Solar Energy Utilization - Lecture 10-12 Updated

Solar Energy Utilization

ByDr. Khuram PervezAssistant Professor

Mechanical Engineering DepartmentMirpur University of Science and Technology

Equipment in solar energy system

Equipment in solar energy system

Equipment in solar energy system

What is a solar cell?

• Solid state device that converts incident solar energy directly into electrical energy

• Efficiencies from several percent up to 20-30%.

• No moving parts• No noise• Lifetimes of 30-40 years or more

PV Cells• Photovoltaic energy is the conversion of sunlight into

electricity. A photovoltaic cell, commonly called a solar cell or PV, is the technology used to convert solar energy directly into electrical power. A photovoltaic cell is a non mechanical device usually made from silicon alloys.

• Sunlight is composed of photons, or particles of solar energy.  These photons contain various amounts of energy corresponding to the different wavelengths of the solar spectrum.

• When photons strike a photovoltaic cell, they may be reflected, pass right through, or be absorbed.

PV Cells

PV Cells

PV Cells

PV Cells

PV Cells

PV Cells

PV Cells

PV Cells

PV Cells

• Only the absorbed photons provide energy to generate electricity.  When enough sunlight (energy) is absorbed by the material (a semiconductor), electrons are dislodged from the material's atoms.  Special treatment of the material surface during manufacturing makes the front surface of the cell more receptive to free electrons, so the electrons naturally migrate to the surface.

• When the electrons leave their position, holes are formed.  When many electrons, each carrying a negative charge, travel toward the front surface of the cell, the resulting imbalance of charge between the cell's front and back surfaces creates a voltage potential like the negative and positive terminals of a battery.  When the two surfaces are connected through an external load, electricity flows.

How Solar Cells Work 1. Photons in sunlight hit the

solar panel and are absorbed by semiconducting materials, such as silicon.

2. Electrons (negatively charged) are knocked loose from their atoms, allowing them to flow through the material to produce electricity.

3. An array of solar cells converts solar energy into a usable amount of direct current (DC) electricity.

• The photovoltaic cell is the basic building block of a photovoltaic system.  Individual cells can vary in size from about 1 centimeter (1/2 inch) to about 10 centimeter (4 inches) across.  However, one cell only produces 1 or 2 watts, which isn't enough power for most applications. 

• To increase power output, cells are electrically connected into a packaged weather-tight module.  Modules can be further connected to form an array.  The term array refers to the entire generating plant, whether it is made up of one or several thousand modules.  The number of modules connected together in an array depends on the amount of power output needed. 

• Photovoltaic Systems consist of several electronic components which work together to collect solar radiation and convert it into electricity.

– Collectors – Energy Storage System– Inverter – Distribution Center

Available Cell Technologies• Single-crystal or Mono-crystalline Silicon

• Polycrystalline or Multi-crystalline Silicon • Thin film– Ex. Amorphous silicon or Cadmium Telluride

Monocrystalline Silicon Modules • Most efficient

commercially available module (11% - 14%)

• Most expensive to produce

• Circular (square-round) cell creates wasted space on module

Polycrystalline Silicon Modules• Less expensive to make

than single crystalline modules

• Cells slightly less efficient than a single crystalline (10% - 12%)

• Square shape cells fit into module efficiently using the entire space

Amorphous Thin Film Most inexpensive technology

to produce Metal grid replaced with

transparent oxides Efficiency = 6 – 8 % Can be deposited on flexible

substrates Less susceptible to shading

problems Better performance in low

light conditions that with crystalline modules