Solar Panels are becoming more and more popular with every passing day and the main component of these solar panels is the electronic systems called Photovoltaic Cells. In this article, we will explain the working principle of PV cells as well as other details that you need to know about regarding the subject in a clear and simple manner readers can understand.
What is a Photovoltaic Cell?
In the simplest manner, it is a chemical composition that takes the energy from the reflected light and turns that energy. The PV cells, which have a semiconductor feature, create voltage and current by providing electron movement between (+) and (-) poles as a result of the photons that hit them. In the picture below, you can see the chemical structure of a PV cell and the electric current flow in detail.
If we were to explain the terms in the picture briefly:
SiO2: It is the basic element of semiconductor segments. This chemical is used in the making of the transistors and diodes that are used in electronic circuits.
Silicon Wafer: The silicon wafer is responsible for creating a semiconductor environment. The process of separation to the poles occurs with SiO2.
Flow of Electrons: The extra electrons that come out as a result of the photons move from (-) pole to (+) pole and generate electricity.
Working Principle of Photovoltaic Cells
Let's see how PV cells work in a more detailed manner. In the picture below, you see the normal state of a PV cell and the voltage it produces. In a PV cell on which there is no light, (+) and (-) poles seem to be in balance.
Picture - 1
If you look at the second picture (Picture 2) it can be observed that on the PV cell which has light on it the (-) pole intensity increases and as a result of this there is also an increase in the voltage in the voltmeter. The photons in the light cause the number of electrons on the silicon surface to increase by activating them; this causes the two poles to generate electricity.
Basically, as long as there is a light falling on the silicon surface which causes the photon --> electron transformation, this generation continues to occur.
Note: A silicon surface cannot completely transform the power of the light which falls on it into electricity. The main reason for this is that even though there are many colors in light only the red color is transformed into electricity.
How does a Solar Cell Produce Electricity?
We gave brief explanations above on how photovoltaic solar cells produce electricity. If we were to explain them in more detail:
The cells which are made of semiconductor matter absorb the light that is reflected on them and transform it into electric energy. The major process here is provided by the flow of the extra electrons in the (-) pole to the holes in the (+) pole by means of the photons. During this flow the generation of electricity occurs. In the picture below you can see how the flow process works.
How much Electricity is produced by Photovoltaic Cells?
The amount of the electric energy produced by Photovoltaic cells is in proportion to the power and the angle of the light that comes to the unit area.
- The light that comes with a right angle provides more power generation
- The light that comes from a higher level provides more power generation
Today, the sun cells which have the best conversion rate work with 15-40% efficiency. For example, let's assume that on a PV with a 10cm2 surface area, a light with 10W of power falls. The maximum electric power that this cell can produce would be 3W. This will have electricity and current values such as;
I = 6A
V = 0.5V
I = 1A
V = 3V
Generally, generated PV cells generate a maximum voltage of 0.5V. By connecting these cells as parallel or series, the current and voltage can be changed.
Types of Photovoltaic Solar Cells
There are 4 types of PV cells according to their manufacturing technology.
a.) Single or Mono Crystalline Cells: Monocrystalline cells, which are made of pure silicon surface and a thin structure, are known to have high efficiency. They have two different manufacturing technologies - Si (Silicon) and Gallium Arsenide (GaAS). The PV cells with the highest efficiency today are those made of Gallium Arsenide.
b.) Polycrystalline: Has a crystalline structure. It has a manufacturing technology in the form of a thin-film. Cadmium telluride (CdTe) or Copper indium diselenide (CIS) is used in the structure. Efficiency is not more than 10%.
c.) Amorphous silicon: Has a non-crystalline structure. Rate of efficiency is not very high. It is used in small devices such as calculators and digital dictionaries.
d.) Hybrid Solar Cell: It is one of the newest technologies. Organic and chemical substances are used together in its structure. Even though it has quite a high rate of energy efficiency, it is not yet in the industrial manufacturing phase.
