With Reference to St. Mary's Island, UK
Abstract
St. Mary’s Island part of the Isles of Scilly is providing 5,000
m2 of land to be fully utilised for a renewable energy project.
This is a solar power plant feasibility study and design with
reference to St. Mary’s island one of the major isles of the Isles of Scilly,
UK.
The aim of this project is to research possible solar power system
solutions and decide on the most feasible one. A solar power system is then to
be designed and evaluated within the variables provided to be implemented on
the location provided.
For
decades humans have been heavily reliant on fossil fuels to meet our increasing
energy demands. For long has fossil fuels been the most feasible choice for
most energy production systems. Humans have discovered most of the fossil fuel
reserves and are currently in the process of exploiting it all, and since
fossil fuels are limited in supply this exploitation cannot continue forever.
On top of the long-term unreliability of fossil fuels the burning of fossil
fuels also produces carbon emissions which in turn are responsible for aiding
the greenhouse effect which raises the temperature of our planet causing other
serious implications on our environment.
One form
of alternative and renewable energy is solar power, although it could also be
considered as the only form since the sun is the original energy source for all
natural energy on earth including wind and fossil fuels. On the other hand, a
solar energy source provides pollution-free, self-contained, reliable, quiet, long-term,
maintenance-free, and year-round continuous and unlimited operation at moderate
costs. Despite all these benefits of solar cells and nearly 55 years after
their invention, PV solar cells are generating only 0.04 percent of the world
on-grid electricity due to the high cost of solar cells, which is beyond the
reach of the common consumer.[1]
When it
comes to capitalising on solar power, the UK as a whole is considered behind
most other European countries in the proportion of its total energy demands
being generated from solar power systems. This could be due to the UK’s
relatively poor record of sun exposure.
For the
purposes of discovering the solar energy potential in the United Kingdom, St.
Mary’s Island is providing 5000m2 to be utilised for a large scale
solar power plant that is to supply power to the national grid.
This
project is to design and study the feasibility of a building large-scale solar
power system that feeds the national grid. The power system is to be compatible
with UK and EU regulations and standards and is to be open for larger future
expansion to increase its generation capacity.
2. An Evaluation of Present Available Forms Solar Power Technology
Most
solar power plants can be classified into two main categories, photovoltaic plants
or concentrated thermal power plants. Concentrated power plants depend on
mirrors or lenses reflecting a large area of solar light into concentrated
thermal beams. This section is to evaluate both categories and test their
suitability to perform as cost effective solar power plants on the location
chosen.
2.1. Photovoltaic
Photovoltaic solar cells generate electricity
from solar radiation by semiconductors that exhibit the solar effect. This
section will survey the status of the technology, and its suitability to
provide cost effective and a renewable source of energy to Greenville.
2.1.1. History and Development
The photovoltaic effect was
discovered more than 150 years ago in 1839 with Becquerel's discovery of a
photo-voltage when he directed light onto an electrode in an electrolyte. A few
decades’ later Adams and Day reported similar behaviour in solid selenium. By
the early 1900's the efficiency of solar cells had reached to 1% only. It
wasn't until the 1940's that solid state
crystalline silicon and p/n was
discovered which raised the efficiency bar of solar cells up to 6%. [[2]]
During the energy crises in the
1970's the US government started a major push on developing more efficient
solar cells practical for terrestrial solar energy conversion. The dominant
technology by the 1990's was based on single cell multi-crystalline silicon
cells. Another innovation of the industry based on other material was GaAS
systems, InP, CuInSe2 and CdTe. Solar array panels for terrestrial use were
sold at a volume of $6.5/W in the early 1990's.
As Silicon microelectronics
developed the prospects for a cost effective electricity generation from solar
power kept improving. During the last 40 years the technology behind solar
cells has gone a long way.
2.1.2. Principle of Solar Cell Operation
A Typical configuration for a solar
cell is shown schematically in Figure 1 below. The figure demonstrates a
standard n/p junction, rectifying diode with contact metallization partially
converting its emitter to allow light entrance.
