ERCOT Solar Modeling – ETWG Meeting

1. ERCOT Solar Modeling – ETWG Meeting April 30, 2013

2. Project Overview • Objective: Produce 20 years of high-quality hourly solar production data for several different solar technologies in all 254 Texas counties • Methodology: Utilize National Solar Radiation Database (NSRDB) Class I and Class II weather station data and solar production modeling software to generate 4,452 individual datasets with 8,760 points each

3. Agenda • Origin and quality of raw data • How solar production modeling software works • Weather station-county grouping • Summary of results • Quality assurance and statistical analysis • Q&A

4. Project Overview

5. Project Overview

6. Task 1: Collect Data Meteorological Data Required for Solar Simulations System Advisory Model (SAM) Weather Data Documentation- 12/7/2011

7. National Solar Radiation Database (NSRDB) • 20 years (1991-2010) of measured/modeled solar radiation data with accompanying meteorological fields for weather stations across the US • Solar radiation data generated by the NREL Meteorological-Statistical Model (METSTAT) and a State University of New York (SUNY) developed model based on satellite data • Weather data from National Climate Data Center (NCDC)

8. NSRDB • Four levels of data-filling methods • Short-term interpolation - up to 5 hour gaps and gaps at night • Medium-term filling - gaps up to 24 hours • Long-term filling - gaps up to 1 year • Last-ditch filling - gaps greater than a year • Level of data filling required determines Class of weather station

9. NSRDB • Class I Stations • Complete period of record (all hours 1991–2010) for solar and key meteorological fields • Highest-quality solar modeled data (16 sites in Texas) • Class II Stations • Complete period of record but significant periods of interpolated, filled, or otherwise lower-quality input data for the solar models (37 in Texas). • Class III Stations • Have some gaps in the period of record but have at least 3 years of data that might be useful for some applications (36 in Texas) National Solar Radiation Database (NSRDB) 1991-2010 User’s Manual

10. Class I / II Weather Stations in TX 53 Class I/II NSRDB Weather Stations in TX Red = Class I White = Class II URS GIS Dept.

11. Raw Data for this Project NSRDB Meteorological Data 20 years (1991-2010) of hourly meteorological and solar radiation data for 53 weather stations in and around Texas, including: Dry-bulb temperature Dew-point temperature Relative humidity Wind speed Wind direction Atmospheric pressure Global horizontal radiation Direct normal radiation Diffuse horizontal radiation Typical Meteorological Data (TMY) TMY files for 53 weather stations (Class I & II) Composed of 12 typical meteorological months (January through December) that are concatenated to form a single year. One TMY file contains a single representative year (8,760 data points). TMY Algorithm Statistical analysis selects 12 “typical” months from 20-year data set to complete one full year

12. Data Conversion • NSRDB data conversion process • National Renewable Energy Laboratory (NREL) System Advisor Model (SAM) requires weather data in TMY2, TMY3 or EPW format • URS converted NCDC-formatted NSRDB data to the TMY3 format for use as an input to SAM. The conversion process was automated using Bash shell scripts and Unix programming languages, including AWK and SED. • Result was 21 TMY3-formatted meteorological data files for each of the 53 Class I/II weather stations (1,113 TMY3 files total)

13. Project Overview

14. National Renewable Energy Laboratory (NREL) System Advisor Model (SAM)

15. NREL SAM • Available for free at NREL SAM website: • https://sam.nrel.gov/ • URS used most recent version (2013.1.15) • Selected for many reasons over other options: • Transparency/replicability of study results • Flexibility in raw data sourcing • Ability to run automated scripts for fast data processing

16. Solar Technologies • Fixed tilt crystalline silicon • Single-axis tracking (SAT) • Residential rooftop (fixed C-Si) • Concentrating Solar Power (CSP)

17. Fixed Tilt Crystalline Silicon (C-Si) • Majority of PV arrays composed of C-Si cells • Lowest initial cost per watt • Polycrystalline efficiency: 13-16% • Monocrystalline efficiency: 14-20% • Ideally oriented due south with slope (tilt) of modules equal to latitude

18. Single-Axis Tracker (SAT) • Increase the energy produced by a solar array by tracking the sun from east to west diurnally • Tilt of SAT systems are usually kept flat, normal to the zenith, and have a total east-west tracking range of 90°. • SAT systems are designed to maximize land use without causing self-shading

19. Rooftop Residential • Utilize the same components of a fixed-tilt system, but is constrained to the orientation of the building roof • Typically range from 2kW to 16kW

20. Concentrating solar power (CSP) • Utilize concentrated solar radiation to generate thermal energy, which is used to power a conventional electricity producing steam turbine generator • Two primary types of plants: parabolic troughs and power towers • URS elected to model a parabolic trough type CSP plant

21. Solar Radiation Levels across US

22. CSP Resource in Texas

23. Final Datasets • Individual models configured in SAM for each technology type • Fixed tilt C-Si = 1MW • SAT = 1MW • Residential = 10kW • CSP = 50MW • 20° selected for slope of fixed tilt system – most typical installation in Texas

24. Project Overview

25. Station-County Grouping • US DOE used algorithms to define “zones of influence” around Class I/II weather stations at 10km2 blocks

26. Station-County Grouping

27. Station-County Grouping

28. Final Model Result Datasets • Each of 1,113 TMY3 files fed into each model using automated script • Output was 4,452 individual solar production model results containing 8,760 rows • Post-production of data to generate total hourly AC output zeroing out any overnight consumption • Results for each of four technologies available for any county in Texas based on associated weather station

29. 20-Year Production Model Results

30. 20-Year Production Model Results

31. 20-Year Production Model Results Model results normalized to 50 MW to match CSP system

32. 20-Year Production Model Results

33. 20-Year Production Model Results

34. 20-Year Production Model Results

35. Project Overview

36. Data Quality & Statistical Analysis • Final datasets reviewed for data quality and alignment with typical production profiles using URS internal technical review (ITR) process Austin Mueller production model results – PVFT (blue), SAT (red) – 7/1/10 – 7/8/10

37. Statistical Variability Calculations • Purpose: calculate the likelihood that a solar plant will generate a certain amount of electricity in any given year • Exceedance probabilities (P50 & P90) can be calculated by fitting the dataset to a standard probability distribution and determining value from the cumulative distribution function (CDF). • P50/P90 calculations prepared for six stations across TX using 20 years of production model results

38. Exceedance Probabilities

39. Weather Station Variance Analysis • Graph below shows the % variance in total annual production model estimates between the Class I station shown and a nearby Class I or II station • Many Class II stations relied upon inferior statistically derived cloud cover data prior to 1998 when satellite imagery data was introduced

40. Angle of Incidence and SAT • During winter months, SAT systems have “dip” in production during middle of day due to angle of incidence SAT production model results - Odessa (blue), Nacogdoches (red) – 1/1/10 – 1/2/10

41. Angle of Incidence and SAT Black & Veatch Solar Diagnostics Presentation

42. 2011 Data • Kevin contacted Michael Milligan at NREL to ask about availability of 2011 NCDC format NSRDB hourly solar data with the filled meteorological fields for the Class I & II weather stations in Texas • No reliable 2011 meteorological data acquired in time for this project

43. Q&A • Mike Hoffman, Project Manager mike.hoffman@urs.com W: (512) 419-6092 C: (512) 297-5116