You Be the Judge: A Ratings Tool for Selecting the Best Solar Module

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What is the best PV module for a particular application? Is it one with the lowest cost per watt? Ultimately, it is the amount of energy produced that is the key factor in the economics of investment recovery and profit.

The Principal Solar Institute (PSI) has developed a tool for analyzing this key element: The PSI PV Module Rating, an energy assessment tool for comparing the Lifetime Energy Production of PV modules over a 25-year period. Using the PSI Rating, solar energy professionals can finally make easy, meaningful energy-economics comparisons of PV modules between manufacturers or within one manufacturer’s product line.

Hear Matt Thompson PhD, Executive Director of the Principal Solar Institute, and Kenneth Allen, COO of Principal Solar, Inc. and Principal Solar Institute Ratings Expert Panelist give an overview of the PSI PV Module Rating and explain how to use the ratings in financial calculations and comparisons of modules and manufacturers. Also, Steven Hegedus, PhD, scientist at the University of Delaware Institute of Energy Conversion, will present an overview of PV module field testing and performance metrics.Then discover specific applications for your business during a LIVE question-and-answer segment following the presentation.

PSI has just published a whitepaper detailing the PSI PV Module Ratings. You should download it free of charge here.
http://www.principalsolarinstitute.org/uploads/custom/3/_documents/PSIRatingsSystem.pdf

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  • Scheduled time (:00) – Welcome to $WebinarTitle. We have several people still joining the audio portion of the webinar, so we’ll get started in a couple minutes.[Start recording]Start + :02 – Hello I’m Rick Borry and will be your host today. Before we get started, I have a few housekeeping notes. This webinar is XX minutes long. All participants are muted, but if you have trouble hearing the audio, you can send a text chat to me via the chat dialog in the lower right corner of your viewer window. Also, if you have any questions you can send those to me via text chat at any time. I will collect all questions and ask them of the presenter at the end of the session. The webinar is being recorded, and it will be posted online along with a copy of the slides later today.Today’s webinar is “Solar Energy in the Military”. This webinar is part of the Principal Solar Institute webinar series, for professional installers, developers, owners, and operators of solar systems. We thank XX and YY for sponsoring this webinar. [Host should go on mute]
  • The Principal Solar Institute was created by Principal Solar Incorporated to foster unbiased thought leadership that elevates the solar industry.
  • The Principal Solar Institute was created by Principal Solar Incorporated to foster unbiased thought leadership that elevates the solar industry.
  • The Principal Solar Institute was created by Principal Solar Incorporated to foster unbiased thought leadership that elevates the solar industry.
  • Scheduled time (:00) – Welcome to $WebinarTitle. We have several people still joining the audio portion of the webinar, so we’ll get started in a couple minutes.[Start recording]Start + :02 – Hello I’m Rick Borry and will be your host today. Before we get started, I have a few housekeeping notes. This webinar is XX minutes long. All participants are muted, but if you have trouble hearing the audio, you can send a text chat to me via the chat dialog in the lower right corner of your viewer window. Also, if you have any questions you can send those to me via text chat at any time. I will collect all questions and ask them of the presenter at the end of the session. The webinar is being recorded, and it will be posted online along with a copy of the slides later today.Today’s webinar is “Solar Energy in the Military”. This webinar is part of the Principal Solar Institute webinar series, for professional installers, developers, owners, and operators of solar systems. We thank XX and YY for sponsoring this webinar. [Host should go on mute]
  • You Be the Judge: A Ratings Tool for Selecting the Best Solar Module

