Solar Energy Flashcards
What are the main types of solar energy?
Photovoltaics (PV), solar thermal, and concentrating solar
Solar intensity at Earth’s surface?
950 W/m² from an original 1370 W/m² from outter atmosphere
Global average insolation?
240 W/m², equals 2100 kWh/m²/year
How do PV systems differ from other solar technologies?
PV converts visible light to electricity; others use broader light for heat
What are single and dual-axis solar tracking?
Single-axis follows sun on one axis. Dual-axis eliminates all angle losses
Role of semiconductors in PV?
Allow electron movement for electricity generation; depends on band gap size
What’s the Shockley-Queisser Limit?
Maximum energy a single “p-n” junction can harness from sunlight
Key to solar thermal efficiency?
Lower temp difference between collector and air increases efficiency
Why concentrate solar radiation?
To collect heat efficiently, limited by radiation and convection losses
Contribution of solar energy to global electricity generation?
Solar contributes significantly, with global generation around 27000 TWh
What extends the effectiveness of PV beyond visible wavelengths?
Advanced PV materials can absorb up to 1100nm, increasing efficiency
How is solar energy stored in systems other than PV?
Through thermal energy, which can be used directly or stored for later use
Key strategies for reducing solar energy cost?
Lowering production cost, using thin-film technologies for less material use
Difference in efficiency focus between solar thermal and PV?
Solar thermal focuses on collecting heat efficiently; PV on converting light to electricity
What limits CSP efficiency?
- Thermal Losses
- Optical Losses
- Material Limits
- Conversion Efficiency
- System Design
- Ambient Temperature
- Availability of Sunlight
How long does it typically take for a solar cell to recover its embodied energy?
It takes about a year and a half for a solar cell to offset the energy used in its production, a measure known as the energy payback time.
What is the significance of the band gap in solar photovoltaics?
Crucial as it determines the energy needed to excite an electron from the valence band to the conduction band, thereby allowing for electrical current flow.
What does the band gap range between?
Band gap typically ranges from 0.5 eV to 2.9 eV, depending on the material.
How can you calculate the rate at which heat is collected?
𝑄̇ = 𝐴_c𝐼 − 𝐴_r 𝜎 𝑇_h^4
How can you calculate the maximum possible power?
𝑊̇ = 𝜂_carnot𝑄̇
How can you calculate Carnot efficiency?
𝜂_carnot= 1 − 𝑇_c/T_h
Overall efficiency?
𝜂_overall = 𝑊̇/𝐴_c𝐼
Absorption efficiency?
𝜂_absorption = 1 - 𝜎𝑇_h^4/C𝐼
C = A_c/A_r
What is the T_c in the atmosphere?
300K
What has led to a significant reduction LCOE?
Coupling with storage
What are some ongoing developments?
- Crystalline silicon
- Multijunction cells
- Thin-film technology
What is good and bad about the thin film tech?
Lower efficiency, but low cost, material usage and embedded energy
What is good and bad about multijunction cells?
Higher efficiency with aim of being cost-effective, low material usage and embedded energy
What types of solar thermal collectors are there?
- Plastic absorber
- Air collector
- Flat plate collector
- Evacuated tube collector
Which collector maintains highest efficiency?
Evacuated tube collector
What is good about thermal energy storage?
relatively easy and cheap, at range of scales
What is good and bad about crystalline silicon?
Moderate efficiency, high embedded energy
What is the band gap in solar photovoltaic technology?
The band gap is the energy required to excite an electron from the valence band to the conduction band in a material
How can electrons cross band gap?
Incident sunlight provides energy in the form of photons
How much solar intensity is reflected back into space?
30%
What is the incident sunlight passing through an area?
0.7I_0A
