Issues and Best Practices in Grid Integration of Solar Photovoltaic Power Plants

Transcription

1 Issues and Best Practices in Grid Integration of Solar Photovoltaic Power Plants Professor Saifur Rahman Virginia Tech Advanced Research Institute Virginia, USA University of Manchester Manchester, England 02 Sep 2015 Virginia Tech Research Center Arlington, Virginia, USA PPT slides will be available at

2 Global PV Annual and Cumulative Installed Capacity Top 10 countries (2014) (Source: IEA International Energy Agency 2014 Snapshot of Global PV Markets, Photovoltaic Power System Programme (PVPS) Report T1-26:2015 Global Annual and Cumulative Installed Capacity (2014) 4 (Source: IEA International Energy Agency 2014 Snapshot of Global PV Markets, Photovoltaic Power System Programme (PVPS) Report T1-26:2015 2

3 5 (Source: IEA International Energy Agency 2014 Snapshot of Global PV Markets, Photovoltaic Power System Programme (PVPS) Report T1-26: (Source: IEA International Energy Agency 2014 Snapshot of Global PV Markets, Photovoltaic Power System Programme (PVPS) Report T1-26:2015 3

4 At the end of 2010, the world s cumulative installed PV capacity was more than 40 GW. One year later it was 70 GW and at the end of 2012, the 100GW mark was exceeded. In 2013, it grew to almost GW and by 2014, more than 178GW of PV had been installed globally an amount capable of producing at least 200 terawatt hours (TWh) of electricity every year. This is also the equivalent of the electricity produced by over 40 large coal power plants. (Source: Global Market Outlook Europe remains the world s leading region in terms of cumulative installed capacity, with 88 GW by end of This represents about 49% of the world s cumulative PV capacity, down from 59% in 2013 and from about 70% in Asia Pacific countries grew fast, with more than 35GW installed by 2014, up 13GW from the previous year. The rest included the Americas (22GW), China (27GW), Middle East/Africa (4.5GW) and Rest of the World (2GW). (Source: Global Market Outlook

5 Global PV Cumulative Installed Capacity (Source: European Photovoltaic Industry Association, Global Market Outlook PV Annual Capacity Additions, GW (Source: International Energy Agency Renewable Energy Medium Term Report Outlook for Solar PV Deployment to

6 Projected Growth of Global PV Market, Cumulative Capacity ( ) (Source: International Energy Agency Solar Photovoltaic Roadmap Foldout U.S. Grid-connected PV Capacity , , , , , , U.S. Annual Capacity Additions (MW) U.S. Cumulative Capacity (MW) (Source: Lawrence Berkeley National Laboratory & US DOE Sunshot Program An Historical Summary of the Installed Price of PV in the United States,1998 to 2013) 6

7 Map of Direct Normal Irradiance (DNI) and Utility-Scale Solar Project Locations in the U.S. (Source: Lawrence Berkeley National Laboratory (LBNL) & US DOE Sunshot Program - Utility-Scale Solar 2013: An Empirical Analysis of Project Cost, Performance, and Pricing Trends in the US) (Source: Solar Energy Industries Association (SEIA)- SOLAR ENERGY FACTS: 2014 YEAR IN REVIEW) 7

8 Customer-owned Solar PV Benefits/Charges in the US Federal and State PV installation credits Renewable Energy Credits (REC) varies from state to state Net metering benefits, but no feed-in tariff In some states (eg, Arizona) residential PV installations are charged a monthly connection fee (Source: Global Market Outlook Price Drop Of Utility-scale Solar PV Projects (Source: Energy.Gov- rice-utility-sc ale-sola r-p hotovolt aic-pv-projec ts) 8

9 Evolutionary Utility-scale (1-axis Tracking) PV System Price Reductions & DOE Target, * (Source: NREL - Residential, Commercial, and Utility-Scale Photovoltaic (PV) System Prices in the United States: Current Drivers and Cost-Reduction Opportunities) Operational Issues Impacts of high PV penetration Reverse power flow Power flow direction through lines can get reversed when PV generation offsets the feeder load Affects those devices which are not designed to operate in bidirectional mode (e.g. conventional overcurrent protection devices and line voltage regulators) Overvoltage and voltage fluctuations Due to reverse power flow bus voltage at the load end can increase Fast cloud movement can cause sudden voltage fluctuations Effects on voltage control devices Very fast transients cannot be effectively removed by traditional voltage regulation devices (e.g. On-Load Tap Changer (OLTC), Switched Capacitor Banks (SCB) and line Voltage Regulators (VR)) Existing voltage control devices tend to operate more frequently than usual which can reduce their life expectancy Source: Shibani Ghosh 18 9

10 Research Challenges Variability and uncertainty in solar energy production PV-induced overvoltage and voltage fluctuations Excessive tap changing operations of the VR s Effective utilization of curtailed solar energy 19 Source: Shibani Ghosh Local overvoltage prevention with PV inverters Inverter is assumed to have smart inverter functionalities like variable reactive power injection and active power curtailment Reactive power injection technology can calculate estimated amount of VAR injection or absorption to keep the local voltage within pre-defined limits For preventing overvoltage, active power can be curtailed (from MPPT generation) to further expand the range of inverter reactive power capability 20 Source: Shibani Ghosh 10

