ICT role in 21st century education and it's challenges.
Unit 2
1. Unit-II
Solar and Wind Energy System
BY
R.ARULJOTHI
M.Tech( 2nd YEAR)
15EE302
Under the guidance of
DR. N.P. SUBRAMANIAM, M.E.,Ph.D.,
ASSISTANT PROFESSOR
DEPARTMENT OF ELECTRICALAND ELECTRONICS
ENGINEERING
PONDICHERRY ENGINEERING COLLEGE
2. SOLAR CELL
• A Solar cell is a solid state electrical device that converts energy of
light directly into electricity by Photoelectric Effect.
• A Solar cell is also known as Photovoltaic Cell or Photoelectric Cell.
• Solar cell is a semiconductor device which is nothing but a P-N
junction diode and can converts sun lights into electrical energy.
• Solar PV module when in touch of sunlight generates voltage and
current at its output terminals.
• In recent trends, this technology is highly effective because of less
maintenance and continuous availability of solar energy in the most
cleanest form.
3. SOLAR PHOTOVOLTAIC SYSTEMS
• A photovoltaic system, also photovoltaic power system, solar PV system, PV
system or casually solar array, is a power system designed to supply usable solar
power by means of photovoltaics.
• It consists of an arrangement of several components, including solar panels to
absorb and convert sunlight into electricity, a solar inverter to change the electric
current from DC to AC, as well as mounting, cabling and other electrical
accessories to set up a working system.
• PV systems range from small, rooftop-mounted or building-integrated systems with
capacities from a few to several tens of kilowatts, to large utility-scale power
stations of hundreds of megawatts.
• Nowadays, most PV systems are grid-connected, while off-grid or stand-alone
systems only account for a small portion of the market.
• Operating silently and without any moving parts or environmental emissions.
• Photovoltaics (PV) is a method of converting solar energy into direct current
electricity using semiconducting materials that exhibit the photovoltaic effect.
A photovoltaic system employs solar panels composed of a number of solar cells to
supply usable solar power.
5. Types of Solar cell
• Based on the types of crystal used, soar cells can be classified as,
1. Monocrystalline silicon cells
2. Polycrystalline silicon cells
3. Amorphous silicon cells
The Monocrystalline silicon cell is produced from pure silicon (single crystal).Since
the Monocrystalline silicon is pure and defect free, the efficiency of cell will be higher.
In polycrystalline solar cell, liquid silicon is used as raw material and polycrystalline
silicon was obtained followed by solidification process. The materials contain various
crystalline sizes. Hence, the efficiency of this type of cell is less than Monocrystalline
cell.
The Amorphous silicon is obtained by depositing silicon film on the substrate like
glass plate.
• The layer thickness amounts to less than 1µm – the thickness of a human hair
for comparison is 50-100 µm.
6. • The efficiency of amorphous cells is much lower than that of the other two cell
types.
• As a result, they are used mainly in low power equipment, such as watches and
pocket calculators, or as facade elements.
Comparison of Types of solar cell
7. Photovoltaic effect
Light
energy
n-type semiconductor
p- type semiconductor
Electrical
Power
p-n junction
Definition:
The generation of
voltage across the PN
junction in a semiconductor
due to the absorption of light
radiation is called
photovoltaic effect. The
Devices based on this effect
is called photovoltaic device.
8. Basics of solar cells
• If two differently contaminated semiconductor layers are combined, then a
so-called p-n-junction results on the boundary of the layers.
• By doping trivalent element, we get p-type semiconductor. (with excess
amount of hole)
• By doping pentavalent element, we get n-type semiconductor ( with excess
amount of electron).
n-type semiconductor
p- type semiconductor
p-n junction layer
9. Electron Hole Formation
• Photovoltaic energy conversion relies on the number of photons
striking the earth. (photon is a flux of light particles)
• 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 - those with energy in excess of the
band gap - can be converted into 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.
11. HOW IT WORKS..?
• 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 a 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, there are so few, that they aren't very useful. But our impure
silicon with phosphorous atoms takes a lot less energy to knock loose one
of our "extra“ electrons because they aren't tied up in a bond with any
neighboring atoms.
12. • As a result, we have a lot more free carriers than we would have in pure
silicon to become N-type silicon.
• 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 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.
