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CIVE40010 - Energy and environmental engineering > Solar Energy > Flashcards

Solar Energy Flashcards

1
Q

What are the main types of solar energy?

A

Photovoltaics (PV), solar thermal, and concentrating solar

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2
Q

Solar intensity at Earth’s surface?

A

950 W/m² from an original 1370 W/m² from outter atmosphere

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3
Q

Global average insolation?

A

240 W/m², equals 2100 kWh/m²/year

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4
Q

How do PV systems differ from other solar technologies?

A

PV converts visible light to electricity; others use broader light for heat

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5
Q

What are single and dual-axis solar tracking?

A

Single-axis follows sun on one axis. Dual-axis eliminates all angle losses

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6
Q

Role of semiconductors in PV?

A

Allow electron movement for electricity generation; depends on band gap size

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7
Q

What’s the Shockley-Queisser Limit?

A

Maximum energy a single “p-n” junction can harness from sunlight

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8
Q

Key to solar thermal efficiency?

A

Lower temp difference between collector and air increases efficiency

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9
Q

Why concentrate solar radiation?

A

To collect heat efficiently, limited by radiation and convection losses

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10
Q

Contribution of solar energy to global electricity generation?

A

Solar contributes significantly, with global generation around 27000 TWh

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11
Q

What extends the effectiveness of PV beyond visible wavelengths?

A

Advanced PV materials can absorb up to 1100nm, increasing efficiency

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12
Q

How is solar energy stored in systems other than PV?

A

Through thermal energy, which can be used directly or stored for later use

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13
Q

Key strategies for reducing solar energy cost?

A

Lowering production cost, using thin-film technologies for less material use

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14
Q

Difference in efficiency focus between solar thermal and PV?

A

Solar thermal focuses on collecting heat efficiently; PV on converting light to electricity

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15
Q

What limits CSP efficiency?

A
  • Thermal Losses
  • Optical Losses
  • Material Limits
  • Conversion Efficiency
  • System Design
  • Ambient Temperature
  • Availability of Sunlight
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16
Q

How long does it typically take for a solar cell to recover its embodied energy?

A

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.

17
Q

What is the significance of the band gap in solar photovoltaics?

A

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.

18
Q

What does the band gap range between?

A

Band gap typically ranges from 0.5 eV to 2.9 eV, depending on the material.

19
Q

How can you calculate the rate at which heat is collected?

A

𝑄̇ = 𝐴_c𝐼 − 𝐴_r 𝜎 𝑇_h^4

20
Q

How can you calculate the maximum possible power?

A

𝑊̇ = 𝜂_carnot𝑄̇

21
Q

How can you calculate Carnot efficiency?

A

𝜂_carnot= 1 − 𝑇_c/T_h

22
Q

Overall efficiency?

A

𝜂_overall = 𝑊̇/𝐴_c𝐼

23
Q

Absorption efficiency?

A

𝜂_absorption = 1 - 𝜎𝑇_h^4/C𝐼
C = A_c/A_r

24
Q

What is the T_c in the atmosphere?

A

300K

25
Q

What has led to a significant reduction LCOE?

A

Coupling with storage

26
Q

What are some ongoing developments?

A
  • Crystalline silicon
  • Multijunction cells
  • Thin-film technology
27
Q

What is good and bad about the thin film tech?

A

Lower efficiency, but low cost, material usage and embedded energy

28
Q

What is good and bad about multijunction cells?

A

Higher efficiency with aim of being cost-effective, low material usage and embedded energy

29
Q

What types of solar thermal collectors are there?

A
  • Plastic absorber
  • Air collector
  • Flat plate collector
  • Evacuated tube collector
30
Q

Which collector maintains highest efficiency?

A

Evacuated tube collector

31
Q

What is good about thermal energy storage?

A

relatively easy and cheap, at range of scales

32
Q

What is good and bad about crystalline silicon?

A

Moderate efficiency, high embedded energy

33
Q

What is the band gap in solar photovoltaic technology?

A

The band gap is the energy required to excite an electron from the valence band to the conduction band in a material

34
Q

How can electrons cross band gap?

A

Incident sunlight provides energy in the form of photons

35
Q

How much solar intensity is reflected back into space?

A

30%

36
Q

What is the incident sunlight passing through an area?

A

0.7I_0A

CIVE40010 - Energy and environmental engineering (21 decks)

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