An electro statically charged
depletion region penetrating a depth xE into the the emitter of thickness tE
and also penetrating a depth xB into the base of thickness tB. Light absorption
generates creates an equal amount of non- equilibrium electron hole pairs in concentration
much higher than equilibrium minority-carrier levels but typically less than
the equilibrium majority-carrier concentrations.
It is these nonequilbream
minority-carrier and their potential energy changes that transform the absorbed
photon energy into a DC voltage. The main challenge lies in converting the
nonequilbream minority-carrier into majority-carriers with as little loss in
their potential energy as possible. It is the majority-carriers that ultimately
flow through contacts to external circuit for electrical use.
Figure 1 – Schematic diagram for a
typical n/p solar cell configuration.
Because velocity is random, only
half of these electrons at x
2.1.3. Module and Array
The
solar cell described above is the basic building block of the PV power system.
Typically, it is a few square inches in size and produces about one watt of
power. For obtaining high power, numerous such cells are connected in series
and parallel circuits on a panel (module) area of several square feet.
Cook [[3]] defines
the solar array or panel is as a group of several modules electrically
connected in series-parallel combinations to generate therequired current and
voltage.
Figure 2-Basic construction of PV cell with performance
enhancing features (current collecting mesh, anti-reflective coating and cover
glass protection) [[4]].
2.1.4. Photons
A photon
is an elementary particle in physics that allows the photovoltaic process to
take place. A photon is a massless
energy that has no electric charge and does not decay when traveling in empty
space. Photons also have two polarization states and are described by
components of their wave vectors [[5]].
Photon
energy and momentum are related by the equation E=pc where p stands for
magnitude of the momentum of vector p. The equation is derived from the
relativity theory where the mass, m=0
E2=p2c2+m2c4
The
energy and momentum of a photon is proportional to its frequency (v) or the
inverse of their wavelength (λ)
E= hw=hv=h/λ
P=hk
Where k is the wave
vector.
2.2. Concentrating Solar Power
Among the wide range of concentrated solar powered plants, parabolic troughs are considered to be among the most developed forms of this concentrated solar technology.
The sun's energy is concentrated by parabolic curved,
trough-shaped reflectors onto a pipe
running along the inside of the curved surface. This energy heats a the pipe, and the heat energy is then used to
generate electricity in a conventional steam generator.
A parabolic trough consists of a
linear parabolic reflector that concentrates light onto a receiver positioned
along the reflector's focal line. The receiver is a tube positioned right above
the middle of the parabolic mirror and is filled with a working fluid. The
reflector is made to follow the Sun during the daylight hours by tracking along
a single axis. .
Concentrating linear parabolic through
reflectors are generally used in both large or more compact plants.
3. Location- St. Marys, Isles of Scilly
The Isles of
Scilly form an archipelago off the
south-western tip of the Cornish
peninsula of Great Britain. The islands have had a unitary authority council since 1890, and are separate from the Cornwall unitary authority, but some services are combined with
Cornwall and the islands are still part of the ceremonial county of Cornwall. This council is part of the UK and currently
known as the Council of the Isles of Scilly. St. Mary’s is the major and
biggest island of the isles, with a population of 1,700.
The Isles of Scilly are considered a relatively
good candidate for a solar power plant due the isles southern latitude and
higher solar irradiation rate in comparison with rest of the UK. The Island is
providing an area of 5,000m2 to be utilised for a renewable energy system
usage.
Figure 3-Location of Isles of Scilly within the United
Kingdom
Figure 4-Showing a
satellite view of St. Mary’s
Figure 5-Showing a
satellite view of candidate project location with 5,000 m2 available
3.1. Current energy usage within St. Mary [[6]]
|
Domestic Consumers
|
Commercial and Industrial
Consumers
|
All Consumers
|
|||
|
Sales 2009 - GWh
|
Number of MPANs (thousands)
|
Sales 2009 - GWh
|
Number of MPANs (thousands)
|
Sales 2009 - GWh
|
Number of MPANs (thousands)
|
|
7.8
|
1.1
|
8.4
|
0.5
|
16.2
|
1.6
|
3.2.