    1. 1. Principal Solar Institute You Be the Judge: A Ratings Tool for Selecting the Best PV Module Matthew Thompson, Ph.D. Kenneth Allen Steve Hegedus, Ph.D. Executive Director Chief Operating Officer Institute of Energy Conversion Principal Solar Institute Principal Solar, Inc. University of Delaware Hosted by Rick Borry, Ph.D. Chief Scientist, Principal Solar Institute
    2. 2. PV Module Rating System Matthew A. Thompson Ph.D. December 18, 2012
    3. 3. Why Principal Solar Created aPV Module Rating Principal Solar, Inc. needed a simple, comprehensive metric to use in their due diligence process. – Lifetime Energy Production is only one item in a long checklist for potential acquisitions. – It is essential for a utility operator to understand Lifetime Energy Production. Any purchaser of PV modules can use the PSI PV Module Rating in their own comparative cost-benefit analysis.
    4. 4. History of the Approach  Lifetime Energy Production – The quantity of energy a PV module is expected to produce in 25 years. – A calculated quantity based on PV module characteristics, and a model of irradiance and temperatures.
    5. 5. The Seven Characteristics  Available to the public through organizations such as the California Electric Commission, and datasheets provided by PV module manufacturers.  Seven characteristics of PV modules that affect energy production: – Actual Maximum Power vs. Advertised: “Actual” is Vmp x Imp, STC – Negative Power Tolerance: Actual maximum power is reduced – Nominal Operating Cell Temperature: NOCT – Temperature Coefficient at Maximum Power: Gamma – Power at Low to High Irradiance Ratio: Low power is 200 W/m2 incident – Total Area Efficiency: Energy produced divided by module area – Annual Power Reduction: Manufacturer’s 25 year power warranty
    6. 6. Modeling the LEP  PV module characteristics that affect energy production depend on Irradiance and Temperature.  The Phase 1 model samples representative ranges of values for these conditions.
    7. 7. PSI PV Module Rating is Comparative The impact on energy of each PV module characteristic is calculated hourly through the model of irradiance and temperature over a 25 year period.  The result is divided by the energy that would be produced by an ideal PV module to determine the PSI PV Module Rating: PSI Rating = Calculated Module LEP / Calculated Ideal Module LEP The Rating is a comprehensive metric for comparing the energy performance of PV modules.
    8. 8. Phase 2 Model Models under development will include regional insolation levels and historical temperature data. This enhancement will show in a comparative way how PV modules’ performance is affected by region.
    9. 9. The Comprehensive PSI Rating The PSI Rating is most useful as a side-by-side comparison of energy production performance.  The PSI Rating does not include: – Manufacturer financial strength – Pricing – Delivery – Reliability – System components – Regional differences (until Phase 2)
    10. 10. Ranking and Rating PV Modules The Principal Solar Institute Rating webpages provide: – Two classifications: Crystalline and Thin Film – Rank within classification – PV Module Rating, a comparative number based on LEP – Percentile Rank: across 10,000 modules, both classifications
    11. 11. Conclusion The PSI PV Module Rating is a comparative score based on Lifetime Energy Production. PSI does not currently test PV modules, but uses publicly available test data. Developing a model with regional conditions. Working to develop interactions with University, Industry and Government. We welcome feedback and suggestions.
    12. 12. Application of thePSI PV Module Rating Kenneth G. Allen, COO Principal Solar Incorporated December 18, 2012
    13. 13. Direct Comparison Nameplate rating of PV modules does not provide the detail needed to differentiate Lifetime Energy Production. Model Type Power (W) PSI Rating “A” …275 Poly-crystalline 275 8.6 “B” …275P… Poly-crystalline 275 7.8 Lifetime Energy Production from “A” is (8.6/7.8) = 110% of “B” A 10% difference is a substantial difference to a utility operator
    14. 14. Energy Cost Comparison – Small Project Assume you have a list of available PV modules. Go to the PSI Ratings website and pick the highest rated one, then make a comparison to others of interest. Model Type Power PSI Cost # PV 2kW (W) Rating ($/W) Cost ($)“A” …250p… Poly-crystalline 250 8.7 1.0 8 2000“B” …P200A… Mono-crystalline 200 6.9 0.9 10 1800 Lifetime Energy Production of “A” is (8.7/6.9) = 126% of “B” Lifetime Energy Cost of “B” is (8.7/6.9)x( $1800/$2000) = 113% of “A” In this case lower upfront cost, but higher cost of energy produced
    15. 15. ConclusionThe PSI PV Module Rating: – is a comprehensive, comparative metric based on Lifetime Energy Production – is a performance metric, unlike the nameplate wattage rating – allows for a quantified cost-benefit analysis
