Physics and Performance Limits of Bifacial Solar Cells: A Global Perspective. M. A. Alam, X. Sun, R. Khan, C. Deline

Transcription

1 Physics and Performance Limits of Bifacial Solar Cells: A Global Perspective M. A. Alam, X. Sun, R. Khan, C. Deline (alam@purdue.edu) 1

2 17 orders A magnificent multiscale problem: Time decade Atom-to-farm perspective Jupiter year Solar Farm s Storage Reliability ns Process Device Module Material 16 orders nm cm m km Mm An atom-to-system approach for PV research. Length 2

3 Solar Farm Reliability Module Device Process Thermodynamic

4 Like politics PV is local Mono-HIT Bi-HIT PVK-HIT 4

5 Outline Physics of bifacial solar cells Solar Cell: A not-so-efficient technology Efficiency of bifacial solar cells Energy yield of actual solar farms Three types of bifacial solar farms Standalone bifacial solar farms Vertical and Ground Sculpted Solar Farms LCOE and Optimally tiled Bifacial Solar Farms Opportunities Simulator, Tandem, tracking solar cells 5

6 PV: An inefficient machine Tracking, multi-junction, bifacial 6

7 Sun and SQ Triangle I mp = 2qθ s k B T D c 2 h 3 E g 2 e E g k B T s E 1 V mp I mp E 2 qv mp = E g 1 T D T k B T D ln θ D J mp E g = J sun 1 βe J = S 70 θ S V g mp = J sun 1 mp β V = 0.95E g 0.3 Khan & Alam, APL, 107, , 2015, Also, see AJP,

8 SQ Triangle and Tandem PV J mp = V mp P out = J mp V mp J sun J sun /2 J mp V mp,1 V mp (E g ) J SUN 1 3 J SUN J mp 2 3 J SUN V mp (X g ) J SUN N 1 N J SUN η = 33% 44% 66% 1 N J SUN J mp V mp (X g ) η N = η 1 2N N+1 8

9 SQ Limit of Bifacial Solar Cell N crit 1 + R 1 S N S 1 = S N S 1 = N N R N 2 R + 1 2R 8R 1 + R N 2 2R 2N 2 + 4N + 1 9R 2 1 Alam, APL, 2016 Alam, PVSC, 2018

10 Outline Physics of bifacial solar cells Solar Cell: A not-so-efficient technology Efficiency of bifacial solar cells Energy yield of actual solar farms Three types of bifacial solar farms Illumination and electrical model of bifacial PV Standalone bifacial solar farms Vertical and Ground Scuplted Solar Farms LCOE and Optimally tiled Bifacial Solar Farms Opportunities Simulator, Tandem, tracking solar cells 10

11 Cell-to-module eff. gap, (%) Output Power Density (W/m 2 ) Photon flux den. (m -2 nm -1 s -1 ) log 10 (N IT F ) (cm -2 ) End-to-end modeling of Bifacial Si- Heterojunction Cell,, 5 x Voc (V) ,,, ] i a-si n c-si,,, TCO p + a-si i a-si n c-si i a-si n + a-si TCO Process model Device model Module model (a) Process variation from cell to cell, Module, J Light (ma cm -2 ) a-si c-si l (nm) (a) J Light (ma cm -2 ) (i) 10 (ii) 10 (iii) V (V) V (V) (c) log 10 (N IT B ) (cm -2 ) J Light (ma cm -2 ) (b) V (V) Shunt variation within a cell Dead Area Res. Loss Shnt. Loss Proc. Var. Total (a) Process variation, s (%) (b) Chavali, Stefaan De Wolf, M.A.Alam, PIP, 2018.

