Curtailment of Renewable Energy in California and Beyond California is blazing a path to a low-carbon future through greater use of renewable electricity. But as wind and solar rapidly grow, grid operators are raising concerns about periods of over-generation and the specter of large amounts of curtailment. Curtailment is an easy response, but it is wasteful and undermines the investor confidence needed to transition the California power system. A host of supply-side and demand-side measures can keep curtailment to minimal levels, but policy reforms also are needed to make curtailment a viable tool. Rachel Golden and Bentham Paulos I. Introduction As a result of the passage of AB327, the California Public Utilities Commission is authorized to increase the renewable portfolio standard (RPS) beyond the current goal of 33 percent by 2020. SB350, pending in the California legislature, would set a goal of 50 percent by 2030. Along with the multiple benefits of renewables, higher penetration of variable renewable energy also brings several challenges. This article examines some of these challenges, particularly over-generation and curtailment of renewables in California and other states. The article addresses the use of low levels of Rachel Golden is a graduate student in the Energy and Resources Group and the Goldman School of Public Policy at University of California, Berkeley. At UC Berkeley, she has served as a student researcher on multiple energy policy issues at the California Governor’s Office, California Public Utilities Commission, California Energy Commission, U.S. Environmental Protection Agency Region 9, and Natural Resources Defense Council. Before returning to school, she was a Senior Program Associate at the Energy Foundation, where she focused on statewide and national strategies to accelerate the transition from coal to clean energy resources. Ms. Golden holds a B.A. in International Development Studies from UC Berkeley. Bentham Paulos is Principal of PaulosAnalysis, consulting and writing on clean energy policy, industry trends, and philanthropy. He is currently directing the Power Markets Project, looking at the impact of renewable energy on electricity market designs in Germany and the U.S. Previously he managed America’s Power Plan, a policy roadmap for moving to a high-renewable-energy future. He was a program director with the Energy Foundation from 2000 to 2013, making grants to promote renewable energy, utility efficiency, and advanced biofuels. He previously worked for the Energy Center of Wisconsin, the Union of Concerned Scientists, and Abt Associates, and has an M.A. in Energy Policy from the University of Wisconsin-Madison and a B.A. from Tufts University. The Power Markets Project (www. powermarkets.org) studies and promotes market policies that align with clean energy goals. It is a project of PaulosAnalysis, with financial support from the Heinrich Bo¨ll Foundation, the Cynthia and George Mitchell Foundation, and the Rockefeller Brothers Fund. 36 1040-6190/# 2015 Elsevier Inc. All rights reserved., http://dx.doi.org/10.1016/j.tej.2015.06.008 The Electricity Journal
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Curtailment of Renewable Energy in California and Beyond · 2015. 8. 4. · are several causes forcurtailment ofrenewable energy. Curtailment can be the result of excess generation
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Rachel Golden is a graduate student inthe Energy and Resources Group and the
Goldman School of Public Policy atUniversity of California, Berkeley. At UC
Berkeley, she has served as a studentresearcher on multiple energy policy issues
at the California Governor’s Office,California Public Utilities Commission,
California Energy Commission, U.S.Environmental Protection Agency Region9, and Natural Resources Defense Council.Before returning to school, she was a Senior
Program Associate at the EnergyFoundation, where she focused on statewide
and national strategies to accelerate thetransition from coal to clean energy
resources. Ms. Golden holds a B.A. inInternational Development Studies from
UC Berkeley.
Bentham Paulos is Principal ofPaulosAnalysis, consulting and writing onclean energy policy, industry trends, and
philanthropy. He is currently directing thePower Markets Project, looking at the
impact of renewable energy on electricitymarket designs in Germany and the U.S.Previously he managed America’s Power
Plan, a policy roadmap for moving to ahigh-renewable-energy future. He was a
program director with the EnergyFoundation from 2000 to 2013, making
grants to promote renewable energy, utilityefficiency, and advanced biofuels. He
previously worked for the Energy Center ofWisconsin, the Union of Concerned
Scientists, and Abt Associates, and has anM.A. in Energy Policy from the University
of Wisconsin-Madison and a B.A. fromTufts University.
The Power Markets Project (www.powermarkets.org) studies and promotes
market policies that align with clean energygoals. It is a project of PaulosAnalysis, with
financial support from the Heinrich BollFoundation, the Cynthia and George
Mitchell Foundation, and the RockefellerBrothers Fund.