    16. 16. kWhr/kW Performance: Comparison of ReportedField Data from Different PV Module Technologies Steve Hegedus Institute of Energy Conversion University of Delaware December 18, 2012
    17. 17. OutlineIntroduction to IECWhy kWhr/kWSTC as a metric?Scope of literature reviewCritical issues in determining kWhr and kWSTCInterpretation: measurement variability, TCE, LLESummary 17
    18. 18. Institute of Energy Conversion at U of Delaware Founded in 1972 to perform thin-film PV research World’s oldest continuously operating solar research facility First 10% efficient thin film solar cell (1980) 6 chamber Dept of Energy University Center of Excellence PECVD for Photovoltaic Research and Education (1992) Soft funded - government and industry contracts First flexible Over 20 deposition systems, complete integrated PV R&D 10% cell lab: film growth, device fab, characterization 2012 staff: 15 professional/tech, 5 post doc, >14 grad students (4 depts) Fundamental science, engineering, tech transfer and workforce supply 4x4” monolithic interconnected CIGS minimodule 18
    19. 19. IEC Technology Thrust Areas Thin film polycrystalline CuInGaSe2-based (CIGS) solar cells  Wide bandgap alloys (Ag, S), flexible R2R vs glass, high temp substrates Thin film polycrystalline CdTe solar cells  Higher temperature substrate + TCO Silicon-based solar cells  Front and back heterojunction (a-Si/c-Si): first SHJ-IBC cell  Thin film tandem a-Si and nc-Si at higher growth rate Reliability and stability; D-H under light and voltage bias Characterization: in-line monitoring, device imaging/mapping 19
    20. 20. I. Why kWhr/kWSTC as a metric?kWhr: energy produced over time (1 vs 20 yr)  Directly related to how much $ someone will be paid (PPA, contract) or will save (offset electric bill)  Includes effects of varying weather, degradation, shading, dust, seasonal annealingkWSTC : power produced by module at STC  Directly relates to how much someone paid for modules typically $/WSTC based on initial power rating  Standard Test Conditions (STC: 1 kW/m2, 25°C module, AM1.5 spectra) may occur a few minutes a year  Largest source of uncertainty has been initial kWSTC 20
    21. 21. II. Why kWhr/kWSTC as a metric?kWhr/kWSTC units of ‘hours’: equivalent to # hours the array produced STC rated powerMust be specified over specific time (typ. 1 year)Sometimes called final yield YFkWhr can be DC or AC (after inverter)Typical kWhr values: assume 5 hrs equivalent ‘1 sun’ irradiance per day, 20% system and module losses kWhr= (5 hrs ‘1 sun’ per day) x 365 day/year x 0.8 = 1460 kWhrs/year 21
    22. 22. Scope of Literature Survey Widely reported for >20 years that thin film (TF) PV modules have higher kWhr/kW performance compared to c-Si modules Consistent with some well-established fundamental differences but magnitude of advantage often too large  Most obvious difference is that TF devices have smaller negative temperature coefficient of efficiency (TCE); i.e. lower loss in efficiency at higher module temperature Many different TF materials, processes and device structures Recently new c-Si device architectures  Higher efficiency (>20%) and lower TCE Asked to write a review of published performance data comparing TF and c-Si module field data for new Wiley WIRE Energy and Environmental (abstract at end) 22
    23. 23. Typical data from 2 widely referenced studiesfrom 1990’s: 3 European cities, 4 technologies  I grouped all different modules by technology  Mallorca: sunniest, hottest  Lugano: moderate  Oxford: cloudiest, coolest  Mono and multi Si similar  TF a-Si and CIGS similar  TF a-Si and CIGS higher by 16-20% all 3 locations!!! From: Hegedus, Review of photovoltaic module energy yield (kWh/kW): comparison of crystalline Si and thin film technologies, 23 Wiley WIREs Energy Environ 2012. doi: 10.1002/wene.61
    24. 24. Select sources of field data comparing moduletechnologies – not complete! 2007-2010 study by Univ Cyprus (Nicosia) and Univ Stuttgart: compared 13 module technologies in both locations (Makrides, Georghiou, Zinsser, Schubert)  Detailed reports of YF, degradation, detectors, tracking, STC rating issues Consultant Steve Ransome Consulting Ltd (SRCL, UK)  Wide range of EU and US data, variability, uncertainty, predictive models Two Japanese studies of different PV technologies  Ito et al: Hokuto City: 20 systems of 10-100 kW  Ueda et al: Ota City: 553 residential rooftop systems Arizona Public Service and Tucson Electric Power (c-Si only)  Moore, Post et al: detailed YF, O+M costs, fixed vs 1 axis vs 2 axis tracking, 2 kW to 3.5 MW PV Trade Mag Photon International (Aachen DE)  130 modules on test, 97% are c-Si, very small difference in YF :~5-7% 24
