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Questions and Answers
What is the maximum efficiency of a silicon solar cell?
What is the maximum efficiency of a silicon solar cell?
Which semiconductor has a band gap most suitable for efficient solar cells?
Which semiconductor has a band gap most suitable for efficient solar cells?
What phenomenon limits the conversion of blue light (400 nm) in silicon solar cells?
What phenomenon limits the conversion of blue light (400 nm) in silicon solar cells?
What is the open circuit voltage of a typical solar panel with 36 cells?
What is the open circuit voltage of a typical solar panel with 36 cells?
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Which type of silicon solar cell is the cheapest to produce?
Which type of silicon solar cell is the cheapest to produce?
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What is the average global energy consumption in terawatts?
What is the average global energy consumption in terawatts?
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What is the expected trend for global energy consumption by 2100?
What is the expected trend for global energy consumption by 2100?
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Which of the following sources alone cannot meet the global energy demand of 21 TW by 2050?
Which of the following sources alone cannot meet the global energy demand of 21 TW by 2050?
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How much energy can be obtained if we solely use biomass for energy?
How much energy can be obtained if we solely use biomass for energy?
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What number of new nuclear power plants would need to be built to achieve 8 TW?
What number of new nuclear power plants would need to be built to achieve 8 TW?
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What is the total energy production potential if we place dams in all remaining rivers on the planet?
What is the total energy production potential if we place dams in all remaining rivers on the planet?
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Why is generating enough energy for future generations considered a massive challenge?
Why is generating enough energy for future generations considered a massive challenge?
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What is the average solar power flux hitting the earth’s surface?
What is the average solar power flux hitting the earth’s surface?
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How much land area is estimated to be required to generate 15 TW of power using 10% efficient solar-energy systems?
How much land area is estimated to be required to generate 15 TW of power using 10% efficient solar-energy systems?
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What is the primary function of doping in semiconductors?
What is the primary function of doping in semiconductors?
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What type of particles are generated in a P-N junction when a photon liberates an electron?
What type of particles are generated in a P-N junction when a photon liberates an electron?
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Which method is not considered a direct way of harvesting solar energy?
Which method is not considered a direct way of harvesting solar energy?
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In the context of semiconductors, what role does the Fermi level play?
In the context of semiconductors, what role does the Fermi level play?
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What phenomenon occurs at the P-N junction when electrons and holes diffuse across the interface?
What phenomenon occurs at the P-N junction when electrons and holes diffuse across the interface?
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What were Archimedes' mirrors purportedly used for in the context of solar energy?
What were Archimedes' mirrors purportedly used for in the context of solar energy?
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What is the significance of the 'air-mass' 1.5 spectrum in solar energy?
What is the significance of the 'air-mass' 1.5 spectrum in solar energy?
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Which of the following describes an intrinsic semiconductor?
Which of the following describes an intrinsic semiconductor?
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Study Notes
Frontiers in Chemistry - CHEM1008
- Lecture 4: Solar Cells
- Lecturer: Darren Walsh
- Location: Room A09, GSK Carbon Neutral Laboratory for Sustainable Chemistry
Lecture 4 Learning Outcomes
- Students will understand the massive challenge of generating enough energy for future generations
- Students will appreciate that conventional methods cannot meet future energy demand and that solar power could be a solution
- Students will understand why semiconductors can conduct electricity using band theory
- Students will comprehend how P-N junction photovoltaics function and their limitations
- Students will be aware of other emerging technologies with the potential to improve solar cell efficiencies
Energy Demand
- Global energy consumption is approximately 500 x 1018 joules, equivalent to an average of 16 terawatts (TW)
- This energy consumption is expected to double by 2050 and triple by 2100
- Current alternative energy sources (Biomass, Nuclear, Wind, Hydroelectric) are insufficient to meet the projected energy demand.
- Calculated potential from these sources combined is roughly 21 TW.
Solar Power
- Solar power provides ~1360 W m−2 outside Earth's atmosphere.
- Only ~175 W m−2 reaches Earth's surface after passing through and reflecting off the atmosphere. This varies with the angle of the sun.
- This represents 89,000 TW of potentially usable solar power
- This is sufficient to meet current global energy needs in a relatively short period (1.5 hours).
Land Requirements for Solar Power
- To generate the current global energy needs, 860,000 km2 of land area would need to be covered with 10% efficient solar energy conversion systems
- This is roughly equivalent to the land area of Venezuela.
Harvesting Solar Energy - An Old Example
- Ancient Greeks, specifically Archimedes, are credited with demonstrating the use of mirrors to focus solar energy to damage enemy ships.
Harvesting Solar Energy - Modern Methods
Different methods for harvesting solar energy: direct (PV and solar thermal) and indirect (Ocean thermal, wave, wind, biomass, and hydroelectric)
The Solar Spectrum
- The maximum intensity of solar energy occurs at around 1eV photon energy.
- An "air-mass" 1.5 spectrum is used as a standard spectrum.
Photovoltaics - Band Theory
- Molecular Orbital (MO) theory explains the overlapping of atomic orbitals to produce bonding and antibonding orbitals.
- In semiconductors, the bonding and antibonding orbitals combine to form energy bands.
- Understanding band theory is crucial for designing efficient solar cells.
- The Fermi level represents the highest occupied molecular orbital at 0K.
Band Gap Width
- The band gap width in semiconductors influences their conductivity.
- Metals have overlapping valence and conduction bands.
- Semiconductors have a narrow band gap, allowing for conductivity through thermal excitation.
- Insulators have wide band gaps, exhibiting no electrical conductivity under normal conditions except at very high temperatures.
Intrinsic and Extrinsic Semiconductors
- Intrinsic Semiconductors (like silicon and germanium): Naturally have low band gaps and few charge carriers.
- Extrinsic Semiconductors: Created by doping, adding impurities, so they exhibit enhanced conductivity.
- N-type doping introduces impurities with more valence electrons than the host material.
- P-type doping introduces impurities with fewer valence electrons than the host material.
P-N Junction Photovoltaics
- Contacting P-type and N-type semiconductors creates a depletion region with a built-in electric field.
- When sunlight strikes the junction with photons, electron-hole pairs are generated.
- The field separates the electrons and holes, creating a potential difference that can be harnessed via a circuit.
What Should We Make Our Cells From?
- Si (band gap = 1.1 eV) and GaAs (band gap = 1.4 eV) are suitable for solar cells because their band gaps have high solar intensity.
- Single-crystal silicon solar cells are effective but costly.
- Polycrystalline silicon cells are somewhat less efficient but cheaper to make.
- Amorphous silicon is the cheapest per watt, with a lower efficiency.
Newer Technologies for Increasing Efficiency
- Recent advancements in solar cell technology are continuously improving efficiency.
What is Limiting Maximum Efficiency?
- Approximately 23% of sunlight is reflected or passes through, while 54% is lost as heat.
- Sunlight with a spectrum exceeding 1.1 μm is not converted to electricity.
Using PVs to Store Energy
- PV cells act as small batteries with voltages as low as 0.58 V.
- Combining multiple solar cells in series creates higher voltages suitable for charging batteries (such as 12 V)
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Description
This quiz covers key concepts from Lecture 4 of CHEM1008, focusing on solar cells and their role in meeting future energy demands. Students will explore the limitations of conventional methods and understand how solar power and semiconductor technology, specifically P-N junction photovoltaics, could provide sustainable energy solutions.
