19-03-2011, 09:29 AM
Presented by:
David Toub
A Review of Photovoltaic Cells (David Toub).ppt (Size: 1.11 MB / Downloads: 287)
A Review of Photovoltaic Cells
Introduction
• Clean Energy
• PV System
– Cells
– Energy storage
– Charge Controller
– AC/DC converter
Functionality
• pn diode
• No illumination
– Diode behavior
– e, h separated
• Illumination
– Incident photons create e-h pairs
– E fieldàe-h pairs separate
Semiconductor
• Absolute 0 à Perfect insulator
• Temp increases à conduction increases
• External energy raises temperature
• VTC
• Performance Limits
• Pm = Vmax x Imax
• Incorporate load
Energy Conversion Efficiency
• η =Pm/(E x Ac)
• Primary Challenge
• Incident photons
– Ep<Ebg à Elost
– Ep>Ebg à Ee- + Elost
– Ep=Ebg à Ee-
• Silicon tradeoff
– High bg à loss
– Low bg à E, V reduced
– Optimal at bg=1.4eV
Loss Tradeoffs
• Cell Top
– Must be transparent
– Too thin à bad conduction
• Cell Interior grid
– Large grid helps e-’s
– Large grid blocks photons
Auxiliary Design
• Heavy modules
– structural stress
– Wind tension
• Pollution
• Fan Example
– Speed
– Acceleration
– Without illumination
• E/V àAh
Applications
• Electric grid extensions not offered
• Clean
• Solar powered house
• Water pumping systems
• Garden lights
• Automobiles
• Source utility grid
• Satellites, shuttles
Research
• Thin Film
– Cheap
– Increased unit loss
– Multilayer àEfficiency
• Nanocrystalline
– Thin film + mesoporous MO
– Increased internal reflection
– Great efficiency à expensive
Conclusions
• Environmentally benign
• Inefficient à uncommon à Still fuel
• Future à Efficiency increasing àCheaper