    25. 25. Examples of kWhr/kW data from differentstudies: Japan and CyprusYF for 20 arrays of 10-30 kW in Hokuto YF for 11 arrays of ∼1 kW in Nicosia,Japan monitored from 2008-2009*. Cyprus over 2007–2009** Hegedus WIRE review. Data from *Ito et al, Prog in Photovoltaics 19 (2011) 878-886. 25 **Makrides et al, Prog in Photovoltaics 20 (2011)
    26. 26. I. Meteorological conditions are coupled:complicated trade-off on module outputWhat happens when clouds/humidity reduce incident solar irradiance on the module?  1st order effect: ~ linear decrease in output (-)  Less light: lower module T, less T-related loss (+)  Less light: less current, less I2R power loss in module (+)  More scattered light: collection of indirect light (±)  More scattered light: spectra shifts to blue, advantage for cells with high bandgap, high blue response (±)  Changes with low light intensity grouped together as Low Light Efficiency (LLE) =Eff (200 W/m2) / Eff (1000 W/m2) 26
    27. 27. II. Meteorological conditions are coupled:trade-off between LLE and TCE Model output with real weather data for hot sunny and cool cloudy locations* Compare typical values of LLE and TCE for TF and c-Si PV Graph: 5-6% gain in kWhr/kW performance for TF over c-Si Trade-off between LLE, TCE Technology TCE LLE c-Si -0.45%/°C 0.95 TF -0.25%/°C 1.05 *From Hegedus WIRE review, data taken from 27 Ransome et al Proc 37th IEEE PVSC Seattle 2011
    28. 28. Uncertainty in kWSTC and irradiancekWSTC Irradiance  Manu. rated power can  Pyranometers ±2% with range ±10% or 0/+3% annual calibration  Flash test individual  Compare results from 2 module can be ±2% for locations same detector: c-Si, ±3% for TF ±4%  Stabilization and pre-  Differences in dust biasing (IEC standard) accumulation, T, shading  Short vs long term  Si detector more sensitive degradation to spectrum, T but cheaper 28
    29. 29. Effect of ± manufacturers rating on tolerances:results from Nicosia and Stuttgart, different moduletechnologies * Zinnser et al Proc 35th IEEE PVSC 2010 29
    30. 30. Effect of uncertainty indetermining initial kWSTC Three methods of measuring initial kWSTC  Manu. rating, flash test, and field rating (over 1 yr) Data for Stuttgart below for range of kWhr/kW Cannot distinguish using manu rating!range Manu. Flash FieldkWhr/kW 18% 12% 9%uncertainty ±4-18 ±4- ±4 8%Zinnser et al Proc 35th IEEE PVSC 2010 30
    31. 31. Summary Comparison of field data complicated by uncertainty in module kWSTC rating and irradiance Experts estimate ±5% is best uncertainty we can achieve at present (same location)  Comparing data from different locations has much larger uncertainty due to detector, calibration, module rating procedures, weather Response to meteorological conditions complicated  Depends on module technology and location  TCE and LLE 2nd order, weaker compared to linear dependence on irradiance, most important in hotter climates  But responsible for ~3-6% advantage for CdTe, advanced Si (HIT, IBC) 31
    32. 32. Questions and Discussion Please enter your questions in the chat window. Matthew Thompson, Ph.D. Kenneth Allen Steve Hegedus, Ph.D. Executive Director Chief Operating Officer Institute of Energy Conversion Principal Solar Institute Principal Solar, Inc. University of Delaware Hosted by Rick Borry, Ph.D. Chief Scientist, Principal Solar Institute
    33. 33. kWhr/kW Performance: Comparison of ReportedField Data from Different PV Module Technologies APPENDIX – EXTRA SLIDES 33
    34. 34. Power rating uncertaintiesQuoted from paper by Zinsser* (Univ Stuttgart) titled “Rating of AnnualEnergy Yield More Sensitive to Reference STC Power than ModuleTechnology”“If we assume an error of ±3% in STC power measurement (calibration)and ±2% for the energy determination (detector), there could be adifference of 10% between the annual yield of two PV systems at thesame location. . . . For thin film technologies, the error is even bigger dueto nominal power variations. The worst case would be comparing twothin film technologies on the basis of rated power at different locations.The tolerance of (±10%) plus flasher measurement error (±6%) plusenergy measurement error (±2%) plus irradiance measurement error(±2%) sum up to a possible total difference of 40%.” * Zinnser et al Proc 35th IEEE PVSC 2010 34
    35. 35. Abstract of Hegedus review paper “Review of photovoltaicmodule energy yield (kWh/kW): comparison of crystalline Si andthin film technologies” Wiley WIREs Energy Environ 2012. doi:10.1002/wene.61 35
    36. 36. Brief comparison of PV module technologiesModule Mono HIT IBC c-Si a-Si CIGS CdTeTechnology or c-Si (Sun- (1J, 2J, (First multi-Si (Sanyo) power) 3J) Solar)STC Eff (%) 14-18 18-20 18-21 6-9 8-12 9-12Manu- Many 1 1 Many 2 1facturersTCE (%/°C) -(0.45- -0.30 -0.36 -(0.20- -(0.35- -0.25 0.50) 0.25) 0.45)Comment Std Si Adv. c-Si Adv. c-Si TF- TF- #1 TF- wafer heterojnctn all-back many Pilot Single process contact versions scale Source 36

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