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Nano solar cells
Nano solar cells utilize tiny nanorods or nanoparticles to convert sunlight into electricity in a thin, inexpensive layer. These dye-sensitized or "nano" solar cells consist of a thin layer of nanorods dispersed in a polymer that can be easily mass produced. While efficiency is still low, nano solar cells have potential for low-cost electricity generation due to inexpensive manufacturing using solution-based coating or printing techniques.
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Nano solar cells
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- 2. Contents • Introduction • Solarcells • Solar product availability • Thin film materials • Cadmium Telluride solar cells • CIGS solar cells • CIGS manufacturing process • Nanosolar • Conclusion 2
- 3. What is aSolar Cell • A device that converts solar energy directly to electricity by the photovoltaic effect – It supplies voltage and current to a resistive load (light, battery, motor) – It supplies DC power • Solar Module or Solar Panel – Solar Module: Solar cells are wired in series – Solar Panel: Solar Modules are assembled together and placed into a frame 3
- 4. Photovoltaic Solar Cells Generateelectricity directly from sunlight 2 Main types: Single-crystal silicon (traditional) Silicon-based solar • Widespread cell • Expensive to manufacture Dye-sensitized (“nano”) • Newer, less proven • Inexpensive to manufacture • Flexible Dye-sensitized solar cell 4
- 5. Current Technology: PhotovoltaicCells Short Version: Light in, electricity out. • If the energy of the incident photons equals or exceeds the band gap energy of the material, then the valence electrons will get excited, and enter the conduction band. • They are susceptible to an electric field and form electricity. 5
- 6. …But Not AllEnergy is Converted… • Like chloroplasts in plants, solar cells can only absorb specific wavelengths of light. • In both, light that isn‟t absorbed is either transmitted through or reflected back. • Whether a certain wavelength of lights gets absorbed depends on its energy. Chlorophyll molecules absorb blue and red light, but reflect green light 6
- 7. Nanotechnology To TheRescue • Chemists at the University of California, Berkeley, have designed a „plastic‟ solar cell which utilizes tiny nanorods to convert light into electricity • These solar cells consist of a layer of tiny nanorods only 200 nanometers thick, dispersed within a polymer. • So far these cells can produce only 0.7 volts, so they are only appropriate for low-power devices. • These cells could be mass produced because the nanorod layers could simply be applied in separate coats. 7
- 8. • Nanorods behave as wires because when they absorb light of a specific wavelength they generate electrons. • These electrons flow through the nanorods until they reach the aluminum electrode where they are combined to form a current and are used as electricity. This type of cell is cheaper to manufacture than conventional ones for two main reasons. • Plastic cells are not made from silicon, which can be very expensive. • Manufacturing these cells does not require expensive equipment like conventional silicon based solar cells. 8
- 9. How a Dye-SensitizedCell Works • Light with high enough energy excites electrons in dye molecules. • Excited electrons infused into semiconducting TiO2, transported out of cell • Positive “holes” left in dye molecules • Separation of excited electrons and “holes” creates a voltage 9
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- 11. Thin film solarcells • Made by depositing one or more thin layers (thin film) of photovoltaic material on a substrate. • A thin film of semiconductor is deposited by low cost methods • Less material is required • Cells can be flexible and integrated directly into roofing material. • Categorized based on the material used – Amorphous silicon (a-Si) and other thin-film silicon (TF-Si) – Cadmium telluride (CdTe) – Copper indium gallium selenide (CIS or CIGS) – Dye-sensitized solar cell (DSC) 11
- 12. Sources of energyloss Thermalization of excess energy Efficiency limits CB Below band gap photons not absorbed VB 12
