An
important requirement of electric power distribution systems is the need for
automatic operation. In particular, the rapid and reliable transfer of the
system from one power source to another during certain system events is
important to achieving the reliability goals for such systems and the facility
serves. However, the design of such an automatic transfer system is
all–too-often considered “less important” than many other aspects of the
overall power system design.
Nowadays,
electrical power supply is one of the important elements in human being needs.
The most of the human activities is dependent on electrical power supply. In
other words, without electrical power supply, almost the whole of activities is
become postponed or worse cancelled. For usage of daily routine, voltage
supplied is within 240V ac. The need for power supply is paramount for the
growth of a country, access to electricity as the basic form of energy supply
to the masses is vital for the development of a nation’s economy. The strategic
role and policy of generation electricity in the development of an economy has
always been appreciated by most developed nations, with the likes of France,
Germany, and Italy. All these mentioned countries are well and truly developed
countries that sustain the supply of energy to it environment for the purpose
if industrial development.
The power sector provides a platform for economic development;
electricity has brought about development in all area of productions and
services. Electricity has become indispensable to socio-economic and industrial
development of any nation. Using uninterrupted power supply in an automated
mode, we always have a substitute arrangement as backup to take place of main
power supply in case of power-cut in an emergency case, where the power cut
cannot be avoided.
|
Rated
Capacity at STC (Wp)
|
Isc
|
Imp
|
Voc
|
Vmp
|
Length (mm)
|
Width (mm)
|
Weight
(kg)
|
|
50Wp
|
3.04
|
2.8
|
21.77
|
17.89
|
608
|
666
|
4.6
|
|
100Wp
|
6.11
|
5.57
|
21.84
|
17.99
|
1152
|
666
|
8
|
|
200Wp
|
8.1
|
7.48
|
32.65
|
26.74
|
1486
|
982
|
15.5
|
|
250Wp
|
8.71
|
8.18
|
37.55
|
30.58
|
1639
|
982
|
17.45
|
|
300Wp
|
8.74
|
8.05
|
45.1
|
37.28
|
1956
|
992
|
27
|
WORKING
Solar System Works
The solar panel converts
sunlight into direct current (“DC”) electricity. This DC electricity is used to
charge a battery through a charge controller. The inverter converts that
"DC" power from the solar panel or battery into alternating current
or "AC" power. AC power output from inverter can be used to operate
light, fan, TV, computer etc. It is also possible to operate DC loads like DC
lights, DC pump, computer, mobile charger, etc. directly from the solar panel
or battery.
Movement of Sun across the sky
On 21st June the Sun reaches highest
position in the northern hemisphere sky and on the 21st December the Sun
position is lowest in the sky. In the summer season the days are long and the
Sun is high in the sky. The days during summer are longer than the days during
the winter season.
Seasonal variation of solar radiation
due to earth’s movement
Tilt Angles
Solar modules should be installed so
that as much radiation as possible is collected. Ideally the solar modules
should be tilted at an angle to the horizontal (β°) as shown, facing true south
(if installed in the northern hemisphere such that there is 90 degrees between
the sun (at solar noon) and the solar module. To have a module face directly
towards the sun at all times would require a solar tracking frame to be
installed. This can be expensive, so it is not common practice for most PV
applications.
To have a module face directly towards the sun at all times would
require a solar tracking frame to be installed. This can be expensive, so it is
not common practice for most PV applications.
Modules mounted on a fixed structure
should be tilted up from the horizontal. The correct tilt angle varies with the
times of year the system is used, and the latitude of the site.
The tilt should be within 10 degrees of the listed angle.
For example, a system used throughout the year at a latitude of 25° can have a
tilt angle of 15° to 35° without a noticeable decrease in annual performance.
Peak Sun Hour
In solar PV system design practice, the average daily solar insolation in units of kWh/m2/day is referred to as "peak sun hours". Since the peak solar radiation is 1kW/m2, the number of peak sun hours is numerically identical to the average daily solar insolation. For example, a location that receives 5kWh/m2 per day can be said to have received 5hours of sun per day at 1kW/m2. This helps to calculate energy generation from a PV power plant as PV modules are rated at an input rating of 1kW/m2.
Operations of a PV Module
A typical silicon solar cell produce
only about 0.5 volt. A solar module is basic building block of any solar system
where multiple cells are connected in series. Usually 36 solar cells are
connected together to give a voltage of about 17V, which is enough to charge
12V battery. Similarly, a 72 cells module produces about 34V, which can be used
to charge a 24V battery.
