Sub: Renewable Energy Power Plants
Solar PV System::
Solar cell is a device or a structure that converts the solar energy i.e. the energy obtained from the sun, directly into the electrical energy. The basic principle behind the function of solar cell is based on photovoltaic effect.
Solar cell is also termed as photo galvanic cell. The electricity supplied by the solar cell is DC electricity / current which is same like provided by batteries but a little bit different in the sense the battery is providing constant voltage.
Another way of defining the solar cell it is a solid state electrical device that converts energy of light directly into electricity by Photoelectric Effect.
Construction of Solar Cell
Mainly Solar cell is constructed using the crystalline Silicon that consists of a n-type semiconductor. This is the first or upper layer also known as emitter layer. The second layer is p-type semiconductor layer known as base layer. Both the layers are sandwiched and hence there is formation of p-n junction between them. The surface is coated with anti-reflection coating to avoid the loss of incident light energy due to reflection.
construction of solar cell
Working of Solar Cell
As soon as the solar cell is exposed to sunlight, the solar energy which is present in the form of light photons is absorbed by semi conductor materials. Due to this absorbed energy, the phenomena of photovoltaic occurs and electrons are liberated and produce the external DC current. The DC current is converted into 240-volt AC current using an inverter for different applications.
Photovoltaic cells are made of special materials called semiconductors such as silicon. An atom of silicon has 14 electrons, arranged in three different shells. The outer shell has 4 electrons. Therefore a silicon atom will always look for ways to fill up its last shell, and to do this, it will share electrons with four nearby atoms.
Now we use phosphorus (with 5 electrons in its outer shell). Therefore when it combines with silicon, one electron remains free. When energy is added to pure silicon it can cause few electrons to break free of their bonds and leave their atoms. These are called free carriers, which move randomly around the crystalline lattice looking for holes to fall into and carrying an electrical current.
However, they are very few and are not very useful. But impure silicon with phosphorous atoms takes a lot less energy to knock loose of “extra“ electrons because they are not tied up in a bond with any neighboring atoms. As a result, we have a lot more free carriers than we would have in pure silicon to become N-type silicon.
How Current Flows in Solar Cell
The other part of a solar cell is doped with the element boron (with 3 electrons in its outer shell) to become P-type silicon. Now, when this two type of silicon interact, an electric field forms at the junction which prevents more electrons to move to P-side. When photon hits solar cell, its solar energy breaks apart electron-hole pairs. Each photon with enough energy will normally free exactly one electron, resulting in a free hole as well. If this happens close enough to the electric field, this causes disruption of electrical neutrality, and if we provide an external current path, electrons will flow through the P side to unite with holes that the electric field sent there, doing work for us along the way. This electron flow provides the current.
Electron Hole Formation
As we know that photon is a flux of light particles and photovoltaic energy conversion relies on the number of photons striking the earth. On a clear day, about 4.4 x 1017 photons strike a square centimeter of the Earth’s surface every second. Only some of these photons that are having energy in excess of the band gap are convertible to electricity by the solar cell. When such photon enters the semiconductor, it may be absorbed and promote an electron from the valence band to the conduction band, that creates a hole in the valence band. After that the electron in the conduction band and hole in valence band combine together and forms electron-hole pairs.
Thus when we connect these p and n layers to external circuit, electrons flow from n-layer to p-layer, hence current is generated. The electrons that leave the solar cell as current give up their energy to whatever is connected to the solar cell, and then re-enter the solar cell. Once back in the solar cell, the process begins again to produce more solar energy.
Types of Solar cell & Efficiency Levels
Depending upon the crystalline structure there are three types of solar cells:
Mono crystalline silicon cells
Polycrystalline silicon cells
Amorphous silicon cells
The Mono crystalline silicon cell is produced from pure silicon (single crystal). Since the Mono crystalline silicon is pure and defect free, the efficiency of cell is higher. Efficiency of this type of solar cell is 14-17 %.
