#1This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 792059 go! PV Jun. 21st 2022 Solar PV Modules Market Trends, Materials & Manufacturing Processes Olatz Arriaga Arruti - EPFL co-organized with STVDIVM Università di Catania GLOBAL OPTIMIZATION OF INTEGRATED PHOTOVOLTAIC SYSTEM FOR LOW ELECTRICITY COST 1434 (11:30-12:30) # in#2go PV PV Modules: Market Trends, Materials & Manufacturing Processes EPFL Session Contents 1. PV Module Fabrication Steps 2. PV Technology Market and Costs 3. Crystalline Silicon Solar Cells 4. Solar Cell Interconnections 5. Lamination Process & PV Module Materials 6. Some Degradation Mechanisms 7. Manufacturing of Reliable Silicon Heterojunction Glass/Glass Modules GoPV Project | SUM.MER SCHOOL PV SYSTEMS TECHNOLOGIES AND DESIGN#3go PV 1. PV Module Fabrication Steps 1. Single cells 2. Stringing 3. Lamination DO D Cells are connected (in series or parallel) to match the module power output. Single cells are tested (I-V curve @ STC*) and sorted (similar current/power). Stringed cells are protected with a polymeric foils (encapsulant) provide the adhesion between components. front glass and a rear cover. Two *STC Standard Test Conditions: 1000 W/m² @ 25°C. EPFL 4. Junction box The junction box is glued at the rear and an aluminum frame is placed around the module. GoPV Project | SUMMER SCHOOL 3 PV SYSTEMS TECHNOLOGIES AND DESIGN#4go PV 1. PV Module Fabrication Steps 1. Single cells 2. Stringing 3. Lamination DO Single cells are tested (I-V curve @ STC*) and sorted (similar current/power). series or parallel) to match the module power output. Cells are connected (in Stringed cells are protected with a polymeric foils (encapsulant) provide the adhesion between components. front glass and a rear cover. Two *STC Standard Test Conditions: 1000 W/m² @ 25°C. = EPFL 4. Junction box The junction box is glued at the rear and an aluminum frame is placed around the module. GoPV Project | SUMMER SCHOOL 4 PV SYSTEMS TECHNOLOGIES AND DESIGN#5go PV 2. PV Technology Market and Costs Crystalline Silicon 95% market share PV Technology Trends Market Thin Films 3-5 % market share III-V solar cells Space application Concentrator PV Failed market entrance R&D stages Perovskites (+ tandems) Other technologies Organic, DSSC, quantum dots... EPFL GoPV Project | SUMMER SCHOOL 5 PV SYSTEMS TECHNOLOGIES AND DESIGN#6дору , go PV 2. PV Technology Market and Costs Crystalline Silicon (c-Si) Thin film Wafer based (bulk semiconductor) Processing of wafers • Series connection of individual solar cells Deposition on large area substrate "Monolithic series integration" of the cells . • a a aramy a EPFL III-V multi-junction lan ala afers Grown epitaxially on crystalline wafers Developed for space applications very costly Used in concentrated PV (CPV) → GoPV Project | SUMMER SCHOOL PV SYSTEMS TECHNOLOGIES AND DESIGN 6#7дору go PV 2. PV Technology Market and Costs Figure 3: Evolution in solar PV module costs by quarter, 2018-2022* USD per watt peak (Wp) EPFL 0.40 Shipping costs 0.35 Coatings and glass ■Polysilicon Module assembly Metal commodities Cell assembly Wafer processing Production costs [cts$/Wp] 0.30 2017 2020 0.25 Total 37 20 0.20 Polysilicon 8.7 3 0.15 Wafer 5.8 3 0.10 0.05 Cells Module 8.6 4 13.8 10 0.00 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 3 2018 2019 2020 2021 2022 *Forecast third-quarter