1040-6190/# 2015 Elsevier Inc. All rights reser
Curtailment of RenewableEnergy in California andBeyond
California is blazing a path to a low-carbon future throughgreater use of renewable electricity. But as wind and solarrapidly grow, grid operators are raising concerns aboutperiods of over-generation and the specter of largeamounts of curtailment. Curtailment is an easy response,but it is wasteful and undermines the investor confidenceneeded to transition the California power system. A host ofsupply-side and demand-side measures can keepcurtailment to minimal levels, but policy reforms also areneeded to make curtailment a viable tool.
1. For instance, what some operatorslike ERCOT and MISO considersystem-wide ‘‘downward dispatch,’’others consider and count ascurtailment.
2. Lori Bird, Jaquelin Cochran, and XiWang, ‘‘Wind and Solar EnergyCurtailment: Experience and Practices
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in the United States,’’ NationalRenewable Energy Lab, March 2014,http://www.nrel.gov/docs/fy14osti/60983.pdf
3. Jaquelin Cochran, Mackay Miller,Owen Zinaman, Michael Milligan,Doug Arent, Bryan Palmintier, MarkO’Malley, Simon Mueller, EamonnLannoye, Aidan Tuohy, Ben Kujala,Morten Sommer, Hannele Holttinen,Juha Kiviluoma, S.K. Soonee,‘‘Flexibility in 21st Century PowerSystems,’’ 21st Century PowerPartnership (NREL, University
College Dublin, IEA, EPRI, NorthwestPower and Conservation Council,Energinet.dk, VTT Technical ResearchCentre of Finland, Power SystemOperation Corporation), May 2014,http://www.nrel.gov/docs/fy14osti/61721.pdf
4. Bird et al., ‘‘Wind and Solar EnergyCurtailment: Experience and Practicesin the United States.’’
5. Ibid.
6. More research is needed todetermine the threshold forcurtailment in California below whichthe renewables industry will not behurt. There is no reliable nationalaverage for how much curtailment isacceptable. Rather, the thresholddiffers depending on state and federalpolicies. For example, if generators arefully compensated for curtailment(including lost PTC revenue) and ifthere is investor confidence that thecontract and policy environment isreliable and stable, then the threshold
ved., http://dx.doi.org/10.1016/j.tej.2015.06.008
for curtailment is likely much higherthan in a territory where generatorsare not compensated for curtailment.
7. Jonathan Cheszes, ‘‘Impact ofCurtailment on Wind Economics,’’Renewable Energy World.Com,March 20, 2012, http://www.renewableenergyworld.com/rea/news/article/2012/03/impact-of-curtailment-on-wind-economics
8. Cochran et al., ‘‘Flexibility in 21stCentury Power Systems.’’
9. Energy+Environmental Economics,‘‘Investigating a Higher RenewablesPortfolio Standard in California,’’ Jan.2014. https://ethree.com/documents/E3_Final_RPS_Report_2014_01_06_with_appendices.pdf
10. Bird et al., ‘‘Wind and SolarEnergy Curtailment: Experience andPractices in the United States.’’
11. Jaquelin Cochran, Lori Bird, JennyHeeter, and Douglas J. Arent,‘‘Integrating Variable RenewableEnergy in Electric Power Markets: BestPractices from InternationalExperience,’’ National RenewableEnergy Lab, April 2012, http://www.nrel.gov/docs/fy12osti/53732.pdf
12. Cochran et al., ‘‘Flexibility in 21stCentury Power Systems.’’
13. Jacobsen, H.K., Schroder, S.T.Curtailment of renewable generation:economic optimality and incentives.Energy Policy 49, 663–675, Postprint2012, DTU Management Engineering,Technical University of Denmark.
14. The specific threshold-level issystem-specific and depends on thesystem flexibility supply curve. There isno rule-of-thumb number that appliesto energy markets across the U.S.
