Photovoltaics: Energy for the New Millennium

Transcription

1 Photovoltaics: Energy for the New Millennium Thomas Surek National Renewable Energy Laboratory Golden, Colorado, U.S.A

2 Photovoltaics (PV) Direct conversion of sunlight to electricity Advantages Modular (mw to many MW) No (or few) moving parts Noise and pollution free Reliable; low operating costs Abundant, indigenous resource (30,000 km 2 PV for 700 GW)

3 Photovoltaic Technology Progress and Status World PV Module Shipments Consumer and Commercial (MW) Rest of the World Europe Japan U.S Source: PV News, February Efficiency (%) CuInSe 2 CdTe Amorphous silicon (stabilized) Boeing Monosolar Matsushita Boeing Univ. of Maine 1980 Kodak Boeing Kodak 1985 Univ. of So. Florida Boeing ARCO BP Solar EuroCIS Boeing Univ. of So. FL Photon Energy AMETEK NREL United Solar The Best One-of-a-Kind Laboratory Cell Efficiencies for Thin Films (Standard Conditions) NREL 2000 World market (1999): MW, ~$1.7 billion Average growth rate ( ): >20% Remote markets (telecommunications, developing countries); PV/buildings Module and system prices decreasing New products and applications Manufacturing capacities increasing: crystalline Si dominates, but thin film scale-up underway Record laboratory efficiencies, new materials, and innovations Commercial product efficiencies and reliability increasing Multiple technology paths Crystalline silicon (ingot- and non-ingot-based) Thin films (amorphous Si, CdTe, copper indium diselenide) Concentrators and high efficiency

4 National Center for Photovoltaics World PV Module Shipments Consumer and Commercial (MW) Rest of the World Europe Japan U.S Source: PV News, February

5 Conversion efficiency (%) Progress in Laboratory Efficiencies Concentrator cells Flat-plate crystalline silicon cells Flat-plate thin films Commercial module efficiencies lag years behind laboratory efficiencies

6 20 Efficiency (%) CuInSe 2 CdTe Amorphous silicon (stabilized) Matsushita Monosolar Boeing Kodak Boeing Univ. of Maine Kodak Boeing Univ. of So. Florida BP Solar EuroCIS Boeing Boeing ARCO Univ. of So. Florida Photon Energy AMETEK NREL United Solar The Best One-of-a-Kind Laboratory Cell Efficiencies for Thin Films (Standard Conditions) NREL

7 Crystalline Silicon (Ingot-Based) PV Progress Progress and Status Key companies: BP Solarex, Siemens Solar, Kyocera, AstroPower, Solec/Sanyo, Sharp, Photowatt, Shell ~85% of today's market 150 MW capacity (to double in near-term) Proven products, 20-year warranties Large ingots: 100 kg CZ, 200 kg casting Multiple ingots w/ melt replenishment Wire saw: < 300 µm wafers, < 200 µm kerf Well-developed technology base new understanding Efficiency Status Cells Modules Float-zone Czochralski Cast poly Batch/continuous processing High-efficiency devices in production of defects/impurities Continuous electromagnetic casting in production

8 Crystalline Silicon (Ingot-Based) PV Research Issues and Directions B Concentration (atoms/cm 3 ) vs. Depth (µm) µm Impurity/defect gettering and passivation High-throughput, low-cost, high-efficiency processes rapid thermal processing? Environmentally benign processing; waste-stream reduction Manufacturing automation and module packaging for 30-year life Czochralski tri-crystals to strengthen thin wafers Thin-wafer (down to 100 µm) handling Wire-saw slurry recycling Dedicated silicon feedstock supply new processes for solar grade silicon? Novel purification for mg-silicon (e.g., porous silicon etching/gettering)

