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DigSILENT PF - 01 pilot project palau

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Himmelstern

The document presents preliminary results from a pilot study assessing grid stability on the island of Palau with increasing levels of solar PV penetration. At current PV levels (5% penetration), simulations show the frequency remains stable within limits after a load disturbance. Higher penetrations of 30% and 70% were also modeled. Additional reserves are needed to accommodate PV output fluctuations. Further data is required to fully validate the dynamic model and assess other stability aspects like voltage stability. Recommendations will be provided in the final report.

Engineering
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Pilot Study on Grid Stability Assessment for the Island of Palau (Preliminary results) Flavio Fernández, Stefan Weigel, José Gomez and Julius Susanto DIgSILENT GmbH, Germany Grid Stability Workshop. Pacific Islands 1
Grid Stability Workshop. Pacific Islands 2 Overview of the Presentation  Introduction  Project background  Solar resource metrics  Characterization of power output fluctuations  Impact on the system stability  Frequency Stability (PV penetration 5%(current), 30%, 70%)  Power balance and generation dispatch  Assessment of dynamic frequency stability  Fault-Ride Through  Conclusions and recommendations. The way forward.
Grid Stability Workshop. Pacific Islands 3 Project Background  Part of the IRENA Islands Initiative project to assist islands in the Pacific Region with their planning for renewable energy integration, especially the grid stability assessment and identification of specific technology solutions  Objectives  Develop a methodology of assessing the impact of different levels of variable generation on power quality (focus on frequency stability)  Set up a simulation model to assess the dynamic stability of the system (pilot project: the system of Palau island has been chosen)  Identify the amount of renewable generation that the system can accommodate without affecting the power quality  Identify specific technology solutions (like for instance storage) where required
Grid Stability Workshop. Pacific Islands 4 Project Background  What has already been done:  Steady-state data from a previous PPA’s loss study converted from EasyPower software into DIgSILENT PowerFactory.  Results validated for load flow.  Collection and modeling of load/PV-resource profiles:  PV power output available for one year in 1hs resolution  Load profile available for 1 week, in 1hs resolution  Model setup using standard dynamic data.  Preliminary results:  Assessment of frequency stability for PV penetration levels of 5% (current status), 30%, 50% and 70%.  Subject to validation of the dynamic model
Grid Stability Workshop. Pacific Islands 5 Project Background  Next steps:  Validation of dynamic data  Collection and verification of missing data:  Load shedding scheme (incl. tripping times)  Contingency reserve  Voltage/Frequency dependency of loads  Investigate voltage stability and transient stability (contingent on receiving the necessary dynamic data)  Delivery of the study report including results, conclusions and recommendations.
Solar Resource Metrics Characterization of PV power output fluctuations Grid Stability Workshop. Pacific Islands 6
Penetration-Level Metrics Grid Stability Workshop. Pacific Islands 7
Grid Stability Workshop. Pacific Islands 8  Characterization of PV power output fluctuations is important to assess the impact of PV plants on system stability  Fluctuations of PV power output depend mainly on:  Size of the PV plant  Geographical dispersion of the PV plants  Ramp rate interval (i.e. time interval during which fluctuations occur)  Weather conditions  Time-based measurements can be used to statistically characterize the amplitude and frequency of occurrence of the fluctuations, usually presented as:  Distribution of changes (how often they occur) as a function of the fluctuation amplitude for given ramp rate intervals  Percentage of maximum fluctuations as a function of the ramp rate interval PV Power Output Variability
Grid Stability Workshop. Pacific Islands 9 PV Power Output Variability  Power fluctuations for four ramp rate intervals of a 1MW PV plant (at STC) and the existing PV plants in Palau (installed capacity 770 kW) 0.0 1.0 2.0 3.0 4.0 5.0 -60 -40 -20 0 20 40 60 RelativeFrequency(%) Power Fluctuation (% of PV rating) 1 hour 10 m 1 m 10 s Palau (1 hour)
Grid Stability Workshop. Pacific Islands 10  Time-series measurements provided by PPA over a 1 year period for the currently existing PV plants (installed power approx. 770 kW) with an hourly time resolution:  Reserve requirement based on a confidence level of 99.7% (corresponds to 3δ): 35% of PV power output (orange curve in previous slide, Palau’s case)  For the characterization of short-term fluctuations, measurements with a higher time resolution are required (seconds to minutes)  A reliable characterization of short-term PV power output fluctuations (from 1s to aporox. 10 minutes) will allow an accurate calculation of minimum spinning reserves and therefore an optimization of diesel dispatch and/or additional solutions (such as storage) PV Power Output Variability
Frequency Stability Spinning Reserve and PV Output Fluctuations Grid Stability Workshop. Pacific Islands 11
Frequency Stability: Spinning Reserve  Incremental need for additional operating reserves due to higher penetration- levels of non-dispatchable generation:  Disturbance (contingency) reserve: current 2 MW for Palau grid  Additional reserve: 35% of installed PV generation for Palau grid  Additional reserve calculated based on the probability distribution of PV power output fluctuations:  35% of PV power output  Demand time-series are not available (for the same period of PV measurements) so that no correlation between load and PV generation can be considered (conservative assumption) Grid Stability Workshop. Pacific Islands 12
