Solar Cells and Solar panels definitions, types, and fabrication

 Solar cells and solar panels

A solar cell is the basic part used in a solar power system, where the photovoltaic panels (PV) produce electricity. The system also includes supporting equipment like Maximum Power Point Tracking (MPPT) and energy storage elements like batteries and supercapacitors working with PVs to utilize and optimize the system to get the maximum designed power from the system at the same time handle any conditions that may affect and decrease the system output power like shading and dust accumulated on panels surface.

 

Solar panels produce electrical energy

  

What is the photovoltaic?

The photo voltaic effect is the technology used to generate current when the solar cell is exposed to sunlight. The photovoltaic effect is a physical phenomenon of current generation in the semiconductor materials when the photons in sunlight hit the semiconductor materials. The semiconductor material is the best choice because it has a narrow energy band-gab in its atomic construction which enables free electrons by visible light.

 

What is the solar cell?

Solar Cells

The solar cell is an electronic device made from semiconductor elements. it is used in the solar power system and it is used to generate electricity from solar energy through a photovoltaic effect (PV). A group of solar cells are collected together in one module to increase the generated power. for a solar panel, the basic technology used for solar cells is the photovoltaic effect.

 

How does the solar cell work?

semiconductor materials are materials in between metals and insulators where the valance and conduction gabs are interfered in metals while in insulators, this gap is very wide and the electrons cannot jump from valance to conduction.

In semiconductors, the gap between valance and conduction is narrow so the exited electron by sunlight in the valance band can jump easily and cross the gap to the conduction band and be free electrons. 

The doping process is used to increase the free electrons (negative charges) and free holes (positive charges) to control the electrical and optical properties. As The doping is to create the P-N junction. The negative charges from the N-type combine with the positive charges from the P-type by diffusion at the meet point.

At the point of meet of P and N an electric field is built up. As the combination between free electrons and free holes increases, the electric field increases till reaches the state that prevents the combination of negative and positive charges by diffusion.

 When light hits the silicon cell and frees electrons from silicon atoms, these electrons which represent the electric current have no way to pass through the P-N junction and they pass through the cell contact ribbons.

What are the advantages of silicon semiconductor material in solar cell fabrication?

Silicon is the most semi-conductor material element used in solar cell fabrication compared to other elements like germanium or selenium, it has many advantages over other semiconductors:

• It has wide availability on earth as a silica sand form which is composed of 95% silicon dioxide.
• It has a band gap of 1.1 electron volt gap-width (ev) which is close to the optimal energy gap of (1.34ev) for power generation from sunlight.
• It is cheap and easily available
• Silicon is not a toxic element.

What are the solar cell types?

• Monocrystalline solar cells where a mono-crystalline wafer is used in solar cells. It uses a single silicon crystal to form the ingot with a cylinder shape. The ingot is cut into a silicon wafer and trimmed into an octagonal form.
• Polycrystalline solar cells where a small particle of monocrystalline is used to produce polycrystalline wafer from the ingot. The shape of the Polycrystalline ingot is cubical shape.    
• Silicon ribbons were a thin layer to produce a durable and flexible solar cell.

What are the basic stages of solar cell fabrication?

The solar cell is a very sensitive product that is produced in a special sequence starting from the collecting of sand through a purification process till ending with the assembly and packing

1. purifying the silicon by changing the sand form to a pure silicon where a high-purity silicon. The high silicon purity, and the high efficiency of the solar cell. The impurity level for silicon is determined by the number of nines where 5N % represents 99.999%. the more nines is higher the purity level.
2. Ingot formation which is pure silicon raw material used to produce solar cells. The shape of the ingot depends on the type of solar cell produced.
3. Wafer formation is where the ingot is cut into a solar cell with the required shape.
4. Doping process where impurities are injected into the intrinsic semiconductor to control the conductivity of the semiconductor by forming the P-N junction.
5. Forming of cell contacts to harvest the generated electrons.
6. Applying an anti-reflection coating increases the absorbed light and prevents any reflected light or decreases the generated current.
7. assembly and packing of the solar cell.

What is the solar module?

The Solar module is a PV module that combines a group of solar cells connecting together to drive electrical power according to the panel design and no of cells. The available standard in the local market standard no of cells are 36, 72, and 144 per module. It could reach more cells in some panels but it is not common.

What is the solar cell or solar panel efficiency?

The efficiency of the solar panel or solar cell is the ratio between the output electrical power and the total solar power exposed to the solar cell or solar panel. The developers are working on improving the solar cell efficiency to get more benefits by increasing the efficiency. 

The max value reached in solar panel efficiency is 39.46. benefits of increasing the efficiency could be represented in increasing the power generated from the solar panel, decreasing the area needed for installing the PV panels, and finally decreasing the initial cost, especially for the mega projects that need to generate large amounts of power to be generated from solar panels.

What are the parameters of the solar module?

The parameters for the PV module are defined at the Standard test condition which is at 25  Celsius degree temperature and 1000 watts per square meter irradiance.

• Module maximum power.
• Short circuit current.
• Open circuit voltage.
• Current at the maximum power point.
• The voltage at the maximum power point.
• efficiency.

What is the MPPT?

The Maximum Power Point Tracking is an electronic device that keeps the solar panel at its maximum value at any time. It is used also to control the charging of the storage system and control the power delivered to the load at the same time.

What are the Storage systems?

These are elements or systems like batteries and supercapacitors used to store energy generated from solar panels and used at times where no sunlight during the night or bad weather of shading or high dust.