9 Crystalline Silicon (Non-Ingot Ingot-Based) PV Progress and Status Key companies: ASE Americas, Evergreen Solar, AstroPower, Ebara Solar, Bayer, Pacific Solar, Kaneka Status varies from prototype modules to pilot production to commercial products Proven products (~ 3% of market) Capacity increases underway few tens of MW in near term Efficiency Status Cells Modules EFG String ribbon Thick Si/substrate 16.6 >10 Dendritic web Thin Si/substrate up to 11 n/a Improved performance from defect/ impurity and passivation studies New interest in thin silicon growth

10 Crystalline Silicon (Non-Ingot Ingot-Based) PV Research Issues and Directions Manufacturing yield and throughput Novel processing for continuous sheets Impurity/defect gettering and passivation New technology directions ASE Americas 1 m diameter cylinders Evergreen < 100 µm thick, wide ribbon AstroPower < 50 µm, monolithic interconnects on substrate Thin silicon on low-cost substrate Fast deposition rate (> 1 µm/min) Grain size comparable to thickness Diffusion length greater than thickness Insulating substrate for interconnects Many novel approaches: solid-state recrystallization, nucleation and growth, LPE, CVD, CVT, laser ablation, Orientation-independent processes for light-trapping and passivation in thin Si

11 EFG Silicon Cylinders ASE Americas Current: 0.5 m diameter 150 µm thick Future: 1.0 m diameter <100 µm thick

12 Thin-Film Amorphous Silicon PV Progress Progress and Status Key companies: BP Solarex, United Solar/ ECD, EPV, Iowa Thin Films, Sanyo, Canon, Phototronics, DunaSolar Multi-MW/year in consumer products 5 and 10 MW plants operational; few tens of MW in near term Unique products for building integration (e.g., roofing, cladding) Efficiency status: Cell 12.7 (stabilized) Submodule 10.4 Module 7 8 Commercial 5 7 Engineered solution for degradation: thin absorber layers and multijunctions Extensive fundamental research, leveraged by many other applications

13 Thin-Film Amorphous Silicon PV Research Issues and Directions Manufacturing throughput and yield Novel growth techniques e.g., hot-wire deposition, VHF plasma Gas-phase chemistry and control Nucleation and growth High rate deposition ( vs. 1 3 Å/s) Amorphous to microcrystalline structures; mediumrange ordering Improved fundamental understanding: Metastability (e.g., hydrogen collision model and kinetics) Molecular dynamics models Alloys with Ge, C, Role of hydrogen Characterization techniques Improved cell/module efficiencies; new device structures Long-term field performance

14 Thin-Film Cadmium Telluride PV Progress Progress and Status 8 Array efficiency 130 Array efficiency (%) 6 4 SCI CdTe 1 kw System: Efficiency vs. Time Air temperature 0 6/1/95 5/31/ /31/99 Temperature ( o C) Key companies: First Solar, BP Solarex, Matsushita, Antec ~1 MW/year in consumer products Manufacturing expansions underway: High-rate vapor transport (vacuum) Electrodeposition (non-vacuum) Few tens of MW in near term Field testing of modules shows promise Efficiency status: Cell 15.8 Module 10.8 Commercial 7 9 Many approaches for >10% efficiency Lacking fundamental scientific and engineering base for materials/devices ES&H issues studied and under control (e.g., recycling) Cd perception issue?

15 Thin-Film Cadmium Telluride PV Research Issues and Directions GRAIN BOUNDARY SIMS Profile of Cu Diffusion Thin ZnTe:Cu Thick ZnTe:Cu Film deposition development Nucleation and growth Gas-phase or surface chemistries Annealing and heat treatment (CdCl 2 ) Grain growth, native defects, dopants CdS/CdTe interdiffusion Alternate transparent conductors; impact on film growth Successful first-time manufacturing Front and back contacts Alternate transparent conductors Low resistance, stable back contacts Role of Cu; Cu-free contact strategies? Close efficiency gap (cell > module) Compatibility of manufacturing process steps (e.g., tie to glass float-line?) Low-cost module packaging for long-term reliability (>20 years) Accelerated module test procedures

