1. New Energy Horizons
Opportunities and Challenges
Validation of Solar PV Power
Forecasting Methods for High
Penetration Grid Integration
IEEE Power and Energy Society
General Meeting
July 26, 2012
James Bing, NEO Virtus Engineering, Inc.
Obadiah Bartholomy, Sacramento Municipal Utility District
Pramod Krishnani, Belectric North America Inc.

2. Project Sponsors and Partners New Energy Horizons
Opportunities and Challenges
CPUC
CSI Solar RD&D Program
www.calsolarresearch.ca.gov
CSI RD&D
Program Manager
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3. TOPICS New Energy Horizons
Opportunities and Challenges
• PROJECT BACKGROUND
• TECHNICAL BACKGROUND
• EXPERIMENTAL DESIGN
• PRELIMINARY RESULTS
• ONGOING WORK
• CONCLUSIONS
3

4. PROJECT BACKGROUND New Energy Horizons
Opportunities and Challenges
• California Public Utilities
Commission High Penetration PV
Program
• Sacramento Municipal Utility District
100MW Feed-in-Tariff
• Parallel Research Effort (DOE FOA:
Improving the Accuracy of Solar Forecasting)
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5. CPUC High Penetration PV Program New Energy Horizons
Opportunities and Challenges
• CPUC established CSI RD&D Program in 2007
– Allocated $50 million for research, development,
demonstration and deployment (RD&D) projects to further
the overall goals of the CSI Program
– Adopted the “CSI RD&D Plan”
• CSI RD&D Plan established:
– Goals and objectives
– Allocation guidelines for project funding
– Criteria for solicitation, selection and project funding
• Three Target Areas Established for Program Funding:
– Grid-Integration: 50-65%
– Production Technologies: 10‐25%
– Business Development and Deployment: 10‐20%
5

6. Sacramento Municipal Utility
District 100MW Feed-in-Tariff New Energy Horizons
Opportunities and Challenges
• SMUD max summer load ~3GW
• Feed in Tariff = 100MW or ~3% of peak load
• ~36 MW of hidden “behind the meter” PV
• SMUD capacity expected to grow, goal of 125 MW
net metered PV by 2016
• Power integration issues are very (grid) site
dependant: Forecast capability addresses/informs
planning, automation and curtailment/mitagation
issues
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7. NDFD Grid, Primary & Secondary Sites
SMUD Service Territory New Energy Horizons
Opportunities and Challenges
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8. Sacramento Municipal Utility District
Multi-forecaster Benchmarking New Energy Horizons
Opportunities and Challenges
•SMUD will be using irradiance network and FiT systems to
benchmark forecast performance for 4 forecasters in
addition to Neo Virtus beginning in August
•Forecasters will provide hourly forecasts, uncertainty and
5 minute variability on hour ahead up to 5 days in
advance for each irradiance sensor and FiT system
output
•Sandia Labs will quantify forecast accuracy for various
weather conditions and timeframes
•Goal is to understand broadly state of the art in forecast
accuracy and ability to trust forecast performance for
different timeframes
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9. TOPICS New Energy Horizons
Opportunities and Challenges
• PROJECT BACKGROUND
• TECHNICAL BACKGROUND
• EXPERIMENTAL DESIGN
• PRELIMINARY RESULTS
• ONGOING WORK
• CONCLUSIONS
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10. TECHNICAL BACKGROUND New Energy Horizons
Opportunities and Challenges
• Irradiance Fundamentals
• PV Power Simulation Fundamentals
• Current Solar Forecasting Methods
• NEO Virtus Day Ahead Forecasting
of AC Power
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11. Irradiance Fundamentals New Energy Horizons
Opportunities and Challenges
• Direct Normal Irradiance (DNI)
• Diffuse Horizontal Irradiance (DHI)
• Global Horizontal Irradiance (GHI): GHI = DNI cos ϴ +DHI
• 1000W/m2 GHI ≈ Full Scale or 1pu (nominal at sea level)
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12. Irradiance Fundamentals New Energy Horizons
Opportunities and Challenges
• Plane of Array Irradiance (POA) = Incident Irradiance on PV array
• POA can be calculated with a knowledge of:
– Direct Norman Irradiance (DNI) and Diffuse Horizontal Irradiance (DHI) and
– PV system Azimuth, Tilt, Lat/Lon, Shading Obstruction, Date & Time
12

