Essential Reliability Services From PV Plants Mahesh Morjaria, Ph. D. VP, PV Systems Enabling a world powered by reliable, affordable solar electricity.
Utility-Scale PV Plants Support Grid Stability & Reliability Utility-Scale PV Plants Provide Grid Friendly Features Required by NERC: Voltage regulation Real power control, ramping, and curtailment Primary frequency regulation Frequency droop response Short circuit duty control Fault ride through Utility-Scale PV Plants Contribute to Grid Stability & Reliability Like Conventional Generation Source: NERC: 2012 Special Assessment Interconnection Requirements for Variable Generation 2
PV Plant Schematic Sunlight to DC Power DC Power to AC Power AC Power to Grid DC AC SOLAR ARRAYS COMBINER BOX POWER CONVERSION STATION SWITCHGEAR SUBSTATION POWER GRID 69 to 765kV (AC) DC Typical DC Voltage 1kV or 1.5kV Typical AC Collection Voltage 34.5kV (Alternatives 4.16kV to 27.6kV) 3
Plant Control System Enables Grid Friendly Features Sunlight to DC Power DC Power to AC Power AC Power to Grid DC AC 69 to 765kV (AC) SOLAR ARRAYS Patent No. 8,774,974. Real-time photovoltaic power plant control system COMBINER BOX DC Typical DC Voltage 1kV or 1.5kV POWER CONVERSION STATION SWITCHGEAR Typical AC Collection Voltage 34.5kV (Alternatives 4.16kV to 27.6kV) SUBSTATION POWER GRID Checks grid s actual conditions and required set points Sends individual instructions to each inverter based on location, losses, and performance Controls quality of power coming out of the PV plant Closed-loop controls at 100 milliseconds! 4
Passage of Clouds at a 290 MW PV Plant ~20 minutes Large Plant Size Attenuates Impact of Cloud Passages on Power Output 5
AGUA CALIENTE 290MW AC CONNECTING ON 500 KV TRANSMISSION LINE Palo Verde Nuclear Generating Station Agua Caliente Hassayampa Substation California Arizona Hoodoo Wash Substation North Gila Substation 500kV Palo Verde-Hassayampa Transmission Line 6
Power (PU) and Reactive Power (PU) Voltage (PU) and Power Factor TYPICAL PLANT OPERATION (UNITY POWER FACTOR) 1.2 0.9 Normalization Values Active Power: 300MW Reactive Power: 20MVAR Voltage: 530kV Typical Operating Day Power (PU) 110% 105% 0.6 Voltage (PU) 0.3 Power Factor 100% 0.0 Reactive Power (PU) 95% -0.3-0.6 90% 4:00 8:00 12:00 16:00 20:00 Time of Day Plant Is Maintained At Constant Power Factor as Required 7
MARCH 21 ST 2014 EVENT Agua Caliente Palo Verde Nuclear Generating Station Hassayampa SubstationO Line Taken Out of Service Hoodoo Wash Substation North Gila Substation 500kV Palo Verde-Hassayampa Transmission Line 8
Voltage Support from PV Plant Grid Operator Seeks Voltage Support Power (PU) Voltage (PU) Voltage (PU) Voltage (PU) Night Shutdown Power (PU) Voltage Control Started Reactive Power (PU) Maintain Voltage Even Under Changing Power Conditions 9
Demonstration of Essential Reliability Services by a 300-MW Solar PV Power Plant
Can variable energy resources provide essential reliability services to reliably operate the grid? NERC identified three essential reliability services to reliably integrate higher levels of renewable resources 1. Frequency Control 2. Voltage Control 3. Ramping capability or Flexible Capacity Test results demonstrated utility-scale PV plant has the capability to provide these essential reliability services Advancement in smart controls technology allows these plants to provide services similar to conventional resources VERs (Variable Energy Resources) with the right operating characteristics are necessary to decarbonize the grid Page 11
PV Power Plant Description First Solar PV modules 4 MVA PV inverters 8 x 40 MVA blocks 34.5 kv collector system Two 170 MVA transformers 34.5 kv Collection Tie with 230 kv transmission line PMUs collecting data on 230 kv side 170 MVA Transformer 230 kv Transmission 4MVA Inverter 40 MVA Block PMU 12
Reactive Power Capability PV Plant vs Synchronous Generator P (MW) October 2017 Reactive power capability of a typical synchronous generator compared to a PV Inverter Proposed CAISO Reactive Capability for Asynchronous Resources Q (MVAR) 13
Real Power (P) Typical Grid Requirement (e.g. ERCOT in Texas) Provide leading and lagging reactive power at Point of Interconnection (POI/POC) for all real power ranges from 10% to 100% Example: Real Power: P n = 300 MW Reactive Power: Q n = ~100 MVAr Apparent Power: S n = ~315 MVA Power Factor pf = 0.95 The PV plant must be capable of either producing or absorbing up to 100 MVAr when real power is from 30 MW to 300 MW Q n Inductive (Q-I) 0.95 pf Line P n P max Reactive Power (Q) 0.95 pf Line S n Corner Point driving design Q n (P n,q n ) Q = S 2 P 2 pf = P S Capacitive (Q-C) Grid POI Requirement 14
