Types of Windmills

There are two types of windmills based on their axis of rotation, and they are:
 Vertical axis windmills
 Horizontal axis windmills
Vertical axis windmill: In these types of windmills, the main rotor shaft is placed transverse to the
wind. While the main components are located at the base of the turbine.
Horizontal axis windmill: In these types of windmills, turbines have the electrical generator and main
rotor shaft placed at the top of a tower pointing to the wind.
Working of Windmill
The windmill features vanes known as sails or blades and also has a powerful engine. A windmill is a
device that converts the kinetic energy of the wind into mechanical energy. The wind energy is
converted into rotational energy. The working of the windmill is explained in the figure below.

When the high-speed wind blows over the windmill, the blades or sails are turned. The blades move
such that the shaft starts to spin, resulting in the production of electricity. Blades control the functioning
of rotor speed. The generator converts the mechanical energy into electrical energy. The blades always
rotate in a clockwise direction. After lots of research and trials, it was found that a windmill with three
blades was more efficient.

Hydro Power Plant Definition:

Hydro Power Plant is an electricity-producing plant in which the water is an essential fuel, the potential
energy is being converted into kinetic energy and kinetic energy is further converted into mechanical
and into electrical energy with the help of a turbine and motor.
We will understand how it works in very detail. So now let’s study construction.
Hydro Power Plant Layout or Construction:
The following Construction or Layout of Hydro Power Plant:
1. Headpond or Reservoir
2. Control gate
3. Penstock
4. Turbine
5. Draft Tube
6. Tail Race
7. Transmission Line
8. Generator
9. Transformer
10. Power House
Headpond:
There is one reservoir which is having a large area in which A huge amount of water is being stored
here. So the energy here is in the form of Potential energy.
We Know Potential Energy is mgh [Mass*Gravitational force* Height]
Control Gate:
There are having multiple control gates in a single hydro power plant. The work of control gate is to
regulate the flow of water. When the control gate is fully opened the speed of water flowing is
maximum.
Penstock:
The penstock is also called Pipe. The water stored at the dam or head pond is being released by the
control gate, the water starts moving to the turbine. The Head pond is having high heights and the
Turbine is situated below.
So the speed of water gets increased because of gravitational force. The material of the penstock is hard
steel being used.
Valve and Nozzle:
The valve work is similar to the control gate and Nozzle work is striking water in a specific direction
[Pressure is high] that is a turbine blade.
Surge tank:
Surge tank is an additional and essential component which is used to accumulate the water which is in
pipe when we want to close the turbine working. Or you can say it is used for avoiding the pipe burst.
Turbine:
Turbine is a device which is used for generation of electricity. Turbine work is, the fluid having kinetic
energy is being converted into rotational energy.
The high kinetic energy water comes through the penstock to the nozzle and strikes the turbine blades.
The turbine blades start rotating. So the rotational energy can also be called mechanical energy.
Draft Tube:
Drat tube is mechanical component which is used for enlarging the area of pipe for sending maximum
fluid to the other side.
Tail Race:
Tailrace carries water away from the plant. Hence the water is sent to the river.
Transmission Line:
The transmission line carries power from the power unit or transformer and transfers or supplies from
one source to another. It is made up of conductor.
Generator:
When the turbine buckets starts rotating, the turbine shafts also rotating. the motors are attached to the
turbine shafts which is also rotating and generator is attached to them which generates electricity.
Transformer:
The transformer is attached to the generator. The electricity genearted is now controlled by the
transformr. The work of transformer is to set up or set down the voltage.
Power House:
The name power house means there is a house in which the power is being stored ]and released to the
transformer and so on.
Hydro Power Plant Working:
In a large amount of water is available or you can say a river. The water is being stored in the reservoir
which is in the form of potential energy. With the use of the control gate, the water is being released
and water starts flowing into the penstock. Here two components are attached 1. Surge tank, Valve, and
Nozzle.