13. PV Power Simulation Fundamentals
New Energy Horizons
Opportunities and Challenges
13

14. Current Solar Forecasting Methods New Energy Horizons
Opportunities and Challenges
Technology Time Horizon Coverage
Satellite 12hr to 7 days Global
Mesoscale 12hrs to months Global/
NWP models Regional
Aggregated 1hrs to 3hrs Regional
Ground Sensors
SkyImager 30min to 3hrs 2 to 10km radius
Array Scale 1 to 30 minutes Array Size
Sensors
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15. NEO Virtus Method for Day Ahead
Forecasting AC Power New Energy Horizons
Opportunities and Challenges
CLOUDCOVER
Collect Forecast Cloud-cover (NEO uses NDFD data): FORECAST+
PV ARRAY SPECS
 Cloud fraction (%)
SOLAR
GEOMETRY
Collect PV Array Data: MODEL
 Azimuth, Tilt, Lat/Lon, Shading, Capacity, Inverter, etc. IRRADIANCE
TRANSMITTANCE
MODEL
Simulate:
PV ARRAY
GEOMETERY+
• Sun Position Model: zenith & azimuth angles (º) SHADING
• Irradiance Transmittance Model: DNI & DHI (W/m^2) PV CONVERSION
MODEL
• PV Array Geometry & Shading Model: POA (W/m^2)
INVERTER+
• Photovoltaic Conversion Model: DC Power (Wdc) LOSSES MODEL
• Inverter & Losses Model: AC Power (Wac) AC POWER
OUT
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16. TOPICS New Energy Horizons
Opportunities and Challenges
• PROJECT BACKGROUND
• TECHNICAL BACKGROUND
• EXPERIMENTAL DESIGN
• PRELIMINARY RESULTS
• ONGOING WORK
• CONCLUSIONS
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17. EXPERIMENTAL DESIGN New Energy Horizons
Opportunities and Challenges
 Build & deploy irradiance monitoring network
 Monitor utility scale PV system power production
 Validate irradiance forecast performance territory-wide
 0-3 hour ahead
 Day ahead
 Validate PV power production forecast for SMUD
Feed-In-Tariff (FIT) PV Systems
 0-3 hour ahead
 Day ahead
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18. Primary & Secondary Irradiance
Monitoring Station Specifications New Energy Horizons
Opportunities and Challenges
• Irradiance Monitoring Network
– 5 primary monitoring stations
• GHI, DHI, DNI
• Ambient temperature
• 1 minute averages
– 66 secondary monitoring stations
• GHI
• Ambient temperature
• 1 minute averages
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19. Secondary Station Design & Fabrication
New Energy Horizons
Opportunities and Challenges
• Irradiance Monitoring
Network
– 5km grid Sacramento
– NDFD Lambert conformal
projection
– Installed on SMUD utility
poles
– Automated data retrieval
via cellular modem
– 14 month continuous data
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20. Primary & Secondary Monitoring Stations
New Energy Horizons
Opportunities and Challenges
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21. Day Ahead Irradiance & PV Power
Forecast Validation New Energy Horizons
Opportunities and Challenges
1-minute, 5km
resolution GHI &
Temp database
NEO Forecast vs.
NEO Forecast vs. Measured PV
Measured power production
irradiance validation
validation
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22. Solar Forecasting Error Analysis New Energy Horizons
Opportunities and Challenges
Relative (percent) Error*:
 RMSE/Capacity
 MAE/Capacity
 MBE
Data were filter for zenith angle >90 (no night
time data were used).
No plant availability information was
provided: we assumed 100% availability.
* Hoff, Perez, Kleissl, Renne, Stein: “Reporting of Relative Irradiance Prediction Dispersion Error”
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23. TOPICS New Energy Horizons
Opportunities and Challenges
• PROJECT BACKGROUND
• TECHNICAL BACKGROUND
• EXPERIMENTAL DESIGN
• PRELIMINARY RESULTS
• ONGOING WORK
• Territory-wide measured irradiance data
animation
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24. PRELIMINARY RESULTS New Energy Horizons
Opportunities and Challenges
• NEO 20-36 Hour (Day Ahead) Forecasting
Model PV Production 5/1/12 to 7/2/12
• R2 = 0.9398