Demonstrated the Capability to Change System Voltage October 2017 MVAR Set Point Voltage MVAR Output By changing the reactive output of the plant from +100 MVAR to -100 MVAR, the voltage at the POI changed from 242 kv to 227 kv Demonstrated the ability of the plant to produce or absorb reactive power (±100 MVAR) even at nearly zero power output 15
Frequency Droop Tests Example of 3% droop test (under-frequency) Droop = P/P rated f/60hz 3% and 5% under and over-frequency tests Frequency Power 20% headroom ±36 mhz dead band Used actual frequency event time series measured in the U.S. Western Interconnection 16
Examples of Over-Frequency Droop Tests Example of 5% droop test (over-frequency) Power Frequency Measured droop response 5% Measured droop response 5% Measured droop response 3% Measured droop response 3% 17
Measured Reactive Power Capability and Voltages at POI Reactive power tests at high and low power production levels The plant meets the proposed CAISO reactive power requirements The plant is capable of providing +/- 100MVAR of dynamic reactive power response at any point when operating on this P-Q plane 18
Active Power Curtailment Test Active Power Set Point Active Power 19
POWER (MW) POWER (MW) AGC Participation Tests 300 MW Utility-Scale PV Plant MORNING 230 Available MW Min allowed MW Commanded MW Measured MW 220 210 200 30MW Headroom Commanded MW Available MW Measured MW 190 180 Minimum Allowed MW 170 285 280 275 270 265 260 255 250 245 240 0 200 400 600 800 1000 1200 1400 RELATIVE TIME (sec) MIDDAY Avaliable MW Min Allowed MW Commanded MW Measured (MW) 30MW Headroom Commanded MW Available MW Measured MW Minimum Allowed MW 0 200 400 600 800 1000 1200 1400 RELATIVE TIME (sec) 30MW headroom 4-sec AGC signal provided to Plant Controller Tests were conducted for Sunrise Middle of the day Sunset 20
PV Plants Outperform Conventional Resources in Frequency Regulation 100% 90% 80% 70% 60% Regulation accuracy by PV Plant is about 24-30% points better than fast gas turbines 63% 87-93% 50% 40% 40% 30% 20% 10% 0% Steam Turbine Pump Turbine Hydro Combined Cycle Limited Energy Storage Gas Turbine Solar PV (Middle of the Day) Solar PV (Sunset) Solar PV (Sunrise Blue bars taken from the ISO s informational submittal to FERC on the performance of resources providing regulation services between January 1, 2015 and March 31, 2016 http://www.caiso.com/documents/testsshowrenewableplantscanbalancelow-carbongrid.pdf 21
Summary of Conducted Tests Regulation-up and regulation-down, or AGC tests during sunrise, middle of the day, and sunset Frequency response tests with 3% and 5% droop settings for over- frequency and under- frequency conditions Curtailment and APC tests to verify plant performance to decrease or increase its output while maintaining specific ramp rates Voltage and reactive power control tests Voltage control at near zero active power levels (nighttime control) 22
TESTS SUCCESSFULLY CONDUCTED ON 300 MW SOLAR PV PLANT Power Ramping Ramp its real-power output at a specified ramp-rate Provide regulation up/down service Voltage Control Control a specified voltage schedule Operate at a constant power factor Produce a constant level of MVAR Provide controllable reactive support (droop setting) Provide reactive support at night Frequency Provide frequency response for low frequency & high frequency events Control the speed of frequency response Provide fast frequency response to arrest frequency decline Utility-Scale PV Plant Contributes to Grid Stability & Reliability Like Conventional Generation 23
Utility-scale PV solar is a flexible resource that can enhance grid reliability Dispatchable PV Plant Solar can provide NERC-identified essential services to reliably integrate higher levels of renewable resources, including: Frequency Control Voltage Control Ramping capability or flexible capacity Automated Generation Control (AGC) regulation accuracy of 24-30 %points better than fast gas turbines Reduces need for services from conventional generation Goes beyond simple PV energy value Enables additional solar Reduces need for expensive storage CAISO: Grid Friendly Utility-Scale PV Plants are Essential for Large-Scale PV Integration http://www.caiso.com/documents/testsshowrenewableplantscanbalancelow-carbongrid.pdf 24