- 13. Advantages of thinfilms • Efficient and high performing materials – Direct bandgap semiconductors – Better energy output –kWh/KW – CIGS record at 20%+ conversion efficiency • Significantly reduced costs – Less material usage – Not affected by silicon supply shortages – Potential for improving costs throughout value chain • Advanced manufacturing techniques – Fewer processing steps – Monolithic integration of circuits – Automation • Better aesthetics 13
- 14. Comparison of materials Technology Maximum Advantages Disadvantages Demonstrate d Efficiency for small cells a-Si 12.2% Mature Low efficiency manufacturing High equipment costs technology CdTe 16.5% Low-cost Medium efficiency manufacturing Rigid glass substrate CIGS 19.9% High efficiency Film uniformity challenge Glass or flexible on large substrates substrates 14
- 15. Cadmium Telluride (CdTe)Solar Cells glass CdS/CdTe • Direct bandgap, Eg=1.45eV • High efficiency (Record:16.5%; Industry: 11%) • High module production speed • Long term stability (20 years) 15
- 16. Disadvantages of CadmiumTelluride • Cadmium is toxic • Tellurium is a limited reserve – First Solar used half of the world‟s annual production of Te in 2009 – The cost of Te could go up a lot before affecting the price of solar cells Search for other abundant materials… 16
- 17. CIGS solar cells CIGS- Copper Indium Gallium (di)Selenide • The material is a solid solution of copper indium selenide (1.0 eV) and copper gallium selenide (1.7 eV ) • Because the material strongly absorbs sunlight, a much thinner film is required than of other semiconductor materials. The CIGS absorber is deposited on a glass backing, along with electrodes to collect current • CIGS solar cells has efficiencies greater than 20% as compared to 10% for silicon based solar cell 17
- 18. CIGS solar cells Shell Solar, CA Global Solar Energy, AZ Energy Photovoltaics, NJ ISET, CA ITN/ES, CO NanoSolar Inc., CA DayStar Technologies, NY/CA MiaSole, CA HelioVolt, Tx Solyndra, CA SoloPower, CA Wurth Solar, CIS Solartechnik and Solarion, Germany Solibro, Sweden CISEL, France Showa Shell and Honda, Japan Mosar Baer and Rays Expert, India 18
- 19. CIGS manufacturing process •The most common vacuum-based process co- sputters CIG, then anneals the resulting film with a selenide vapor to form the final CIGS structure. • NanoSolar uses a non-vacuum-based process that mixes the materials into a liquid then deposits nano-particles of the precursor materials on the substrate and then sinters it. • SoloPower uses electroplating to apply the CIGS layer. • Another technique is to dissolve the material into a liquid, apply it to a surface and bake it. 19
- 20. Nanosolar 20
- 21. Solar Farms 21
- 22. Future of Nanosolar cells • There is huge demand for use of renewable resources due to its low carbon footprint with solar energy is leading the race as a viable alternative for fossil fuels • Low efficiency and expensive silicon wafers, makes nano solar cells the future of solar panels • Along with silicon and CIGS, other materials are being studied which produce higher efficiencies and at a low cost 22
- 23. PV Solutions forUrban Solarcells Future of Nano solar Applications 23
- 24. Commercial flat roof(attached & ballasted) 24
- 25. Pitched roof (tiles& rack mount) 25
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- 27. Covered areas (walkways,outdoor Cafés, etc..) 27
- 28. Sunshades 28
- 29. Balance of Systems(Mounting,wiring, inverters, etc.) 29
- 30. Thank You 30
- 31. References • http://www.utexas.edu/pmcs/sustainability/documents/UTHelioVoltPresentati on.pdf • http://www.youtube.com/watch?v=EYy0beorZHk • http://www.stanford.edu/group/mcgehee/presentations.html 31
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Editor's Notes
- #15 Silicon wafers are 150 µm thick, the wafers demand multiple processing steps before they can be integrated into a module. On the contrary, thin-film solar cells utilize only a 1-4 µm-thick layer of semiconducting material to produce electricity, thus requiring less processing and fewer materials.
- #19 World record efficiency = 20.0 %.Many companies are evaporating, printing, sputtering and electro-depositing it.Handling a 4-element compound is tough.
- #20 Sputering: Atoms are ejected from a solid due to bombardment of energetic particlesSintering: Creating objects from powders
- #33 TCO - transparent conductive oxideIn chemistry, a precursor is a compound that participates in the chemical reaction that produces another compound.