1. Managing Intermittency:
Standards and Recommended Practices in Solar Power Forecasting
ERCOT Emerging Technologies Working Group
April 25, 2011
Tony Daye, Green Power Labs Inc.

2. Green Power Labs: About Us
Green Power Labs is a company of solar resource experts and solar engineers
Est. in 2003, Green Power Labs is a leader in state-of-the-art solar power forecasting, satellite-based solar data processing, and solar energy management

3. Solar Power Forecasting: Standard Industry Requirements
8-Day Ahead
3-Day Ahead
1-Day Ahead
Hour Ahead
- 105 minutes
Intra-Hour Forecasts
- 15 minute time line – out 2 hours
Event Prediction:
Large changes in short periods
Energy + Probabilistic Forecasts
Source: CAISO 2011

4. Conceptual Forecasting Roadmap
100
Assumed limit of predictability
Statistical approaches,
cloud motion analysis
Accuracy%
NWP
Climatology
Persistence
Now Hours
Days
Months
Years
Forecast Time Scale

5. Key Technologies and Applications
Sate-of-the-art solar forecasts are based on the following data sources and technologies:
SCADA and meteo data from customer’s site
TSI (if available)
GOES vis. spectrum images
Integrated NWP (ECMWF, GFS, NAM, GEM) for probabilistic forecast
Climatology (Satellite- derived, local data)
Time Horizon
Instruments
Uses
Minutes ahead
SCADA, TSI, Satellite
Operation optimization
Hours ahead
TSI, Satellite, Meteo
intertie (import-export) transactions
Days ahead
Ensemble NWP, MOS
Unit commitment
Weeks ahead
NWP
Maintenance planning
Months-years ahead
Climatology
ROI/IRR, bankability

6. Key Technology Components
Satellite Data Processing
Numerical Weather Prediction
Real-time Data Processing
weather and power
IPP
Weather Model Integration
Service Delivery
Utility
ISO
Power Plant Modeling
Forecast
Nowcast (0 – 6 hrs)
Short term (24 – 72 hrs)
Long term ( 2 weeks)

7. Key Technology Components: Satellite Data Processing

8. Ensemble NWP

9. PV Power Plant Modeling
Current Practices:
Sandia Array Performance Model (about 30 PV module parameters)
California Energy Commission/University of Wisconsin five-parameter model;
Single-point efficiency model with a temperature coefficient.
Standardisation:
NERC: Standard Models for Variable Generation
Sandia: Models Used to Assess the Performance of Photovoltaic Systems
IEA PVPS Task 11: Design and simulation tools for hybrid PV systems
Modeling Improvement based on Field Experience
Solar Power Input
Solar Irradiation Model
Site-Specific Obstructions Model
PV Module Model
PV Array Model
Inverter Model
Transformer Model
PV Plant Power Output

10. Importance of Site Considerations

11. Aggregate Power Forecasts

12. Towards Industry Standards
Industry Standards are required to establish and maintain best practices in solar power forecasting
Current practices in forecast performance evaluation feature different approaches even when using similar metrics such as RMSE and MAE, e.g.
Based on daily or hourly comparisons
Night hours excluded or included in calculations
Reporting absolute or relative errors
In relation to what (mean power, median, range, peak?)
Assessed over which time span?
Recommended Industry Standards include:
Forecasting timelines and deliverables
Technology requirements for specific forecasting timelines
Standard metrics for forecast performance evaluation

13. Thank You Tony Daye Green Power Labs Inc. T: 902.466.6475