15. Interview with Andrew Mills,Lawrence Berkeley NationalLaboratory, Aug. 11, 2014.
16. GE Energy, ‘‘Western Wind andSolar: Integration Study,’’ Prepared forthe National Renewable Energy Lab,May 2010, http://www.nrel.gov/docs/fy10osti/47781.pdf
17. Interview with Heather Sanders,Deane Lyon, and Karl Meeusen,CAISO, Aug. 11, 2014.
18. Steven Greenlee, CAISO, personalcommunication with the authors, June5, 2015.
19. Bird et al., ‘‘Wind and SolarEnergy Curtailment: Experience andPractices in the United States.’’
20. CPUC, D.11-04-030 ApprovesIOUs’ procurement plans for 2011 RPSsolicitations and integrated resourceplan supplements.
21. Conversation with Cheryl Lee,CPUC, June 23, 2014.
22. Bird et al., ‘‘Wind and SolarEnergy Curtailment: Experience andPractices in the United States.’’
23. Federal limits on dissolved gassesand fish habitat protectionrequirements mean that hydrooperators cannot use spillways (theonly alternative to generation) tolower high river water levels.
24. Greenlee, personalcommunication.
25. Dr. Karl Meeusen, DirectTestimony on behalf of the CAISO,Order Instituting Rulemaking toIntegrate and Refine ProcurementPolicies and Consider Long-TermProcurement Plans, CPUC R.13-12-010, Submitted Aug. 13, 2014.
26. Bird et al., ‘‘Wind and SolarEnergy Curtailment: Experience andPractices in the United States.’’
27. Interview with Greg Brinkman,NREL, Aug. 14, 2014.
28. The assumption of unlimitedeconomic renewable curtailment is notnecessarily a practical assumption. Dr.Karl Meeusen (CAISO) is ‘‘not awareof any contracts with renewablecapacity that allows for unlimitedcurtailment provisions of therenewable resources. . .Further, thesecontracts may not provide for anyeconomic curtailment. Renewableresources without curtailmentprovisions are offered into the CAISOas self-schedules. This means that theCAISO can only curtail the output ofthese resources based on reliabilityconcerns.’’ Source: Dr. Karl MeeusenDirect Testimony to CPUC, Aug. 13,2014.
30. Dr. Karl Meeusen, DirectTestimony to CPUC, Aug. 13,2014.
31. Energy+EnvironmentalEconomics, ‘‘Investigating a Higher
Renewables Portfolio Standard inCalifornia.’’
32. Bentham Paulos, ‘‘California Plansfor Even More Renewable Power in ItsFuture,’’ POWER Magazine, 12/17/2014. http://www.powermag.com/california-plans-for-even-more-renewable-power-in-its-future/?pagenum=1
34. Solomon, A.A., Kammen, D.M.,Callaway, D., 2014. The role of large-scale energy storage design anddispatch in the power grid: a study ofvery high grid penetration of variablerenewable resources. Appl. Energy134, 75–89.
35. Official definition from CAISO:‘‘Generation equipment thatautomatically responds to signalsfrom the CAISO’s energymanagement system control in
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real-time to control the power outputof generating units within aprescribed area in response to achange in system frequency, tie-line loading, or the relationfrequency and the establishedinterchange with other BalancingAuthority Areas within thepredetermined limits.’’
36. Manual curtailment is used byAPS, Salt River Project, TucsonElectric, ISO-NE, PacifiCorp, SPP, andMISO (NREL, March 2014).
37. Cochran et al., ‘‘IntegratingVariable Renewable Energy in ElectricPower Markets: Best Practices fromInternational Experience.’’
38. Bird et al., ‘‘Wind and SolarEnergy Curtailment: Experience andPractices in the United States.’’
39. Ibid.
40. Regulatory Assistance Project,‘‘Meeting Renewable Energy Targetsin the West at Least Cost: theIntegration Challenge,’’ WesternGovernors Association, June 10, 2012,http://www.raponline.org/featured-work/meeting-renewable-energy-targets-in-the-west-at-least-cost-the-integration
41. ‘‘How the West’s new EnergyImbalance Market is building asmarter energy system,’’ Utility Dive,Feb. 19, 2015.
42. Various studies of a larger EIM inthe Western Interconnection couldresult in benefits ranging from $50million to several hundred millions ofdollars per year under current RPStargets, with much of the benefitresulting from reduced renewableintegration costs. Source: Energy +Environmental Economics,‘‘Investigating a Higher RenewablesPortfolio Standard in California,’’ Jan.2014. https://ethree.com/documents/E3_Final_RPS_Report_2014_01_06_with_appendices.pdf
43. Utility Dive, Feb. 19, 2015.
44. Dr. Shucheng Liu, DirectTestimony on behalf of the CAISO,Order Instituting Rulemaking toIntegrate and Refine ProcurementPolicies and Consider Long-Term
48. California Legislative Information,http://leginfo.legislature.ca.gov/
49. One of the integration solutions E3modeled analyzes the impact ofincreased coordination betweenCalifornia and other regions inreducing integration costs. Under thisscenario, California exports up to6,500 MW of power.
