2014 PV Performance Modeling Workshop: Optimizing PV Designs with HelioScope: Paul Gibbs, Folsom Labs
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2014 PV Performance Modeling Workshop: Optimizing PV Designs with HelioScope: Paul Gibbs, Folsom Labs

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2014 PV Performance Modeling Workshop: Optimizing PV Designs with HelioScope: Paul Gibbs, Folsom Labs

2014 PV Performance Modeling Workshop: Optimizing PV Designs with HelioScope: Paul Gibbs, Folsom Labs

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2014 PV Performance Modeling Workshop: Optimizing PV Designs with HelioScope: Paul Gibbs, Folsom Labs 2014 PV Performance Modeling Workshop: Optimizing PV Designs with HelioScope: Paul Gibbs, Folsom Labs Presentation Transcript

  • NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC. Improvements to PV System Modeling in SAM Sandia/EPRI PV Modeling Workshop Aron P. Dobos 5 May 2014
  • 2 What’s new in SAM for Photovoltaics? We’ve been working on a number of projects that will help optimize the design of PV systems and more accurately model their performance. In 2013, we held a technical review committee that recommended several areas for improvement. • New “11 parameter” module model using IEC-61853 test data • Much more flexible inverter models • Validation work shows SAM and other models are able to predict performance well • SAM Shade Calculator for 3D scenes • Historical NSRDB database update for inter-annual variability (P50/P90) analysis We are thankful for the support of DOE SunShot Systems Integration subprogram that facilitates these efforts.
  • 3 IEC-61853 Module Model (1) Problem: • Sandia module model is accurate but requires complex testing, and predicts only 5 points on the IV curve • 5/6 parameter single diode models can be inaccurate at low irradiances and for some module technologies Proposed solution: • Create a backwards-compatible extension of the single diode model whose additional parameters can be automatically calculated from IEC-61853 test data. • Parameters measured at each test condition : Pmp, Vmp Voc, Isc IRRADIANCE Spectrum Module Temperature W-m-2 15 C 25 C 50 C 75 C 1100 AM1.5 NA 1000 AM1.5 800 AM1.5 600 AM1.5 400 AM1.5 NA 200 AM1.5 NA 100 AM1.5 NA NA
  • 4 IEC-61853 Module Model (2) Recall: single diode models consist of two parts: o The nonlinear I-V curve equation defined by parameters: a, IL, Io, Rs, Rsh o These five parameters are STC values (@ 1000 W/m2 & 25 C) o A set of auxiliary equations that translate the five parameters from STC to operating conditions (temperature & irradiance) Rs is assumed constant! OK OK OK ? NOT OK NOT OK  Egref is fixed at 1.121 eV
  • 5 IEC-61853 Module Model (3) Observation: the I-V curve equation can fit module performance data quite well for many technologies. Auxiliary translation equations for parameters however are not adequate. Approach: define new auxiliary equations that fit the data better. Procedure: at each IEC-61853 test condition: IRRADIANCE Module Temperature W-m-2 15 C 25 C 50 C 75 C 1100 NA 1000 800 600 400 NA 200 NA 100 NA NA 1. Estimate the diode factor a from Voc & temperature coefficient 2. Numerically solve for the remaining 4 parameters IL, Io, Rs, Rsh given Pmp, Vmp, Voc, Isc 3. Fit the behavior of these parameters as a function of temperature and irradiance
  • 6 IEC-61853 Module Model (4) Result: an 11 parameter model. For a thin film module, these parameter values were obtained from the automated solution procedure: Improved auxiliary equations for Rs and Rsh:
  • 7 IEC-61853 Module Model (5) • For a First Solar thin film module, the improved model reduces power prediction error on average from 6.1% with the 5 parameter model to 1.3% • Next version of SAM (Autumn 2014) will include an implementation of the module model and solver • This model can help you optimize system design by having a more accurate representation of module performance based on measured test data
  • 8 Inverter Model Improvements (1) By default, SAM uses the Sandia Model for Grid-connected Inverters in conjunction with the CEC inverter database. We’ve added two options: • Enter inverter weighted efficiency (European or CEC) • Enter part-load inverter efficiency curve Model uses operating range inputs to calculate clipping losses. Voltage ranges are not enforced, but warnings are issued during simulation.
  • 9 Model Validation and Intercomparison (1) • Validation of SAM model against 9 systems with measured data • Annual agreement* within ± 3% • Hourly agreement*: o RMSE within 5.1% o MBE within ± 1.0% • Download report: http://www.nrel.gov/do cs/fy14osti/60204.pdf * Mesa Top and DeSoto excluded from these results. Annual numbers based on quality- controlled data, with system downtime, outages, snow hours, etc removed.