16 Thin-Film Copper Indium Diselenide (CIS) PV Progress and Status MgF 2 (0.1 µm) anti-reflection coating ZnO (0.4 µm) transparent conducting oxide CdS (0.05 µm) n-type window CuInGaSe 2 (3.0 µm) p-type absorber Mo (1.0 µm) back contact Glass (1 3 mm), plastic, or stainless steel foil structural support Key companies: Siemens Solar, Global Solar/ITN, ISET, EPV, Wurth Solar, Showa/Shell Prototype production started in 1998: First commercial products (5 10 W) Efficient, large modules (>12%) Expansion to multi-mw in near term Field testing of modules shows promise; >10 years outdoors, no degradation Efficiency status: Cell 18.8 Submodule 14.7 Module 12.1 Commercial >10 Others: Stainless steel substrate 17.5 Electrodeposition 15.4 With ZnO (no buffer) 15.0 Alloying with Ga and S; role of Na Progress mostly empirical; little understanding of materials/devices/processes

17 Electrodeposited CIGS Precursor Film Thin-Film Copper Indium Diselenide (CIS) PV Research Issues and Directions Absorber CIGS from Electrodeposited Precursor Film Scalability of current processes Predictive models of materials growth, devices, and processes Real-time process controls Yield and throughput New techniques and materials Non-vacuum approaches Low-temperature depositions Device research and development Heterojunction vs. homojunction Role of window materials; improvements in blue response Alternate front and back contacts Higher bandgaps and multijunctions Device models and characterization Theory: Band structures, optoelectronic properties, defect physics, doping

18 High-Efficiency and Concentrator PV Progress Progress and Status Key companies: PV International, Entech, Amonix, Sunpower, Tecstar, Spectrolab, Honda, BP Solar Manufacturability demonstrated Low-concentration, line focus High-concentration, point focus High efficiency cells (Si, GaAs, multijunctions) in production Limited applications in today's markets >20% (Si), >24% (GaAs), 28% (GaInP 2 /GaAs/Ge at 10X Efficiencies: Si (up to 400X) 27 GaAs (up to 1000X) 28 GaInP 2 /GaAs (1X) 30.3 GaInP 2 /GaAs (180X) 30.2 GaInP 2 /GaAs/Ge (40 560X) 32.3 Module efficiencies: 15-17% (Si); best prototypes: Large space markets drive GaInP 2 /GaAs commercial cell production

19 High-Efficiency and Concentrator PV Research Issues and Directions Want 1 ev material lattice-matched to GaAs Try GaInNAs Calculated efficiencies (ideal) 500X AM1.5D: 36% 47% 52% one sun AM0: 31% 38% 41% Energy (ev) GaInP 1.8 ev GaAs 1.4 ev In production GaInP GaInP 1.8 ev 1.8 ev GaAs GaAs 1.4 ev 1.4 ev New New 1.0 ev 1.0 ev Ge 0.7 ev Future generation High-efficiency (>40%) multijunctions GaInAsN and Ge for 3rd and 4th cells Lattice match to GaAs Short diffusion lengths to date Monolithically integrated modules (e.g., for dish concentrators) New products for today's markets Novel concentrating concepts: Reflecting troughs Concentrating dish PV/thermal hybrids Non-imaging optics Low-profile concentrators Standards for qualification and performance testing of concentrators

20 Novel PV Concepts and New Materials Research Issues and Directions Nanoparticle-derived precursors for PV Potential for very low cost Low process temperatures, non-vacuum Potential for smooth, dense films Absorbers (CdTe, CIS,...) Transparent conductors (SnO 2, CdS,...) Contacts (Ag, Au, Pt,...) Nanocrystals, nanotubes, nanorods Nanocharacterization Dye-sensitized TiO 2 photochemical cells Potential for very low cost Nanocrystalline TiO 2, with monolayer dye sensitizer, in liquid electrolyte 11%-efficient cell; scale-up for consumer products underway Dye stability issue Gel or solid-state electrolytes Photoelectrochromic window (with WO 3 )