12 Sun and the solar cells... Purdue University Meteorological Tool (PUMET):Available on nanohub global meteorological database Irradiance Model Optical view-factor based approach Light Collection Electrical Output PUB in PVLiB, Cliff Hansen & J. Stein thermal electrical 12

13 PUMET database PSM ( ) SUNY ( ) MTS2( ) MTS1( ) 13

14 PUMET database 14

15 decompose irradiance Diffuse Diffuse Circumsolar I Diff(Cir) What is the sunlight intensity? Isotropic I Diff(Iso) Horizon Brightening I Diff(Hor) Direct Solar Energy of Thermal Processes. Gloabl I GHI = Direct I Dir cos θ Z + Diffuse(I Diff ) Anisotropic Diffuse Light Measured I GHI k T = Global Extraterrestrial Orgill/Hollands model Simulated I Dir and I Diff Perez model I Diff(Cir) I Diff(Iso) 15 I Diff(Hor)

16 X. Sun et al, Applied Energy, 2018 Stand-alone Bifacial PV Light to electricity by opto-electro-thermal model Location (Type) Elevation / Module Height (m) Cairo (Sim.) [11] Cairo (Sim.) [11] (Exp.) [16] The National Renewable Energy Albuquerque Laboratories (Exp.) [16] (Golden, CO) Table. 1 Modeling Framework Validation Against Literature Albedo / Bifaciality Tilt Angle / Facing Reported Bifacial Gain (%) Calculated Bifacial Gain (%) (%) Albedo + Diffuse Sim. Only Exp. + Direct Moreover, Golden (Exp.) our model 1.02 / 1.02 has been 0.2 / 0.6 validated 30 o against / South field 8.3 data from North 8.6 America, -0.3 Africa, **** Europe, * Only data and from Asia May to (<6.4% August were used difference). to eliminate snow effects. Our here. model will be available on nanohub and pvpmc.sandia.gov (Sandia). Difference 1 / / o / South / / o / South Oslo (Sim.) [11] 0.5 / / o / South Oslo (Sim.) [11] 0.5 / / o / South Hokkaido* (Exp.) [46] Hokkaido* (Exp.) [46] Albuquerque (Exp.) [16] Albuquerque Albuquerque*** (Exp.) [16] 0.5 / / o / South / / o / South / / o / South 32.5** / / o / West 39** / / o / South 19** / / o / South 30.5** ** Average bifacial gain of multiple test modules was used. *** The east-west-facing vertical modules measurement in [16] shows great discrepancy between two modules; therefor, it is not included **** Bifacial measurement (12/2016 to 08/2017) performed by the National Renewable Energy Laboratory.

17 Bifacial Gain (%) Bifacial Gain (%) Bifacial Performance/Orientation Albedo = 0.25 Albedo = 0.25 Albedo = 0.5 Albedo = 0.5 Albedo = 0.25 Albedo = 0.5 Albedo = 0.5 Elevation = 0 m Elevation = 0 m (a.1) (a.1) Elevation = 0 m Elevation = 0 m (b.1) (b.1) Elevation = 0 m (a) Elevation = 1 m Elevation = 1 m (c.1) (c.1) Bi EW /Bi SN (%) Shanghai Shanghai Albedo = 0.5 Albedo = 0.25 Elevation = 0 m Cairo Elevation = 0 m (a.2) (a.2) (a) (b.2) Bi EW /Bi SN (%) (b) (c.2) Bi EW /Bi SN (%) Albedo = 0.25 Albedo = 0.5 Albedo = 0.5 m Elevation = 0 m Elevation = 1 m (a) Bi EW /Bi SN (%) (b) Bi EW /Bi SN (%) (c) Bi EW /Bi SN (%) 17

18 global optimization: orientation Lat < Lat Cri : Bi EW Lat > Lat Cri : Bi SN Lat Cri Lat Cri Lat o = E/H 44R A R A + 12 Bi SN Bi EW If Lat o 0, Lat Cri = 0 o and If Lat o > 0, Lat Cri = Lat o X. Sun et al, Applied Energy,

19 Scaling theory of stand-alone Bifacial X. Sun and M. Alam, Applied Energy, 2018 E 95 in meter for a module height of H E o = H ( Lat (0.028 R A ) R A + 0.4) (A1) E 95 is the minimum elevation to achieve at least 95% of the self-shading absent maximum energy yield, i.e., further elevation only provides limited energy boost. If E o 0, E 95 = 0 and If E o > 0, E 95 = E o (A2) Lat Cri of bifacial solar module for a given elevation (E), module height (H), and albedo (RA) Lat o = E/H (44 R A 62) + 37 R A + 12 (A3) Lat Cri is the critical latitude below which BiEW produces more electricity than BiSN and vice versa. If Lat o 0, Lat Cri = 0 o and If Lat o > 0, Lat Cri = Lat o (A4) Optimal Tilt Angle β Opt for BiSN for a given latitude (Lat), elevation (E), module height (H), and albedo (RA) β o = a Lat + b (A5) β Opt is the optimal tilt angle for BiSN for maximum electricity yield a = R A exp ( E/H) (A6) b = R A exp ( E/H) If β o 90 o, β Opt = 90 o and If β o < 90 o, β Opt = β o (A7) (A8) 19