 Dispatch of diesel generators: • Dispatch to meet minimum operating reserve (contingency reserve + additional reserve) • Observation of maximum and minimum power output operational limits • Merit order according to fuel costs • Analysis carried out for 7 days for which demand data is available • From May 2014, two new diesel units in Aimeliik (2 x 4.5 MW) will also available Grid Stability Workshop. Pacific Islands 13 Frequency Stability: Spinning Reserve
Grid Stability Workshop. Pacific Islands 14 5% PV Penetration Level (current status) 166,0132,899,6066,4033,200,000 [-] 1.55E+4 1.30E+4 1.05E+4 8.00E+3 5.50E+3 3.00E+3 Dispatch Merit Order: Net load in kW Dispatch Merit Order: Minimum dispatch pow er in kW Dispatch Merit Order: Maximum dispatch pow er in kW Dispatch Merit Order: Required dispatch pow er in kW 166,0132,899,6066,4033,200,000 [-] 1.60E+4 1.40E+4 1.20E+4 1.00E+4 8.00E+3 6.00E+3 800,00 600,00 400,00 200,00 0,00 -200,00 Dispatch Merit Order: Net load in kW Dispatch Merit Order: Renew able generation in kW Dispatch Merit Order: Required dispatch pow er in kW DIgSILENT
Grid Stability Workshop. Pacific Islands 15 5% PV Penetration Level (current status) 166,0132,899,6066,4033,200,000 [-] 1.6E+3 1.2E+3 8.0E+2 4.0E+2 0.0E+0 -4.0E+2 MALAKAL_SiteMIT13: Active Pow er in kW MALAKAL_SiteMIT12: Active Pow er in kW 166,0132,899,6066,4033,200,000 [-] 6000,00 5000,00 4000,00 3000,00 2000,00 1000,00 MALAKAL_SiteNIIGATA1: Active Pow er in kW MALAKAL_SiteNIIGATA2: Active Pow er in kW 166,0132,899,6066,4033,200,000 [-] 6,00 5,00 4,00 3,00 2,00 1,00 Dispatch Merit Order: Number of dispatched generators DIgSILENT
 As dynamic data of diesel generators is not available, model has been set up using standard controllers and parameters.  An indirect validation exercise was done by simulating a load step change:  2.5 MW of 12 MW dispatched generation (Nigatta 1 and 2, Mit13) and comparison against the maximum frequency excursion allowable in the system  PPA advised that the system remains stable and within frequency limits after such a load step:  Max. allowed deviation: +/- 1.0 Hz (steady state)  First under frequency relay: 58,2 Hz  The simulation results confirmed these observations.  It is strongly recommended to validate the model against records of system perturbations (not available at this time). Grid Stability Workshop. Pacific Islands 16 5% PV Penetration Level (current status)
5% PV Penetration Level (current status) Grid Stability Workshop. Pacific Islands 17 20,0016,0012,008,004,000,00 [s] 60,50 60,00 59,50 59,00 58,50 58,00 MALAKAL_SitePP-MALAKAL-BUS4: Electrical Frequency in p.u. (base: 0,02 ) 59.5 Hz 1st Underfrequency Relay @58.2 Hz 0.702 s 58.475 p.u. 20,0016,0012,008,004,000,00 [s] 6,00 5,00 4,00 3,00 2,00 1,00 MALAKAL_SiteMIT13: Positive-Sequence, Active Pow er in MW MALAKAL_SiteNIIGATA1: Positive-Sequence, Active Pow er in MW MALAKAL_SiteNIIGATA2: Positive-Sequence, Active Pow er in MW 20,0016,0012,008,004,000,00 [s] 8,00 6,00 4,00 2,00 0,00 -2,00 Base Load: Total Active Pow er in MW Variable Load: Total Active Pow er in MW 0.005 s 2.561 MW DIgSILENT
Grid Stability Workshop. Pacific Islands 18 30% PV Penetration Level 166,0132,899,6066,4033,200,000 [-] 2.20E+4 1.80E+4 1.40E+4 1.00E+4 6.00E+3 2.00E+3 Dispatch Merit Order: Net load in kW Dispatch Merit Order: Minimum dispatch pow er in kW Dispatch Merit Order: Maximum dispatch pow er in kW Dispatch Merit Order: Required dispatch pow er (incl. PV reserve) in kW 166,0132,899,6066,4033,200,000 [-] 1.65E+4 1.40E+4 1.15E+4 9.00E+3 6.50E+3 4.00E+3 5.0E+3 3.8E+3 2.5E+3 1.3E+3 0.0E+0 -1.3E+3 Summary Grid: General Load, Active Pow er in kW Dispatch Merit Order: Renew able generation in kW Dispatch Merit Order: Required dispatch pow er (incl. PV reserve) in kW Dispatch Merit Order: Required dispatch pow er (w /o PV reserve) in kW DIgSILENT
Grid Stability Workshop. Pacific Islands 19 30% PV Penetration Level 166,0132,899,6066,4033,200,000 [-] 4.0E+3 3.0E+3 2.0E+3 1.0E+3 0.0E+0 -1.0E+3 AIMELLIK_SiteNew Unit-1: Active Pow er in kW AIMELLIK_SiteNew Unit-2: Active Pow er in kW 166,0132,899,6066,4033,200,000 [-] 6000,00 5000,00 4000,00 3000,00 2000,00 1000,00 MALAKAL_SiteNIIGATA1: Active Pow er in kW MALAKAL_SiteNIIGATA2: Active Pow er in kW 166,0132,899,6066,4033,200,000 [-] 6,00 5,00 4,00 3,00 2,00 1,00 Dispatch Merit Order: Number of dispatched generators X = 60,000 3.000 DIgSILENT
Grid Stability Workshop. Pacific Islands 20 30% PV Penetration Level 30,0023,0016,009,0002,000-5,000 [s] 60,30 59,90 59,50 59,10 58,70 58,30 MALAKAL_SiteNIIGATA1: Frequency Output in p.u. (base: 0,02 p.u.) X = -3,500 s 60.000 p.u. X = 20,000 s 59.130 p.u. Y = 58,200 p.u. 30,0023,0016,009,0002,000-5,000 [s] 4,00 3,00 2,00 1,00 0,00 -1,00 Total PV Generation: Total PV Generation in MW X = -3,500 s 3.523 MW X = 20,000 s 0.000 MW 30,0023,0016,009,0002,000-5,000 [s] 6,25 5,00 3,75 2,50 1,25 0,00 MALAKAL_SiteNIIGATA1: Positive-Sequence, Active Pow er in MW MALAKAL_SiteNIIGATA2: Positive-Sequence, Active Pow er in MW MALAKAL_SiteWART1: Positive-Sequence, Active Pow er in MW X = -3,500 s 0.800 MW 2.000 MW 3.432 MW X = 20,000 s 1.354 MW 3.743 MW 4.646 MW 30,0023,0016,009,0002,000-5,000 [s] 9800,00 9700,00 9600,00 9500,00 9400,00 9300,00 Summary Grid: General Load, Active Pow er in kW X = -3,500 s 9610.513 kW X = 20,000 s 9566.671 kW DIgSILENT
 Power balance/ dispatch • Renewable generation sees as negative load • Additional spinning reserve required to cover most of PV power output variability: in Palau’s case +35% of PV generation for time intervals of 1 hour  Frequency stability • Even the sudden loss of all PV power output (previous simulation) does not cause a frequency instability in the system but the diesel generators can manage the PV output fluctuation • Same frequency behavior expected as in the current system with no (or very low level) of renewable penetration Grid Stability Workshop. Pacific Islands 21 30% PV Penetration Level
