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Photovoltaic Solar Energy

Content

• Brief History of Photovoltaic Systems• How a Solar PV Cell Works• Types of Photovoltaic Cells• Manufacturing Process Crystalline Photovoltaic Modules• Efficiency of Cells and Modules• Performance of Photovoltaic Modules• Characteristics of Photovoltaic Modules• Configurations of Photovoltaic Systems• PV Module Mounting System

Brief History of Photovoltaic Systems

• The photovoltaic effect was discovered in 1839 by the French Edmond Becquerel.

• In 1883, Charles Fritts applied for the first patent for solar cell, but was very inefficient.

• There were several developments between 1839‐1953, when Bell Labs made a breakthrough to "dope" silicon.

• This led to a prominent and pioneering solar cell use in applying them to a satellite industry in 1958 and quickly progressed from there.

Alexandre Edmond Becquerel

Bell Labs engineer testing a cell in 1954. Credit: Bell Labs website

How a Solar PV Cell Works

https://www.youtube.com/watch?v=2AX0qvnjSnM

https://www.youtube.com/watch?v=K76r41jaGJg&feature=related

Types of Photovoltaic Cells

• Monocrystalline silicon• Multicrystalline silicon or polycrystalline• Thin film• Multi‐junction

Polycrystalline, is the best selling and cheaper.Monocrystalline, is favored for large projects because it has higher efficiency. Thin Film have lower production group.Multi‐union, are more efficient, it is not commercially manufactured, only to provide energy to the space devices.


• Monocrystalline Silicon cells ‐Made from a single large crystal, cut from ingots. More efficient but also the most expensive. Something better in low light (not as good as advertised).


• Polycrystalline silicon cells ‐ are basically molten silicon blocks that can contain many small crystals. It is probably the most common type so far. A little less efficient than monocrystalline, but once established in a module with 35 or more cells, the actual difference in watts per square meter is not much.


• Thin Film cells ‐ In this scheme the silicon is directly transmitted in large sheets, typically using something such as stainless steel. Cheaper to produce, but often much less efficient, which means larger for the same power panels.


• Thin film cells can be classified depending on the type of material used for its manufacture:• Silicon thin film

• Amorphous silicon (a‐Si)• Protocrystalline silicon• Nanocrystalline silicon (nc‐Si)

• Cadmium‐Tellurium (CdTe)• Copper‐Indium‐Galium‐ Selenide (CIGS)• Gallium arsenide (GaAs)• Dye‐sensitized solar cells (DSSCs) ‐ Research

• Quantum dot solar cells (QDSCs) ‐ Research• Organic/polymer solar cells (OPVC) ‐ Research


• Multi‐junction cells.• Cells are developed for very high efficiency ~ 40%.• They are very expensive• They have application mainly in power generation for space devices where the cost is offset by savings in weight

• Lately they are being used in photovoltaic concentrators

Manufacturing Process Crystalline Photovoltaic Modules


Wafer Manufacturing Process

https://www.youtube.com/watch?v=AMgQ1‐HdElM


Solar Cell Manufacturing Process

https://www.youtube.com/watch?v=uRnJxBMv1kw


PV Module Manufacturing Process

(EVA)

(EVA)

Ethylene‐Vinyl‐Acetate (EVA)Tedlar from DuPont (polyvinyl fluoride film ‐ PVF)

(Tedlar)

https://www.youtube.com/watch?v=BKrOZ6OogmQ

Efficiency of Cells and Modules

• The efficiency of a photovoltaic cell is measured as the amount of electrical energy that can occur with respect to the amount of solar energy received for a given area.

• The energy considered standard is 1000 W for an area of 1 square meter.• The manufacturers of photovoltaic systems express its efficiency in the modules. For example, a photovoltaic module 230 W maximum power with an area of 1.65 m2, has a power per unit area of 139.4 W/m2 and its efficiency will divide that number by the standard solar 1000 W/m2, so that the module efficiency is 0.1394 or 13.94%.