Polycrystalline solar cells use liquid silicon as raw material. Since the polycrystalline silicon involves solidification process the materials contain various crystalline sizes. Hence, the efficiency of this type of cell is less than Mono crystalline solar cell. Efficiency of this type of solar cell is 13-15 %.
Amorphous silicon cells are developed by depositing silicon film on the substrate like glass plate. The thickness of the layer is less than 1µm. Efficiency of this type of solar cells is 5-7 %.
Technology wise there are three types of solar cell technology:
Discrete Cell technology,
Integrated Thin Film technology and
Multi crystalline Silicon technology.
Solar panel (or) solar array (or) Solar module
The solar panel (or) solar array is the interconnection of number of solar module to get efficient power. A solar module consists of number of interconnected solar cells. These interconnected cells embedded between two glass plate to protect from the bad whether. Since absorption area of module is high, more energy can be produced.
Solar Cell Advantages
Solar energy is clean and non-polluting.
This is best renewable energy
Solar cells do not produce noise
Solar cell needs little maintenance
Highly reliable and long lasting
Operation costs are minimal
Solar panel cost is now reducing
Q.Describe solar PV system
Ans: Solar PV System.
A solar PV (photovoltaic) system converts sunlight directly into electricity using solar panels. Here's a quick breakdown of the components and how it works:
Key Components:
1. Solar Panels (PV Modules)
Made up of solar cells (usually silicon-based) that capture sunlight and generate DC electricity.
2. Inverter
Converts DC (direct current) from the panels into AC (alternating current), which is used by most household appliances.
3. Mounting Structure
Supports the panels on rooftops, the ground, or poles at the optimal angle and orientation.
4. Battery (optional)
Stores excess electricity for use at night or during power outages (used in off-grid or hybrid systems).
5. Charge Controller (optional)
Protects batteries from overcharging or deep discharging.
Regulates voltage and current from the panels to the batteries.
6. Metering and Monitoring
Measures electricity production and consumption, often integrated into smart systems.
7.Electrical Panel (Breaker Box)
Distributes electricity to home circuits.
___________________________
Q. Classify solar PV system
Ans: Types of Solar PV Systems:
1. Grid-Tied
Connected to the utility grid; excess power can be fed back (net metering).
Sends excess electricity back to the grid or draws from it when needed.
2. Off-Grid
Completely independent from the grid; relies on batteries for backup.
3. Hybrid
Combines both grid and battery backup.
Diagram:
Grid tied:
SUNLIGHT
↓
+---------------+
| Solar Panels |
+---------------+
↓ (DC electricity)
+------------------+
| Inverter | <-- Converts DC to AC
+------------------+
↓
+------------------+ +----------------+
| Main Breaker |<------>| Utility Grid |
+------------------+ +----------------+
↓
+------------------+
| Appliances |
+------------------+
(Optional Battery Storage can be connected between Solar Panels and Inverter)
_________________________________
Q Describe PV panels.
Ans: PV Panels (Photovoltaic Panels) are the core of a solar power system.
Devices that convert sunlight directly into electricity using the photovoltaic effect known as PV panels.
Key Components of a PV Panel:
1. Solar Cells (usually silicon-based)
2. Glass Cover – Protects the cells from weather.
3. Encapsulant – Holds the layers together.
4. Backsheet – Provides insulation and protection.
5. Aluminum Frame – Gives structure and allows mounting.
6. Junction Box – Where electrical connections are made.
Output:
Produces DC electricity (direct current).
Typical residential panels produce 250W to 450W each under full sun.
______________________________
Q What is Solar PV cell?
Ans:Solar PV cell: A Solar PV Cell (Photovoltaic Cell) is the basic building block of a solar panel. Here's a clear breakdown:
Solar PV Cell:
A semiconductor device that converts sunlight directly into electricity using the photovoltaic effect.