Total final energy
consumption: 2009 in ktoe for electricity[7]
|
Electricity
|
Current Renewable energy
|
|
||
|
Industrial and Commercial
|
Domestic
|
Total
|
Total
|
Total Energy Produced
|
|
0.7
|
0.7
|
1.4
|
0.6
|
2
|
3.3. Current Consumption and Future Prospects after Project Completion
This would put the current renewable electricity
production of St. Mary at 20% of the total electrical energy produced.
4. Solar Power System Physics and Effect of Ambient Parameter Variation
In order
to acquire optimal results the design must consider the atmospheric climatic
and environmental factors that affect the output power performance of solar
power cells. This section will research
those factors assessing their effects on the results of the project, with reference to the
selected location, St. Mary’s Island.
4.1.
Energy Conversion Efficiency
Solar cell
conversion efficiency is the percentage of power converted from absorbed solar
irradiance when connected to an electrical load. The efficiency is calculated
using a ratio considering the maximum power point Pmaxdivided by the
impacted solar irradiance,E, measured in W/m2, on the surface of a
PV module Ac in m2 under standard test conditions.
η= Pmax/ E x Ac.
The efficiency of
a solar cell is an accumulation of the following factors:
·
Reflectance efficiency
·
Thermodynamic efficiency
·
Charge carrier separation efficiency
·
Conductive efficiency
4.2.
Cell Temperature
Ambient
temperature has direct effect on the power output of a solar cell,as the
ambient temperature increase, the output voltage decreases. From an operational
point of view, the net effect of the rise in temperature minimally affects the
output current. However the net effect translates into a reduction of open
circuit voltage. Likewise a decrease in the ambient temperature increases the
open circuit voltage.[[8]]
When operating
under high temperature almost all PV modules exhibit voltage drops and an
increase in current that results in output deterioration. When the exposure to
heat is extended PV modules encapsulations may deteriorate causing the module
to degrade permanently. This property of solar cell can be considered an
advantage in the candidate location due to the UK’s relatively low temperature
in comparison to other sunnier countries with higher current solar power
production.
When designing
solar power systems, a cell temperature value multiplier referred to as a
temperature rise coefficient is used to calculate compensation for solar
irradiance under various conditions.
The formula used
to estimate the temperature compensations is:
TCELL= TAMB+(TRISE x
E)
When TCELL =
Cell temperature (in ºC)
TAMB = Ambient
temperature (in ºC)
TRISE = Temperature-Rise
Coefficient (in ºC)
E= solar irradiance (in kW/m2 )
Cell temperature
rise, TRISE = (TCELL – TAMB)
Cell-Temperature
rise, TRISE, Likewise can be calculated by using the following
formula:
TRISE =
(TCELL –TAMB)/E
Temperature-coefficient
parameter, the
temperature-coefficient parameter is defined as the rate of change in voltage
and current caused by temperature change [[9]].
A negative
coefficient implies that the parameter decreases with cell temperature increase
whereas positive coefficient means that the parameter decreases with cell
temperature increase.
Different PV
modules have different Temperature coefficients, however typical temperature
coefficients for silicone cells are as follow:
Voltage = -0.00225
V/ ºC +/-0.10%/ ºC
Current =
0.0000037 A/ ºC +/-0.0010%/ ºC
4.3.
Thermodynamic Efficiency Limit
Solar cells are
subjected to a thermodynamic efficiency limit. Thermodynamic efficiency limit
refers to a condition when photons with energy below the band gap PN junction
cannot generate a hole-electron pair. As a result energy absorbed is not
converted to useful output and instead is converted to kinetic energy.
4.4.
Fill Factor
Fill factor is a ration that defines the overall
power performance characteristics of a solar cell. Fill factor can be expressed
in the following formula:
FF = Pm / Voc x Isc
FF = Pm / Voc x Isc
Where Pm:
Maximum Power
Vop = Open circuit
voltage
Isc= short circuit
current
4.5. Comparative Analysis of Solar Cell Energy Conversion Efficiencies
Solar efficiency depends on many
external environmental factors such as ambient temperature, solar irradiance
spectrum and other atmospheric factors. It is thus important to consider all
factors when considering St. Marry as a
potential solar powered village. It is also useful to compare the performance
of PV modules in the location to recommendations of local and international
standards. Such standards include the IEC international standard 61215, which
will be referred to later on.