70% PV Penetration Level Grid Stability Workshop. Pacific Islands 22 166,0132,899,6066,4033,200,000 [-] 2.00E+4 1.60E+4 1.20E+4 8.00E+3 4.00E+3 0.00E+0 Dispatch Merit Order: Net load in kW Dispatch Merit Order: Minimum dispatch pow er in kW Dispatch Merit Order: Maximum dispatch pow er in kW Dispatch Merit Order: Required dispatch pow er (incl. PV reserve) in kW 166,0132,899,6066,4033,200,000 [-] 1.60E+4 1.30E+4 1.00E+4 7.00E+3 4.00E+3 1.00E+3 1.0E+4 7.5E+3 5.0E+3 2.5E+3 0.0E+0 -2.5E+3 Dispatch Merit Order: Net load in kW Dispatch Merit Order: Renew able generation in kW Dispatch Merit Order: Required dispatch pow er (incl. PV reserve) in kW Dispatch Merit Order: Required dispatch pow er (w /o PV reserve) in kW DIgSILENT
70% PV Penetration Level Grid Stability Workshop. Pacific Islands 23 166,0132,899,6066,4033,200,000 [-] 6000,00 5000,00 4000,00 3000,00 2000,00 1000,00 MALAKAL_SiteNIIGATA1: Active Pow er in kW MALAKAL_SiteNIIGATA2: Active Pow er in kW 166,0132,899,6066,4033,200,000 [-] 2.0E+3 1.0E+3 0.0E+0 -1.0E+3 -2.0E+3 -3.0E+3 Storage: Active Pow er in kW 166,0132,899,6066,4033,200,000 [-] 4.0E+3 3.0E+3 2.0E+3 1.0E+3 0.0E+0 -1.0E+3 AIMELLIK_SiteNew Unit-1: Active Pow er in kW 166,0132,899,6066,4033,200,000 [-] 5,00 4,00 3,00 2,00 1,00 0,00 Dispatch Merit Order: Number of dispatched generators DIgSILENT
The Role of Storage with Increasing Penetration Levels  At high PV penetration-levels, storage could be used to cover short time fluctuations in PV supply and hence to allow for significant reductions in the consumption of fuel (reduction of the number of running diesel generators)  The main system reserve remains the diesel generation  However, the amount of storage is generally driven by the cost of energy (COE) and economics.  Additional studies are required to determine the optimal integration conditions  Storage technologies  Freewheels (discharge time ~ seconds to few minutes, power rating < 1MW)  Li-Ion and Lead-Acid Batteries (discharge time ~ minutes, power rating < 1MW) Grid Stability Workshop. Pacific Islands 24
Grid Stability Workshop. Pacific Islands 25 30,0023,0016,009,0002,000-5,000 [s] 60,30 59,80 59,30 58,80 58,30 57,80 MALAKAL_SiteNIIGATA1: Frequency Output in p.u. (base: 0,02 p.u.) X = -2,000 s 60.000 p.u. 58.200 p.u. X = 20,000 s 58.993 p.u. 58.200 p.u. Y = 58,200 p.u. 30,0023,0016,009,0002,000-5,000 [s] 9,00 8,00 7,00 6,00 5,00 4,00 Total PV Generation: Total PV Generation in MW X = -2,000 s 7.321 MW X = 20,000 s 5.246 MW 30,0023,0016,009,0002,000-5,000 [s] 5,00 4,00 3,00 2,00 1,00 0,00 MALAKAL_SiteNIIGATA1: Positive-Sequence, Active Pow er in MW MALAKAL_SiteWART1: Positive-Sequence, Active Pow er in MW X = -2,000 s 0.800 MW 2.132 MW X = 20,000 s 1.441 MW 3.560 MW 30,0023,0016,009,0002,000-5,000 [s] 1.01E+4 1.01E+4 1.00E+4 9.96E+3 9.91E+3 9.86E+3 Summary Grid: General Load, Active Pow er in kW X = -2,000 s 10094.035 kW X = 20,000 s 10086.038 kW DIgSILENT 70% PV Penetration Level
70% PV Penetration Level (without additional reserve for PV Generation) Grid Stability Workshop. Pacific Islands 26 166,0132,899,6066,4033,200,000 [-] 2.00E+4 1.60E+4 1.20E+4 8.00E+3 4.00E+3 0.00E+0 Dispatch Merit Order: Net load in kW Dispatch Merit Order: Minimum dispatch pow er in kW Dispatch Merit Order: Maximum dispatch pow er in kW Dispatch Merit Order: Required dispatch pow er in kW 166,0132,899,6066,4033,200,000 [-] 1.60E+4 1.30E+4 1.00E+4 7.00E+3 4.00E+3 1.00E+3 1.0E+4 7.5E+3 5.0E+3 2.5E+3 0.0E+0 -2.5E+3 Dispatch Merit Order: Net load in kW Dispatch Merit Order: Renew able generation in kW Dispatch Merit Order: Required dispatch pow er in kW DIgSILENT
Grid Stability Workshop. Pacific Islands 27 166,0132,899,6066,4033,200,000 [-] 5.0E+3 3.8E+3 2.5E+3 1.3E+3 0.0E+0 -1.3E+3 MALAKAL_SiteNIIGATA1: Active Pow er in kW MALAKAL_SiteNIIGATA2: Active Pow er in kW 166,0132,899,6066,4033,200,000 [-] 2.0E+3 1.0E+3 -2.3E-1.. -1.0E+3 -2.0E+3 -3.0E+3 Storage: Active Pow er in kW 166,0132,899,6066,4033,200,000 [-] 4.0E+3 3.0E+3 2.0E+3 1.0E+3 0.0E+0 -1.0E+3 AIMELLIK_SiteNew Unit-1: Active Pow er in kW 166,0132,899,6066,4033,200,000 [-] 5,00 4,00 3,00 2,00 1,00 0,00 Dispatch Merit Order: Number of dispatched generators DIgSILENT 70% PV Penetration Level (without additional reserve for PV Generation)
Grid Stability Workshop. Pacific Islands 28 70% PV Penetration Level: Without Additional Reserve for PV Generation 30,0023,0016,009,0002,000-5,000 [s] 60,20 59,90 59,60 59,30 59,00 58,70 MALAKAL_SiteNIIGATA1: Frequency Output in p.u. (base: 0,02 p.u.) X = -2,000 s 60.001 p.u. X = 25,000 s 59.158 p.u. 30,0023,0016,009,0002,000-5,000 [s] 7,80 7,50 7,20 6,90 6,60 6,30 Total PV Generation: Total PV Generation in MW X = -2,000 s 7.606 MW X = 25,000 s 6.410 MW 30,0023,0016,009,0002,000-5,000 [s] 4,00 3,70 3,40 3,10 2,80 2,50 MALAKAL_SiteNIIGATA1: Positive-Sequence, Active Pow er in MW X = -2,000 s 2.652 MW X = 25,000 s 3.841 MW 30,0023,0016,009,0002,000-5,000 [s] 1.01E+4 1.01E+4 1.00E+4 9.96E+3 9.91E+3 9.86E+3 Summary Grid: General Load, Active Pow er in kW X = -2,000 s 10092.506 kW X = 25,000 s 10084.094 kW DIgSILENT
Frequency Stability After a Fault Grid Stability Workshop. Pacific Islands 29
Grid Stability Workshop. Pacific Islands 30 5% PV Penetration Level: FRT Capability 10,008,006,004,002,000,00 [s] 60,60 60,40 60,20 60,00 59,80 59,60 MALAKAL_SiteNIIGATA1: Frequency Output in p.u. (base: 0,02 p.u.) 10,008,006,004,002,000,00 [s] 1,00 0,80 0,60 0,40 0,20 0,00 Total PV Generation: Total PV Generation in MW 10,008,006,004,002,000,00 [s] 1,25 1,00 0,75 0,50 0,25 0,00 MALAKAL_SiteNIIGATA1: Terminal Voltage in p.u. MALAKAL_SitePP-MALAKAL-BUS4: Voltage, Magnitude in p.u. F-AIRAI-10: Voltage, Magnitude in p.u. DIgSILENT
Grid Stability Workshop. Pacific Islands 31 30% PV Penetration Level: FRT Capability 10,008,006,004,002,000,00 [s] 5,00 4,00 3,00 2,00 1,00 0,00 Total PV Generation: Total PV Generation in MW MALAKAL_SiteNIIGATA1: Positive-Sequence, Active Pow er in MW MALAKAL_SiteWART1: Positive-Sequence, Active Pow er in MW 10,008,006,004,002,000,00 [s] 1,20 0,90 0,60 0,30 0,00 -0,30 MALAKAL_SiteNIIGATA1: Terminal Voltage in p.u. MALAKAL_SitePP-MALAKAL-BUS4: Voltage, Magnitude in p.u. F-AIRAI-10: Voltage, Magnitude in p.u. 10,008,006,004,002,000,00 [s] 60,90 60,60 60,30 60,00 59,70 59,40 MALAKAL_SiteNIIGATA1: Frequency Output in p.u. (base: 0,02 p.u.) MALAKAL_SiteNIIGATA1: Frequency Output in p.u. (base: 0,02 p.u.) DIgSILENT
