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 Describe the components and construction of a typical flat plate solar module Calculate efficiency of solar module Explain purpose and operation of bypass diode Describe typical deterioration/failure modes of solar modules 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

Silicone Crystalline Cells a) Monocrystalline b) Polycrystalline Thin Layer Cells a) Amorphous silicon b) CIS c) CdTe Reference 2 Solar Cell Types

PolycrystallineMonocrystalline Crystalline Silicone Reference 2

Thin Film Cell Examples Reference 2

Differences in Cell Type Efficiencies

Crystalline Silicone Highest cell efficiencies Well established manufacturing technology Durable product Thin Film Cells Con’s Less efficient than crystalline silicon Harder to control / MPPT tracking devices (flatter IV curve) Pro’s Wider spectral response (sunlight wavelengths) More efficient at low irradiance levels Use less energy and material to produce More flexible than crystalline silicone More 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