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07_Photovoltaics

07_Photovoltaics. Background Photovoltaic (PV) energy: Cost is the „only“ BIG issue The good news : for some areas solar cells are competitive The bad news : for many not, this is by far the largest part yet

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07_Photovoltaics

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  1. 07_Photovoltaics Background Photovoltaic (PV) energy: • Cost is the „only“ BIG issue • The good news: for some areas solar cells are competitive • The bad news: for many not, this is by far the largest part yet • BUT: prediction for competitiveness for residential (peak power) application had to be modified over the last 5 years: 2018  2015  2013 (prediction last year • This year: We are there W. Bergholz GEE2 Spring 2012

  2. 07_Photovoltaics PV Competitiveness(after W. Hoffmann, RWE Schott) Update 2012 W. Bergholz GEE2 Spring 2012

  3. 07_Photovoltaics PV Competitiveness(after W. Hoffmann, RWE Schott):available at peak power demand during the day W. Bergholz GEE2 Spring 2012

  4. From the presentation of K.H. Küsters, Conergy PV integration in the overall energy system PV integration up to 10 GW without change of total energy system, but we are already approaching 20GW! W. Bergholz GEE2 Spring 2012

  5. 07_Photovoltaics PV share(after W. Hoffmann, RWE Schott):still very small! W. Bergholz GEE2 Spring 2012

  6. Update 2011: Germany 3% PV !!!! W. Bergholz GEE2 Spring 2012

  7. 07_Photovoltaics PV share(after W. Hoffmann, RWE Schott):renewables will be needed in the long term! W. Bergholz GEE2 Spring 2012

  8. 07_Photovoltaics Projected growth according to EPIA and OECD: Prediction by OECD / European Photovoltaics Industry Association (EPIA) for Photovoltaics capacity growth (annual installation capacity) and implications for the demand on the labourmarket. (1MWpeak at present translates into approx. 5 Million $ turnover in 2006) W. Bergholz GEE2 Spring 2012

  9. From the presentation of K.H. Küsters, Conergy People working in renewable energy sector people employed (2006, vs 2004 (grey)) From 157000 employed people in 2004 to 231000 in 2006 PV ca. 25000 (2006), Trend: strong increase of engineers in PV W. Bergholz GEE2 Spring 2012

  10. 07_Photovoltaics Cost reduction follows a generic experiece curve(after W. Hoffmann, RWE Schott): • this is true for cars, airplanes, watches,.... W. Bergholz GEE2 Spring 2012

  11. 07_Photovoltaics Cost reduction follows a generic experiece curve(after W. Hoffmann, RWE Schott): W. Bergholz GEE2 Spring 2012

  12. 07_Photovoltaics The analogous curve from a different source: W. Bergholz GEE2 Spring 2012

  13. From the presentation of K.H. Küsters, Conergy Price learning curve of crystalline Si PV modules W. Bergholz GEE2 Spring 2012 Key levers to reduce price: material cost, production, h

  14. 07_Photovoltaics 4 main markets(after W. Hoffmann, RWE Schott), 3 are econically viable already to-day ! W. Bergholz GEE2 Spring 2012

  15. 07_Photovoltaics SINCE 2010!!! Expected market penetration by grid parity (competitive prices for peak demand): In a few years: South of Italy W. Bergholz GEE2 Spring 2012

  16. 07_Photovoltaics SINCE 2011!!! Expected market penetration by grid parity (competitive prices for peak demand): In 7 years: Spain and other Mediterranian Countries W. Bergholz GEE2 Spring 2012

  17. 07_Photovoltaics NOW!!! Expected market penetration by grid parity (competitive prices for peak demand): In 12 years: in Germany and Central Europe W. Bergholz GEE2 Spring 2012

  18. History of PV • Einstein, Photoelectric effect 1921 Nobel Prize (not for the Theory of Relativity) 1954 RCA: Report on the photovoltaic (PV) effect 1954 Bell Labs: The first solar cells with  = 4-6% 1958 Solar cells for space applications,  = 9% W. Bergholz GEE2 Spring 2012