11 Smart Inverter: Common Functions Low/High Voltage Ride-Through (L/HVRT) L/HVRT functionalities are to be implemented with user-configurable X (duration)-y (voltage parameter) arrays. L/HVRT function is defined with two curves- Must Disconnect (in blue: LM1-LM5 or HM1-HM5), and Must Remain Connected (in orange: LC1-LC6 or HC1-HC4) Must Disconnect curves are assumed to extend downward or upward from the first point (LM1 or HM1) and horizontally to the right from the last point (LM5/HM5). Must Remain Connected curves are assumed to extend horizontally to the left below the first point (LC1 or HC1) in the array and to the right from the last point (LC6 or HC4) (Source: EPRI-Common Functions for Smart Inverters, Version 3) Smart Inverter: Common Functions Maximum Generation Limit Time window is used to define the duration over which a new setting would take effect Ramp time expresses the duration over which the inverter linearly places the new limit into effect Read & Set Maximum Generation Level command is used to set the maximum generation level as a percent of peak generation (in Watts) (Source: EPRI-Common Functions for Smart Inverters, Version 3) 11

12 Smart Inverter: Common Functions Volt-VAR function An array of voltage points (% of reference voltage) and VAR levels (% of available VARs) are used to define piece-wise linear curve of the desired Volt-VAR behavior Available VARs implies the reactive injection level the inverter is capable of providing at the moment, without compromising its Watt output. The VAR level is assumed to remain constant for voltages below P1 output (at the Q1 level) and above the highest voltage point for P4 (at Q4) At least two points (P2, V2 and P3, V3) are required to set up the ramping functions (Source: EPRI-Common Functions for Smart Inverters, Version 3) Three directives in Germany The BDEW medium voltage directive The VDE code of practice The Renewable Energy Sources Act, 2014 For PV plants connected to LV grid or less than 100 kw of nominal power connected to MV grid VDE-AR-N 4105 (effective since January 1, 2012) Relevant requirements: Phase balancing Frequency-based power reduction Reactive power control Inverter reconnection conditions Output power control BDEW: Bundesverband der Energie- und Wasserwirtschaft (German Association of Energy and Water Industries) VDE: Verband der Elektrotechnik, Elektronik und Informationstechnik (The Association for Electrical, Electronic & Information Technologies) Sources: VDE-AR-N 4105 Generators connected to the low-voltage ( co m/ en/ dk e/st d/vde ap plic atio ng uid es/p ubli cati on s/pa ge s/vde -AR-N a spx ) SolarEdge Inverter Compliance with New German Grid Code ( ed ge. co m/fil es/ pd fs/ pr od ucts /inv er te rs/s e-i nvertercompliance-with -lv gc. pdf ) SMA- PV grid integration ( e/dl / /PV -N etzi nt-ae N123016w. pdf ) 12

13 Frequency-based Power Reduction P m = Instantaneously available power P= Power reduction f network = Network frequency Figure: Active power reduction of renewables- based generating units in the case of over- frequency Frequency requirements to be met by PV systems or other controllable generators (VDE- AR- N 4105) In the frequency range between 50.2 Hz and 51.5 Hz, PV systems should in future lower (in the event of a rise in frequency) or increase (in the event of a reduction in frequency) the currently generated active power P m with a gradient of 40 % of P m per Hz At mains frequencies > 51.5 Hz, the PV systems must disconnect immediately from the network (safety shutdown) The PV system may only be connected or re- connected to the network if the mains voltage is within the tolerance range of 85 % to 110 % of nominal voltage and the mains frequency is within the tolerance range of 47.5 Hz to Hz for a period of at least 60 seconds Sources: VDE, Transmissionco de 2007 ( m/ de /fn n/ dok u me nte /d ocu m ent s/t ra ns missi onc od e% _en gl. pdf ) The 50.2 Hz problem ( m/ en /fn n/ pa ges /5 0-2-hz. asp x) Large Scale Deployment Technical Solutions Storage Smart inverter Demand response Revised codes and standards (Source: EPIA.org: Connecting the Sun: SOLAR PHOTOVOLTAICS ON THE ROAD TO LA RGE/SCA LE GRID INTEGRATION) 13

14 10 MW Plant near Carlsbad, New Mexico, USA System Owner: SunEdison Utility: Xcel Energy System Integrator: SunEdison System Size: 9.9 MWdc (arrays with tracking system) Network Type: Radial, Dedicated Feeder for PV Plant Special Interconnection Requirements: Fixed power factor to avoid high voltages Inverters required to energize incrementally (Source: NREL: High Penetration Photovoltaic Case Study Report, 2013) Colorado State University Foothills Campus, Fort Collins, Colorado, USA System Owner: Colorado State Univ. Utility: Xcel Energy, Public Service Company of Colorado System Size: 5.2 MWac (single axis tracking and fixed-axis arrays) Network Type: Radial Special Interconnection Requirements: Inverters required to energize incrementally Required to set inverters to absorb 100 kvar or 150 kvar at utility request to avoid high voltages (Source: NREL: High Penetration Photovoltaic Case Study Report, 2013) 14

15 9/2/15 IEEE Power & Energy Society Election for President-elect Professor Saifur Rahman from Virginia Tech, USA is running for President- elect of PES. He is a former VP of Publications in IEEE and PES. Please vote electronically on the PES website. More information at:

16 Thank You Professor Saifur Rahman Virginia Tech Advanced Research Institute Virginia, USA ( 16