2020 7th International Conference on Electrical and Electronics Engineering
A Case Study on the Use of Energy Storage in Industrial Plants with a Renewable
Energy Plan
Hasan Basri Cetinkaya
Bayram Kurucay
Smart Infrastructure / Digital Grid
SIEMENS A.S.
Istanbul, Turkey
e-mail: hasan.cetinkaya@siemens.com,
Smart Infrastructure / Digital Grid
SIEMENS A.S.
Istanbul, Turkey
e-mail: bayram.kurucay@siemens.com
Panagiotis Stamoulis
Turan Turhan
FLUENCE ENERGY
Erlangen, Germany
e-mail: panagiotis.stamoulis@fluenceenergy.com
TUPRAS Izmir Refinery
Izmir, Turkey
e-mail: Turan.Turhan@tupras.com.tr
Oktay Erisik
Mehmet Ozkan
TUPRAS Izmir Refinery
Izmir, Turkey
e-mail: Oktay.Erisik@tupras.com.tr
TUPRAS Izmir Refinery
Izmir, Turkey
e-mail: Mehmet.Ozkan@tupras.com.tr
Erman Ozderli
TUPRAS Izmir Refinery
Izmir, Turkey
e-mail: Erman.Ozderli@tupras.com.tr
examined and home loads have been used in general.
Technical concerns for transmission and distribution systems
are represented in [1]. The benefits of storage in distribution
grid an optimization for siting and sizing is investigated in
[2]. Systematic integration of energy storage systems into
low voltage grid is studied in [3]. Coordinated control
structures for electric distribution grid operation are
envisaged in [4]. Role of storage systems based on ancillary
services in active distribution network management is
analyzed in [5]. Future roles are defined in [6] and [7].
In this paper, a refinery is studied. Its 80% of load is
motor load. It has a decoupling scheme together with load
shedding scenarios. Additionally, a concept to be used for
unlicensed energy production (provided that all internally
generated energy is consumed internally) has also been
reported.
Because the wind power plant (WPP) is planned to be
operated unlicensed, there should be no power export to the
transmission grid. In order to optimize energy use and
minimize power exchanges at the point of coupling, it is
aimed to use an Energy Storage System (ESS) together with
the wind farm. A Power Management System (PMS) will
also be integrated to manage the new configuration. In order
to increase the efficiency of the plant in the structure, PMS
will be able to control all conventional power plants and the
ESS. When WPP and ESS are used together, the PMS
management system will become a more critical requirement,
which will monitor the 34.5 kV network and continuously
Abstract—Industrial plants aim to increase their electricity
generation volume due to their growing load structure.
Industrial plants would also like to integrate renewables even
though there is no conventional power plant in their structure.
One of the biggest refineries in Turkey would like to integrate
10 MW of wind power, in addition to its conventional power
plants. Wind integration will be done without the necessity of
meeting the grid regulation annex-18 criteria and will be
within the framework of the “Unlicensed Energy Generation
Regulation”. All the energy generated from wind generation
should be consumed in the plant. The structure should be
configured according to this principle.
The main aim of this paper is to illustrate the philosophy to be
established and to show the working profiles of energy storage
systems according to different scenarios. Real wind profile and
real load profiles are used in the analyses. Also, the suitability
of different type of wind generators according to their type and
functionality are investigated for grid connected and island
mode operation. For island mode operation, stability of the
system for the loss of wind generation and/or storage is also
studied.
Keywords-energy storage; wind integration; SINCAL; PMS;
load profile study; refinery
I.
INTRODUCTION
In many studies, the benefits of energy storage in the
distribution network or transmission network have been
978-1-7281-6788-6/20/$31.00 ©2020 IEEE
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control active and/or reactive power exchange. It will operate
as a system to manage both the existing power plants and the
wind farm together with the ESS according to this power
exchange.
II.
REFINERY STRUCTURE
The refinery has a maximum power consumption of 63
MW and most of it is motor loads. There are 4 generators (2
gas turbines and 2 steam turbines) in operation which cover
approximately 90% of the maximum load. The gas turbines
alone cover 70% of the load.
