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Basics of Solar PV Systems

Solar power is the ultimate source of energy, which is naturally replenished in a short period of time, for this reason it is called a renewable energy or a sustainable energy source. To take advantage of solar energy, a variety of technologies is used to covert solar energy to heat and electricity. The use of solar energy first and foremost demands energy conservation, because it is the way to use a free energy source that comes from the nature and use it more wisely and efficiently. The way to do this involves a Solar Cell, which is described underneath.

What is a Solar Cell?

Solar Cell or a Photovoltaic (PV) cell is a device that is made up of semiconductor materials such as Silicon, Gallium Arsenide and Cadmium Telluride, etc., that convert sunlight directly into electricity. When solar cells absorb sunlight, free electrons and holes are created at positive/negative junctions. If the positive and negative junctions of solar cell are connected to DC electrical equipment, current is delivered to operate the electrical equipment.  

Solar cell types
There are three major cell types that are classified by their manufacturing technology and the semiconductor used in the process.

     

Mono Crystalline Silicon
PV Module

Polycrystalline Silicon
PV Module

Amorphous Silicon
PV Module

 

1.

Crystalline Silicon PV Module: Two types of crystalline silicon (c-Si) are used to produce PV module; single/mono crystalline silicon or known as monocrystalline silicon and multi-crystalline silicon, also called polycrystalline silicon. The polycrystalline silicon PV module has a shade lower conversion efficiency than single crystalline silicon PV module but both of them have high conversion efficiencies that average about 12-17%.

2.

Amorphous Silicon PV Module: Amorphous silicon (a-Si) PV module or thin-film silicon PV module absorbs light more effectively than crystalline silicon PV module, so it can be made thinner. It suits for any applications that high efficiency is not required and low cost is important. The typical efficiency of amorphous silicon PV module is around 6%.

3.

Hybrid Silicon PV Module: A combination of single crystalline silicon surrounded by thin layers of amorphous silicon provides excellent sensitivity to lower light levels or indirect light. The Hybrid silicon PV module has highest level of conversion efficiency about 17% plus.

Solar cell structure
The most widely used semiconductor material currently in use for solar cell production is Silicon. It has some advantages over others as it can be easily found in nature, does not pollute, does not harm the environment and it can be easily melted, handled and formed into monocrystalline silicon form, etc. Commonly solar cell is configured as a large-area p-n junction made from Silicon.

How solar cell works?

When sunlight strikes solar cell surface, the cell creates charge carrier as electrons and holes. The internal field produced by junction separates some of positive charges (holes) from negative charges (electrons). Holes are swept into positive or P-layer and electrons are swept into negative or N-layer. When a circuit is made, free electrons have to pass through the load to recombine with positive holes; current can be produced from the cells under illumination.

The individual solar cells are connected together to make a module (called ‘solar module‘ or ‘PV module’) to increase current and the modules are connected in an array (called ‘solar array’ or ‘PV array’). Depending on current or voltage requirement, solar arrays are connected in a variety of ways:

If the solar arrays are connected in parallel, the output current will increase.

If the solar arrays are connected in series, the output voltage will increase.

Solar PV system
Solar cells produce Direct Current (DC), therefore they are only used for DC equipments. If alternating current (AC) is needed for AC equipments or backup energy is needed, solar photovoltaic systems require other components in addition to solar modules. These components are specially designed to integrate into solar PV system, that is to say they are renewable energy products or energy conservation products and one or more of components may be included depending on type of application. The components of solar photovoltaic system are

1.

Solar Module is the essential component of any solar PV system that converts sunlight directly into DC electricity.

2.

Solar Charge Controller regulates voltage and current from solar arrays, charges the battery, prevents battery from overcharging and also performs controlled over discharges.

3.

Battery stores current electricity that produces from solar arrays for using when sunlight is not visible, night-time or other purposes.

4.

Inverter is a critical component of any solar PV system that converts DC power output of solar arrays into AC for AC appliances.

5.

Lightning protection prevents electrical equipments from damages caused by lightning or induction of high voltage surge. It is required for the large size and critical solar PV systems, which include the efficient grounding.

Solar cell advantages
Solar cell or PV cell produces clean ener with non-polluting energy source of electricity that is environmental-friendly. Since it uses no fuel other than sunlight, gives off no waste, no burning, and involves no moving parts when it operates. It reduces collection of gases such as carbon monoxide, sulphur dioxide, hydrocarbon and nitrogen, etc., which generate from fuel, coal and fossil fuel burning power plants. Solar PV systems hence decrease the impacts of energy production on the environment by alleviating GHGs and greenhouse effect, global warming, acid rain and air pollution, etc. They are easy to install and are transportable. With the modular characteristics, they can be constructed to any sizes as required. Moreover, Solar PV Systems require minimal maintenance and have long life span (more than 25 years) and stable efficiency.

Solar applications

Home Indoor and outdoor lighting system, electrical equipment, electric gate opener, security system, ventilator, water pump, water filter and emergency light, etc.
Lighting system Bus stop lighting, telephone booth lighting, billboard lighting, parking lot lighting, indoor and outdoor lighting and street lighting, etc.
Water pumping Consumption, public utility, livestock watering, agriculture, gardening and farming, mining and irrigation, etc.
Battery charging system Emergency power system, battery charging center for rural village and power supply for household use and lighting in remote area, etc.
Agriculture Water pumping, agricultural products fumigator, thrashing machines and water sprayer, etc.
Cattle Water pumping, oxygen filling system for fish-farming and insect trapped lighting, etc.
Health center Refrigerator and cool box for keeping medicines and vaccines and medical equipment, etc.
Communication Air navigational aid, air warning light, lighthouse, beacon navigation aid, illuminated road sign, railway crossing sign, street lighting and emergency telephone, etc.
Telecommunication Microwave repeater station, telecommunication equipment, portable communication equipment (e.g. communication radio for service and military exercise) and weather monitoring station, etc.
Remote area Hill, island, forest and remote area that the utility grids are not available, etc.
Space Satellite, international space station and spacecraft, etc.