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26 pvpmc presentation_mac_alpine_final


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8th PVPMC Workshop, May 9-10 2017

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26 pvpmc presentation_mac_alpine_final

  1. 1. Progress Toward Efficient Bifacial Rear Irradiance Models Sara MacAlpine Chris Deline, Bill Marion 8th PV Performance Modeling and Monitoring Workshop May 10, 2017
  2. 2. 2 β€’ Importance of rear side irradiance for bifacial modules β€’ Discussion of rear side irradiance models β€’ Validation of efficient models under development at NREL β€’ Model sensitivity and key considerations Outline
  3. 3. 3 Bifacial Energy Gain = Module Bifaciality * Rear Side Irradiance Ratio π΅π‘–π‘“π‘Žπ‘π‘–π‘Žπ‘™π‘–π‘‘π‘¦ = 𝑃 π‘šπ‘,π‘Ÿπ‘’π‘Žπ‘Ÿ 𝑃 π‘šπ‘,π‘“π‘Ÿπ‘œπ‘›π‘‘ (from single side flash data) π‘…π‘’π‘Žπ‘Ÿ 𝑆𝑖𝑑𝑒 πΌπ‘Ÿπ‘Ÿπ‘Žπ‘‘π‘–π‘Žπ‘›π‘π‘’ π‘…π‘Žπ‘‘π‘–π‘œ = 𝑓(π‘Žπ‘™π‘π‘’π‘‘π‘œ, 𝑑𝑖𝑙𝑑, π‘Ÿπ‘œπ‘€ π‘ π‘π‘Žπ‘π‘–π‘›π‘”, β„Žπ‘’π‘–π‘”β„Žπ‘‘, π‘Ÿπ‘Žπ‘π‘˜π‘–π‘›π‘”, π‘šπ‘œπ‘‘π‘’π‘™π‘’ π‘‘π‘Ÿπ‘Žπ‘›π‘ π‘π‘Žπ‘Ÿπ‘’π‘›π‘π‘¦, π‘π‘™π‘–π‘šπ‘Žπ‘‘π‘’) Bifacial Gain Calculation Month Performance%
  4. 4. 4 β€’ PVSyst – 2D β€œunlimited sheds” model for back side irradiance, module types have individual bifaciality factors β€’ Solar World β€œBoost Calculator” – web interface for user input, tailored to specific modules β€’ Various manufacturers of bifacial PV modules have in house tools PV modelers need an efficient model for rear side irradiance that can be used for any bifacial module! Industry Bifacial Models
  5. 5. 5 β€’ NREL developing and validating two efficient rear side irradiance models β€’ Ray Tracing model (Radiance) o Fast run time *if using preprocessing* o Suitable for standalone calculator o User can create complex scenes if necessary β€’ 2D View Factor model o Very fast run time and low memory requirement o Suitable for SAM or standalone calculator o Use for systems with regular row layouts NREL Rear Side Irradiance Models
  6. 6. 6 Radiance GenCumulativeSky Robinson, Stone β€œIrradiation modelling made simple: the cumulative sky approach” 2004 β€’ Radiance simulations typically use Perez model to generate hourly sky description β€’ Runtimes = hours for annual simulations β€’ GenCumulativeSky bins annual irradiance into 145 sky patches o Runtime reduced 1000x completing annual simulation in seconds.
  7. 7. 7 β€’ GenCumulativeSky benchmarked in literature with 2.2% RMS error relative to Perez workflow β€’ Unclear what this means for rear side irradiance ratio (validation underway) Radiance GenCumulativeSky, cont. Spatial resolution is reduced for single timepoint Gendaylit GenCumulativeSky
  8. 8. 8 β€’ Ground divided into n segments in row-to-row direction and shading determined for each β€’ Irradiance on each ground segment found using view of the sky (configuration factors) β€’ Rear side irradiance is sum of sky, ground reflected, object reflected components β€’ Runtime 4 seconds for annual simulation NREL View Factor Model
  9. 9. 9 Irradiance Validation: NREL Rooftop System β€’ Array of monofacial modules with regular row spacing β€’ Irradiance measurements taken in center of the upper array β€’ Challenges include racking, tilted roof, nearby objects β€’ Front and rear side measurements taken in plane of array using reference cells β€’ Rooftop albedo measured, varies with soiling
  10. 10. 10 Irradiance Validation: NREL Rooftop System, cont. Measured Rear Side Irradiance Ratio 17.4% 17.7% 16.4% NREL VF NREL Raytrace Predicted Rear Side Irradiance Ratio
  11. 11. 11 Irradiance Validation: NREL Rooftop System, cont. Measured Rear Side Irradiance Ratio 14.2% 14.1% 14.7% NREL VF NREL Raytrace Predicted Rear Side Irradiance Ratio
  12. 12. 12 Performance Validation: SolarWorld System Solar World Bifacial/Monofacial Test Bed in VA β€’ Monitored for 7 months β€’ 10 degree tilt, 0.15m height, 1.5m row spacing β€’ Grey/white roof 0.62 albedo β€’ Model uses TMY data (source of uncertainty) Measured Bifacial Performance Gain 8.2% 8.1% 7.0% 7.9% Solar World NREL VF NREL Raytrace Predicted Gains Credit:
  13. 13. 13 Rear Side Irradiance Sensitivity Varying Parameters for NREL and SolarWorld Models (β€œerror” bars are just the range of irradiance on module rear sides)
  14. 14. 14 β€’ Rear side irradiance nonuniform, especially for modules close to high albedo ground cover. Recommend middle points for resource estimation β€’ Albedo can vary seasonally and has large effect on rear side irradiance (linear) Key Considerations
  15. 15. 15 β€’ Both Raytrace and View Factor models at NREL undergoing continued validation β€’ View Factor model will be presented at PVSC: "A Practical Irradiance Model for Bifacial PV Modules" is in the oral session entitled "Modeling of System Components" which will be on Wednesday, June 28 at 10:30 AM. β€’ View Factor model will ultimately be embedded in NREL SAM tool β€’ Raytrace model will be deployed as standalone tool Future Plans
  16. 16. Thank you!