21 Absorbance (%) National Center for Photovoltaics Novel PV Concepts and New Materials Research Issues and Directions SnO 2 Cd 2 SnO Wavelength (µm) Transparent conducting oxides Critical component in thin-film devices Conventional TCOs: In, Sn, Zn-based New/improved materials: high mobility key Non-oxides, p-type TCOs, single crystals Theory for defects, doping, role of grain boundaries For PV: thin, high rate/low T, non-toxic, good electrooptical properties, easy to etch Room heat Quartz shield PV array Exhaust Combustion Cooling Cooling air air Fan air Room heat Window Matched emitter Cooling fins Propane Thermophotovoltaics (TPV) Conversion of IR radiation ( K) by low-bandgap ( ev) PV cells Many fuel choices and radiators; system design includes heat recycling/recovery High power densities (1 5 W/cm 2 ) Single and multijunction III-V cells: GaSb, InGaAs, GaInAsSb; thin-film PV cells Many applications and system concepts; prototypes available on market

22 PV Cell and Module Efficiency Measurements Eff = 10.4% Eff = 18.8% Efficiency measurements with respect to standard reporting conditions Multiple test-beds for accurate and reliable results Any PV cell or module technology Spectrally adjustable light sources for multijunction devices Concentrator cells (to 2000 suns) Reference cell calibrations Spectral response measurements: - Extended wavelength range - QE of each cell in a module - Measure non-uniformities in photocurrent

23 Analytical Microscopy Microcharacterization Labs AFM ASEM (a) M o CIGS ITO (c) Device junction EPMA STEM Twin boundary (b) 5 nm Structural, topographical, chemical, defect, and electrical properties of PV materials and devices Down to atomic-scale resolution (a) AFM studies of recrystallization of polycrystalline CdTe versus treatment (b) ASEM cross-section of CdS-less CIGS with EBIC linescan showing junction location (c) Atomic structure of defects in CdTe by TEM

24 Submicron Ultrafast Studies on PV Materials Photoluminescence (arb. units) Ultrafast Near-Field Scanning Optical Microscopy (NSOM): Spatial resolution = 0.1 micron Time resolution = 1 psec Directly probe effects of passivation on recombination at defects Time (nsec) Time-resolved photoluminescence (TRPL) across a grain boundary: CdTe bicrystal lifetime at grain boundary(lower curve) decreases by factor of 2 compared to few microns from boundary (upper curve)

25 PV Markets and Applications International Rural electrification: Water pumping Desalination/disinfection Brazil India Brazil India China South Africa Home and security lighting

26 PV Markets and Applications International Rural electrification: Schools and clinics Zambia India Brazil South Africa Mexico Village power

27 PV Markets and Applications Domestic Remote, off-grid power: Telecommunications Signaling Disaster mitigation Emergency power

28 PV Markets and Applications Domestic Remote, off-grid power: Water pumping National Parks Stand-alone power EV charging

29 PV Markets and Applications Buildings Grid-connected: Commercial and residential

30 Some FAQs Concerning Photovoltaics Balance-of-Systems (BOS) components issues? Materials availability: limits to large-scale PV? Is photovoltaics safe? What is energy payback period for PV systems? How much land area for large-scale PV?

31 Balance-of of-systems (BOS) Components Key companies: Trace, S&C (Omnion), Applied Power (Ascension), UPG, AES, Mastervolt, NKF, Nippon Denchi, Toshiba BOS related to area (e.g., installation), power (e.g., inverter, storage), and applications (e.g., pumps, lights) 30 70% of today's system cost; source of nearly all reliability issues Proven inverters (2 4 kw and 20 kw); experimental for 100s of kw Hybrid systems; new ac-modules Reliability addressed by HALT and quality programs in manufacturing: - Improved MTBF (30,000 to 114,000 h) - Reduced failure rates (14% to 2%) Research issues and directions: - Interconnection and islanding - Surge resistance (lightning, transients) - Advanced inverters (e.g., soft switching) - Battery management - Reliability testing; standards - Lower costs and improved reliability

