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PV System Design and Installation
LO 5A - PV Module Fundamentals
PV Module Fundamental (15% of test questions)
5.1. Explain how a solar cell converts sunlight into electric power
5.2. Label key points on a typical IV curve
5.3. Identify key output values of solar modules using manufacturer literature
5.4. Illustrate effect of environmental conditions on IV curve
5.5. Illustrate effect of series/parallel connections on IV curve
5.6. Define measurement conditions for solar cells and modules (STC, NOCT, PTC)
5.7. Compute expected output values of solar module under variety of environmental conditions
5.8. Compare the construction of solar cells of various manufacturing technologies
5.9. Compare the performance and characteristics of various cell technologies
5.10. Describe the components and construction of a typical flat plate solar module
5.11. Calculate efficiency of solar module
5.12. Explain purpose and operation of bypass diode
5.13. Describe typical deterioration/failure modes of solar modules
5.14. Describe the major qualification tests and standards for solar modules
How PV modules work
Sun –
Radiant Energy
PV module
Shading issues
Silicon Atom
Four electrons in outer shell
Reference 3
Crystalline Silicon Models
Reference 2
Definitions - Electrons and Holes
When sunlight (photon) hits silicon atom, an electron in its outer shell can be “liberated” and start moving throughout the crystalline structure.
A “hole” with a positive charge is “left” behind at the silicon atom that lost its electron.
Recombination - Eventually free electron combines with another hole.
Step 1 – Photoelectric effect
Reference 3
Doping - Process of adding impurities to prevent free electrons randomly “moving” in PV cell.
Step 2 – Doping process
Addition of Phosphorus
Addition of phosphorous creates N-type (negative) semiconductor material
Addition of Boron
Addition of boron creates P-type (positive) semiconductor material
Step 3 – Putting PV cell together
Free electrons from phosphorus atom cross over to fill “holes” in boron atoms. This creates a permanent electric field at p/n junction.
Reference 3
Electrical Field at P/N Junction
Space Charge Zone
Depletion Region
Step 4 – Sunlight hits PV module and current (electron movement) occurs
Reference 3
Reference 2
Typical PV Cell
How PV Cells Work Illustration
http://projectsol.aps.com/inside/inside_pv.asp
Silicone Crystalline Cells
a) Monocrystalline
b) Polycrystalline
Thin Layer Cells
a) Amorphous silicon
b) CIS
c) CdTe
Reference 2
Solar Cell Types
Polycrystalline Monocrystalline
Crystalline Silicone
Reference 2
Thin Film Cell Examples
Reference 2
Differences in Cell Type Efficiencies
Crystalline Silicone
Highest cell efficienciesWell established manufacturing technologyDurable product
Thin Film Cells
Con’s Less efficient than crystalline silicon Harder to control / MPPT tracking devices(flatter IV curve)
Pro’sWider spectral response (sunlight wavelengths)More efficient at low irradiance levels Use less energy and material to produceMore flexible than crystalline siliconeMore tolerant of shading issues
Advantages / Disadvantages of Cell Types
Typical PV Module Construction
Reference 2
Typical Polycrystalline Cell Efficiency
PV output = 12 to 15% Solar Irradiance
3% - Reflection and shading by front contacts
23% - Insufficient photon energy of long-wave radiation
32% - Surplus of photo energy of short wave radiation
8.5% - Recombination losses
20% - Electrical gradient in cell, especially in space charge zone
0.5% - Due to serial resistance (electric heat loss)
Reference 2
Typical PV module energy losses