National Renewable Energy Laboratory (NREL) Home Page - … · 2020. 9. 23. · “Quasi-Static...

Evaluating Dynamic, Flexible Interconnection Options for Distributed Photovoltaic Resources

Distributed Generation Integration Collaborative (DGIC) Webinar

February 27, 2020

Kelsey Horowitz, NREL

Nadav Enbar, EPRI

Devin Van Zandt, EPRI

Steven Coley, EPRI

Welcome and Webcast Logistics

Webcast being recorded for re-listen and review. Please end your participation if you do not consent to being recorded.

▪Time: 3:00-4:00 pm Eastern (12:00-1:00 pm Pacific)

▪Format: Presentation, followed by Q&A– Phone lines muted to reduce background noise

– Please use webcast console to submit questions

– Phones will be unmuted during Q&A session

▪ Following the webcast, PPT and recording will be available on the DGIC website (https://www.nrel.gov/dgic/) as well as www.EPRI.com

https://www.nrel.gov/dgic/

http://www.epri.com/

NREL | 3

Distributed Generation Integration Collaborative (DGIC) • Formed in Oct 2013 as part of U.S. DOE SunShot Initiative• Focus: info exchange and innovation related to DER integration

processes and practices– Evolved from distributed PV interconnection processes and

practices• EPRI leading DGIC as of 2019


• What research questions, needs, and industry gaps should the DGIC explore? Let us now: [email protected]

• Stay connected: subscribe to the DGIC newsletter


mailto:[email protected]

https://www.nrel.gov/dgic/newsletter.html

© 2020 Electric Power Research Institute, Inc. All rights reserved.w w w . e p r i . c o m4

Background

Firm Interconnection • Typical arrangements for distributed PV

• Static hosting capacity assuming uncontrolled PV output

• Infrastructure upgrades to increase hosting capacity

• Upgrades typically based “worst-case” conditions given reliability objectives and limited visibility/control

Flexible Interconnection• Emerging arrangements

• Application of time-series or dynamic hosting capacity concepts

• Use controls to dynamically curtail PV systems in response to grid needs

• Acknowledge time-varying nature of grid constraints with failsafe mechanisms to ensure reliability



Outline

• Dynamic Hosting Capacity

• Flexible Interconnection

o What is it and why care?

o Case studies

o Assessing curtailment risk

• Key Challenges and Next Steps

• Ongoing work at EPRI and NREL



Dynamic Hosting Capacity

Recognizing the time-varying nature of grid constraints



Dynamic Hosting Capacity without Flexible Interconnection

Jain, Akshay Kumar, Kelsey Horowitz, Fei Ding, Nicolas Gensollen, Barry Mather, and Bryan Palmintier. “Quasi-Static Time-Series PV Hosting Capacity Methodology and Metrics.” In 2019 IEEE Power Energy Society

Innovative Smart Grid Technologies Conference (ISGT), 1–5, 2019. https://doi.org/10.1109/ISGT.2019.8791569.

▪ Should feeder capacity be expanded to be used only a few hours per year?

▪ Traditional snapshot hosting capacity may be conservative in terms of ANSI standard requirements

▪ Grids may operate outside of the limits enforced on PV during interconnection without PV


https://doi.org/10.1109/ISGT.2019.8791569


Dynamic Hosting Capacity without Flexible Interconnection

▪ Acknowledging the time-varying nature of constraints can result in higher hosting capacity with grid operation still meeting standards and not unduly taxing equipment

Jain, Akshay Kumar, Kelsey Horowitz, Fei Ding, Nicolas Gensollen, Barry Mather, and Bryan Palmintier. “Quasi-Static Time-Series PV Hosting Capacity Methodology and Metrics.” In 2019 IEEE Power Energy

Society Innovative Smart Grid Technologies Conference (ISGT), 1–5, 2019. https://doi.org/10.1109/ISGT.2019.8791569.


https://doi.org/10.1109/ISGT.2019.8791569


What is Flexible Interconnection?



Dynamic Hosting Capacity with Flexible Interconnection

Curtailment based on time-varying constraint periods can be minimal, and can enable more DER generation capacity while operating the grid within acceptable limits

Date

Time-Varying Grid Export Limit

PV Output (Fixed Capacity Limit)

Fixed Capacity Limit

PV Output (Flexible Limit)

60% increase in PV capacity

<0.1% energy curtailment

<20 hours per year

Available PV Output



What is Flexible Interconnection?

Arrangements enabling more DER capacity to interconnect by using controlsto manage real-power output of DER to stay within grid-level constraints.