• Efficiency is a factor representing the production of the greatest amount of energy with less area.


• The cell efficiencymainly affects the area required to generate a certain amount of energy.

• The following table shows the efficiency of different technologies and the area required to produce a kilo‐Watt peak power (kWp).

Cell Material Module Efficiency Surface Area need for 1 kWp

Monocrystalline silicon 11 – 16 % 7 – 9 m2

Polycrystalline silicon 8 – 10 % 9 – 11 m2

Thin film (CIGS) 6 – 8 % 11 – 13 m2

Thin film (Amorphous silicon) 4 – 7 % 16 – 20 m2

Consideration should be given to access the system (Can increase up to 20% of the area required)


http://en.wikipedia.org/wiki/Solar_cell_efficiency


• Module efficiency is the combination of cells placed in a module.• Many manufacturers often point to these statistics to promote the achievements of its modules.

• However, the true measure of a module is in "Energy production".• Energy efficiency is the actual output in kilowatt‐hours (kWh) as measured by an instrument in time.


• Photovoltaic modules vary greatly in power and physical size.• A typical module is in the range 175‐200 W within an area of 0.9 m (3 ft) 1.5 m (5 ft)

• Therefore, the "rule of thumb" that each module can be is 1.35 m2

(15 ft2).• If we have 200 W and we want to place 2,000 W, how many square meters will be used?10 modules x 1.35 m2 = 13.5 m2

(10 modules X 15 ft2 = 150 ft2)


1,366 W/m2

(127 W/ft2)

Solar Constant

90 to 130 W/m2 (8 to 12 W/ft2)30 to 55 W/m2 (3 to 6 W/ft2)

800 W/m2

(75 W/ft2)

Crystalline modules 11‐16% efficiencyAmorphous modules 4‐7% efficiency

about 55% of sunlight passes through the module surface

average energy received by atmospheric attenuation

Performance of Photovoltaic Modules

• The characteristics of a photovoltaic module can be seen in the performance curve called IV curve.

• The curve is plotted at Standard Test Conditions (STC) of 1,000 W/m2

radiation, 25 °C cell temperature and air mass 1.5 (Atmospheric Mass ‐ AM).

• The graph shows three important points:• Maximum Power Point (MPP)• Open Circuit Voltage (Voc)• Short Circuit Current (Isc)


I‐V curve at different levels of radiation I‐V curve of a Crystalline Cell

At MPP Voltage is 80% of Voc and the current is 95% of Isc


I‐V curve at different temperatures of the cell

TC = Cell temperatureTA = ambient temperatureNOCT = Nominal Operating Cell TemperatureG = Solar radiation (kW/m2)

NOTC is the temperature reached in the assembled cell module when operating at TA = 20°C, AM = 1.5, G = 0.8 kW/m2, wind speed = 1 m/s.

Characteristics of Photovoltaic Modules


• Effect of Temperature Coefficients on the module performance• Usually the temperature coefficients are %/K or %/°C for STC (25°C)

• Temperature Coefficient of Power (TCP)• Temperature Coefficient of Voltage (TCV) ‐ is referenced to Voc• Temperature Coefficient of Current (TCI) ‐ is referenced to Isc

• The formula for determining the power delivered at a given moment by the module


Junction Box• The junction box located at the rear of the module has the function of interconnecting the cells to the connecting wires of the module.

• Usually the connection boxes have bypass diodes.• When a cell is shaded or open circuit, it is reverse biased. The bypass diode serves to divert the flow cell shaded cells or preventing the cell circuit current is interrupted.


Bypass diodes

Normal condition

Condition when a cell is shaded

Configurations of Photovoltaic Systems

Direct‐Coupled PV System Self‐Regulated PV System

Off‐Grid PV System

With Load Control

Without Load Control

Grid‐TiedPV System

Multimode System Hybrid System

PV Module Mounting System

Photovoltaic Solar Energy

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