• The electron flow provides the current, and the cell's electric field causes a
voltage.
13. • Now to protect the solar cell, we use antireflective coating to reduce the losses and then a
glass plate to protect the cell from elements.
14. Stand alone PV System
Stand-alone systems are not connected with utility power lines and these are
self sufficient systems.
These systems could either be used to charge the batteries that serve as an
energy storage device or could work directly using the solar energy
available in the daytimes.
These systems consist of the following:
Solar panels mounted on the roof or in open spaces. Photovoltaic
modules produce direct current (DC) electrical power.
Batteries to store DC energy generated by the solar panels.
Charge controller to prevent overcharging the battery.
Inverter to convert electricity produced by the system from DC to
AC power.
15. • The following diagram shows PV system powering AC loads with battery
bank. DC loads can also be connected directly to the battery bank. It is also
possible to power the AC load without battery, but in that case it would be
confined only to daytime when solar radiation is sufficient to generate
required electricity.
16. Determination of PV Array Size
• PV system powering loads: used every day,
• Size of the array = Daily energy requirement
The sun-hours per day
• PV system powering loads: used weekly,
• Weekly energy requirement = Energy requirement*
7days
• The size of the array= Daily energy requirement
The sun-hours per day * 7days
• Area of the PV system,
17. Solar Cell characterisitics
• The above figure shows the I-V characteristics.
• I= Isc-Io {Exp( V/Vt)-1}
• Where Io is the reverse saturation current , Vt is the voltage equivalent of
temperature and at room temperature its value is 26 mV.
• We have Vt=KT/q
• Where K is the boltzmann’s constant, T is the temperature in °K and q is
the charge of an electron.
18. Solar PV Cell: Basic Model
• Solar cell is a device that converts the light energy into electrical energy based on
the principles of photovoltaic effect.
• A typical silicon PV cell is composed of a thin wafer consisting of an ultra-thin
layer of phosphorus-doped (N-type) silicon on top of a thicker layer of boron-doped
(P-type) silicon.
• Current flow caused by light is known as light generated current 𝐼𝐿.
𝑰 𝒕𝒐𝒕𝒂𝒍 = 𝑰 𝟎 𝒆
𝒒𝑽
𝒌𝑻 − 𝟏 − 𝑰 𝑳
Dark condition
Illumination
I
V
19. Solar PV Diode Model
Equivalent circuit of PV cell
Matlab simulation model of PV cell for Isc 1 amp
and Voc 0.55 V, Insolation of 1000 W/𝑚2
I-V curve of PV cell
P-V curve of PV cell
20. Advantages
• Non-polluting: Solar energy is an alternative for fossil fuels as it is
non-polluting, clean and reliable
• Solar energy is a renewable source of energy as it can be used to
produce electricity as long as the sun exists.
Dis-Advantages
• The primary disadvantage of solar power is that it obviously cannot
be created during the night.
• The power generated is also reduced during times of cloud cover
(although energy is still produced on a cloudy day).
Applications
• Solar water heater
• Solar water pump
• Solar furnaces
• Traffic light, Street light and railways signal
• Solar cooker
21. Wind Energy
• Wind turbine technology is the most promising renewable energy
technology. It started in 1980’s with a few tens of kW production of power
per unit. And today multi-MW size wind turbines are being installed.
• Wind power production in the beginning, did not have any impact on the
power control system and was based on the induction generator where the
pulsations in the wind was directly transferred to the grid. There was no
control on active and reactive power which are the important control
parameter to regulate frequency and voltage.
• As the power range of the turbines increases those control parameters
become more important and it is necessary to introduce power electronics
as an interface between the wind turbine and the grid. The power
electronics is changing the basic characteristic of the wind turbine from
being an energy source to be an active power source.
22. Wind Energy Conversion
• Wind energy conversion systems convert wind energy into electrical
energy, which is then fed into electrical grid.
• •The turbine rotor, gear box and generator are the main three
components for energy conversion.
• •Rotor converts wind energy to mechanical energy.
• •Gear box is used to adapt to the rotor speed to generator speed.
• •Generator with the variable speed wind turbine along with electronic
inverter absorbs mechanical power and convert to electrical energy.
• •The power converter can not only transfer the power
23. Modern Power Electronics
The interface of Wind power converter between generator and power grid
should satisfy the requirements on both the sides. It has to store the active
power and boost up the voltage from generator side to grid side.