  19. History of PV 1970 – 1980 First commercial PV solar cells companies 1983 WW Solar cell production: 21.3 MW peak power for $ 250 million  $ 12 000 per KW peak W. Bergholz GEE2 Spring 2012

  20. 07_Photovoltaics 1990s PV companies: Arco Solar, BP Solar, Kyocera, Sharp, Siemens, Solar Power,... 2003 Largest solar power plant in Hemau, Bavaria with 4 MW peak (nuclear plants: >1000MW) Cost 2012: 1700€ per KW peak (large plants) <17 Cents per KWh W. Bergholz GEE2 Spring 2012

  21. Basicshttp://www.solarserver.de/wissen/photovoltaik-e.html. Strong trend to thinner cells, 0.15 mm is the „standard“ now W. Bergholz GEE2 Spring 2012

  22. Basics Approx. Intensity of solar radiation approx. operating point – here the power U x I is maximized! Isc Light intensity up Uoc W. Bergholz GEE2 Spring 2012

  23. Basics (this and the following slides from T. Dinkel, PhD proposal • To understand this performance, we need to remind ourself of the diode principles and develop an equivalent circuit: W. Bergholz GEE2 Spring 2012

  24. Basics (this and the following slides from T. Dinkel, PhD proposal • In a homogenously doped semiconductor, due to the balance between • the diffusive motion • the drift • of carriers leads to the space charge, electric field and potential within diode junction W. Bergholz GEE2 Spring 2012

  25. Basics (this and the following slides from T. Dinkel, PhD proposal In the last semester, we saw that this leads to the upper I(U) curve of a diode (solution of drift and diffusion PDEs leads to Shockleys equation) Ilumination sets up an additional photocurrent (from electron hole pairs which are generated by the light) This shifts the I(U) curve down by the short circuit current W. Bergholz GEE2 Spring 2012

  26. Basics (this and the following slides from T. Dinkel, PhD proposal Equivalent circuit (without material resistances) has takes into account both the space charge region and the quasi neutral zones: W. Bergholz GEE2 Spring 2012

  27. Basics (this and the following slides from T. Dinkel, PhD proposal Practical example: Note: the larger FF, the larger the efficiency W. Bergholz GEE2 Spring 2012

  28. Basics (this and the following slides from T. Dinkel, PhD proposal In reality, the series resistance Rs (material, metal bus bars) and the shunt resistance Rsh have to be taken into account and can seriously degrade performance: W. Bergholz GEE2 Spring 2012

  29. Basics (this and the following slides from T. Dinkel, PhD proposal Effect of Rs: Rs consumes some of the voltage available to the load FF smaller! W. Bergholz GEE2 Spring 2012

  30. Basics (this and the following slides from T. Dinkel, PhD proposal Effect of Rsh: Rsh consumes some of the current from the current source  FF smaller! W. Bergholz GEE2 Spring 2012

  31. Basics Typical Si wafer parameters • Uoc  0.6V, Isc  2A/100cm-2 at standard illumination and 25 C (for higher T, efficiency goes down, about 0.4% reduction of energy havest per degree!) • Operation point at U x I = max • Max. theoretical efficiency: 28% W. Bergholz GEE2 Spring 2012

  32. Basics Typical Si wafer parameters • Losses due to: • Heating of module (efficiency goes down, look at the previous equations) • Reflection • Sun spectrum below band gap not usable • shadowing of the front surface by metal lines • losses due to Rsh and R s (Si material resisistance and bus bars) • Losses due to contamination and defects W. Bergholz GEE2 Spring 2012

  33. Basics Typical efficiencies of cells, module 2 % lower: Type Max. lab max production • Si crystalline 24 – 27% 17 – 21% • Si multicrystalline 18% 16 – 18% • Si amorphous 13% 5 – 7% W. Bergholz GEE2 Spring 2012