values shown for 2022 Source: Rystad Energy SolarSupplierCube GoPV Project | SUMMER SCHOOL PV SYSTEMS TECHNOLOGIES AND DESIGN 7#8go PV 3. Crystalline Silicon Solar Cells What is a solar cell? (n) c-Si + p-n junction . (p) c-Si • Intrinsic (pure) semiconductor material (e.g. Si). . • - Doped with impurities to become conductor -> +(p) or (n) charges transporting the current. Under light → absorption of photons if hv > Eg (Eg: semiconductor bandgap). Photogenerated carriers move towards the junction and cross it. EPFL Anti-reflective coating Top electrode (p) c-Si absorber p h+ e www Load V Bottom electrode + A J. Hurni (2022) Metallic contacts extract the current GoPV Project | SUMMER SCHOOL 8 PV SYSTEMS TECHNOLOGIES AND DESIGN#9go PV PV 3. Crystalline Silicon Solar Cells Low Temperature Process Silicon Heterojunction Aluminium Back Surface Field (Al-BSF) Front metal grid ARC (SIN) (p) c-Si ΑΙ Passivated Emitter and Rear Contact (PERC) Front TCO (SHJ) Front metal grid - i/p a-Si:H (n) c-Si <i/n a-Si:H Front metal grid ARC (SiNX) Rear TCO Rear metal grid SiOX n* emitter (p) c-Si BSF - SiO2 or Al2O3 ΑΙ SiNX 100% 90% 80% 70% 60% 50% 40% World market share [%] IHS Markit data ITRPV 2022 High Temperature Process High Temperature Passivating Contact (HTPC) Front metal grid ARC (SiNX) (p) c-Si ΑΙ Siox n* emitter SiO2 p+ polysilicon EPFL 30% Siox 20% n* emitter 10% 0% IHSM 2021 2021 2022 2024 2026 2029 2032 BSF PERC/PERL/PERT/TOPCon BSF Si-heterojunction (SHJ) Si-based tandem back contact (incl. metal wrap through) GoPV Project | SUMMER SCHOOL PV SYSTEMS TECHNOLOGIES AND DESIGN 9 ITRPV (2022)#10go PV PV 3. Crystalline Silicon Solar Cells Low Temperature Process Silicon Heterojunction Better passivation (rear surface) • Optical losses . Similar manufacturing High temperature processing Aluminium Back Surface Field (Al-BSF) Front metal grid ARC (SIN) SiOx (p) c-Si ΑΙ Passivated Emitter and Rear Contact (PERC) Front TCO (SHJ) Front metal grid - i/p a-Si:H (n) c-Si <i/n a-Si:H Front metal grid ARC (SiNX) Rear TCO Rear metal grid SiOX n* emitter (p) c-Si BSF ΑΙ - SiO2 or Al2O3 SiNX n* emitter Challenges: Optical losses reflection of → photons at rear surface Recombination losses → at metallic contact Ohmic losses → high series resistance at interfaces BSF High Temperature Process High Temperature Passivating Contact (HTPC) Front metal grid ARC (SiNX) Siox (p) c-Si n* emitter SiO2 ΑΙ p+ polysilicon Better passivation EPFL Simple manufacturing processes → no patterning GoPV Project | SUMMER SCHOOL 10 PV SYSTEMS TECHNOLOGIES AND DESIGN#11go PV PV 3. Crystalline Silicon Solar Cells Low Temperature Process Silicon Heterojunction Front TCO (SHJ) Front metal grid - i/p a-Si:H (n) c-Si <i/n a-Si:H EPFL Aluminium Back Surface Field (Al-BSF) Front metal grid (p) c-Si ΑΙ ARC (SIN) SiOx n* emitter BSF Challenges: → Optical losses reflection of photons at rear surface Recombination losses → at metallic contact Ohmic losses → high series. resistance at interfaces Rear TCO Rear metal grid Advantages: Better passivation ↓ Processing temperature Thickness, ↓ cost go PV ↑ Open-circuit voltage (Voc) Temperature coefficient Challenges: Need of ECA for soldering adhesion fingers/TCO ECA: electrically conductive adhesive GoPV Project | SUMMER SCHOOL 11 PV SYSTEMS TECHNOLOGIES AND DESIGN TCO: transparent conductive oxide#12дору go PV 