32 Materials Availability: Limits to Large-Scale PV? 40 Percent of Today s Production for 1 GW PV Drinkard Metalox Indium Tellurium Gallium* *<1% if all Ga is recovered. Si availability: limited only by quality and cost. Solar-grade silicon? Rare metals are by-products of primary metal refinement: Te (from Cu), In (from Zn), Ga (from Al) Other pure materials (e.g., CdS, TCOs) Today's production and costs are functions of demand; competing uses 2 to 3-fold price increases will not impact PV costs; >8-fold increase will Thinner layers; higher cell efficiencies Better materials utilization in deposition Substitutions: Ga for In, S (or Zn) for Te, ZnO for CdS,. Recycling in manufacturing and disposal Improved recovery techniques and new sources for production of rare metals

33 Photovoltaics IS Safe! Brookhaven National Laboratory: Photovoltaic EH&S Assistance Center Work with industry and labs EH&S from R&D to manufacturing to deployment to disposal/recycling Toxic, explosive, and carcinogenic materials in manufacturing (e.g., SiH 4, H 2 Se, Cd, Pb, As, solvents, effluents) Small amounts in products; well-sealed and in inert form Proactive approach: hazard identification; monitoring and control strategies Semiconductor industry experience Codes and regulations: - Manufacturing (OSHA, EPA, States) - Deployment (UL, NEC) - Disposal (EPA, States) Reduced solvents and waste streams Pb-free solder Recycling: <$0.05/W 1 kw PV system in typical location: - Avoids about 2 MT of CO 2 per year - Reduces other pollutants (NO x,so x ) PV offsets projected C increase (~2025)

34 Energy Payback for PV Systems Years Energy Payback for PV Systems Multicrystalline present Thin-film present Multicrystalline future PV technology System components Balance of system Frame Module Thinfilm future MWh clean energy Cumulative Net Clean Energy Payoff For PV System (415 kwh/month) Meeting Half of Average Household Use Investment Return Years Conventional technology is energy intensive (Si purification and growth, cell processing, module packaging) - 4 years for present technology - 2 years for future technology Thin films use less materials, lower-energy processing; substrate and module packaging are key - 3 years for present technology - < 1 year for future technology BOS components and support structures add less than 1 year to energy payback - Will decrease as efficiency increases Energy credit for PV as building component (e.g., rooftop, facade) With 30-year projected life, PV system provides 15 to >30-fold energy return Avoidance of emissions (CO 2,NO x, SO x, particulates) during PV system life

35 Good for our economy and energy independence National Center for Photovoltaics Photovoltaics is Solar Electricity Good for our environment DOE PV Program Goal: U.S. leadership in technology, industry, and markets Solar can supply all electricity for the U.S. using this area (100 x 100 mi.) in the SW OR Distributed applications throughout the U.S. (vacant land, building-integrated, etc.) Clean and abundant energy for the 21st Century High-technology manufacturing jobs

36 Module cost ($/W p ) National Center for Photovoltaics Photovoltaic Technology Prospects and Future Directions Average Direct Manufacturing Cost for PVMaT Partners Projected Total manufacturing capacity (MW) GWp per year U.S. and Worldwide PV Module Shipments (25% per Year Growth) Total world shipments (GWp/yr) U.S. industry shipments worldwide (GWp/yr) Cumulative U.S. shipments worldwide (GWp) U.S. cumulative shipments (GWp) PV works, reliable, competitive in many rapidlygrowing markets Continuing technical advances: higher efficiencies and lower costs Significant manufacturing expansions underway: few 100s of MW in near term Crystalline silicon dominates markets Many challenges for new technologies: technical, market, and financial risks PV industry projection of 25% growth rate Significant contributions to energy and environment starting in Market incentives support manufacturing expansion, but impact on cost reduction not apparent Sustainable markets require lower cost technology Key: continued technology development