•Generator side: It should control stator current and adjust the rotating speed.
Extract maximum power from turbine.
•Power grid side: It should have the ability to control the inductive/capacitive
reactive power and perform fast active power response. Frequency and voltage
should be fixed for normal operation .Harmonic distortion should be
maintained low.
24. Types of Wind Turbines
• Modern wind turbines fall into two basic groups: the horizontal-axis
variety, as shown in the photo, and the vertical-axis design, like the
eggbeater-style Darrieus model, named after its French inventor.
• Horizontal-axis wind turbines typically either have two or three blades.
These three-bladed wind turbines are operated "upwind," with the blades
facing into the wind.
• Utility-scale turbines range in size from 100 kilowatts to as large as several
megawatts. Larger turbines are grouped together into wind farms, which
provide bulk power to the electrical grid.
• Single small turbines, below 100 kilowatts, are used for homes,
telecommunications dishes, or water pumping.
26. • Anemometer: Measures the wind speed and transmits wind speed
data to the controller.
• Blades: Most turbines have either two or three blades. Wind
blowing over the blades causes the blades to "lift" and rotate.
• Brake: A disc brake, which can be applied mechanically,
electrically, or hydraulically to stop the rotor in emergencies.
• Controller: The controller starts up the machine at wind speeds of
about 8 to 16 miles per hour (mph) and shuts off the machine at
about 55 mph. Turbines do not operate at wind speeds above about
55 mph because they might be damaged by the high winds.
• Gear box: Gears connect the low-speed shaft to the high-speed
shaft and increase the rotational speeds from about 30 to 60
rotations per minute (rpm) to about 1000 to 1800 rpm, the rotational
speed required by most generators to produce electricity. The gear
box is a costly (and heavy) part of the wind turbine and engineers
are exploring "direct-drive" generators that operate at lower
rotational speeds and don't need gear boxes.
• Generator: Usually an off-the-shelf induction generator that
produces 60-cycle AC electricity.
27. • High-speed shaft: Drives the generator.
• Low-speed shaft: The rotor turns the low-speed shaft at about 30 to
60 rotations per minute.
• Nacelle: The nacelle sits atop the tower and contains the gear box,
low- and high-speed shafts, generator, controller, and brake. Some
nacelles are large enough for a helicopter to land on.
• Pitch: Blades are turned, or pitched, out of the wind to control the
rotor speed and keep the rotor from turning in winds that are too
high or too low to produce electricity.
• Rotor: The blades and the hub together are called the rotor.
• Tower: Towers are made from tubular steel (shown here), concrete,
or steel lattice. Because wind speed increases with height, taller
towers enable turbines to capture more energy and generate more
electricity.
• Wind direction: This is an "upwind" turbine, so-called because it
operates facing into the wind. Other turbines are designed to run
"downwind," facing away from the wind.
28. • Wind vane: Measures wind direction and communicates with the
yaw drive to orient the turbine properly with respect to the wind.
• Yaw drive: Upwind turbines face into the wind; the yaw drive is
used to keep the rotor facing into the wind as the wind direction
changes. Downwind turbines don't require a yaw drive, the wind
blows the rotor downwind.
• Yaw motor: Powers the yaw drive.
29. Power
• These blades use airfoils to generate mechanical
power. The aerodynamic power of wind energy is given
by the formula:
P =
1
2
ρπR2v3Cp
Where
ρ is the air density
R is the turbine radius
v is the wind speed
Cp is the turbine power coefficient
which determines the power efficiency of the wind
turbine. Charles F.
30. ADANTAGES:
• Energy For Free Of Cost.
• Produces Electricity Throughout The Day.
• Pollution Free And Clean.
• Vast Wind Energy Is Available. (10 Million Mw)
• Can Supply The Power To Remote Areas.
• Economically Competitive.
• Mechanical Power For Grading, Pumping Etc. ; Using Wind Energy.
• Up To 95 % Land Of Wind Farms Can Be Used For Ranching, Farming
And Forestry.
DISADVANTAGES:
• Low energy density.
• Irregular , unsteady wind energy
• Variable speed.
• Variable wind direction.
• Higher capital cost.
• Can be located only in vast open areas .
• Far location from load centers.
• Complex designs.
