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Carl Lenox | SunPower


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Carl Lenox | SunPower

  1. 1. Connecting Variable Solar To The Grid Carl Lenox Principal Engineer GW Solar Institute Symposium April 26th 2011 © 2011 SunPower Corporation
  2. 2. Does PV Variability Present A Barrier?Some have used the following argument: BADHowever, this does beg a few important questions, such as:• How rapid are these changes, and how often do they occur?• Does the observed behavior of a single system scale? If so, how?• What are the impacts of variability on the utility infrastructure and the customer?• How do these impacts change as penetration increases?• What mitigations are available for these impacts? What are the best solutions? © 2011 SunPower Corporation 2
  3. 3. Geographical Diversity Is A Crucial FactorHigh Irradiance Variability At Single Sites Is Reduced With A Portfolio Of Sites Single Location 20 Locations Source: Source: Weimken Mills et. et. al. al. 2010 2001 © 2011 SunPower Corporation 3
  4. 4. Operational Timeframes & Impacts of Variability M. Milligan, NREL Timeframe System Local Impacts Impacts Seconds to Regulation Voltage Minutes Fluctuation 10’s of Minutes Load Voltage to Hours Following Profile Hours to Days Scheduling The Electrical System Is Designed To Manage Load Variability Variable Generation Is Not Fundamentally Different © 2011 SunPower Corporation 4
  5. 5. System Level Impacts Of Short Duration Variability• System level impact is cost required to provideincremental frequency regulation due to added sub-10 minute variability from PV.• PV integration cost per recent LBNL (Mills &Wiser) study - comparable to wind, because • Geographical diversity substantially damps short duration fluctuations • Reserves can be scheduled based on deterministic “clear sky” envelope• Regulation costs for wind (up to ~ 30%penetration) across multiple studies are generallyvery modest at <$1 / MWh. © 2011 SunPower Corporation 5
  6. 6. Diurnal Variability Must Also Be Considered• Daily solar cycle adds load following and unitcommitment integration costs; bigger ramps.• LBNL, NREL (EWIS / WWIS) and others findmodest total integration cost up to ~30%energy penetration: typically less than $5 /MWh (for wind and solar).• Forecast error dominates cost, PV Denholm et al 2008 (% system energy)forecasting is new, often assumed to be veryinaccurate in integration studies (5-20% error)• However 4-5% RMSE is achieved in practicefor regional-level PV forecasts in Germany,comparable to best in class wind forecasting.• Example: Spain at ~16% VER energy: 14%wind, 2% PV (3.4 GW), with limited interties CPUC 33% RPS Reference Case:but world-class operations. Peak of 54% of ~25% energy from VERs ; 11% solar © 2011 SunPower Corporationsystem demand served by wind. 6
  7. 7. Cost Of Integrating PV Is A Function Of FlexibilityAs VER penetration increases beyond20-30% of energy:• Marginal (offset) generation costs drop.• Traditional flexible resources may bedisplaced or dispatched “out of meritorder”; though flexibility may increase atsome penetrations due to part-loadoperation. Denholm et al 2008• Eventual conflict with “must run” baseload generation, leading to VERcurtailment (increased cost); though PVload coincidence helps (compared towind).• Fleet flexibility is key – more flexibilitymeans more room for VERs. © 2011 SunPower Corporation 7
  8. 8. What Impacts Flexibility?Physical• Available Generator Attributes• Transmission (diversity)• Responsive Load (incl. xEVs)• Energy StorageInstitutional Denholm 2008• Use of Forecasts• Balancing Area Size / Coordination• Unit Commitment & Dispatch Approaches• Market Transparency• Ancillary Service Markets Existing Physical Flexibility Is Often Inaccessible Due To Institutional Barriers © 2011 SunPower Corporation 8