Grid Stability Workshop. Pacific Islands 32 70% PV Penetration Level: FRT Capability 10,008,006,004,002,000,00 [s] 61,50 61,00 60,50 60,00 59,50 59,00 MALAKAL_SiteNIIGATA1: Frequency (considering Storage) MALAKAL_SiteNIIGATA1: Frequency (w ithout Storage) 10,008,006,004,002,000,00 [s] 10,00 7,50 5,00 2,50 0,00 -2,50 Total PV Generation: Total PV Generation in MW MALAKAL_SiteNIIGATA1: Positive-Sequence, Active Pow er in MW 10,008,006,004,002,000,00 [s] 1,30 1,00 0,70 0,40 0,10 -0,20 MALAKAL_SiteNIIGATA1: Terminal Voltage in p.u. MALAKAL_SitePP-MALAKAL-BUS4: Voltage, Magnitude in p.u. F-AIRAI-10: Voltage, Magnitude in p.u. DIgSILENT
Grid Stability Workshop. Pacific Islands 33  PV generators operate in “voltage support” mode and therefore inject reactive power during the fault.  As a consequence, the active power output of PV generators is automatically reduced during faults.  Hence for increasing levels of PV penetration, the power reduction (in absolute terms) during the fault will increase and therefore the system will experience a higher transient frequency deviation.  Transient frequency behavior depends on:  Voltage and frequency dependency of the loads (modelled as PQ loads in these simulations – may not be a good assumption)  The fault clearing times (assumed 150ms in these simulations)  These models parameters were not known at the time of the study and therefore the results have to be verified Fault-Ride-Through Capability
Grid Stability Workshop. Pacific Islands 34  A relative small storage system (Battery or Flywheel) can help to reduce frequency deviations and improve the frequency response during faults.  Size of the battery/storage system depend on the maximum frequency deviations that want to be achieved  However, unknown relevant model parameters (fault clearing times, voltage dependency of the loads) have be verified firstly. Fault-Ride-Through Capability
Conclusions The Way Forward Grid Stability Workshop. Pacific Islands 35
Grid Stability Workshop. Pacific Islands 36  PV penetration level ≤ 30%  Can be integrated without any special control requirements (change in dispatch strategy, balancing mechanisms, storage, etc.) • Complexity of system operation remains the same  Power balancing/dispatch: • Renewable generation seen as negative load • Additional spinning reserve required to cover most of PV power output variability: in Palau’s case +35% of PV generation for time intervals of 1 hour (confidence level of 99.7% of the variations on a Gaussian distribution, i.e. 3δ)  Frequency stability • PV power output variability for time intervals from 1s up to 10m do not negatively impact the dynamic behavior of the frequency • Same frequency behavior expected as in the current system with no (or very low level) of renewable penetration Conclusions
Grid Stability Workshop. Pacific Islands 37  PV penetration level > 30%  In order to avoid curtailing PV output during time times of high PV generation, the number of diesel generators dispatched can be reduced (in order to minimize fuel costs).  A reduced number of running diesel machines reduces the spinning reserve and therefore the maximum PV power output fluctuation that the system can allow (for 70% PV penetration the maximum allowable PV fluctuation is of about 16%).  Based on the currently available PV time-series measurements, higher fluctuations cannot be precluded.  Additional spinning reserve and frequency control can be achieved by the installation of flywheels or batteries (storage)  Amount of storage generally driven by economics • Additional studies required to determine the optimal level of storage (economics) Conclusions
Grid Stability Workshop. Pacific Islands 38  PV penetration level > 30% (cont.)  Increased need for control and operational requirements (e.g. change in dispatch strategy, balancing mechanisms, storage, etc.) leads to increased complexity of system operation  However, simulation tools with an adequate model of the power system can be used to automatically calculate required reserves and diesel dispatch Conclusions
Grid Stability Workshop. Pacific Islands 39  Short and medium term plan:  Up to 30% of PV penetration level (instantaneous, i.e. power penetration) no changed required  To minimize PV power output fluctuations and hence reduce the total amount of spinning reserve, a geographical dispersed PV generation should be preferred.  Long term plans  To allow PV penetration levels > 30%:  High quality of PV generation/ solar irradiance measurements would be of a great advantage  Dynamic stability can be guaranteed by an adequate allocation of additional reserves (in terms of diesel generation or storage)  Additional studies required to determine economically optimal penetration level (i.e. balance between diesel reserve and additional storage reserve in terms of flywheels or batteries) The Way Forward
Grid Stability Workshop. Pacific Islands 40 Thanks for your attention

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DigSILENT PF - 01 pilot project palau

  • 1. Pilot Study on Grid Stability Assessment for the Island of Palau (Preliminary results) Flavio Fernández, Stefan Weigel, José Gomez and Julius Susanto DIgSILENT GmbH, Germany Grid Stability Workshop. Pacific Islands 1
  • 2. Grid Stability Workshop. Pacific Islands 2 Overview of the Presentation  Introduction  Project background  Solar resource metrics  Characterization of power output fluctuations  Impact on the system stability  Frequency Stability (PV penetration 5%(current), 30%, 70%)  Power balance and generation dispatch  Assessment of dynamic frequency stability  Fault-Ride Through  Conclusions and recommendations. The way forward.
