Shingled bifacial photovoltaic modules Jai Prakash Singh, Wang Yan, Khoo Yong Sheng Solar Energy Research Institute of Singapore National University of Singapore 25 th October 2017 bifipv workshop, Konstanz, Germany 1
Outline Introduction Bifacial PV module overview Bifacial module performance and challenges Losses in standard bifacial PV modules Approaches to reduce the losses Shingled bifacial PV modules Design optimization Loss analysis in shingled and standard bifacial modules Summary 2
Introduction Double-glass bifacial PV modules: Higher energy yield: 10-20% gain is achievable in outdoor conditions by using albedo from surroundings. Improved reliability (double-glass) Levelized cost of electricity (LCOE) can be reduced illumination front side glass EVA bifacial cell EVA Direct light Bifacial module rear side glass illumination Diffuse light 3
Introduction Bifacial PV module performance and challenges: Key performance indicator for bifacial PV modules Module front side power Rear side current response (bifaciality) Key challenges Measurement and characterization methods Higher optical and electrical losses compared to monofacial modules. Bifacial solar cells and modules are measured, rated and sold at front side power only. For wide acceptance of bifacial PV technology, losses in bifacial modules must be minimized 4
Losses in bifacial modules: optical Reflection (1, 2 and 3) and absorption (4 and 5): same as standard glass/backsheet modules Long wavelength light transmission through bifacial cell and rear glass (6) Transmission through cell-gap area (7) 5
normalised module current Losses in bifacial modules: optical air 1.10 1.08 double-glass glass/backsheet glass/backsheet_simulated 1.06 front glass encapsulant bifacial cell encapsulant rear cover 1.04 1.02 1.00 Bifacial cell transmittance losses: ~1.30% compare to the glass/backsheet structure. Cell-gap losses: 2-3% compared to glass/backsheet modules. 0.98 J. P. Singh, et al. IEEE Journal of Photovoltaics, vol. PP, pp. 1-9, 2015. 0 5 10 15 cell-gap [mm] 6
FF [%] Losses in bifacial modules: resistive monofacial module bifacial module Current flow pattern is different for monofacial and bifacial cells Higher resistive losses in bifacial modules are mainly due to rear side cell and ribbon resistances. S. Guo, J. P. Singh, I. M. Peters, A. G. Aberle, and J. Wong, Solar Energy, vol. 130, pp. 224-231, 2016 82 81 80 79 78 77 76 75 74 73 CTM resistive loss front resistance (cell) front ribbon rear ribbon stringed cell FF 75.58% front resistance (cell) rear resistance (cell) front ribbon rear ribbon stringed cell FF 74.30% 2.45% 2.85% 7
Approaches for loss reduction#1 reflective coating air front glass encapsulant bifacial cell encapsulant rear cover Selective white reflective coating in the cell-gap region Half-cut cells Additional issues with glass alignment and stringing. Bifaciality reduces (5-7%) white reflective coating (cell-gap) 8
Approaches for loss reduction#2 Shingled bifacial PV modules Recently, shingled concept becoming popular for monofacial modules: high power density Shingled type interconnection is suitable option for bifacial modules Minimizes the optical and resistive losses High power density, further reducing the module cost. 9
Shingled bifacial module: design optimization In-house developed simulation tool Griddler is used for simulations of shingled and standard interconnections of bifacial cells. First, bifacial cells were optimized for grid metallization (number of fingers, busbar width, etc.). Same cell parameters were used except the cell metallization (optimized for shingled interconnection). The shingled bifacial interconnection design is optimized for number of cell cuts cell-overlap Electrical parameters of 5-BB bifacial cell 9.45 648.0 78.47 19.74 10
Simulated module power [W] Shingled bifacial module: design optimization 295 290 285 280 3-cut 4-cut 5-cut 6-cut 275 270 265 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 Cell overlap [mm] Number of cell cuts is limited by throughput and cutting losses. Cell overlap is limited by lay-up and stringing m/c capability. 11
optical losses [%] Optical losses: shingled vs standard Standard bifacial: 5-BB, 0.9 mm ribbon width, 2.5 mm cell-gap, 3 mm string gap. Shingled bifacial: 5-cut, 1 mm cell-overlap, 3 mm string-gap Shingled module have ~ 2.1% less optical loss 18 16 14 12 10 8 6 4 2 0 front finger shading cell-overlap/busbar shading cell transmittance cell-gap transmittance shingled bifacial standard bifacial 12
FF [%] FF [%] FF losses: shingled vs standard Standard: 5-BB, 0.9mm ribbon, Shingled: 5-cut and 1mm cell overlap 82 81.85 Standard bifacial module 80.35 0.47.69 78 1.36.31.46 76.87 1.12 0 76.21 82 81.68 Shingled bifacial module.25 80 78 1.21.56 0.28 1.34.62 0.12 77.30 76 pff front contact front finger front semiconductor front ribbon rear contact rear finger rear semiconductor rear ribbon ECA contacts module FF 13
simulated module power [W] Shingled bifacial vs standard bifacial Bifacial shingled module performance is ~ 3.6% higher For the same glass-size, the module power will be even higher (higher packaging density, 68 cells) 330 320 310 standard bifacial module reduced optical loss reduced resistive losses 300 290 280 270 260 standard bifacial (60-cell) shingled bifacial (60-cell) shingled bifacial (68-cell) 14
Summary Shingled bifacial modules can improve the front side power due to reduced optical and resistive losses: higher selling price. Module power can be enhanced further by using more number of cells, further reducing the cost. For shingled modules, cell metallization design and modules design should be optimized. Module design (cell-cut, overlap) can be optimized by considering the throughput and the performance. (our study:5-cut with 1.0mm) Losses in cell-cut process and shingled interconnection (e.g. cost of ECA, alignment) are the main challenges for shingled bifacial modules. 15
Thank you for your attention! More information jaiprakash.singh@nus.edu.sg 16