency
under high RE penetration. Under such conditions,
the part of the load that is allocated to diesel generators
for security reasons can be supplied by renewable sources
with synthetic storage providing necessary ancillary services
(an illustration is provided in Figure 6(a), where the
spilled RE acts as the reserve in the system allowing diesel
generators to be disconnected).
Utilization of an energy storage system represents
the state-of-the-art approach for enabling high renewable
generation in HIPSs. There are two main types of
energy storage. The first type, access-oriented storage,
can provide high power with a rapid response, but for a
short duration. These technologies can be used as providers
of system ancillary services. The second type,
capacity-oriented storage, can provide energy over a
long period of time but may lack responsive capabilities.
It can be used for shifting RE from times of favorable
IEEE Electrification - September 2022

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