[Potential Energy to Kinetic Energy to Mechanical Energy to Electrical Energy]

Initially, the valve is closed. But when the water reaches up to the max level that can create high pressure
then we on the valves. The water with high pressure starts flowing and strikes to the turbine blades
through the nozzle.
The turbine blades start rotating. So till now, we observed the water which is having PE is now
converting into KE.
In the turbine blade, an electric motor is attached to the turbine shafts. So rotation of turbine blades also
rotates the turbine shafts, which also rotates the electric motor. Hence Kinematic energy into mechanical
energy and then further it is converted into electric energy.
The energy generated is sent to the powerhouse, Transformer, and Transmission line.
The water which is rotating the turbine blades is now sent to the river via a tailrace.
The hydropower plant is constructed to store the water in a large amount. When the water reaches up
to the max level then it is being released which also causes the flood in some area (due to sudden release
of water).
The following advantages of Hydro Power plant are:
 Hydro-generation has a unique and significant role to play particularly in the operation of
interconnected power systems.
 The operating cost of the hydroelectric plant including auxiliaries is considerably low when
compared with thermal plants. The annual operating and maintenance cost of a thermal plant is
approximately 5- 6 times that of a hydro plant of equal capacity.
 These are simple in design easy to maintain, pollution-free with zero fuelling cost.
 The cost of power generation is less.
 The life expectancy of a hydroelectric power plant is more. The useful life of a thermal plant is
20-25 years as against 100-125 years for the hydro plants.
 There is no problem with handling the fuel and ash and no nuisance of smoke exhaust gases
and spots and no health hazards due to air pollution.
 The fuel needed for the thermal plant has to be purchased, whereas in Hydro-plant the fuel cost
is totally absent.
 Hydroelectric plants are quick to respond to the change of load compared with thermal Power
Plant or nuclear plants.
 The rapidly fluctuating loads are served most economically by Hydro-plant.
 The machines used in hydel plants are more robust and generally run at low speeds at 300-400
RPM, whereas the machines used in thermal plants run at a speed of 3000- 4,000 RPM.
 The efficiency of the hydro plants does not change with age, but there is a considerable
reduction in the Efficiency of thermal as well as a nuclear power plant with age.
 In a hydroelectric plant, there are no standby losses, whereas these are unavoidable for thermal
plants and the number of operations required is considerably small compared with the thermal
power plant.
 It does not contribute to air and water pollution to the greenhouse effect
 Usually, the hydro station is situated away from the developed area therefore the cost of land is
not a major problem.

The following disadvantages of Hydro Power plant are:

 The capital cost (cost per kilowatt capacity) installed) of the hydro plant is considerably more
than the thermal plant.
 It takes a considerable long time for its erection compared with thermal plants.
 Power generation by the hydro plant is only dependent on the quantity of water available which
in turn depends on the natural phenomenon of rain. The dry year is more serious for the
hydroelectric project.
 The site of Hydroelectric station is selected on the criterion of water availability at economical
head such sites are usually away from the load center.
 The transmission of power from the power station to the load center requires along transmission
lines. Therefore investment required for long transmission lines and loss of power during
transmission is an unfavorable factor for the economical selection of hydro plants.
Solar Cell: Working Principle & Construction

 Solar Cell Definition: A solar cell (also known as a photovoltaic cell) is an electrical device that
transforms light energy directly into electrical energy using the photovoltaic effect.
 Working Principle: The working of solar cells involves light photons creating electron-hole pairs
at the p-n junction, generating a voltage capable of driving a current across a connected load.
 Construction Details: Solar cells consist of a thin p-type semiconductor layer atop a thicker n-
type layer, with electrodes that allow light penetration and energy capture.
 Material Characteristics: Essential materials for solar cells must have a band gap close to 1.5 ev,
high optical absorption, and electrical conductivity, with silicon being the most commonly used.
 Practical Uses: Solar cells power devices from small calculators and wristwatches to large-scale
applications in spacecraft, highlighting their versatility and growing importance in renewable
energy systems.

What is a Solar Cell?