  • 3. Grid Stability Workshop. Pacific Islands 3 Project Background  Part of the IRENA Islands Initiative project to assist islands in the Pacific Region with their planning for renewable energy integration, especially the grid stability assessment and identification of specific technology solutions  Objectives  Develop a methodology of assessing the impact of different levels of variable generation on power quality (focus on frequency stability)  Set up a simulation model to assess the dynamic stability of the system (pilot project: the system of Palau island has been chosen)  Identify the amount of renewable generation that the system can accommodate without affecting the power quality  Identify specific technology solutions (like for instance storage) where required
  • 4. Grid Stability Workshop. Pacific Islands 4 Project Background  What has already been done:  Steady-state data from a previous PPA’s loss study converted from EasyPower software into DIgSILENT PowerFactory.  Results validated for load flow.  Collection and modeling of load/PV-resource profiles:  PV power output available for one year in 1hs resolution  Load profile available for 1 week, in 1hs resolution  Model setup using standard dynamic data.  Preliminary results:  Assessment of frequency stability for PV penetration levels of 5% (current status), 30%, 50% and 70%.  Subject to validation of the dynamic model
  • 5. Grid Stability Workshop. Pacific Islands 5 Project Background  Next steps:  Validation of dynamic data  Collection and verification of missing data:  Load shedding scheme (incl. tripping times)  Contingency reserve  Voltage/Frequency dependency of loads  Investigate voltage stability and transient stability (contingent on receiving the necessary dynamic data)  Delivery of the study report including results, conclusions and recommendations.
  • 6. Solar Resource Metrics Characterization of PV power output fluctuations Grid Stability Workshop. Pacific Islands 6
  • 7. Penetration-Level Metrics Grid Stability Workshop. Pacific Islands 7
  • 8. Grid Stability Workshop. Pacific Islands 8  Characterization of PV power output fluctuations is important to assess the impact of PV plants on system stability  Fluctuations of PV power output depend mainly on:  Size of the PV plant  Geographical dispersion of the PV plants  Ramp rate interval (i.e. time interval during which fluctuations occur)  Weather conditions  Time-based measurements can be used to statistically characterize the amplitude and frequency of occurrence of the fluctuations, usually presented as:  Distribution of changes (how often they occur) as a function of the fluctuation amplitude for given ramp rate intervals  Percentage of maximum fluctuations as a function of the ramp rate interval PV Power Output Variability
  • 9. Grid Stability Workshop. Pacific Islands 9 PV Power Output Variability  Power fluctuations for four ramp rate intervals of a 1MW PV plant (at STC) and the existing PV plants in Palau (installed capacity 770 kW) 0.0 1.0 2.0 3.0 4.0 5.0 -60 -40 -20 0 20 40 60 RelativeFrequency(%) Power Fluctuation (% of PV rating) 1 hour 10 m 1 m 10 s Palau (1 hour)
  • 10. Grid Stability Workshop. Pacific Islands 10  Time-series measurements provided by PPA over a 1 year period for the currently existing PV plants (installed power approx. 770 kW) with an hourly time resolution:  Reserve requirement based on a confidence level of 99.7% (corresponds to 3δ): 35% of PV power output (orange curve in previous slide, Palau’s case)  For the characterization of short-term fluctuations, measurements with a higher time resolution are required (seconds to minutes)  A reliable characterization of short-term PV power output fluctuations (from 1s to aporox. 10 minutes) will allow an accurate calculation of minimum spinning reserves and therefore an optimization of diesel dispatch and/or additional solutions (such as storage) PV Power Output Variability
  • 11. Frequency Stability Spinning Reserve and PV Output Fluctuations Grid Stability Workshop. Pacific Islands 11
  • 12. Frequency Stability: Spinning Reserve  Incremental need for additional operating reserves due to higher penetration- levels of non-dispatchable generation:  Disturbance (contingency) reserve: current 2 MW for Palau grid  Additional reserve: 35% of installed PV generation for Palau grid  Additional reserve calculated based on the probability distribution of PV power output fluctuations:  35% of PV power output  Demand time-series are not available (for the same period of PV measurements) so that no correlation between load and PV generation can be considered (conservative assumption) Grid Stability Workshop. Pacific Islands 12
  • 13.  Dispatch of diesel generators: • Dispatch to meet minimum operating reserve (contingency reserve + additional reserve) • Observation of maximum and minimum power output operational limits • Merit order according to fuel costs • Analysis carried out for 7 days for which demand data is available • From May 2014, two new diesel units in Aimeliik (2 x 4.5 MW) will also available Grid Stability Workshop. Pacific Islands 13 Frequency Stability: Spinning Reserve
  • 14. Grid Stability Workshop. Pacific Islands 14 5% PV Penetration Level (current status) 166,0132,899,6066,4033,200,000 [-] 1.55E+4 1.30E+4 1.05E+4 8.00E+3 5.50E+3 3.00E+3 Dispatch Merit Order: Net load in kW Dispatch Merit Order: Minimum dispatch pow er in kW Dispatch Merit Order: Maximum dispatch pow er in kW Dispatch Merit Order: Required dispatch pow er in kW 166,0132,899,6066,4033,200,000 [-] 1.60E+4 1.40E+4 1.20E+4 1.00E+4 8.00E+3 6.00E+3 800,00 600,00 400,00 200,00 0,00 -200,00 Dispatch Merit Order: Net load in kW Dispatch Merit Order: Renew able generation in kW Dispatch Merit Order: Required dispatch pow er in kW DIgSILENT