DER Capacity

DER

Pro

du

ctio

n

Alternative Control

Schemes

Var

Su

pp

ort

Curtailed Production

Unconstrained Var Managed Operation

Firm Capacity

Limit



Control Techniques Supporting Flexible Interconnection

Level of Complexity Control Technique DER ManagedNumber and Location of Monitoring Points

Fixed constraintsTimed capacity

connectionSingle DER

or co-collocatedSingle monitoring

location at DER site

Simple, localized constraints

Export limiting devices

Single DERor co-collocated

Single monitoring location at DER site

Local management schemes


Single monitoring location at DER site

Remote inter-trip schemes


Single distant monitoring location

Multiple constraints,

potentially nested

and/or spanning a wider network area

Active power

management

(centralized or decentralized)

Multiple DER

geographically dispersed

Multiple distant monitoring locations



Firm CapacityParadigm

(no upgrade needed)

Flexible Interconnection Paradigm

(economic to curtail)

Upgrade Paradigm

(economic to upgrade)

Economic Opportunity for Flexible InterconnectionIn

tegr

atio

n C

ost

($

/MW

)

Interconnected Capacity (MW)

Reinforce

$/MW cost of curtailment over lifetime of project

$/MW cost of reinforcement

Firm Capacity

Limit



Flexible Interconnection Can Enhance Customer Value

Drivers▪ Low resource costs

– i.e. cheap/available land

▪ Expensive grid-side mitigation measures

▪ Infrequent need to curtail

Opportunity: Offer DER customers faster and cheaper interconnection to integrate more DER in areas with limited hosting capacity

Benefits▪ DER customers: faster, cheaper

connection; can be temporary

▪ Ratepayers: reduce socialized portion of upgrade costs; improved network utilization

▪ Policy objectives: Accelerate progress towards DER penetration goals and/or emissions targets

Example Use Case:

▪ Avoid construction of dedicated feeders



Case Studies in Flexible Interconnection

How much curtailment is experienced?

Does it make financial sense?

How do you assess curtailment over time, and how does that affect financing and viability of these solutions?



Curtailment for Many Flexible Interconnection Schemes

Can be less than Power Lost to Clipping

Customers willingness to clip available solar energy for optimal PV system design

Inverter Output Power Limit



Curtailment Compared to Clipping

• Clipping can result in a higher percentage energy loss than curtailment in some cases, depending on the DC-AC ratio, configurations, and controls

Azzolini, Joseph A., Matthew J. Reno, Kelsey A. W. Horowitz. “Evaluation of Curtailment Associated with PV System Design Considerations.” 2020 IEEE PES GM, accepted.



Curtailment may also be << Variability in Year-on-Year

Output of PV due to Weather

-600

-500

-400

-300

-200

-100

0

100

200

300

2015 - 2016 2016 - 2017 2017 - 2018

MW

hModeled Results

Curtailment PV production without curtailment



BUT Curtailment Risk Will Vary over Time

• Loads change

• Weather changes

• PV deployment may increase

• And only a subset may participate in flexible interconnection schemes

• The grid will change

• Some upgrades will be required regardless of PV deployment

• And a lot depends on the details of the control scheme

• E.g. how does it behave if there is a communication downtime? Is the PV totally curtailment when there is a constraint, or just stepped back in discrete increments?

• These factors are often not considered during flexible interconnection studies today

• Develop a robust, replicable, transparent methodology for curtailment risk assessment



Example Study

Feeder A Feeder B Feeder C

Feeder D Feeder E



Time Series Data

▪ HC and FICS dependent on time-varying load profiles

▪ Correlation of load and PV output is also a factor

▪ Sensitivity analysis using data sets from different locations



Hosting Capacity Profiles

▪ Hosting Capacity (HC) calculated for each hour of the year

▪ Two constraints considered

– Overvoltage at MV Level

– Thermal Loading

▪ Minimum HC of each constraint defines HC for the hour



Flexible Interconnection Capacity Solution (FICS)

HC Profiles for Feeder Nodes FICS Results for Feeder

Node 1 HC

Node 2 HC

Node n HC

FICS

Analysis



FICS: FICS90 Metric

Feeder Y FICS90 = 1.3 p.u. Feeder X FICS90 = 3.1 p.u.

FICS90 = the increase in DER size (above the baseline HC) that can be made before expected annual production drops to 90% of the uncurtailed value



FICS: Example Results: Feeder B

Widely Varying Flexibility Along a Feeder



FICS: Key Correlations

▪ Over 1,300 locations studied

▪ Variability of hosting capacity drives FICS

▪ Near linear relationship between FICS90 and

▪ May allow for less computationally intensive analysis

Feeder Line Fit (R2)A y = 1.4589x – 0.1075 0.9874B y = 1.5422x – 0.1672 0.9913C y = 1.2828x + 0.0881 0.9973D y = 1.4924x – 0.2640 0.9477E y = 1.0575x + 0.1892 0.9459

൯𝐴𝑣𝑒𝑟𝑎𝑔𝑒(𝐻𝐶 𝑡

൯𝑀𝑖𝑛 (𝐻𝐶 𝑡



Summary, Key Challenges, and Ongoing Research



Summary of Demonstration Projects

Demonstration Hosting Utility DER Type(s)Management Solution Type

Constraint Location Status

Accelerating Renewable Connections (ARC)

SP Energy Networks (UK) Genration (PV, wind, DG)Local & Centralized mgmt.