It is also worth mentioning that
using more efficient PV modules will increase the costs of the production, so
determining a cost effective balance between financial costs and efficiency
will be required.
4.6. Solar Energy and Radiation
The sun consists mostly of hydrogen
in gas form and small amounts of helium. The sun produces its energy through a
process called fusion. Intense
gravitational energy causes hydrogen atoms to fuse together releasing large
amounts of energy in the process. Some of this radiated energy reaches earth in
the form of waves and particles. In addition to the radiated energy the sun
also releases photons. Photons are elementary particles that are fundamental to
the operation of the solar cell.
5. Array Design
The major factors influencing the electrical design of the solar
array are asfollows:
• Sun intensity.
• Sun angle.
• Load matching for maximum power.
• Operating temperature.
These factors are discussed below.
5.1. Solar Irradiance
Solar irradiance is the intensity
of solar energy impacting an imaginary unit surface. Solar irradiance is
expressed as watts per square meter (W/m2). Solar irradiance is used
to measure instantaneous peak power output performance of any solar power
energy device or PV module. As the sun changes its location during its
rise-fall cycle so does solar irradiance. Solar Irradiance is fluctuates more
during the orbit of the sun as the distance to earth changes, and with it the
seasons. Solar irradiance on the surface of the earth rises in the morning
reaches a peak at noon and falls back to zero after dusk.
Solar irradiance can be calculated
by the following formula:
H=E × T
Where H= Solar irradiation (W/m2)
E=
Solar Irradiance (W/m2)
T=
Time (hours)
Figure 6- A Met Office map showing a UK solar Radiation Maps in summer
In accordance to the Met Office Map,
St. Mary’s falls within the region in the UK with maximum solar irradiation,
where solar irradiation average at around 19 MJ/m2 during July and
3.0 MJ/m2 during January.
5.2. Sun Intensity
The magnitude of the photocurrent is maximum under full bright sun
(1.0 sun).
On a partially sunny day, the photocurrent diminishes in direct
proportion to the sun intensity. The i-v characteristic shifts downward at a
lower sun.
Figure 7 - i-v characteristic of pv module shifts down at lower sun
intensity, with small reduction in voltage [[10]].
On a cloudy day, therefore, the short circuitcurrent decreases
significantly. The reduction in the open-circuit voltage,however, is small. The
photo-conversion efficiency of the cell is insensitive to the solar radiation
in the practical working range. For example efficiency is practically the same
at 500 watts/m 2 and 1,000 watts/m2 as shown in appendix of solar cell specs.
This means that the conversion efficiency is the same on a bright sunny day and
a cloudy day. We get lower power output on a cloudy day only because of the
lower solar energy impinging the cell.
5.3. Solar Energy Spectrum
Energy emanated from the sun is
electromagnetic radiation in the form of varying lengths of waves which have
electromagnetic properties. The Solar electromagnetic spectrum therefore
includes a wide range of wavelengths some of which fall within ultraviolet and
infrared visible light.
5.4. Air Mass
As discussed the amount of solar
power radiation reaching the surface of the earth is directly related to the
amount of energy scattered though the atmosphere. When the sum is at its apex or the zenith,
the atmospheric mas has the smallest distance and mas. The zenith angle is the
angle between the sun and the zenith. As the zenith angle increases, the sun’s
ray pass through the atmosphere’s mass, which reduces the rays’ intensity in
proportion to the atmospheric mass.
Air mass is assigned a value of 1
(AM 1.0) when the sun is directly overhead of sea level. At the outer
atmosphere, the value of air mass because of the lack of any irradiance
impediment is AM 0.