  • 15. Grid Stability Workshop. Pacific Islands 15 5% PV Penetration Level (current status) 166,0132,899,6066,4033,200,000 [-] 1.6E+3 1.2E+3 8.0E+2 4.0E+2 0.0E+0 -4.0E+2 MALAKAL_SiteMIT13: Active Pow er in kW MALAKAL_SiteMIT12: Active Pow er in kW 166,0132,899,6066,4033,200,000 [-] 6000,00 5000,00 4000,00 3000,00 2000,00 1000,00 MALAKAL_SiteNIIGATA1: Active Pow er in kW MALAKAL_SiteNIIGATA2: Active Pow er in kW 166,0132,899,6066,4033,200,000 [-] 6,00 5,00 4,00 3,00 2,00 1,00 Dispatch Merit Order: Number of dispatched generators DIgSILENT
  • 16.  As dynamic data of diesel generators is not available, model has been set up using standard controllers and parameters.  An indirect validation exercise was done by simulating a load step change:  2.5 MW of 12 MW dispatched generation (Nigatta 1 and 2, Mit13) and comparison against the maximum frequency excursion allowable in the system  PPA advised that the system remains stable and within frequency limits after such a load step:  Max. allowed deviation: +/- 1.0 Hz (steady state)  First under frequency relay: 58,2 Hz  The simulation results confirmed these observations.  It is strongly recommended to validate the model against records of system perturbations (not available at this time). Grid Stability Workshop. Pacific Islands 16 5% PV Penetration Level (current status)
  • 17. 5% PV Penetration Level (current status) Grid Stability Workshop. Pacific Islands 17 20,0016,0012,008,004,000,00 [s] 60,50 60,00 59,50 59,00 58,50 58,00 MALAKAL_SitePP-MALAKAL-BUS4: Electrical Frequency in p.u. (base: 0,02 ) 59.5 Hz 1st Underfrequency Relay @58.2 Hz 0.702 s 58.475 p.u. 20,0016,0012,008,004,000,00 [s] 6,00 5,00 4,00 3,00 2,00 1,00 MALAKAL_SiteMIT13: Positive-Sequence, Active Pow er in MW MALAKAL_SiteNIIGATA1: Positive-Sequence, Active Pow er in MW MALAKAL_SiteNIIGATA2: Positive-Sequence, Active Pow er in MW 20,0016,0012,008,004,000,00 [s] 8,00 6,00 4,00 2,00 0,00 -2,00 Base Load: Total Active Pow er in MW Variable Load: Total Active Pow er in MW 0.005 s 2.561 MW DIgSILENT
  • 18. Grid Stability Workshop. Pacific Islands 18 30% PV Penetration Level 166,0132,899,6066,4033,200,000 [-] 2.20E+4 1.80E+4 1.40E+4 1.00E+4 6.00E+3 2.00E+3 Dispatch Merit Order: Net load in kW Dispatch Merit Order: Minimum dispatch pow er in kW Dispatch Merit Order: Maximum dispatch pow er in kW Dispatch Merit Order: Required dispatch pow er (incl. PV reserve) in kW 166,0132,899,6066,4033,200,000 [-] 1.65E+4 1.40E+4 1.15E+4 9.00E+3 6.50E+3 4.00E+3 5.0E+3 3.8E+3 2.5E+3 1.3E+3 0.0E+0 -1.3E+3 Summary Grid: General Load, Active Pow er in kW Dispatch Merit Order: Renew able generation in kW Dispatch Merit Order: Required dispatch pow er (incl. PV reserve) in kW Dispatch Merit Order: Required dispatch pow er (w /o PV reserve) in kW DIgSILENT
  • 19. Grid Stability Workshop. Pacific Islands 19 30% PV Penetration Level 166,0132,899,6066,4033,200,000 [-] 4.0E+3 3.0E+3 2.0E+3 1.0E+3 0.0E+0 -1.0E+3 AIMELLIK_SiteNew Unit-1: Active Pow er in kW AIMELLIK_SiteNew Unit-2: Active Pow er in kW 166,0132,899,6066,4033,200,000 [-] 6000,00 5000,00 4000,00 3000,00 2000,00 1000,00 MALAKAL_SiteNIIGATA1: Active Pow er in kW MALAKAL_SiteNIIGATA2: Active Pow er in kW 166,0132,899,6066,4033,200,000 [-] 6,00 5,00 4,00 3,00 2,00 1,00 Dispatch Merit Order: Number of dispatched generators X = 60,000 3.000 DIgSILENT
  • 20. Grid Stability Workshop. Pacific Islands 20 30% PV Penetration Level 30,0023,0016,009,0002,000-5,000 [s] 60,30 59,90 59,50 59,10 58,70 58,30 MALAKAL_SiteNIIGATA1: Frequency Output in p.u. (base: 0,02 p.u.) X = -3,500 s 60.000 p.u. X = 20,000 s 59.130 p.u. Y = 58,200 p.u. 30,0023,0016,009,0002,000-5,000 [s] 4,00 3,00 2,00 1,00 0,00 -1,00 Total PV Generation: Total PV Generation in MW X = -3,500 s 3.523 MW X = 20,000 s 0.000 MW 30,0023,0016,009,0002,000-5,000 [s] 6,25 5,00 3,75 2,50 1,25 0,00 MALAKAL_SiteNIIGATA1: Positive-Sequence, Active Pow er in MW MALAKAL_SiteNIIGATA2: Positive-Sequence, Active Pow er in MW MALAKAL_SiteWART1: Positive-Sequence, Active Pow er in MW X = -3,500 s 0.800 MW 2.000 MW 3.432 MW X = 20,000 s 1.354 MW 3.743 MW 4.646 MW 30,0023,0016,009,0002,000-5,000 [s] 9800,00 9700,00 9600,00 9500,00 9400,00 9300,00 Summary Grid: General Load, Active Pow er in kW X = -3,500 s 9610.513 kW X = 20,000 s 9566.671 kW DIgSILENT
  • 21.  Power balance/ dispatch • Renewable generation sees as negative load • Additional spinning reserve required to cover most of PV power output variability: in Palau’s case +35% of PV generation for time intervals of 1 hour  Frequency stability • Even the sudden loss of all PV power output (previous simulation) does not cause a frequency instability in the system but the diesel generators can manage the PV output fluctuation • Same frequency behavior expected as in the current system with no (or very low level) of renewable penetration Grid Stability Workshop. Pacific Islands 21 30% PV Penetration Level
  • 22. 70% PV Penetration Level Grid Stability Workshop. Pacific Islands 22 166,0132,899,6066,4033,200,000 [-] 2.00E+4 1.60E+4 1.20E+4 8.00E+3 4.00E+3 0.00E+0 Dispatch Merit Order: Net load in kW Dispatch Merit Order: Minimum dispatch pow er in kW Dispatch Merit Order: Maximum dispatch pow er in kW Dispatch Merit Order: Required dispatch pow er (incl. PV reserve) in kW 166,0132,899,6066,4033,200,000 [-] 1.60E+4 1.30E+4 1.00E+4 7.00E+3 4.00E+3 1.00E+3 1.0E+4 7.5E+3 5.0E+3 2.5E+3 0.0E+0 -2.5E+3 Dispatch Merit Order: Net load in kW Dispatch Merit Order: Renew able generation in kW Dispatch Merit Order: Required dispatch pow er (incl. PV reserve) in kW Dispatch Merit Order: Required dispatch pow er (w /o PV reserve) in kW DIgSILENT