The main distribution bus voltage is 34.5 kV which feeds
6.3 kV plant busses via 34.5 kV/6.3 kV transformers. Since
all generators, mains and loads are connected to 34.5 kV
busbar, the design of this busbar is 40 kA.
The refinery can work in island mode. It decouples from
the transmission grid in case of possible frequency and
voltage problems that may occur in the grid. It also has a
load shedding system in island mode to maintain system
stability in case of possible generation losses. The generators
power output and grid exchange are managed by system
operators. Structure of the Refinery is given in Figure 1.
Figure 2. Power system model used in Load Profile Studies
III.
OPERATION PHILOSOPHY & POSSIBLE MODES
PMS system will control conventional generation, wind
generation and energy storage in order to balance the power
exchange with the transmission grid. Primarily, PMS system
will focus on the energy storage part of the system. If energy
storage becomes insufficient to balance the power, it will
send signals to conventional power plants and to wind
turbines when necessary. The PMS system should be able to
command all power plants within the plant, receive the
energy production amounts of the relevant power plants, and
read the operating modes.
In parallel with the grid, the main control of the damping
of power fluctuations will be in the ESS. The Battery
Management System (BMS) of energy storage will generate
power when the active power flow direction is inward and
store power when the active power flow direction is outward
in order to balance the power at the point of coupling.
Energy storing / Energy generation selection should also be
made with the signal coming from the PMS system. Energy
storage system should be able to generate “Island” and
“Parallel” modes with the signal coming from PMS. The
control logic should be able to change according to these
modes.
The PMS system should be able to send a “power
decrease” signal to all plants above a certain frequency level.
The wind farm should also be able to receive this signal and
decrease its power output. The energy storage system should
also be able to switch to “store” mode with this signal.
At a certain maximum State Of Charge (SOC) level of
energy storage, the conventional turbines should be able to
decrease the power with the signal coming from the PMS
system. Likewise, at a certain minimum SOC level, the
conventional turbines must be able to increase power and the
storage system must be able to switch to “storage” mode.
The Refinery performs a parallel operation with the
network for a significant percentage of the working period.
Only in the case of critical voltage and frequency failures in
the network, disconnection from the network is performed.
Possible modes of operation can be classified as in Table I.
Figure 1. Structure of the Refinery
Refineries can become critical in the event of a power
failure. It is known that uncontrolled blackout can cause
damages on equipment and system as well as causing
production losses. Negative environmental effects may also
occur. At this point, it can become an unrivaled option, as
energy storage is a sustainable resource for critical loads.
The power system analysis model that is used for Load
Profile studies is shown in Figure 2.
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TABLE I.
POSSIBLE MODES OF OPERATION
Parallel Mode
operation and the required minimum conventional generator
configuration is very important.
Island Mode
No
Gas &
Steam
Wind
Energy
Storage
Gas &
Steam
Wind
Energy
Storage
1
2
3
4
5
6
7
8
ON
ON
ON
OFF
-
ON
OFF
ON
ON
-
ON
ON
OFF
ON
-
ON
OFF
OFF
ON
ON
ON
OFF
ON
ON
ON
ON
OFF
V.
A. Load Flow & Short Circuit Analysis
For the load flow analysis, Newton-Raphson is selected
for the procedure. For short circuit analysis, VDE 0102/2016
- IEC 909/2016 short circuit method is selected. In order to
represent the worst loading scenario, wind turbines are
assumed to work at full active power and at full inductive
working mode.
The results of the study are used to determine the feeder
cable of renewable sources, as well as the transformer power
that should be used. The bigger the cross section, the lower
the losses. For the 3-phase maximum short circuit analysis,
the wind turbine is assumed to be Double Fed Induction
Generator (DFIG) type in order to have the highest short
circuit contribution. The 3-phase maximum short circuit
analysis is carried out mainly to control the limits of the
main 34.5 kV distribution bus.
Load flow results show that voltage will remain at
acceptable operating state limits (+/-105%). No overloading
is observed. According to short circuit calculations, the
maximum short circuit level is found to be well below the
design limits. The required transformer power and the cross
section of the related feeders are determined.