Photovoltaic Solar Cells Efficiency Comparison
- Monocrystalline Cells (Silicon) : 15 – 20%
- Monocrystalline Cells (Gallium Arsenide) : 20 – 35%
- Polycrystalline : 10%
- Amorphous: 7 – 10%
- Hybrid: 30 – 45%
When it comes to manufacturing technology the most expensive one is Hybrid and the cheapest is Amorphous PV cells.
Photovoltaic Solar Cells and New Technology
We mentioned it briefly above. PV cells generate electricity by absorbing only the red light and that is why the efficiency has always been at low levels. Recently, during the studies which have been carried out at Cambridge University, electricity was generated by absorbing blue wavelengths along with red light.
In the near future, we will see Solar Power Pv cells that have 25% more efficiency on the market.
Question: A PV Cell generates 0.5V and 0.1A. How many PV cells should be used in order to generate a solar panel which has 20V and 1A output?
Answer: V = 20/0.5 = 40 units, I = 1/0.1 = 10 units 40x10 = 400 units of PV cells should be used.
Question: How much power does a monocrystalline gallium arsenide PV cell that works with an efficiency of 25% and has 1cm2 surface area generate, under 800W/m2 sunlight?
Answer: 1m2 = 10.000cm2. 800/10.000 = 0.08W. Since the PV cell works with an efficiency of 25%, it generates 0.08x0.25 = 0.02W or 20mW of power.
Frequently Asked Questions (FAQ)
Question: What are photovoltaic cells made of?
Answer: The basic ingredients are semiconductor chemicals such as Silicon, Gallium arsenide, Cadmium telluride and Copper indium diselenide.
Question: In the simplest terms, what do PV cells do?
Answer: Convert solar energy to electrical energy
Question: What are the most known PV cell producers in the world?
Answer: Recently, lots of firms stated to produce goods relating to renewable energy. Some of the better known and the most popular PV cell producers are: Kyocera, Canadian Solar, Yingli Solar, Sharp, Astronergy, Samsung, Schott Poly, Trina, SolarWorld, BP, Panasonic, Solartech, Ameresco Solar, LDK Solar, and Sanyo.
Question: Which firms are the best PV cell producers of the world?
Answer: BP, Kyocera, Sharp and Samsung produce high quality PV cells.
Question: What is the basic technology used in PV cells?
Answer: Semiconductor technology. The semiconductor technology is used in converting light to electricity since it has a photosensitive structure.
Question: What is the best solar cell material?
Answer: The best material used in PV Cells with the highest efficiency rate is gallium arsenide.
Question: How can I use solar PV cells at home?
Answer: Since the solar cells have a very tiny structure, they can only be converted into a panel when combined appropriately on a solid base. You can use these panels that are formed with many PV cells coming together, on areas such as a roof or garden.
Question: How do we make a solar cell from a transistor?
Answer: As we explained above, PV cells are made of semiconductor materials. Similarly, transistors are units also made of semiconductor materials with a package on them. The most suitable transistors to make PV cells are those with TO-3 package whose packages are easily removed and that have high current values.
For example: 2N 3055, 2N 3773, 2N 6284, BUX 348. In order to make PV cells out of transistors it is necessary to first know their edges. You can reach the datasheet by searching the transistor model which has Base, Collector and Emitter edges. The generation of electricity occurs between the B-C and B-E edges of the transistor. You can see a picture of a 2N3055 model with an open package and visible silicon surface below.
After you open the package, by directing the silicon surface to light, you will then have a homemade PV cell and you can start generating electricity.
Question: How to buy PV Cells?
Answer: You can buy PV cells as modules, in other words as solar panels from the internet. Some hobby websites sell these cells in segments which you can then combine together.
Question: How can I use Photovoltaic cells with RV (recreational vehicle) and Marine?
Answer: Choose combined solar panels to use PV cells with RV and Marine. You can choose the most suitable model, power and size for your requirements. Also, you may choose the thin film PV cells in order for them to look better aesthetically.