  • 10 Model Validation and Intercomparison (2) Using same measured datasets, compare SAM, PVsyst, PV*SOL, and PVWatts Notes: • PVWatts V1 underpredicts on average by 14% with default inputs (not shown) • PV*SOL does not properly model 1 axis tracking systems • Many thanks to PVsyst and PV*SOL teams for helping review this work Full report forthcoming this year Tool Error ranges for 6 systems SAM -5.0% to 4.1% PVsyst -1.7% to 5.5% PV*SOL -5.5% to 1.4% PVWatts -16.2% to -8.9%
  • 11 Updated Weather Datasets/Formats (1) The NREL TMY2 dataset is based on 30 years of measured and modeled hourly solar data from 1961-1990 at 239 locations in the United States. The underlying actual year data hasn’t been freely available until recently, and there were significant gaps in temperature or other meteorological values which caused simulations to fail. We’ve applied backfilling algorithms to fill missing data with representative values to enable simulations to run. https://sam.nrel.gov/NSRDB We’ve also developed a flexible Excel-editable CSV-based standard file format that will be used in the next version of SAM. • SAM will include 1619 locations • Much easier to import/edit your own weather files
  • 12 New SAM Desktop Application (1) In Autumn 2014, we will release a completely revised SAM desktop application. • Significantly streamlines the user experience • Much better access to hundreds of outputs • Simulations like parametric and Monte Carlo analysis will use parallel processing • Libraries and weather data in Excel-editable CSV files • Much more powerful scripting language and SAM SDK integration
  • 13 Tonight’s Presentation Upcoming major changes to PVWatts algorithms http://pvwatts.nrel.gov Live demo of SAM Shade Calculator Beta http://sam.nrel.gov/shade
  • NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC. Major Updates to PVWatts Sandia/EPRI PV Modeling Workshop Aron P. Dobos 5 May 2014
  • 15 Why Update PVWatts? • PVWatts V1/V2: o Originally developed in the late 90s based on algorithms derived from performance data measured in the 80s • Turns out modern systems perform better • Our own validation work shows that PVWatts underpredicts • Pretty consistent feedback from users that PVWatts underpredicts The web tool also gets a new modern look and feel. http://pvwatts.nrel.gov
  • 16 Key Model Changes • Module type options: “Standard”, “Premium”, or “Thin-film” • Option to specify a DC-to-AC nameplate sizing ratio • System losses are specified as a percentage, default of 14%. • Inverter performance curve updated • One axis tracking systems: linear self-shaded or backtracked
  • 17 Module Types and System Losses • Default losses are roughly equivalent to a V1 derate of 0.825, which is about 7% higher • Energy prediction is actually about 8-9% higher due to the revised inverter performance curve.
  • 18 Inverter • Based on statistically most representative actual inverter in the CEC database since 2010 • Nominal efficiency can be set by the user, default is 0.96.
  • 19 Performance Summary Old PVWatts is on average about 11.8% low. New PVWatts is on average 1.8% low. Notes: The 9 systems are well maintained and are generally considered “unshaded”. The default shading loss of 3% in the new PVWatts was set to zero to match the old PVWatts default. -20 -15 -10 -5 0 5 10 1 2 3 4 5 6 7 8 9 AnnualEnergyPredictionError(%) PVWatts Annual Error for 9 Systems New PVWatts Old PVWatts
  • 20 What’s Next for PVWatts • Draft technical manual available online (see survey link below) • Online survey to get feedback on these changes https://www.surveymonkey.com/s/pvwattsv5 • Changes will be finalized and new algorithms will be rolled out in the next couple of months
  • NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC. SAM Shade Calculator Sandia/EPRI PV Modeling Workshop Aron P. Dobos 5 May 2014
  • 22 SAM Shade Calculator Beta Based on consistent and strong feedback from the user community and our Technical Review Committee in 2013, the Department of Energy funded work to develop a 3D shading loss calculation tool. Download from: http://sam.nrel.gov/shade
  • 23 SAM Shade Calculator Overview Our tool will: o Enable basic analysis of shading impacts for a particular scene o Provide a relatively crude representation of a 3D scene with preprogrammed shapes o Enable intercomparison of many shading tools o Be able to read and write common file formats and ideally provide an open standard for PV shading geometry data Our tool will not: o Render specific modules, racking systems, wiring conduits, or any details of the balance of system o Be able to display a realistic rendering or visualization of a particular PV installation Full roadmap available online.