  34. From the presentation of K.H. Küsters, Conergy Many new technologies competing by E.Weber, ISE Freiburg W. Bergholz GEE2 Spring 2012

  35. ) From the presentation of K.H. Küsters, Conergy How to optimise the efficiency of a solar cell? • Key levers: • minimise reflectivity • absorb light in semiconductor to generate electron-hole pairs, • ensure that maximum of electrons are collected at front side emitter / holes are collected at back contact W. Bergholz GEE2 Spring 2012

  36. From the presentation of K.H. Küsters, Conergy Photovoltaic conversion For a given material only a part of sun light can be converted into electron-hole pairs (Si: max efficiency of cell is 29%, present record is 24,3%, based on GaIn/As based triple junction a record of 41,1% has been achieved) W. Bergholz GEE2 Spring 2012

  37. From the presentation of K.H. Küsters, Conergy Many challenges for engineers …. for example: material enginnering of silicon current The quality of silicon has a strong influence on the efficiency of a solar cell W. Bergholz GEE2 Spring 2012

  38. Si Siliconnitride Si H H H H H H H H H H H From the presentation of K.H. Küsters, Conergy Many challenges for engineers …. for example: min. reflectivity, surface passivation X X X X X X Si X X X • SiNX • Reflectivity : ~ 10 % • green light not reflected • -> blue • wafer Surface texture Passivation (defects, interfaces) H atom X Defect, Microcrack etc. The silicon surface has a strong influence on the efficiency of a solar cell W. Bergholz GEE2 Spring 2012

  39. From the presentation of K.H. Küsters, Conergy Many challenges for engineers …. for example: metallisation / screenprint Front side(Ag) Ni Emitter n+ p-Si Back side(Al) Metallisation Screenprinting of paste & firing The metallisation has a strong influence on the efficiency of a solar cell W. Bergholz GEE2 Spring 2012

  40. Basics A PV SYSTEM consists of: • solar cells built into a solar module • DC – AC converter: INVERTER • Batteries + Charge / Discharge Controller • If applicable: connection to mains grid W. Bergholz GEE2 Spring 2012

  41. A real Residential System PV modules before mounting W. Bergholz GEE2 Spring 2012

  42. A real Residential System Preparation of the roof to mount the modules: W. Bergholz GEE2 Spring 2012

  43. A real Residential System Mounting the modules on the roof: W. Bergholz GEE2 Spring 2012

  44. A real Residential System The PV generator is complete: W. Bergholz GEE2 Spring 2012

  45. A real Residential System The inverter for DC (300V, up to 15A) conversion to AC 230V, up to 19A W. Bergholz GEE2 Spring 2012

  46. Basics A PV SYSTEM EXAMPLE: W. Bergholz GEE2 Spring 2012

  47. Ecological, economic boundary conditions & long term needsArtem Tolokonnikov, Podolsky Silicon PV is the „ideal“ energy source: • No CO2 emission • Local generation possible • No heating of environment • No consumption of non-renewable ressources (except for production) • No radioactivity or other agressive substances produced W. Bergholz GEE2 Spring 2012

  48. From the presentation of K.H. Küsters, Conergy PV value chain Silicon Feedstock Silicon bricks Silicon Wafer Silicon Solar cell Solar Module Solar System A PV producer needs to master all parts of value chain Very few companies active in all parts of value chain W. Bergholz GEE2 Spring 2012

  49. Low Cost Solar Cells from expensive Silicon?(M.J. Stocks et al 2004) • Reduction in Si feedstock + crystal: a „revolutionary approach“: Sliver cell W. Bergholz GEE2 Spring 2012

  50. Low Cost Solar Cells from expensive Silicon?(M.J. Stocks et al 2004) • Reduction in Si feedstock + crystal: a „revolutionary approach“: Sliver cell W. Bergholz GEE2 Spring 2012

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