Distribution, Transmission

In service since 2016

Smart Grid Vendée Enedis (France) Generation (PV, wind) Local mgmt. Distribution In service since 2017

Flexible Interconnection Capacity System (FICS)

Avangrid (US) Generation (PV, DG) Local mgmt. Distribution, SubstationSeveral sites in development

Automated Load Rejection Scheme (ALRS)

Hydro One (Canada) Flexible loads Local mgmt. DistributionCommissioning planned for Q4 2018 – Q1 2019

Driffield Northern Powergrid (UK) Generation Centralized mgmt. DistributionCommissioning planned for Q4 2018

Dumfries and Galloway SP Energy Networks (UK) Generation (wind) Centralized mgmt. TransmissionBeing designed, commissioning planned for 2023

N/A Pepco (US) Generation (PV) Centralized mgmt. Substation In service since 2016

N/A OPPD (US) Generation (PV) Centralized mgmt.Distribution, Substation, Transmission

Online

Evolve 5 Utilities (AU)Generation (PV), storage, load

Centralized mgmt. DistributionPlans to launch end-to-end demos in 2020



Key Learnings and Emerging RequirementsSuccess Factors

▪ Challenging network constraints and strong demand for new DER connections

▪ Geospatial heat maps to signal opportunities to project developers

▪ Stakeholder engagement (dedicated utility teams, monitoring to gather specific usage data, curtailment estimates)

▪ Visibility and transparency to build trust (dispatch rules, cost apportionment rules, auditable constraints logs)

Emerging Solution Components

▪ Various real-time capacity dispatch algorithms tested: LIFO, sensitivity factors, economic dispatch, power injection maximization, etc.

▪ Separate local controller co-located with DER is predominant (vs. inverter responding to signals).

▪ Communications fail-safe modes with specified fallback values are always required.

Strategy around Flexible Connections

▪ Stop-gap measure or enduring solution, depending on severity of constraints and demand for new DER connection.

▪ Current focus on real power management, but reactive power compensation is a logical next step.

Source: SMA

Source: UKPN



Summary

• Flexible interconnection provides a good opportunity for low-cost integration of PV, especially when traditional infrastructure upgrade costs would otherwise be high

• In many scenarios, curtailment can be low

• Even lower than clipping losses

• However, frameworks and analyses for fully understanding curtailment risk over time are still being developed

• More publications forthcoming!

• There are now several flexible interconnection projects coming online in the U.S.

• Flexible interconnection has been implemented more widely in Europe



Key Challenges for Flexible Interconnection

Utility

• Revision to interconnection analysis methodologies

• Visibility, communication, and control

• Cyber security

• Additional field demonstrations in the U.S. to increase confidence

Developer

• Understanding financial risk

✓Important for getting flexible interconnection projects financed!

• Additional field demonstrations in the U.S. to increase confidence

Regulators

• Contractual agreements and “principles of access”

• Rules on payment, compensation, and tariffs

• Utility obligations to accommodate exports beyond hosting capacity

General

• Stakeholder education

• Stop-gap measure vs. enduring solution

• Low data resolution and quality for many distribution systems, loads, and PV



NREL Ongoing Research Areas

▪ Publications accepted or submitted for much of this work… stay tuned!

Replicability and Robust Curtailment Risk

Assessment Methods

Extendibility:What is the firm versus flexible hosting

capacity over many circuits and penetration levels?

Sensitivity:How much does data quality and resolution affect hosting capacity

and curtailment results?

Validation:Track flexible interconnection field

projects. Report grid performance and actual versus expected curtailment.

Novel Control Scheme Development



Thank you!

Questions?

Steven Coley, EPRISenior Project Engineer, Integration of DER [email protected]

Nadav Enbar, EPRIPrincipal Project Manager, Integration of DER [email protected]

Kelsey Horowitz, NRELLead Researcher, Sustainable Technology [email protected]

Devin Van Zandt, EPRITechnical Executive, Integration of DER [email protected]







EPRI Publications on Flexible Interconnection

▪ Understanding Flexible Interconnection – 3002014475

▪ Flexible Interconnection for DER: Emerging Practices at Early-Adopter Utilities – 3002012964

▪ Maximizing DER Hosting and Grid Utilization, Flexible Interconnection Capacity Solutions (FICS) – 3002015742

▪ Quantifying the Technical Benefits of DERMS and Interconnection Principles of Access – 3002015743

▪ Employing Active Power Curtailment of Distribution-Connected Solar Photovoltaics: Economic and Regulatory Considerations – 3002010289

▪ Application of Active Power Management to Increase Hosting Capacity – 3002013440

▪ The Economic Impact of Real-Power Management of Solar PV Systems – 3002013325

Reports downloadable from: www.epri.com


https://www.epri.com/#/pages/product/000000003002014475/?lang=en-US









NREL Publications and Resources

▪ Quasi-static Time-Series PV Hosting Capacity Methodology and Metrics: https://www.nrel.gov/docs/fy19osti/72284.pdf

▪ More forthcoming soon!

– These will be posted on our website: https://www.nrel.gov/solar/advanced-hosting-capacity-analysis.html


https://www.nrel.gov/docs/fy19osti/72284.pdf

https://www.nrel.gov/solar/advanced-hosting-capacity-analysis.html

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