50. Cochran et al., ‘‘IntegratingVariable Renewable Energy in ElectricPower Markets: Best Practices fromInternational Experience.’’
51. North American ElectricReliability Corporation, ‘‘IVGTF Task2.4 Report: Operating Practices,Procedures, and Tools,’’ March 2011,http://www.nerc.com/docs/pc/ivgtf/IVGTF2-4CleanBK(11.22).pdf
52. GE Energy, ‘‘Western Wind andSolar: Integration Study.’’
53. Cochran et al., ‘‘IntegratingVariable Renewable Energy in ElectricPower Markets: Best Practices fromInternational Experience.’’
54. Holttinen, H., et al., 2009.Design and Operation of PowerSystems with Large Amounts of WindPower. Final report, IEA WIND Task25, Phase One 2006–2008. VTT,Vuorimiehentie, Finland. http://www.vtt.fi/inf/pdf/tiedotteet/2009/T2493.pdf
55. Ibid.
56. Cochran et al., ‘‘IntegratingVariable Renewable Energy in Electric
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Power Markets: Best Practices fromInternational Experience.’’
57. Energy+EnvironmentalEconomics, ‘‘Investigating a HigherRenewables Portfolio Standard inCalifornia.’’
58. These imports consist of‘‘baseload’’ power scheduled fromcoal and nuclear resources owned byor contracted to California utilities,surplus hydroelectric generation fromthe Northwest, and economic importsof natural gas power from the
Northwest and Southwest. Duringsome hours, California imports asmuch as 12,400 MW of power over itsinterties with the rest of the WesternInterconnection. California alsocurrently exports a small amount ofpower to the Pacific Northwest duringsome hours in the wintertime;however, these exports are more thanoffset by imports from the Southwest,such that California is never a netexporter of power’’ (Source: E3).
59. Ibid.
60. ‘‘Indeed, while the West-of-Rivertransmission path connectingCalifornia to the Desert Southwest hasan East-to-West rating of 10,600 MW,it does not have a formal West-to-Eastrating. It is therefore unknown at thistime what level of exports fromCalifornia the western grid cansupport. Nevertheless, an analysis ofload growth projections, resourceretirements, and RPS policies inneighboring states suggested that by
ved., http://dx.doi.org/10.1016/j.tej.2015.06.008
2030, it may be possible to export up to6,500 MW of power to the rest of theWest’’ (Source: E3).
61. Ibid.
62. Interview with Greg Brinkman,NREL, Aug. 14, 2014.
63. Ibid.
64. Energy+EnvironmentalEconomics, ‘‘Investigating a HigherRenewables Portfolio Standard inCalifornia.’’
65. GTM Research, Regulating TheUtility Of The Future: Implications for theGrid Edge, Jan. 2015.
66. Adam Langton and NoelCrisostomo, Energy Division,California Public UtilitiesCommission, Vehicle-Grid Integration:A Vision for Zero-EmissionTransportation Interconnectedthroughout California’s ElectricitySystem, http://www.cpuc.ca.gov/PUC/energy/altvehicles/ (March2014).
67. Sierra Martinez and DylanSullivan, ‘‘Using Energy Efficiency ToMeet Flexible Resource Needs andIntegrate High Levels of RenewablesInto The Grid,’’ Natural ResourcesDefense Council, 2014, http://aceee.org/files/proceedings/2014/data/papers/5-1012.pdf
68. California ISO Demand Responseand Energy Efficiency Roadmap:Maximizing Preferred Resources, Dec.2013, http://www.caiso.com/documents/dr-eeroadmap.pdf
69. Dr. Karl Meeusen, DirectTestimony to CPUC, Aug. 13, 2014.
70. Cochran et al., ‘‘IntegratingVariable Renewable Energy in ElectricPower Markets: Best Practices fromInternational Experience.’’
71. Ibid.
72. Ibid.
73. Interview with Andrew Mills,LBNL, Aug. 11, 2014.
74. Cochran et al., ‘‘IntegratingVariable Renewable Energy in ElectricPower Markets: Best Practices fromInternational Experience.’’