At any location of the surface of
the earth, the air mass is calculated with the following formula:
AM = 1/Cos θz
Where AM = air mass valu
Θz=
Zenith angle in degrees
The air mass depends on the
altitude, the time of the year and time of the day. The Air mass of any
location on the surface of the earth is calculated by the following formula:
AM Local – Am x(P Local/ 1013)
AM Local – Am x(P Local/ 1013)
AM = Air Mass at sea level
PLocal= Local
atmospheric Pressure
1013 = Atmospheric level
The air mass can be calculated by
following this procedure:
1 set a measuring ruler to a length
of LR in Inches in vertical position
2 Measure the shadow length from
the base of the ruler (Ls in inches)
3 Calculate the Zenith angle θz +
Arctans (LS /LR)
When solar irradiance reaches the
earth’s surface it loses a significant amount of its energy, such that the
value of the solar constant 1366 W/m 2 is reduced to about 1000 W/m 2
at sea level. Peak sun hours are the number of hours required during the
day for a solar power system to accumulate energy at the peak sun condition.
6. Sun Tracking System
Sun tracking systems are platforms
that orient solar PV panels by tracking the sun’s movement from sunrise to
sunset, thus maximizing solar energy power generation efficiency. All trackers are classified as passive or
active maybe constructed to track in single or dual axis. Single axis trackers can increase power
capture by about 20-25%. Dual axis trackers increase the output by up to 40%.[11]
Fixed axis systems are oriented to maximum power generation for a limited
amount of time and thus generally have very low annual power production.
Compared to the overall cost of PV systems, trackers are relatively inexpensive
devices that significantly increase power output performance, for this reason
most solar power plants rely on trackers for maximum power output. For the purposes of demonstration a sun
tracking panel is to be designed and build as part of this project.
6.1.
Tracking
solar panel mounts:
.
One
method of designing the suntracker is to use two pv cells mounted on two 45°
wedges and connecting them differentially in series through an actuator motor.
When the sun is perfectly normal, the current on both cells are equal to Io ·
cos 45°. Since they are connected in series opposition, the net current in the
motor is zero, and the array stays put. Onthe other hand, if the array is not
normal to the sun, the sun angles on the two cells are different, giving two
different currents: The motor current is therefore:
I1= I0cos(45
+ δ) and, I2 = I0cos(45 − δ)
The
motor current is therefore:
Im=I1-I2=
I0 (45 + δ) − I0 (cos(45 − δ)
Using
Taylor series expansion:
A sun-tracking design can increase the energy
yield up to 40% over the year compared to the fixed-array design. Dual-axis
tracking is done by two linear actuator motors, which follow the sun within one
degree of accuracy. [12]
6.2. Polar Trackers
Polar trackers are designed to have
one axis rotate around its self hence polar.
These types of trackers are never used in large scale solar power
systems because of their poor resistance to wind. They are more common on
astronomical telescopes mounts in which high accuracy solar tracking is
required at all time.
6.3. Horizontal-Axis Trackers
These types of trackers rotate
around a horizontal axis by either passive or active mechanisms. The axles are installed with southern
orientation where PV panels are mounted on axles that rotate east-west. Single axis trackers do not tilt towards the
equator, meaning the power output would be limited in mid-winter
where the sun doesn’t rise as high.
7. System Design Overview
As
discussed earlier the power output capability of a solar power system is
dependent on several considerations regardless of which PV system is used. For
example, the minimum electrical power level needed, the geographical location,
and the average sunlight available per year are the three major considerations.
After an
idea has been formed on the components required,in this case of a
grid-connected power system, the solar arrays and a grid connection from the
commercial electrical utility company are required to meet the consumer
electrical power requirements on continuous basis.a solar power system
designing software will be used to design the system for the project. The system is also to incorporate a double
axis solar tracking system to increase solar exposure and increase
productivity.
7.1. Solar Photovoltaic Power System Components
The main
component of the system is the solar panel. The solar panel supplies the
electricity and charges the batteries. They work in conjunction with
complimentary, inverters, solar tracker isolation transformers, power
distribution panels and storage battery systems that are essential to the solar
power energy conversion process.