3. Crystalline Silicon Solar Cells Potential for bifaciality Aluminium Back Surface Field (AI-BSF) World market share of monofacial and bifacial cells 100% 90% Front metal grid ARC (SiNX) SiOX (p) c-Si ΑΙ n* emitter Conventional Al-BSF cells do not give option for bifaciality BSF Passivated Emitter and Rear Contact (PERC) Front metal grid ARC (SiNX) SiOX n+ emitter World market share [%] 80% 70% 60% 50% 40% ITRPV 2022 EPFL 30% 20% Silicon Heterojunction (SHJ) 10% 0% Front TCO Front metal grid 2021 2022 monofacial 2024 2026 2029 2032 ■bifacial <i/p a-Si:H (p) c-Si BSF (n) c-Si <i/n a-Si:H SiO2 or Al2O3 ΑΙ SiNx Rear TCO Rear metal grid ITRPV (2022) Novel solar cell concepts promote the development of bifacial technology GoPV Project | SUMMER SCHOOL 12 PV SYSTEMS TECHNOLOGIES AND DESIGN#13go PV 1. PV Module Fabrication Steps 1. Single cells 2. Stringing 3. Lamination DO Single cells are tested (I-V curve @ STC*) and sorted (similar current/power). series or parallel) to match the module power output. Cells are connected (in Stringed cells are protected with a polymeric foils (encapsulant) provide the adhesion between components. front glass and a rear cover. Two *STC Standard Test Conditions: 1000 W/m² @ 25°C. EPFL 4. Junction box The junction box is glued at the rear and an aluminum frame is placed around the module. GoPV Project | SUMMER SCHOOL 13 PV SYSTEMS TECHNOLOGIES AND DESIGN#14go PV 4. Solar Cell Interconnections Frame Glass Encapsulant Cells and Interconnections Encapsulant Backsheet Junction Box Cell interconnect ribbons 00 Da EPFL DO String interconnect A. Shah, Solar cells and modules (2020) Chapter 9, A. Virtuani GoPV Project | SUMMER SCHOOL PV SYSTEMS TECHNOLOGIES AND DESIGN 14#15go PV 1. From solar cells to modules Cell interconnections 1 cell 0.6 V, 8 A 3 cells in series Vx3 0.6 V 888 1.8 V, 8 A 1.8 V 3 cells in parallel 1x3 0.6 V, 24 A EPFL Commercial c-Si modules have 60/72 series-connected solar cells Series connection to get high voltage • → Cells must be current-matched 0.6 V Parallel connection currents add up → Voltages of cells/strings need to be balanced A. Shah, Solar cells and modules (2020) Chapter 9, A. Virtuani GoPV Project | SUMMER SCHOOL PV SYSTEMS TECHNOLOGIES AND DESIGN 15#16go PV 4. Solar Cell Interconnections EPFL Busbar technology World Market Share [%] 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% ITRPV 2022 0% 2021 2022 2024 busbarless 2026 2029 2032 I multibusbar technology (more than 12 busbars) A. Shah, Solar cells and modules (2020) Chapter 9, A. Virtuani 11 and 12 busbars 19 and 10 busbars ITRPV (2022) Clear trend for a higher amount of busbars or none at all GOPV Project | SUMMER SCHOOL 16 PV SYSTEMS TECHNOLOGIES AND DESIGN#17go PV 4. Solar Cell Interconnections Interdigitated Back Contact (IBC) solar cells No need of busbars p a-Si:H LIGHT Silicon nitride c-Si wafer n-type TCO Metal n a-Si:H Intrinsic a-Si:H Y. Lee et al., Israel Journal of Chemistry (2015) Advantages: More aesthetically appealing. EPFL • Ideal candidate for Building Integrated V (BIPV). Challenges: • Cost GoPV Project | SUMMER SCHOOL 17 PV SYSTEMS TECHNOLOGIES AND DESIGN#18go PV 4. Solar Cell Interconnections Smart-wire technology (SWCT) • Multi-ribbon/multi-wire technology (MWT) Conventional ribbons and busbars replaced by round wires with small diameter. • Ribbons (3-6) replaced