MODELLING OF BIFACIAL GAIN FOR STAND-ALONE AND IN-FIELD INSTALLED BIFACIAL PV MODULES

Transcription

1 MODELLING OF BIFACIAL GAIN FOR STAND-ALONE AND IN-FIELD INSTALLED BIFACIAL PV MODULES I. Shoukry 1, J. Libal 1, R. Kopecek 1, E. Wefringhaus 1, J. H. Werner * International Solar Energy Research Center Konstanz * University of Stuttgart, Institute for Photovoltaic

2 Overview Motivation: need for bifacial energy yield prediction Optical Model: calculate irradiance on module rear side Electrical Model: calculate bifacial I/V parameters Comparison Simulation vs. Experiment: outdoor data vs. simulated energy yield Applications of Simulation Model: simulated bifacial gain for various scenarios Conclusion and Outlook 2

3 Growing market share of bifacial PV source: International Technology Roadmap for PV, 7th edition, Semi,

4 low LCOE for bifacial PV (2013) LCOE c-si monofacial (e.g PERC or mc-al-bsf ) /kwh LCOE c-si bifacial source: X-GW-Studie by Fraunhofer ISE and IPA, 2013 in this case: bifacial gain = 10% 4

5 low LCOE for bifacial PV (2016) LCOE c-si monofacial (e.g PERC or mc-al-bsf ) 7,10 6,3 source: X-GW-Studie by Fraunhofer ISE and IPA, 2013 and LCOE calculations by ISC 2016 /kwh LCOE c-si bifacial in this case: bifacial gain = 10% 5

6 Tools for energy yield forecast needed for standard (monofacial) PV systems: very sophisticated and reliable energy yield simulation tools are commercially available and play a decisive role in the evaluation of the bankability of large PV systems LCOE depends on energy yield! for bifacial PV systems: no standard tools for prediction of energy yield available 6

7 Optical Model: calculate irradiance on module rear side 7

8 Optical Model GHI = DHI + BHI: Global = Diffuse + Beam (direct) Horizontal Irradiance ground albedo α 8

9 Optical Model Optical Model Front Irradiance Rear Irradiance Direct Diffuse Reflected Direct Diffuse Reflected Perez Model Perez Model View Factor 9

10 View Factor geometric quantity, concept known from heat transfer theory irradiation leaving A 1, that reaches A 2 inpedendent of surface characteristics 10

11 Electrical Model: calculate bifacial I/V parameters 11

12 Electrical Model Power P Electrical Model Yield Y Bifacial Gain BF

13 Electrical Model: P mpp monofacial bifacial bifacial monofacial

14 Electrical Model Power P [W p ] Electrical Model Yield Y [kwh/kw p ] Bifacial Gain BF [%]

15 Comparison Simulation vs. Experiment: outdoor data vs. simulated energy yield 15

16 Simulation: input data Weather Irradiance Sun s Position Diffuse Irradiance Factor fd Results Single Module Tilt Angle γm - Elevation hm Ground Albedo α Module Field Adjacent Modules Row Distance dr Ground Albedo α α 16

17 Module Set-up in El Gouna (Egypt) 17

18 Simulated vs. Measured Bifacial Gain Good correlation between simulated and measured bifacial gain! 18

19 Application of Simulation Model: simulated bifacial gain in various scenarios 19

20 Diffuse Irradiance Factor f D 20

21 Diffuse Irradiance Factor f D higher f D less shadow higher bifacial gain 21

22 Bifacial Gain - Elevation h M h M,opt = 1.5 m BF = 13 % BF = 34 % α = 0.2 α =

23 Bifacial module inside module-field α = 0.5 Single Module: BF = 34 % Module field: BF = % (worst) Module field: BF = % (best) d R =2.5 m h M =1.5 m 23

24 Simple 1-axis ( sun belt ) tracking 24

25 Simple 1-axis ( sun belt ) tracking 25

26 Simple 1-axis ( sun belt ) tracking 26

27 Conclusion Optical model for rear side irradiance of bifacial module (stand-alone as well as in-field installed) established and implemented as a software tool In combination with a simple electrical model, the tool allows the prediction of the bifacial gain (additional kwh/kwp) First validation with 5 months outdoor data (installation in El Gouna/Egypt) successful A simple case of 1-axis tracking has been modeled: for 20% albedo, compared to fixed monofacial module, tracking of a bifacial module results in a 40% gain in energy yield (kwh/kwp) Tool delivers useful indications for design of bifacial PV systems and for selection of geographic location 27

28 Next Steps Refine electrical model on module level and extend model to system level (mismatch between modules, minimum V mpp of inverter, ) Refine optical model (e.g introduce daytime- and seasondependent albedo) Further validation with outdoor data from other bifacial installation sites Reduction of computation time Integration with commercial software for PV system design and yield calculation 28