7.2. Inverter Stacking: Using multiple inverters.
Two
inverters can be installed in a configuration known as stacking that can provide
more power or higher voltage. If two compatible inverters are stacked in series
you can double the output voltage. This would be the technique to use to
provide 120/240 volts AC. On the other hand, if you configure them in parallel,
you can double your power. Two 4000 watt inverters in parallel would give you
8000 watts (8KW) of electricity
Figure
8-Shadow
effect on one long PV string of an array. The power degradation is small until
shadow exceeds the critical limit.[13]
7.3. PreminaryProject Assessment
After establishing solar power area
clearances a set of electronic templates representing standard array
configuration assemblies must be prepared. Solar array templates can be used to
establish a desirable output of DC power. When laying blocks of PV arrays,
consideration must be given to avoid cross shadowing, this can be achieved by
achieving a spefic tilt inclination. Inclination should be about the angle of
the local altitude minus 10 degrees for maximum solar insolation.[14]
This is going to be done using PVSYST in the design section.
Another important consideration
when designing the solar arrays layout is to group the right number of PV
modules that would provide the required series connected voltages and current
required by the inverters specifications. This is because inverters allow
specific margins of DC input depending on the module of inverter used. This is
why an advanced decision needs to be made on the PV module and inverters.
Also, since solar powers require
periodical cleaning and maintained, considerations for future maintenance and
cleaning should also be made when laying out the array, by providing access to
all arrays.
When it comes to cost control, as a
rough rule of thumb the design is to keep a list of all components used and
their prices so that the costs can be calculated per Watts produced.
All environmental parameters
discussed in the previous chapter should be considered , as well as other
factors summed up in the following:
·
Solar platform shading
·
Latitude and longitude
·
Ambient temperature
·
Yearly average insolation
·
Temperature variations.
·
Inverter efficiency and models
·
Isolation transformer efficiency
7.4. Project Site Survey
Investigating the solar panel
location where the solar plant will be located is one of the most significant parts
of the solar power plant project. In order to expose the panels to optimal sun
rays without shading caused by artificial or natural environment. To achieve
this, the solar panels location should be analysed for year-round shading. This
is because seasonal rise and fall of the solar angle can significantly affect
the solar angle.
In addition to shade, the latitude of the location and the PV panel orientation will significantly influence the power output of the solar power system. Specialised solar survey tools are very useful when it comes to site surveying. The site should also be surveyed for all the environmental factors previously mentioned to analyse the feasibility of the project.
In addition to shade, the latitude of the location and the PV panel orientation will significantly influence the power output of the solar power system. Specialised solar survey tools are very useful when it comes to site surveying. The site should also be surveyed for all the environmental factors previously mentioned to analyse the feasibility of the project.
For
design, PVsyst is the software used to assist in designing the solar power
system. The software allows an estimation of production to be made as it also
features design tools for detailed study, hourly meteoroidal data and results
simulations. Computation: PVsyst performs a very simplified simulation, which
runs over one year in daily values. The evaluation of the available irradiance
on the collector plane uses a Monthly Meteo tool algorithms, which calculate
irradiation's monthly averages on the basis of instantaneous data for one day per
month.
8.1. Flow Chart of Design on PVSyst
The flow
chart below demonstrates the basic steps of designing and computing the system
all the way to simulation:
8.2. Geographical Site Parameters
The coordinates of the location are entered so
that the software can fetch the relevant meteorological information previously
discussed in the research section.
Figure(7) of coordinates of Solar Power System
location at St. Marry, Isles of Scilly
The
software would then acquire the sun path for the location of the project from
its meteoroidal database and display the data in a graph:
Figure (8) - Graph of Solar paths plotted by PVSYST after data
input
The
screenshot below show an hourly simulation in progress of the meteorological
data after inputting the geographical site parameters.
Figure(9) - Screenshot of Simulation
The software then displays the results:
Figure (10) – Screenshot of Results Displayed
8.3. Grid System Design
8.3.1. Solar Panel
Suntech's 290W Vd modules where chosen, since they feature an
advanced polycrystalline silicon processing technology, and are designed for
large-scale deployment in power plant installations.A polycrystalline solar
panel module is made from a block of silicon that has multiple
crystals. Polycrystalline cells are
generally considered less efficient than monocrystalline cells but are also
much cheaper and more cost effective in large scale systems. See Appendix for
Data Sheet.