by 20+ wires. • ↑ ribbons current distribution →> → wires with lower EPFL • conductance ↓silver consumption ↓sensitivity of cell/module to cracks/breakages → • ↑ durability A. Shah, Solar cells and modules (2020) Chapter 9, A. Virtuani GoPV Project | SUMMER SCHOOL PV SYSTEMS TECHNOLOGIES AND DESIGN 18#19go PV 4. Solar Cell Interconnections Silicon Heterojunction solar cells Conventional soldering processes require high temperatures need to find a solution for SHJ → Low temperature process → by using: → ribbons are "soldered" Busbar technology → not mainstream Electrically Conductive Adhesives (ECA) • MWT/SWCT. Challenges: Use of more silver. EPFL 5 Busbars Multiwire SWCT A. Shah, Solar cells and modules (2020) More expensive. • Need to adapt stringers in commercial manufacturing processes. GoPV Project | SUMMER SCHOOL 19 PV SYSTEMS TECHNOLOGIES AND DESIGN#20go PV 4. Solar Cell Interconnections EPFL Why don't we install bare cells in the field? • PV modules are exposed to external stressors: Temperature variations due to performance and environment. High humidity conditions → rain, dew... • Mechanical stress → → wind, snow, hail.. • Irradiance → light, UV Solar cells and interconnections are encapsulated/packaged to: 1. Protect electrical circuit from weathering. 2. Provide structural stability and protect mechanical integrity. 3. Isolate electrical circuit from environment (e.g. protect operators from electrical shocks). GoPV Project | SUMMER SCHOOL 20 PV SYSTEMS TECHNOLOGIES AND DESIGN#21go PV 1. PV Module Fabrication Steps 1. Single cells 2. Stringing 3. Lamination DO D Cells are connected (in series or parallel) to match the module power output. Single cells are tested (I-V curve @ STC*) and sorted (similar current/power). Stringed cells are protected with a polymeric foils (encapsulant) provide the adhesion between components. front glass and a rear cover. Two *STC Standard Test Conditions: 1000 W/m² @ 25°C. EPFL 4. Junction box The junction box is glued at the rear and an aluminum frame is placed around the module. GoPV Project | 1st TRAINING COURSES 21 TECHNICAL FOCUS ON FUTURE SOLAR PV SYSTEMS October 26-29th 2020#22go PV 5. Lamination Process & PV Module Materials Vacuum membrane laminator How to we bring all together? ...bringing cohesion to the full module sandwich? The lamination process Frame Glass Encapsulant Cells and Interconnections Encapsulant Backsheet Junction Box EPFL GoPV Project | SUMMER SCHOOL 22 PV SYSTEMS TECHNOLOGIES AND DESIGN#23go PV 5. Lamination Process & PV Module Materials Flexible membrane Upper chamber (P) EPFL • Heating plate (T) Modulé stack Lamination <<recipe»: combination of steps in the process. • • Specific to a given encapsulant. Critical in ensuring the modules' long-term performance. Lamination parameters: • • • Temperature (T) Pressure (P) Time (t) • Poor lamination process → occurrence of failure modes in the field (e.g. delamination). *In a good laminator the temperature uniformity of the heating plate is well controlled below ≤ 2°C. GOPV Project | SUMMER SCHOOL PV SYSTEMS TECHNOLOGIES AND DESIGN 23#24go PV Temperature 7 [°C] 5. Lamination Process & PV Module Materials step Preheating: Curing step 160 Cooling step- 0.9 120 80 40 0.6 0.3 0.0 0 200 400 600 800 1000 Time t[s] An encapsulation cycle can take 10-20 min. Pressure p [bar] - EPFL 1. Pre-heating step (100s to 500s) → the upper and the lower chambers are evacuated. Removal of the air (de-gas) to minimize the risk of voids formation. The softening encapsulant temperature (60-70 °C) is reached. 