  • 23. 70% PV Penetration Level Grid Stability Workshop. Pacific Islands 23 166,0132,899,6066,4033,200,000 [-] 6000,00 5000,00 4000,00 3000,00 2000,00 1000,00 MALAKAL_SiteNIIGATA1: Active Pow er in kW MALAKAL_SiteNIIGATA2: Active Pow er in kW 166,0132,899,6066,4033,200,000 [-] 2.0E+3 1.0E+3 0.0E+0 -1.0E+3 -2.0E+3 -3.0E+3 Storage: Active Pow er in kW 166,0132,899,6066,4033,200,000 [-] 4.0E+3 3.0E+3 2.0E+3 1.0E+3 0.0E+0 -1.0E+3 AIMELLIK_SiteNew Unit-1: Active Pow er in kW 166,0132,899,6066,4033,200,000 [-] 5,00 4,00 3,00 2,00 1,00 0,00 Dispatch Merit Order: Number of dispatched generators DIgSILENT
  • 24. The Role of Storage with Increasing Penetration Levels  At high PV penetration-levels, storage could be used to cover short time fluctuations in PV supply and hence to allow for significant reductions in the consumption of fuel (reduction of the number of running diesel generators)  The main system reserve remains the diesel generation  However, the amount of storage is generally driven by the cost of energy (COE) and economics.  Additional studies are required to determine the optimal integration conditions  Storage technologies  Freewheels (discharge time ~ seconds to few minutes, power rating < 1MW)  Li-Ion and Lead-Acid Batteries (discharge time ~ minutes, power rating < 1MW) Grid Stability Workshop. Pacific Islands 24
  • 25. Grid Stability Workshop. Pacific Islands 25 30,0023,0016,009,0002,000-5,000 [s] 60,30 59,80 59,30 58,80 58,30 57,80 MALAKAL_SiteNIIGATA1: Frequency Output in p.u. (base: 0,02 p.u.) X = -2,000 s 60.000 p.u. 58.200 p.u. X = 20,000 s 58.993 p.u. 58.200 p.u. Y = 58,200 p.u. 30,0023,0016,009,0002,000-5,000 [s] 9,00 8,00 7,00 6,00 5,00 4,00 Total PV Generation: Total PV Generation in MW X = -2,000 s 7.321 MW X = 20,000 s 5.246 MW 30,0023,0016,009,0002,000-5,000 [s] 5,00 4,00 3,00 2,00 1,00 0,00 MALAKAL_SiteNIIGATA1: Positive-Sequence, Active Pow er in MW MALAKAL_SiteWART1: Positive-Sequence, Active Pow er in MW X = -2,000 s 0.800 MW 2.132 MW X = 20,000 s 1.441 MW 3.560 MW 30,0023,0016,009,0002,000-5,000 [s] 1.01E+4 1.01E+4 1.00E+4 9.96E+3 9.91E+3 9.86E+3 Summary Grid: General Load, Active Pow er in kW X = -2,000 s 10094.035 kW X = 20,000 s 10086.038 kW DIgSILENT 70% PV Penetration Level
  • 26. 70% PV Penetration Level (without additional reserve for PV Generation) Grid Stability Workshop. Pacific Islands 26 166,0132,899,6066,4033,200,000 [-] 2.00E+4 1.60E+4 1.20E+4 8.00E+3 4.00E+3 0.00E+0 Dispatch Merit Order: Net load in kW Dispatch Merit Order: Minimum dispatch pow er in kW Dispatch Merit Order: Maximum dispatch pow er in kW Dispatch Merit Order: Required dispatch pow er in kW 166,0132,899,6066,4033,200,000 [-] 1.60E+4 1.30E+4 1.00E+4 7.00E+3 4.00E+3 1.00E+3 1.0E+4 7.5E+3 5.0E+3 2.5E+3 0.0E+0 -2.5E+3 Dispatch Merit Order: Net load in kW Dispatch Merit Order: Renew able generation in kW Dispatch Merit Order: Required dispatch pow er in kW DIgSILENT
  • 27. Grid Stability Workshop. Pacific Islands 27 166,0132,899,6066,4033,200,000 [-] 5.0E+3 3.8E+3 2.5E+3 1.3E+3 0.0E+0 -1.3E+3 MALAKAL_SiteNIIGATA1: Active Pow er in kW MALAKAL_SiteNIIGATA2: Active Pow er in kW 166,0132,899,6066,4033,200,000 [-] 2.0E+3 1.0E+3 -2.3E-1.. -1.0E+3 -2.0E+3 -3.0E+3 Storage: Active Pow er in kW 166,0132,899,6066,4033,200,000 [-] 4.0E+3 3.0E+3 2.0E+3 1.0E+3 0.0E+0 -1.0E+3 AIMELLIK_SiteNew Unit-1: Active Pow er in kW 166,0132,899,6066,4033,200,000 [-] 5,00 4,00 3,00 2,00 1,00 0,00 Dispatch Merit Order: Number of dispatched generators DIgSILENT 70% PV Penetration Level (without additional reserve for PV Generation)
  • 28. Grid Stability Workshop. Pacific Islands 28 70% PV Penetration Level: Without Additional Reserve for PV Generation 30,0023,0016,009,0002,000-5,000 [s] 60,20 59,90 59,60 59,30 59,00 58,70 MALAKAL_SiteNIIGATA1: Frequency Output in p.u. (base: 0,02 p.u.) X = -2,000 s 60.001 p.u. X = 25,000 s 59.158 p.u. 30,0023,0016,009,0002,000-5,000 [s] 7,80 7,50 7,20 6,90 6,60 6,30 Total PV Generation: Total PV Generation in MW X = -2,000 s 7.606 MW X = 25,000 s 6.410 MW 30,0023,0016,009,0002,000-5,000 [s] 4,00 3,70 3,40 3,10 2,80 2,50 MALAKAL_SiteNIIGATA1: Positive-Sequence, Active Pow er in MW X = -2,000 s 2.652 MW X = 25,000 s 3.841 MW 30,0023,0016,009,0002,000-5,000 [s] 1.01E+4 1.01E+4 1.00E+4 9.96E+3 9.91E+3 9.86E+3 Summary Grid: General Load, Active Pow er in kW X = -2,000 s 10092.506 kW X = 25,000 s 10084.094 kW DIgSILENT
  • 29. Frequency Stability After a Fault Grid Stability Workshop. Pacific Islands 29
  • 30. Grid Stability Workshop. Pacific Islands 30 5% PV Penetration Level: FRT Capability 10,008,006,004,002,000,00 [s] 60,60 60,40 60,20 60,00 59,80 59,60 MALAKAL_SiteNIIGATA1: Frequency Output in p.u. (base: 0,02 p.u.) 10,008,006,004,002,000,00 [s] 1,00 0,80 0,60 0,40 0,20 0,00 Total PV Generation: Total PV Generation in MW 10,008,006,004,002,000,00 [s] 1,25 1,00 0,75 0,50 0,25 0,00 MALAKAL_SiteNIIGATA1: Terminal Voltage in p.u. MALAKAL_SitePP-MALAKAL-BUS4: Voltage, Magnitude in p.u. F-AIRAI-10: Voltage, Magnitude in p.u. DIgSILENT
