1-Jeff Smith EPRI High Pen PV US Experience

Jeff Smith Manager, Power System Studies

Workshop: Utility Experience with High Penetration PV

December 3, 2012

US Experience with High Penetration Solar PV

2 © 2012 Electric Power Research Institute, Inc. All rights reserved.

Overview

• US Deployment of Solar PV

• Technical Challenges

– Overview of US Distribution Systems

– Where PV is being installed

• Limiting Factors for PV

• Near Term Solutions

• Key Challenges Moving Forward


US Deployment of Solar PV

10 Largest Utility Solar Profiles in US

Source: The Future of Solar and the Utility Business, New York Electric Utility PV Workshop Sponsored by: NYPA, EPRI and SEPA Nov 28, 2012

-

50,000

100,000

150,000

200,000

250,000

300,000

350,000

400,000

450,000

2010 2015 2020 2025 2030 2035 2040 2045 2050

MW

CSP, No Storage CSP, with 6-hr Storage Solar PV Dist. Solar PV (Estimate)

Bulk Distributed2020 42,430 25,328 2030 121,915 97,736

Solar PV Capacity (MW)

Source: DOE SV + EPRI


What are the Main Technical Challenges?

• First you have to consider – distribution system design characteristics – where PV is being interconnected


Distribution Designs in North America

0 100 200 300 400 500 600 700

# of

feed

ers

3 PH Backbone Length (mi)

0

200

400

600

800

# of

feed

ers

Total Circuit Miles

0

500

1000

1500

2000

0 1 2 3 4 5 6 7 M

ore

# of

feed

ers

# of line regulators

0 200 400 600 800

1000 1200

0-5 5-10 10-15 >15

# of

feed

ers

Peak Load(MW)

- Sample data set from US Utility - No “typical” circuits


Distribution Example 1

Key Characteristics

Voltage class: 15kV

Peak Load: 7.5 MVA

Total 3Phase Miles: 6

Total 1-2Phase Miles: 6

Feeder Regulation: - Substation LTC - No feeder regulation - Fixed cap banks

Total Customers: 600

Small “footprint”

= 1 km2

Substation

Primary Voltages by Phase

“Headroom”


Distribution Example 2

Key Characteristics

Voltage Class: 15kV

Peak Load: 11 MVA

Total 3Phase Miles: 60

Total 1-2Phase Miles: 50

Longest Distance: 11 miles

Feeder Regulation - Substation LTC - 6 feeder regulators - switched capacitor banks

Total Customers: 6700

Large “footprint”

= Line Regulators= 1 km2

Substation

*Previous Circuit

Same Scale

“Headroom”


Where is PV Interconnected?


Residential Rooftop Secondary (LV) Overvoltage Due to Residential Rooftop PV

• Impact at the Customer Level – Customers with PV fed from

same service transformer – Light-load conditions – Each PV system increases

secondary voltage few % – Results in overvoltage on

secondary

Number of utilities have seen secondary overvoltages where PV customers are fed from same transformer


Large Scale PV – Case Study 1 Voltage Impacts Due to Large Scale PV (1.7MW)

• Some utilities experiencing number of interconnect requests for 1 – 20 MW systems

• Utilizing large open spaces such as warehouse rooftops

• Connected directly to distribution

Overvoltage limit

No issues found if same PV Plant were located only a few miles upstream….or if the PV operated at off-unity (inductive) power factor

285kW190 kW

465 kW760 kW

Measured Voltage as Function of PV Output


Large Scale PV – Case Study 2 Minimal Impact on Grid Voltage due to PV (1.0 MW)

Measured Voltage as Function of PV Output

ANSI voltage limit

Existing PV has minimal impact on feeder voltage


What’s the Limiting Factor for PV Penetration? Two Distribution Systems with Different Limiting Factors

Feeder A Feeder Characteristics Feeder B

13.2 Voltage (kV) 12.47 5 MW Peak Load 6 MW

0.8 MW Minimum Load 0.7 MW

1.1 MW Minimum Daytime

Load 0.7 MW

1.0 Existing PV (MW) 1.7

Only @ Substation

Feeder Regulation Yes, highly regulated

28 Total Circuit Miles 58 7 mi2 Feeder “Footprint” 35 mi2

Minimum Hosting Capacity

>3500 kW Due to Voltage

Impacts 250 kW

777 kW Due to

Protection Limits

390kW

1 mi

Substation

PV Site4 miles from Sub

Capacitor BankRegulator

Feeder A Feeder B

Protection Limited

Voltage and Protection

Limited


What are Some of the Near Term Solutions?

Smart inverters for providing grid support functions Volt-Var Control* Volt-Watt Control**

Dynamic Var Control** Volt-Var w/ Hysteresis**

*Currently in OpenDSS **available in OpenDSS Q1 2013


Use of Smart Inverters for Mitigating Voltage Issues

Without Volt/var Control Volt/var Control

PV Hosting Capacity (kW) Without Volt/var With Volt/var

Primary Voltage Deviation

1st violation 938 >2500 50% scenarios with violation 1323 >2500 All scenarios with violation 1673 >2500

Primary Over Voltage

1st violation 540 880 50% scenarios with violation 871 1464 All scenarios with violation 1173 2418

5000 cases shown Each point = highest primary voltage

ANSI voltage limit

ANSI voltage limit

160% increase in hosting capacity

60% increase in hosting capacity

Increasing penetration (kW) M

axim

um F

eede

r Vol

tage

(pu)

Max

imum

Fee

der V

olta

ges

(pu)

Increasing penetration (kW)


Prevention of Unintentional Islands

Most inverters use active anti-islanding

which rely on the creation of an abnormal voltage to detect island

formation

Key communication based methods?

• Direct transfer trip (DTT)

• Power Line Carrier Permissive (PLCP)

• Synchrophasor-based methods

Grid support functions are all about correcting

abnormalities in the voltage/frequency to maintain grid stability

Conflicting

Cost/ effectiveness/ reliability/ coverage area


Key Challenges

• Standards allowing for smart inverter function implementations

• Agreement on “standard” functions • Visibility of PV at the distribution level • Improved screening methods for new interconnection

requests • Circuit reconfiguration


Questions

Contact:

Jeff Smith Manager, Power System Studies EPRI [email protected]

1-Jeff Smith EPRI High Pen PV US Experience

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