• RMSE/Capacity = 8.61%
• MAE/Capacity = 5.57%
• MBE = -2.39%
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25. NEO’s Day Ahead Forecast vs. Measured
One SMUD FIT PV System 5/1/12 to 7/2/12 New Energy Horizons
Opportunities and Challenges
SMUD FIT PV Array R² = 0.9398
1
0.9
0.8
0.7
Forecast ac production (% capacity)
0.6
0.5
0.4
0.3
0.2
0.1
0
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Measured ac production (% capacity)
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26. NEO’s Day Ahead Forecast vs. Measured
PV Production (one system) New Energy Horizons
Opportunities and Challenges
18
16
14
12
10
BP01 measured ac (avg 1 min)
BP01 forecast ac
8
6
4
2
0
6/3/2012 6/4/2012 6/5/2012 6/6/2012 6/7/2012 6/8/2012
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27. Unforeseen Issues, Lessons Learned New Energy Horizons
Opportunities and Challenges
• Shadows cast by overhead lines and crossbars causing
“artifacts” in daily data
– Sandia & SMUD are working out algorithm to filter data
• Data logger flash memory failures
– Code was changed and manufacturer replaced failed units
• Secondary sensors cannot be cleaned economically
– Precision Spectral Pyrranometers which can be cleaned
and maintained are used for system-wide calibration
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28. Overhead Wire Shading Anomalies
New Energy Horizons
Opportunities and Challenges
Global Horizontal Radiation 6/25/11 Global Horizontal Radiation 07/09/11
SMUD/NEO Virtus Secondary Station #64 SMUD/NEO Virtus Secondary Station #64
1100 35 1100 35
1000 1000
30 30
900 900
800 25 800 25
700 700
Irradiance (W/m2 )
Irradiance (W/m2 )
Temperature ( C)
Temperature ( C)
20 20
600 600
500 500
15 15
400 400
300 10 300 10
200 200
5 5
100 100
0 0 0 0
5:30 6:30 7:30 8:30 9:30 10:30 11:30 12:30 13:30 14:30 15:30 16:30 17:30 18:30 19:30 20:30 5:30 6:30 7:30 8:30 9:30 10:30 11:30 12:30 13:30 14:30 15:30 16:30 17:30 18:30 19:30 20:30
Time (Pacific Standard Time) Time (Pacific Standard Time)
DAS# 64 POLE# UD122802 LAT: 38.59662 LON: -121.48561 Temp (⁰C) DAS# 64 POLE# UD122802 LAT: 38.59662 LON: -121.48561 Temp (⁰C)
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29. Global Network Calibration
New Energy Horizons
Opportunities and Challenges
• Eppley Precision
Spectral Pyranometer
(PSP)
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30. TOPICS New Energy Horizons
Opportunities and Challenges
• PROJECT BACKGROUND
• TECHNICAL BACKGROUND
• EXPERIMENTAL DESIGN
• PRELIMINARY RESULTS
• ONGOING WORK
• CONCLUSIONS
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31. ONGOING WORK New Energy Horizons
Opportunities and Challenges
Development of 0-3 hour ahead forecasts
using sensor network
 Territory-wide GHI
 Feed in Tariff PV Systems Production
Filtering of signal noise caused by cross arm
and wire shading
Global calibration of sensor network
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32. TOPICS New Energy Horizons
Opportunities and Challenges
• PROJECT BACKGROUND
• TECHNICAL BACKGROUND
• EXPERIMENTAL DESIGN
• PRELIMINARY RESULTS
• ONGOING WORK
• CONCLUSIONS
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33. CONCLUSIONS New Energy Horizons
Opportunities and Challenges
 Solar forecasting technology is in the earliest
stages of development
 Error metrics, time horizons and benchmarks
are being developed
 Numerous forecasting technologies are under
development
 Performance validation efforts for individual
forecasting technologies are being conducted
 There are front runners but currently no clear
winners in this technology race
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34. NEO Virtus Engineering, Inc. New Energy Horizons
Opportunities and Challenges
QUESTIONS?
James M. Bing, PE
jbing@neovirtus.com
Obadiah Bartholomy
OBartho@smud.org
Pramod Krishnani
pramod.krishnani@belectric-usa.com
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