Cells are connected in
series to make a PV module
In many applications the power
available from one module is inadequate for the load. Individual modules can be
connected in series, parallel, or both to increase either output voltage or
current. This also increases the output power. When a number of modules are
connected in series, it is called a PV string. Voltage of a string is addition
of voltages of individual module. If 10 modules of 34V are connected to make
one string, voltage of the string will be 340V.
When modules or PV strings are
connected in parallel, the current increases. For example, three modules which
produce 34V and 5A, connected in parallel, will produce 34V and 15A. If three
PV strings of 340V are connected in parallel, will produce 340V and 15A.
The collective of multiple strings connected in parallel
for greater power is called PV Array.
PV Module I-V Characteristics
I-V curve represents a ‘snap-shot’ of
all the potential combinations of current and voltage possible from a module
under specified environmental conditions. Every solar cell has a characteristic
I-V curve, where ISC and VOC are quoted to help
characterize a cell.
Short Circuit Current (Isc):
A photovoltaic module will produce its
maximum current when there is essentially no resistance in the circuit. This
would be a short circuit between its positive and negative terminals. This
maximum current is called the short circuit current (Isc). When the
module is shorted, the voltage in the circuit is zero.
Open
Circuit Voltage (Voc):
The maximum voltage in a PV module is
produced when there is a break in the circuit. This is called the open circuit
voltage (Voc). Under this condition the resistance is infinitely
high and there is no current, since the circuit is incomplete.
Maximum Power (Pmax):
The power available from a
photovoltaic module at any point along the curve is expressed in watts (W).
Watts are calculated by multiplying the voltage times the current (W = VA). At the
short circuit current point, the power output is zero, since the voltage is
zero. At the open circuit voltage point, the power output is also zero, since
the current is zero. There is a point on the “knee” of the curve where the
maximum power output is located. Maximum power (Pmax) is the product
of current at maximum power times the voltage at maximum power.
Current at Maximum Power (Imp):
The current that results in maximum
power under given conditions of light and temperature, used as the “rated” current
of a device. This value occurs at the “knee” of the I-V curve.
Voltage
at Maximum Power (Vmp):
The voltage that results in maximum
power under given conditions of light and temperature, used as the “rated”
current of a device and to determine how many cells or modules are needed to
match a load voltage requirement. This value occurs at the “knee” of the I-V
curve.
Module Energy Output
For a specific load, PV module output depends on the
following factors:
·
Irradiance or light intensity
·
Temperature
Solar irradiance directly affects the module energy
output. If light falling on a solar module increases twice, it will produce
twice as much current. The open circuit voltage does not change dramatically
with irradiance; however it increases slightly with higher irradiance. This is
why modules should be completely unshaded during operation. A shadow across a
module can almost stop electricity production.
Module temperature affects the output voltage inversely.
Higher module temperatures will reduce the voltage by 0.04V/°C to 0.1V/°C, for
every one degree centigrade rise in temperature.
This is why the modules should be installed in such way
that there is enough air circulation in the back of each module, so that its
temperature does not rise and reducing its output. An air space of 4 – 6 inches
is usually required to provide proper ventilation.
Standard
Test Conditions (STC):
The specifications in manufacturers’
data sheets are all determined using standard test conditions (STC) which are
considered as below:
·
Cell Temperature 25°C
·
Irradiance of 1000 W/m2
·
Air Mass of 1.5
A summary of typical losses is
provided in the following table. Estimated loss for a solar microgrid system
depends on system design, component selection and site operating temperature
and normally total loss is around 30%.
|
Cause of loss
|
*Estimated Loss (%)
|
De-rating Factor
|
|
Temperature
|
10%
|
0.90
|
|
Dirt
|
3%
|
0.97
|
|
Manufacturer’s Tolerance
|
3%
|
0.97
|
|
Shading
|
2%
|
0.95
|
|
Orientation
|
0%
|
1.00
|
|
Tilt Angle
|
1%
|
0.99
|
|
Voltage Drop
|
2%
|
0.98
|
|
Inverter
|
5%
|
0.95
|
|
Loss due to
irradiance level
|
3%
|
0.97
|
|
Distribution & transmission
|
2%
|
0.98
|
|
Total de-rating factor (multiplying
all de-rating factors)
|
0.70
|
|
Pros
& Cons
pros:
Ø
Power supply can be controlled
from four different sources
Ø
I f any problem occurred in one
source than other source can be used
Cons:
Ø
It is very difficult to install
and maintain the kit
Ø
Cost of equipment is very high
Applications
Power supply can be controlled in:
Ø
Industries
Ø
Hospitals
Ø
Schools
Ø
Multiplexes
Ø
Banks etc