2. Curing step (300s to 900s) → the module layups lie on the heating plate directly. A Enhances the adhesion between the encapsulant and neighboring components. The gel content (crosslink degree) at the end of the process must be >80%. → 3. Cooling step the encapsulated PV modules cool to room temperature. Open the Black Box: Understanding the Encapsulation Process of Photovoltaic Modules, 2013 GoPV Project | SUMMER SCHOOL 24 PV SYSTEMS TECHNOLOGIES AND DESIGN#25go PV 5. Lamination Process & PV Module Materials Module structure <<Sandwich >> or module stack: Front cover EPFL Fragile silicon solar cells need to be protected in order to operate outdoors for 25 years (at least). → 3.2 mm-thick glass Encapsulant Stringed cells Provide the adhesion between components Encapsulant Rear cover Modules generally have 60 or 72 cells (depending on applications). Can be smaller for specific apllications: boats, telcos, etc. Backsheet (or polymeric foil) or a second glass GoPV Project | SUMMER SCHOOL PV SYSTEMS TECHNOLOGIES AND DESIGN 25#26go PV 5. Lamination Process & PV Module Materials Glass Tempered glass about 3.2 mm-thick is used as a front cover. Goal → provide mechanical strength. . Optical improvements → texturized and/or with an antireflection coating. -> 1.50 3.2 mm glass Front Glass Encapsulant Stringed cells Encapsulant Irradiance (W/m²) 1.25 1.00 0.75 0.50 0.25 0.00 Backsheet or Rear glass T 100 20 40 20 80 80 60 60 Transmittance (%) Xenon lamp 0 EPFL 300 320 340 360 380 400 Wavelength (nm) GoPV Project | SUMMER SCHOOL 26 PV SYSTEMS TECHNOLOGIES AND DESIGN#27go PV 5. Lamination Process & PV Module Materials Encapsulant EPFL Front Glass Encapsulant Stringed cells Encapsulant Backsheet or Rear glass Main functions: • . Provide adhesion between components (cells-front glass, cells- backsheet, front glass-backsheet). Physical insulation - protect from weather (UV, rain, humidity, etc.); Electrical insulation - keep high voltage away from people and keep current from flowing out of the array circuit to ground; Good optical properties - couple as much incoming light as possible into the cells; GoPV Project | SUMMER SCHOOL PV SYSTEMS TECHNOLOGIES AND DESIGN 27#28go PV 5. Lamination Process & PV Module Materials Encapsulant Ethylene Vinyl Acetate copolymer (EVA) has the best properties - cost ratio. [CHE_CH₂] [CH n H CH₂ C m EPFL Front Glass Encapsulant Stringed cells Encapsulant H₂C C Multiple additives are present in the commercial EVA rolls: ☐ Backsheet or Rear glass Curing agent → cross-linking reaction during lamination. UV absorbers. UV stabilizers/anti-oxidants = decompose curing agent residues; Adhesion promoters → increase adhesion between EVA and glass. GoPV Project | SUMMER SCHOOL PV SYSTEMS TECHNOLOGIES AND DESIGN 28#29go PV 100% 5. Lamination Process & PV Module Materials Encapsulant alternatives to EVA Encapsulants share market Chemically cross-linked elastomer 80% 60% EPFL Physically cross-linked thermoplastic elastomer 40% 20% 0% ITRPV 2022 2024 2026 2029 2032 2021 2022 ■transparent EVA (Ethylene Vinyl Acetat) ■ Polyolefin ■PVB (Polyvinyl Butyral) ■PDMS (Polydimethyl-Silicone) / Silicone I white EVA (Ethylene Vinyl Acetat) extruded EVA with Polyolefin ITPU (Thermoplastic Polyurethane) ITRPV (2022) Development of alternative polyolefines. Irreversible covalent bondings Cross-linked Polyolefines (POE) Replacement of vinyl acetate group No formation of acetic acid Cross-linking necessary Examples: STR POE Encapsulant, 3M Solar Encapsulant Film PO8100N, Mitsui ASCE, EVA will still remain the dominant encapsulant (...for a while). International Technology Roadmap for Photovoltaic - ITRPV 2018 and G. Oreski, “Encapsulant Innovations for replacement of EVA", EUPVSEC 2019. (Thermo)-reversible bondings (lon and hydrogen bonds, crystallites) Thermoplastic Polyolefines (TPO) Replacement of vinyl acetate group No formation of acetic acid No cross-linking Examples: Borealis Quentys, DOW Engage, DNP Solar encapsulants, DuPont lonomers etc. PCCL Polymer Competence Center Leoben GoPV Project | SUMMER SCHOOL 29 PV SYSTEMS TECHNOLOGIES AND DESIGN#30EPFL go PV 5. Lamination Process & PV Module Materials Polymeric Backsheet Most PV modules → composite polymer sheet as backsheet. · Multi-stack structure of three layers with an overall thickness of 280-400 μm. T-P-T backsheet Front Glass Encapsulant Stringed cells Encapsulant Backsheet or Rear glass 150 μm 75 μm UV Resistant Layer Air Side 75 μm UV Resistant Layer PVF (polyvinyl-fluoride) - TedlarⓇ → protects the internal circuit (and PET layer) from weathering agents PET (Polyethylene terephthalate) → isolates the module electrically and provides mechanical stability. GoPV Project | SUMMER SCHOOL 30 PV SYSTEMS TECHNOLOGIES AND DESIGN#31go PV 5. Lamination Process & PV Module Materials EPFL Modules - Innovative concepts Glass Encapsulant Cells and Interconnections Innovative module concepts target: 1. Increased module performance by reducing Cell-to-Module losses. Increased energy-yield. 2. Encapsulant Backsheet 3. Increased reliability. Junction Box GoPV Project | SUMMER SCHOOL 31 PV SYSTEMS TECHNOLOGIES AND DESIGN#32go PV 5. Lamination Process & PV Module Materials EPFL Modules-Innovative concepts 1. Increased module performance 2. Increased energy-yield 3. Increased reliability Half-cell modules →→↓cell interconnection losses (a) Top view Shingled solar cells - →↓inactive space Light capturing ribbons →→↓shadding losses (b) Side view 1 cell 1 cell World market share of different cell aspect ratios In modules for wafer sizes < 182.0 x 182.0 mm² woru market share [%] A. Shah, Solar cells and modules (2020) Chapter 9, A. Virtuani 100% 90% 80% 70% 60% 50% 40% ITRPV 2022 30% 20% 10% 0% 2021 ■full cell 2022 2024 half cell 2026 ■third cell 2029 2032 quarter cell ITRPV (2022) GoPV Project | SUMMER SCHOOL PV SYSTEMS TECHNOLOGIES AND DESIGN 32#33go PV 5. Lamination Process & PV Module Materials EPFL Modules Innovative concepts 1. Increased module performance 2. Increased energy-yield 3. Increased reliability Anti-reflection coatings (ARC) on front surface of front glass reflection at front glass/air interface Power P max (a) [a.u.] 1.1 2. Large-pyramid texture (PT) 1.0 4. Fine-PT 0.9 Standard 0.8 5. Semitransparent 0.7 0.6 3. Self-cleaning Textured glass -> ↑ collection of light at low angles 0.5 -80 -60 1. AR coating -40 -20 0 Angle of Incidence a (°) A. Shah, Solar cells and modules (2020) Chapter 9, A. Virtuani GoPV Project | SUMMER SCHOOL 33 PV SYSTEMS TECHNOLOGIES AND DESIGN