Structure of a PV Cell:
1. Front Contact – Transparent and conductive layer to allow light in and carry electrons out.
2. Anti-Reflective Coating – Increases light absorption.
3. N-type Semiconductor Layer – Usually silicon doped with phosphorus (has extra electrons).
4. P-type Semiconductor Layer – Silicon doped with boron (has "holes" or missing electrons).
5. PN Junction – The interface where light energy creates a flow of electrons.
6. Back Contact – Conductive layer that closes the circuit.
How It Works (Photovoltaic Effect):
1. Sunlight hits the cell, exciting electrons.
2. Electrons move from the P-type to the N-type layer, creating electric current.
3. Wires carry this DC electricity to the next component (like an inverter).
______________________________
Q.Explain the photovoltaic effect of solar cell.
Ans:The photovoltaic effect (also called the photoelectric effect in this context) is the fundamental principle behind how solar cells convert sunlight into electricity.
Photovoltaic Effect:
It’s the process by which a solar cell converts sunlight (photons) into electrical energy (electrons).
Step-by-Step Process:
1. Sunlight Hits the Cell
Photons (light particles) strike the solar cell surface.
2. Energy Absorption
The energy from photons is absorbed by semiconductor materials (typically silicon).
3. Electron Excitation
This energy excites electrons, knocking them loose from their atoms in the semiconductor.
4. Electric Field Creates Flow
An internal electric field at the PN junction (between p-type and n-type silicon layers) pushes electrons in a specific direction, creating a flow of electric current.
5. Current Collection
Metal contacts collect these moving electrons and send them through an external circuit, powering electrical devices.
Result:
Direct Current (DC) electricity is generated, which can be used directly, stored in batteries, or converted to AC (Alternating Current) via an inverter.
______________________________
Q Describe the rating of solar cell.
Ans: Rating of solar cell:
Rating of a standard solar cell:
The rating of a solar PV cell refers to how much power it can produce under standard conditions. Here's what you need to know:
Typical Rating of a Single PV Cell:
Voltage (V): ~0.5 to 0.6 volts (V)
Current (I): ~2 to 4 amps (depending on cell size and light intensity)
Power (P = V × I):
A standard PV cell produces around 1 to 2 watts of power under Standard Test Conditions (STC).
Standard Test Conditions (STC):
Irradiance: 1000 W/m²
Cell temperature: 25°C
Air Mass (AM): 1.5
From Cell to Panel:
Because one cell only produces ~0.5V, many cells are connected in series to form a solar panel.
For example:
A 60-cell panel = ~30–36V output, and 250–370W total power.
__________________________
Q.Classify the solar panels:
Ans:Various type of solar panels are classified as described-
1. Monocrystalline Solar Panels (Mono-Si)
Appearance: Uniform black or dark color, rounded edges.
Efficiency: 18–24%
Pros:
Highest efficiency
Long lifespan (25–30 years)
Space-efficient
Cons:
More expensive
Best for: Residential rooftops with limited space
2. Polycrystalline Solar Panels (Poly-Si)
Appearance: Bluish color with grainy, crystal-like pattern
Efficiency: 15–18%
Pros:
Lower cost
Good performance in sunlight
Cons:
Slightly lower efficiency than mono
Best for: Budget-friendly systems with ample space
3. Thin-Film Solar Panels
Types: a-Si (Amorphous Silicon), CdTe, CIGS
Appearance: Uniform, often dark and flexible
Efficiency: 6–16% (varies by type)
Pros:
Lightweight and flexible
Easy to install
Cons:
Lower efficiency
Shorter lifespan
Best for: Large commercial roofs, low-load structures, specialty uses (like portable panels)
4. Passivated Emitter and Rear Contact (PERC) Panels
Variation of mono or poly panels with better rear surface treatment
Efficiency: 19–22%
Pros:
Improved low-light performance
Best for: Residential and commercial systems aiming for high output.