The refinery identified 30 different cases for the study.
The grid import power varies from 0 to 8.84 MW in these
identified cases. Grid maximum exchange power becomes
less than 5 MW when 5 MW/10 MWh energy storage is used.
In the island operation mode with only WPP and ESS,
the ESS will be responsible for the voltage and frequency in
the system. However, when its capacity is insufficient to
stabilize the wind output, the wind generation will be
curtailed. The maximum power output of WPP will be fixed
via PMS where necessary. Another scenario is that only the
ESS is ON in island mode. In this case, the Energy Storage
system is responsible for the voltage and frequency in the
system. It has the priority of feeding critical load.
Operational scenarios according to different load and
generation conditions of the Refinery in summer and winter
have been determined. In these scenarios, the energy
generation amounts of conventional power plants and wind
turbines in the facility are specified, and the energy balance
that can be provided by the planned ESS is evaluated.
Energy storage system is expected to be designed in such
a way as to provide support for “critical power”, “voltage
recovery”, “frequency recovery” and “black-start”.
IV.
THE ANALYSIS
CHALLENGES
B. Load Profile Studies
Yearly load profile was obtained for the refinery. The
data have only 3 values per day (13:00, 22:00, 6:00). This
profile is shown in Figure 3. In order to create a more
reasonable study, this profile has been converted to an annual
profile.
For the sizing and suitable operation philosophy for the
suggested system, two-stage analyses are envisaged. In this
paper, the first stage analysis is given.
The first stage analysis includes load flow & short circuit
analyses in order to analyze the effects of WPP and ESS on
load, voltage changes and short circuit levels throughout the
plant. Load profile studies are carried out in order to
determine the optimum ESS capacity and WPP integration.
Stability studies are also carried out in order to analyze the
effects of the tripping of WPP and ESS in island mode.
There exist some challenges with the data obtained. No
data with a lower resolution than hourly data was available
for WPP. The load profile obtained for the facility is 3 data
per day, which is not a good resolution for load profile
studies. There exist no advanced models for ESS. Generic
models are used to carry out the studies.
One of the biggest challenges for island mode operation
of renewables is the required “minimum grid strength”,
because the power electronic devices that renewables use
require a relatively strong grid to control their stability. As
the short circuit power of the busbar (to which the wind
turbines are connected) decreases, the control of the wind
turbines becomes difficult and controller instability may
occur. For these reasons, the possibility of island mode
Figure 3. Yearly variation of generation & load of the refinery
3 years load profile is shown in Figure 4. The maximum
average consumption for 3 years is 62.4 MWh. The
maximum consumption is informed as 64.83 MW. The
minimum average consumption for 3 years is 40.7 MWh.
The maximum energy import for 3 years is 11.9 MWh.
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For load profile analysis, all conventional power plants
generation is assumed to be fixed at informed values for all
the cases, in order to determine the power that should be
compensated by the conventional generation units. Energy
storage is assumed to be 5 MW / 10 MWh according to 30
cases in load flow analysis outputs.
Since hourly values are used for profiles, the envisaged
storage system's power seems not sufficient to completely
eliminate the power exchange. When focused on a specific
date & time, the effect becomes more visible. Figure 7 is
showing active power variations at energy storage and at
point of coupling while focusing on 2 days. Figure 8 is
showing the energy storage state of charge level during these
variations.
Figure 4. Refinery electricity consumption variation for 3 years.
There exist some unexpected changes in annual
consumption. Therefore, the possible fluctuations are rearranged again in the profile in order to remove unexpected
changes (Focused on stable load consumption). Optimized
yearly load profile of the refinery is given in Figure 5.
Figure 7. Active power variations at energy storage & at point of coupling
(Grid connected mode - focused on 2 days)
Figure 5. Optimized yearly load profile of the refinery
Figure 8. State of Charge (SOC) level variations
(Grid connected mode - focused on 2 days)
Annual active power profile of the wind turbines for
refinery location is given in Figure 6.
The power balance graph shown in Figure 9 indicates the
active power changes that the conventional generators must
create for a perfect balance. For the import case, if the
generators do not have reserves, it is not possible for the
generators to compensate. However, for the export case, they
must decrease their power in order to eliminate the export.