  9. 9. PV Variability Is Not A Technical Barrier But PV variability is a real cost allocation challenge! The physical and institutional flexibility of a system has a significant impact of the costto integrate VERs……The same has always been true of the cost to integrate load variability, but no onehas previously considered charging conventional generators (coal, nuclear) for theirinflexibility. “High penetration” studies which assume BAU, deterministic planning and operationspractices, do not challenge institutional constraints, and do not adequately considerflexibility will overstate integration costs (and will show that overbuilding of conventionalgeneration is ”needed” to “back up” wind and solar) Limitations on distribution system penetration of PV are dominated by issues relatedto accommodating and managing DG generally, not due to variability. A systematicapproach to distribution upgrades (i.e. smart grid) could greatly increase DGpenetration levels, along with changes to interconnection standards and statutes. © 2011 SunPower Corporation 9
  10. 10. Changes Are Coming! NERC Integration of Variable Generation Task Force (IVGTF) – Detailed reports addressing all of these topics and many more are in progress, or already published. – Focused on transmission interconnection, but addresses changes needed with high penetration DG that will impact bulk electrical systems. FERC Variable Energy Resource (VER) NOPR – Directly tackles interplay between operational practices and integration costs; proposes that TSOs be able to recover integration costs if operations are modernized. IEEE 1547 Updates – Addresses technical standards changes needed to better accommodate high penetration DG. FERC SGIP (model for California Rule 21 and many others) – IREC proposing updates to address PV specific issues that can pose unnecessary barriers to achieving higher penetration of distributed PV. © 2011 SunPower Corporation 10
  11. 11. © 2011 SunPower Corporation
  12. 12. Local Impacts Of Variability Concerns about flicker and voltage regulation are often expressed, but have not been reported as issues in numerous high penetration circuits being studied:Location Description Penetration NotesOta City, Japan 550 Sites / 2 MW Not Reported Residential energy storage(2003) residential, one circuit evaluated and removed; no issues reported post-removal.Freiburg, 70 Sites / 440 kW multi-unit 110% on capacity (400 Minimal, correctable issuesGermany (2006) residential kVA XFR) reported (phase imbalance)Kona, HI (2009) 700 kWac commercial 35% on capacity (2 No issues reported MVA feeder), backfeed up to 30% in low loadLanai, HI (2009) 600 kWac commercial (1.2 ~12% on capacity, No issues reported. MW system, brought online ~25% in low load, incrementally) weak island systemAnatolia, CA 115 Sites / 238 kW 4% on capacity, 11- No issues reported, PV variability(2009) residential 13% low load less than AC cycling variability.Las Vegas, NV > 10 MW commercial, 35 ~ 50% on capacity, No issues reported(2008) kV interconnection ~100% low loadAtlantic City, NJ 1.9 MW commercial, 23 kV ~24% on capacity, No issues reported(2009) interconnection ~63% low load © 2011 SunPower Corporation 12
  13. 13. Local Impacts Of VariabilityField experience in Germany (15.5 GW PV, 99% DG) and Spain (3.4 GW PV, 98%DG) have not revealed issues with voltage regulation or flicker, even with quite highpenetration levels. Penetrations in excess of 100% (PV production / minimum load)are commonplace in Germany today. The “today” scenarios shown here represent two actual German distribution grids, operating withoutSources: (L) Braun 2010, IEA PVPS Task 14 Workshop; issue. Grid “A” is at 88% penetration*, Grid “B” at(R) Budenbender et al 2010 37% penetration today. * Peak PV capacity (kW) divided by transformer rating (kVA) © 2011 SunPower Corporation 13
  14. 14. Mitigation Of Local Voltage Impacts• Geographical diversity has a substantial (1) Spike inimpact in mitigating variability over small voltage at POI (3) Voltage returns detected to setpointdistances, even within a distribution feeder.• Though uncommon, voltage fluctuationscan result when a single, high penetrationsystem is interconnected to a circuit withhigh impedance (such as a long ruralfeeder).• Reactive power control substantiallyreduces the impacts of output variability on (2) SunPower smart controllervoltage. Simply setting a fixed non-unity commands reactive powerpower factor has been demonstrated to be change to reduce voltageeffective. SunPower has pioneered the• Active voltage regulation (AVR) is implementation of AVR in large-particularly effective, if mitigation is needed. scale PV 2011 SunPower Corporation plants. ©