GroundWork's goal is to deliver high quality ground irradiance data through solar monitoring stations. Their programs include system design, equipment installation, data integration, operations and maintenance, and quality assurance. Ground irradiance data can be used to tune satellite data for resource assessment, capture microclimates, and provide lower uncertainty than satellite-derived data if collected from a maintained, site-specific, secondary standard station. Key considerations for solar monitoring stations include sensor type and placement, redundancy, weather protection, and ongoing maintenance and data validation.

1. Sandia/EPRI 2014 PV Systems Symposium
Ground Irradiance Data
Justin Robinson

2. Proprietary and Confidential
GroundWork Renewables, Inc.

3. Proprietary and Confidential
GroundWork Renewables, Inc.
GroundWork’s goal is to deliver revenue-grade
ground irradiance data to solar power modelers
Our Solar Monitoring Station (SMS) programs include:
! Program and System Design and Submittals
! Equipment Supply, Fabricate and Test
! SCADA Integration
! Install, Commission and Validate
! Operations and Maintenance
! Data Quality Assurance (GroundWatch)

4. Proprietary and Confidential
GroundWork Renewables, Inc.

5. Proprietary and Confidential
GroundWork Renewables, Inc.
Use of Ground Irradiance Data
Gather lower uncertainty irradiance data
if.... secondary standard, site-specific and maintained
Tune satellite data for lower uncertainty resource assessment
Capture micro-climates and albedo
http://kippzonen-blog.nl

6. Proprietary and Confidential
GroundWork Renewables, Inc.
Solar Radiation Terms
GHI: Global Horizontal Irradiance
DNI: Direct Normal Irradiance
DHI: Diffuse Horizontal Irradiance
GPOA: Global Plane of Array Irradiance
http://rredc.nrel.gov

7. Proprietary and Confidential
GroundWork Renewables, Inc.
Component Sum Calculation
Sza: Solar Zenith Angle
GHI = DNI * cos(Sza) + DHI
http://esrl.noaa.gov

8. Proprietary and Confidential
GroundWork Renewables, Inc.
GHI
Calculated from measured DNI and DHI
Measured with Pyranometer
Measured with Si-Photodiode

9. Proprietary and Confidential
GroundWork Renewables, Inc.
GPOA
Measured with pyranometer at tilt and azimuth of array
Estimated from DNI and DHI

10. Proprietary and Confidential
GroundWork Renewables, Inc.
DNI
Measured with pyrheliometer
Calculated by Rotating Shadowband Radiometer (RSR)

11. Proprietary and Confidential
GroundWork Renewables, Inc.
DHI
Measured with shaded pyranometer (shadowball assembly)
Measured with RSR
Calculated from DNI and GHI

12. Proprietary and Confidential
GroundWork Renewables, Inc.
SMS Considerations
Pyranometer class
Sensor orientation and mounting
Redundant irradiance sensors
Temperature correction
Inclement weather
Ancillary measurements
Power budget & diagnostics
Soiling studies

13. Proprietary and Confidential
GroundWork Renewables, Inc.

14. Proprietary and Confidential
GroundWork Renewables, Inc.
SMS Types
Redundant GHI
GHI + GPOA
RSR + GHI
Sun Tracker with GHI, DNI, DHI

15. Proprietary and Confidential
GroundWork Renewables, Inc.
Redundant GHI
Low uncertainty GHI ground data
Provides for both data quality assurance and data continuity
Horizontal position is easy to maintain and verify

16. Proprietary and Confidential
GroundWork Renewables, Inc.

17. Proprietary and Confidential
GroundWork Renewables, Inc.
GHI + GPOA
Fixed GPOA at defined angle
GPOA measures albedo (ground reflection)
Provides some data quality assurance and data continuity
GPOA introduces tilt error
GPOA orientation is more difficult to maintain and verify

18. Proprietary and Confidential
GroundWork Renewables, Inc.

19. Proprietary and Confidential
GroundWork Renewables, Inc.
RSR + GHI
RSR measures DHI and GHI; Calculates DNI
Underestimation of DHI under clear sky conditions
Limited data quality assurance of dissimilar instruments
No data continuity of lower uncertainty GHI
DHI is required by SCE; RSR is an acceptable option

20. Proprietary and Confidential
GroundWork Renewables, Inc.

21. Proprietary and Confidential
GroundWork Renewables, Inc.
Sun Tracker with GHI, DNI, DHI
Measures GHI, DNI, DHI
Calculated GHI has lowest uncertainty
Excellent data quality assurance and data continuity
Upfront investment limits usage in development
Maintenance regime is more rigorous and costly

22. Proprietary and Confidential
GroundWork Renewables, Inc.

23. Proprietary and Confidential
GroundWork Renewables, Inc.
Ground Metadata
Commissioning documentation and change logs
Sensor make, model and class
Datalogger program
Photo-set
Sensor calibration certificates
O&M frequency and logs
Periodicity of data review

24. XX.XXXXXX, -XXX.XXXXX
Solar Project, CA

26. Proprietary and Confidential
GroundWork Renewables, Inc.
Ground Data Reasonableness
Characterize system uncertainty
Correlate data with cleaning events
Compare redundant sensors and/or component sum values
Evaluate symmetry of irradiance curves
Compare clear sky transmittance indices (NREL SERI QC)

27. Proprietary and Confidential
GroundWork Renewables, Inc.
Cleaning Event

28. Proprietary and Confidential
GroundWork Renewables, Inc.

29. Questions