A solar cell (also known as a photovoltaic cell or PV cell) is defined as an electrical device that converts
light energy into electrical energy through the photovoltaic effect. A solar cell is basically a p-n junction
diode. Solar cells are a form of photoelectric cell, defined as a device whose electrical characteristics –
such as current, voltage, or resistance – vary when exposed to light.
Individual solar cells can be combined to form modules commonly known as solar panels. The common
single junction silicon solar cell can produce a maximum open-circuit voltage of approximately 0.5 to
0.6 volts. By itself this isn’t much – but remember these solar cells are tiny. When combined into a
large solar panel, considerable amounts of renewable energy can be generated.

Construction of Solar Cell

A solar cell functions similarly to a junction diode, but its construction differs slightly from typical p-n
junction diodes. A very thin layer of p-type semiconductor is grown on a relatively thicker n-type
semiconductor. We then apply a few finer electrodes on the top of the p-type semiconductor layer.
These electrodes do not obstruct light to reach the thin p-type layer. Just below the p-type layer there is
a p-n junction. We also provide a current collecting electrode at the bottom of the n-type layer. We
encapsulate the entire assembly by thin glass to protect the solar cell from any mechanical shock.

Working Principle of Solar Cell

When light photons reach the p-n junction through the thin p-type layer, they supply enough energy to
create multiple electron-hole pairs, initiating the conversion process. The incident light breaks the
thermal equilibrium condition of the junction. The free electrons in the depletion region can quickly
come to the n-type side of the junction.
Similarly, the holes in the depletion can quickly come to the p-type side of the junction. Once, the newly
created free electrons come to the n-type side, cannot further cross the junction because of barrier
potential of the junction.
Once the newly created holes reach the p-type side, they cannot cross back over the junction due to the
barrier potential. This separation of electrons and holes across the p-n junction allows it to function like
a small battery cell.
A voltage is set up which is known as photo voltage. If we connect a small load across the junction,
there will be a tiny current flowing through it.

V-I Characteristics of a Photovoltaic Cell

Materials Used in Solar Cell

Materials used in solar cells must possess a band gap close to 1.5 ev to optimize light absorption and
electrical efficiency. Commonly used materials are-
1. Silicon.
2. GaAs.
3. CdTe.
4. CuInSe2
Criteria for Materials to be Used in Solar Cell
1. Must have band gap from 1ev to 1.8ev.
2. It must have high optical absorption.
3. It must have high electrical conductivity.
4. The raw material must be available in abundance and the cost of the material must be low.
Advantages of Solar Cell
1. No pollution associated with it.
2. It must last for a long time.
3. No maintenance cost.
Disadvantages of Solar Cell
1. It has high cost of installation.
2. It has low efficiency.
3. During cloudy day, the energy cannot be produced and also at night we will not get solar energy.
Uses of Solar Generation Systems
1. It may be used to charge batteries.
2. Used in light meters.
3. It is used to power calculators and wrist watches.
4. It can be used in spacecraft to provide electrical energy.
Conclusion: Though solar cell has some disadvantage associated it, but the disadvantages are expected
to overcome as the technology advances, since the technology is advancing, the cost of solar plates, as
well as the installation cost, will decrease down so that everybody can effort to install the system.
Furthermore, the government is laying much emphasis on the solar energy so after some years we may
expect that every household and also every electrical system is powered by solar or the renewable
energy source.

Solar cells have many advantages, including:

 Renewable
Solar energy is a renewable energy source, meaning it's not used up and there's always more
available as long as the sun exists.
 Clean
Solar cells are a clean energy source that doesn't produce carbon emissions or other
greenhouse gases.
 Low maintenance
Solar cells have no moving parts, so they require little maintenance and owners usually only
need to clean them a couple of times a year.
 Applicable everywhere
Solar energy can be used anywhere there's sunshine, making it useful in remote areas without
access to other electricity sources.
 Reduces electricity bills
Solar energy can help reduce electricity bills by meeting some of your energy needs.
 Free energy
Solar radiation is free, so the only costs are for maintenance and equipment.
 Good for the environment
Solar cells don't contribute to climate change and avoid the environmental damage of mining
and drilling for fossil fuels.
 Good for areas with limited water resources
Solar cells don't require water or fuel to generate electricity