Download - 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
3 © 2012 Electric Power Research Institute, Inc. All rights reserved.
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
4 © 2012 Electric Power Research Institute, Inc. All rights reserved.
What are the Main Technical Challenges?
• First you have to consider – distribution system design characteristics – where PV is being interconnected
5 © 2012 Electric Power Research Institute, Inc. All rights reserved.
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
6 © 2012 Electric Power Research Institute, Inc. All rights reserved.
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”
7 © 2012 Electric Power Research Institute, Inc. All rights reserved.
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”
8 © 2012 Electric Power Research Institute, Inc. All rights reserved.
Where is PV Interconnected?
9 © 2012 Electric Power Research Institute, Inc. All rights reserved.
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
10 © 2012 Electric Power Research Institute, Inc. All rights reserved.
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
11 © 2012 Electric Power Research Institute, Inc. All rights reserved.
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
12 © 2012 Electric Power Research Institute, Inc. All rights reserved.
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
13 © 2012 Electric Power Research Institute, Inc. All rights reserved.
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
14 © 2012 Electric Power Research Institute, Inc. All rights reserved.
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)
15 © 2012 Electric Power Research Institute, Inc. All rights reserved.
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
16 © 2012 Electric Power Research Institute, Inc. All rights reserved.
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
17 © 2012 Electric Power Research Institute, Inc. All rights reserved.
Questions
Contact:
Jeff Smith Manager, Power System Studies EPRI [email protected]