Figure 6. Yearly active power variations of wind turbines
Figure 9. Active power variations at grid exchange point
(Grid connected mode - focused on 2 days)
All 30 cases for load profile are investigated. Voltage
variation at point of coupling, active power variations at ESS
and at grid connection cable, SOC level of ESS,
conventional generators contribution to eliminate power
exchange at the point of common coupling (PCC) are studied
for both grid-connected mode and island mode operations.
In island mode there will be no exchange with the grid.
However, the fluctuations at wind output should be well
balanced by the energy storage as well as the conventional
generations. Figure 10 is representing active power
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variations at energy storage, wind turbines cable & SOC
level of the battery in island mode focusing on 2 days.
Figure 10. Active power variations at energy storage, wind turbines cable
& SOC level of the battery (Island mode - focused on 2 days)
Figure 12. Remaining generators active & reactive power variations during
energy storage trip in island mode
C. Preliminary Stability Studies
For 2 additional cases, two different stability studies are
carried out. In the first study, energy storage is tripped in
island mode. In the second study, wind turbines are tripped at
maximum power in island mode. For both cases, the other
generating units try to take over the diminishing generation
up to their maximum capacity. The frequency falls below its
nominal but not below 49 Hz. In the first case, energy
storage is tripped at 1 sec with full load output (generating
4.8 MW). From Figure 11, it can be seen that the frequency
decreases to 49.58 Hz while voltage does not have any
significant change. Figure 12 is representing the remaining
generators active & reactive power variations during energy
storage trip in island mode.
In the second study, the wind turbines are tripped at 1 sec
with full load output (generating 4.5 MW each). From figure
13, it can be seen that the frequency decreases to 49.40 Hz
while voltage does not have any significant change. The
energy storage active & reactive power response can be seen
from Figure 14.
Figure 13. 34.5 kV main bus voltage and frequency variation during wind
turbines trip in island mode
Figure 11. 34.5 kV main bus voltage and frequency variation during
energy storage trip in island mode
Figure 14. Energy storage active & reactive power variation during wind
turbines trip in island mode
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VI.
When WPP is integrated, despite the integration of the
storage system, the response to be generated by conventional
power plants should be faster than in the case where wind
energy is not integrated. However, this situation is expected
to be improved when minute-based profiles can be used.
In island operation, the trip of the wind farm and / or
energy storage system does not pose a serious risk. When the
wind farm trips, the energy storage system can switch to
frequency control mode and support the frequency by rapidly
increasing the active power output.
RESULTS AND CONCLUSION
The load profile obtained for the facility is 3 data points
per day, which is not a good resolution for load profile
studies. Also, the wind profile is given hourly. For a more
accurate result for load profile study, a minute-based profile
should be used for future studies. Load is generally varying
from 55 MW to 65 MW. A more stable load may decrease
the MWh of the energy storage that should be used.
Wind data indicates a very fluctuating profile. Therefore,
when wind power is integrated, the power exchange
monitored on the grid side is also very volatile. For this
reason, an energy storage system should be used to reduce
this fluctuation.
From the 30 scenarios obtained from the facility, grid
import is changing from 0 MW to 8.8 MW. When 9 MW
wind is integrated, this fluctuation is likely to drop to 4.5
MW, but this depends on the wind profile. In some cases, the
wind power should be curtailed to 5 MW in order not to
export power to the grid. When the power fluctuation in the
load profile is also evaluated, it becomes clear that the
Energy Storage System should be a minimum of 5 MW/10
MWh.
The power balance graphs in the report indicate the
active power changes that the conventional generators must
create for a perfect balance. For the import case, if the
generators do not have reserve, it is not possible to
compensate for the system. However, for the export case,
they must decrease their power in order to eliminate the
export (input to PMS).
Since hourly or worse resolution profiles are used, it can
be said that the energy storage system used in this study can
partially prevent the fluctuation that is occurring due to wind
integration. It softens the change in production that
generators need to create but cannot create a completely
smooth curve.
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