20 Outline Physics of bifacial solar cells Solar Cell: A not-so-efficient technology Efficiency of bifacial solar cells Energy yield of actual solar farms Three types of bifacial solar farms Illumination and electrical model of bifacial PV Stand-alone bifacial solar farms Vertical and Ground Scuplted Solar Farms LCOE and Optimally tiled Bifacial Solar Farms Opportunities Simulator, Tandem, tracking solar cells 20

21 A bifacial solar farm requires complex opto-electro-thermal modeling 21

22 Vertical Solar Farm has advantages, but. R. Khan and M. Alam, Applied Energy, 2017 even with high albedo, the gain is relatively small 22

23 Ground-sculpting offers significant improvement R. Khan and M. Alam, Applied Energy, 2018 (In review) E W (a) (a) (b) (c) (G1) (G2) r = h/2 r = h/4 r = 0 (d) (G3) (b) (G2) (G3) (e) (c) 23

24 Optimally tilted and LCOE-optimized Farm (a) (b) (a) (a) (a) (b) (b) (b) Bifacial Gain LCOE* Bifacial Gain LCOE* T. Patel and M. Alam, 2018 (Unpublished)

25 Outline Physics of bifacial solar cells Solar Cell: A not-so-efficient technology Efficiency of bifacial solar cells Energy yield of actual solar farms Three types of bifacial solar farms Standalone bifacial solar farms Vertical and Ground Sculpted Solar Farms LCOE and Optimally tiled Bifacial Solar Farms Opportunities Simulator, Tandem, tracking solar cells 25

26 Bifacial tandem cell operation Solar illumination (1-sun) (b4) J rad t V t (t) J SUN t R A J SUN t b (b2) (t3) n LC (coupling) (b1) (t1) (b) J SUN b t (b3) (t2) R A J SUN b H. Chung, Optics Express, Scattered from ground (R A 1-sun) J rad b V b 26 (t4)

27 33% Efficient HIT-Perovskite Cells! R. Asadpour*, R. V. K. Chavali*, M. R. Khan*, and M. A. Alam, APL, 106, p , Jun

28 Technology/location-specific BPV Mono-SHJ Bi-SHJ PVK-SHJ 28

29 Conclusions: A magnificent Multiscale problem Time decade OPVLab PUMET year ADEPT Solar Farm s PVLimits Storage Reliability PUB ns Process Device Module PVPanelSim Material PVAnalyzer nm cm m km Mm Length

30 How to use PUB Specification Simulation Location Module Optimization Electro-thermal Bifacial Energy Yield Bifacial vs. monofacial energy yield 30

31 Conclusions: Geography specific solar Solar cells are fundamentally inefficient. And endto-end perspective provides opportunities for improvement at the cell, module, and farm levels. Thermodynamically, bifacial and bifacial tandems promise dramatic gain.. Vertical bifacial farms may be a good choice for certain regions of world. The energy gain may not be significant, but reduction in cleaning cost and water usage could be make the system economically viable. For other regions tilt-optimized bifacial PV is profitable. Reliability is fundamentally important 5% increase in lifetime may be easier than 5% increase in efficiency. Questions/comments: alam@purdue.edu 31

32 Optimized design ITO (10 nm) 40 nm HTL ARC & 10 nm a-si Perovskite (350 nm) ETL (20nm) 165 μm c-si 165 μm c-si 250 μm p+ 100 μm n+ 250 μm p+ 100 μm n+ W Al Gap W Al Albedo 0.3 Albedo W Al Gap W Al

33 (a) Rochester (NY) Kansas (MO) Phoenix (AZ)