___________End of Note________________
MCQ:
PV cell is also called?
a) IR cell
b) VU cell
c) Solar cell
d) All of the above
2. PV effect in solar cell converts solar energy into _____?
a) Electric energy
b) Mechanical energy
c) Chemical energy
d) All of the above
3. Which of the following parameters are the electrical characteristics of a solar cell?
a) Voltage
b) Current
c) Resistance
d) All of the above
4. Which of the following is the amount of voltage a single solar cell generates?
a) 0.5V to 0.6V
b) 0.7V to 0.8V
c) 0.9V to 1V
d) 1V to 1.1V
5. How many layers does a solar cell have?
a) 2
b) 3
c) 4
d) 5
6. Which of the following are the components of a solar cell?
a) Nickle plating
b) PN Silicon
c) Anti-reflecting coating
d) All of the above
7. A solar cell is a _____ type of energy source.
a) Non-renewable
b) Renewable
c) Decomposable
d) All of the above
8. A solar cell has a lifespan of _____ years.
a) 10
b) 20
c) 30
d) 40
9. A solar cell is a ______.
a) Zenor diode
b) PV cell
c) PN diode
d) Both b and c
10. Which layer of PV cell is thicker?
a) depletion
b)P
c)N
d)None
11. The light energy supplied to solar cell is in the form of_____.
a) Electrons
b) Photons
c) Neutrons
d) None
12. The solar incident light on the cell breaks ______ condition of the diode’s junction
a) Thermal expansion
b) Breakdown
c) Thermal equilibrium
d) None of the above
13. The optical absorption of material used in solar cell must be?
a) Zero
b) Low
c) High
d) Infinite
14. The manufacturing process of a solar cell is same as manufacturing process of ________.
a) Electronic devices
b) Memory chips
c) Electrostatic devices
d) None of the above
15. The majority charge carriers in P-type semiconductor are______.
a) Electrons
b) Neutrons
c) Holes
d) None of the above
16. The majority charge carriers in N-type semiconductor are______.
a) Electrons
b) Neutrons
c) Holes
d) None of the above
17. In a PV cell, the band gap indicates?
a) Material area occupied
b) Material light absorption
c) Size of the cell
d) None of the above
18. Organic based solar cells are designed using ______ rich components.
a) Oxygen
b) Nitrogen
c) Carbon
d) Helium
19. Which of the following functions can be enhanced by using an organic PV cell?
a) Transparency
b) Color
c) Bandgap
d) All of the above
20. Which of the following types of solar cell uses lens for charging?
a) Multi-junction PV
b) Quantum Dots
c) Organic PV
d) Concentrating PV
21. Which of the following materials cannot be used as solar cell materials?
a) Silicon (Si)
b) Gallium Arsenide (GaAs)
c) Cadmium Sulfide (CdS)
d) Lead (II) Sulfide (PbS)
22. The principle of solar cell is same as photodiode.
a) True
b) Falseh
23. What should be the band gap of the semiconductors to be used as solar materials?
a) 0.5 eV
b) 1.0 eV
c) 1.5 eV
d) 1.9 eV
24. Which of the following should not be the characteristic of the solar cell material?
a) High energy band
b) High absorption
c) High conductivity
d) High availability
25. Which region of the following solar cell is coated with metal?
a) A
b) B
c) C
d) D
26. During the collection of electron-hole pairs, holes are collected by_______.
a) Back contact
b) Front contact
c) Finger electrodes
d) Si-wafer
27. What is the difference between solar cell and photodiode?
a) No external bias in solar cell
b) No external bias in photodiode
c) Larger surface area in photodiode
d) No difference
28. Solar cell is made from bulk materials that is cut into wafer of _________ thickness.
a) 120-180µm
b) 120-220µm
c) 180-220µm
d) 180-240µm
29. __________ is one of the most important materials which is also known as solar grade silicon.
a) Crystalline silicon
b) Crushed silicon
c) Silicon
d) Powdered silicon
30. Dye-sensitized solar cells are made from ______ organic dye.
a) Aniline
b) Safranine
c) Ruthium melallo
d) Induline
31. Quantum dot solar cells are based on _______.
a) Gratzel cell
b) Voltaic cell
c) Solar cell
d) Galvanic cell
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