  • 31. Grid Stability Workshop. Pacific Islands 31 30% PV Penetration Level: FRT Capability 10,008,006,004,002,000,00 [s] 5,00 4,00 3,00 2,00 1,00 0,00 Total PV Generation: Total PV Generation in MW MALAKAL_SiteNIIGATA1: Positive-Sequence, Active Pow er in MW MALAKAL_SiteWART1: Positive-Sequence, Active Pow er in MW 10,008,006,004,002,000,00 [s] 1,20 0,90 0,60 0,30 0,00 -0,30 MALAKAL_SiteNIIGATA1: Terminal Voltage in p.u. MALAKAL_SitePP-MALAKAL-BUS4: Voltage, Magnitude in p.u. F-AIRAI-10: Voltage, Magnitude in p.u. 10,008,006,004,002,000,00 [s] 60,90 60,60 60,30 60,00 59,70 59,40 MALAKAL_SiteNIIGATA1: Frequency Output in p.u. (base: 0,02 p.u.) MALAKAL_SiteNIIGATA1: Frequency Output in p.u. (base: 0,02 p.u.) DIgSILENT
  • 32. Grid Stability Workshop. Pacific Islands 32 70% PV Penetration Level: FRT Capability 10,008,006,004,002,000,00 [s] 61,50 61,00 60,50 60,00 59,50 59,00 MALAKAL_SiteNIIGATA1: Frequency (considering Storage) MALAKAL_SiteNIIGATA1: Frequency (w ithout Storage) 10,008,006,004,002,000,00 [s] 10,00 7,50 5,00 2,50 0,00 -2,50 Total PV Generation: Total PV Generation in MW MALAKAL_SiteNIIGATA1: Positive-Sequence, Active Pow er in MW 10,008,006,004,002,000,00 [s] 1,30 1,00 0,70 0,40 0,10 -0,20 MALAKAL_SiteNIIGATA1: Terminal Voltage in p.u. MALAKAL_SitePP-MALAKAL-BUS4: Voltage, Magnitude in p.u. F-AIRAI-10: Voltage, Magnitude in p.u. DIgSILENT
  • 33. Grid Stability Workshop. Pacific Islands 33  PV generators operate in “voltage support” mode and therefore inject reactive power during the fault.  As a consequence, the active power output of PV generators is automatically reduced during faults.  Hence for increasing levels of PV penetration, the power reduction (in absolute terms) during the fault will increase and therefore the system will experience a higher transient frequency deviation.  Transient frequency behavior depends on:  Voltage and frequency dependency of the loads (modelled as PQ loads in these simulations – may not be a good assumption)  The fault clearing times (assumed 150ms in these simulations)  These models parameters were not known at the time of the study and therefore the results have to be verified Fault-Ride-Through Capability
  • 34. Grid Stability Workshop. Pacific Islands 34  A relative small storage system (Battery or Flywheel) can help to reduce frequency deviations and improve the frequency response during faults.  Size of the battery/storage system depend on the maximum frequency deviations that want to be achieved  However, unknown relevant model parameters (fault clearing times, voltage dependency of the loads) have be verified firstly. Fault-Ride-Through Capability
  • 35. Conclusions The Way Forward Grid Stability Workshop. Pacific Islands 35
  • 36. Grid Stability Workshop. Pacific Islands 36  PV penetration level ≤ 30%  Can be integrated without any special control requirements (change in dispatch strategy, balancing mechanisms, storage, etc.) • Complexity of system operation remains the same  Power balancing/dispatch: • Renewable generation seen as negative load • Additional spinning reserve required to cover most of PV power output variability: in Palau’s case +35% of PV generation for time intervals of 1 hour (confidence level of 99.7% of the variations on a Gaussian distribution, i.e. 3δ)  Frequency stability • PV power output variability for time intervals from 1s up to 10m do not negatively impact the dynamic behavior of the frequency • Same frequency behavior expected as in the current system with no (or very low level) of renewable penetration Conclusions
  • 37. Grid Stability Workshop. Pacific Islands 37  PV penetration level > 30%  In order to avoid curtailing PV output during time times of high PV generation, the number of diesel generators dispatched can be reduced (in order to minimize fuel costs).  A reduced number of running diesel machines reduces the spinning reserve and therefore the maximum PV power output fluctuation that the system can allow (for 70% PV penetration the maximum allowable PV fluctuation is of about 16%).  Based on the currently available PV time-series measurements, higher fluctuations cannot be precluded.  Additional spinning reserve and frequency control can be achieved by the installation of flywheels or batteries (storage)  Amount of storage generally driven by economics • Additional studies required to determine the optimal level of storage (economics) Conclusions
  • 38. Grid Stability Workshop. Pacific Islands 38  PV penetration level > 30% (cont.)  Increased need for control and operational requirements (e.g. change in dispatch strategy, balancing mechanisms, storage, etc.) leads to increased complexity of system operation  However, simulation tools with an adequate model of the power system can be used to automatically calculate required reserves and diesel dispatch Conclusions
  • 39. Grid Stability Workshop. Pacific Islands 39  Short and medium term plan:  Up to 30% of PV penetration level (instantaneous, i.e. power penetration) no changed required  To minimize PV power output fluctuations and hence reduce the total amount of spinning reserve, a geographical dispersed PV generation should be preferred.  Long term plans  To allow PV penetration levels > 30%:  High quality of PV generation/ solar irradiance measurements would be of a great advantage  Dynamic stability can be guaranteed by an adequate allocation of additional reserves (in terms of diesel generation or storage)  Additional studies required to determine economically optimal penetration level (i.e. balance between diesel reserve and additional storage reserve in terms of flywheels or batteries) The Way Forward
  • 40. Grid Stability Workshop. Pacific Islands 40 Thanks for your attention