Solar energy is the ultimate source of energy, which is naturally replenished in a short period of time, for this reason, it is called “renewable energy” or “sustainable energy” source. To take advantages of solar energy, the variety of technologies is used to convert solar energy into heat and electricity. The use of solar energy involves ‘energy conservation’ because it is a way to use the energy source that comes from nature and uses it more wisely and efficiently. That way includes Solar Cell, which is described as follows:
What is Solar Cell?
Solar Cell or Photovoltaic (PV) cell is a device that is made up of semiconductor materials such as silicon, gallium arsenide, and cadmium telluride, etc. that converts 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 the 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 classified by its manufacturing technology and the semiconductor.
- Crystalline Silicon PV Module: Two types of crystalline silicon (c-Si) are used to produce the PV module; single crystalline silicon or known as monocrystalline silicon and multi-crystalline silicon, also called polycrystalline silicon. The polycrystalline silicon PV module has lower conversion efficiency than single crystalline silicon PV module but both of them have high conversion efficiencies that average about 10-12%.
- 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%.
- 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 the highest level of the conversion efficiency of about 17%.
Solar cell structure
The most semiconductor material currently used for solar cell production is silicon, which has some advantages 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. The 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 the 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 equipment. If alternating current (AC) is needed for AC equipment 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 the type of application. The components of the solar photovoltaic system are
- Solar Module is the essential component of any solar PV system that converts sunlight directly into DC electricity.
- Solar Charge Controller regulates voltage and current from solar arrays, charges the battery, prevents the battery from overcharging and also performs controlled over discharges.
- The battery stores current electricity that produces from solar arrays for using when sunlight is not visible, nighttime or other purposes.
- the inverter is a critical component of any solar PV system that converts DC power output of solar arrays into AC for AC appliances.
- Lightning protection prevents electrical equipment 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 with the 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 no moving part when it operates. It reduces the collection of gases such as carbon monoxide, sulfur dioxide, hydrocarbon, and nitrogen, etc., which generated from fuel, coal and fossil fuel burning power plants. All decrease the impacts of energy on the environment like the greenhouse effect, global warming, acid rain, and air pollution, etc. It is easy to install and transportable. With the modular characteristic, it can be constructed any sizes as required. Moreover, it requires minimal maintenance and has a long life span (more than 30 years) and stable efficiency.
Solar cell applications