Watt rating: 290Wp
Dimensions: 1956 x 992 x 50 mm
8.3.2. Power Inverter
Since PV
panels generate direct current that can only be used by a limited number of
devices power inverters are needed to invert the current into a more useful
form.
Inverters
convert the current into alternating current which can be used by most
residential, commercial and industrial devise. The inverter has an imbedded
transformer that operates at a very high efficiency.
Synchronized invertersa
synchronized inverter matches the phase to that of the utility company. This
allows a solar panel system to work in unison with the grid; transfering its
generated power to the utlity company. A synchronized inverter is required for a grid-tie solar panel system.
During
the testing of the system it may be advantageous to test it at night time when
the grid is most stable.
The inverter must be correctly wired according
to the manufacturer’s instructions and have proper wire size, fusing and
breaker sizes and types. An inverter that is islanding protecting senses the
loss from the grid and does not back feed into the system preventing system
damage. [15]
Figure (11) – Screenshot of Project Components Specifications
8.3.3. Solar Power System Wiring Guide
Conductors that are suitable for
solar exposure are listed as THW-2, USE-2, and THWN-2 or XHHW-2. All outdoor
installed conduits and wire ways are considered to be operating in wet, damp
and UV-exposed conditions.
For interior wiring where the
cables are not subjected to physical abuse, CNM-, NMB-, and UF-type cable are
permitted. Care must be taken in installing underrated cables within interior
locations to avoid heating.
Colour coded wires are also
recommended for all DC wires , red wire for positive, white for negative, green
for grounding.
The definition of the PV module is
then verified with the data sheet for the module:
Figure (12) – Screenshot of Solar
Module Specs.
Figure(13) - Displaying screenshot of Model Parameters
configuration for Suntech, STP 290-24/Vd
Figure (13) - Displaying graph of current/voltage for incident
irradiation
Figure (14) - Displaying screenshot of SPV 700 – Emerson Control
Tech. inverter configuration.
Figure(14) - Display screenshot of Efficiency Curve configuration
on PVSYST
Figure (15) – Screenshot of Module Management
Simulation Parameters Summary:
Tracking Panel Two Axis: Minimum Tilt 30º Maximum
tilt 80º
Horizon: Free
Horizon
Near Shadings: No
Near Shadings
PV Array Characteristics
PV Module: Si-Poly Model:
STP 290-24/Vd
(Superpoly)
Manufacturer:
Suntech
Number of PV modules: In
series: 18 modules
In
Parallel: 143 strings
Total Number of PV Modules: 2574 PV Modules of Unit Nominal Power: 290Wp
Array Global Power: Nominal (STC): 746kWp
At Operating Conditions: 676kWp
(50ºC)
Array Operating Characteristics (50º): 599V 1128A
Total Area Covered by Modules: 4994m2
Inverter
Model: RPS 0830 MULTI MPPT
Manufacturer: BonfigioloiVectron
Operating Voltage: 500-875 V Nom. Power/Unit: 733 kW AC
PV Array Loss Factor
Thermal Loss Factor: Uc (const) 20 W/m2 K
Nominal Operation Temp. G=
800 W/m2Tamb= 20º C,
Wiring Ohmic Loss Global
Array Resistance: 9.0 m Ohm
Module Layout
8.4. Grounding and Bonding
Grounding and bonding a large scale
PV system is absolutely necessary to comply with to the national electric code.
Figure Typical Utility interactive
PV system components
8.5. Grid Connectivity Configuration
Traditionally,
the power transmission grid is designed as a vertically integrated system. The
electrical power, at the place of generation transformed to high voltages, is
transmitted over high voltage lines to the distribution systems and then to the
loads. In PV systems usually the
negative of the DC output for a wo-wire system or the centre tapped conductor
refers to a conductor that is intentionally grounded
9. Testing and Evaluation
System Production:
After completing the simulation of the
project the following were results
Produced Energy: 909MWh/
Year
Performance Ratio: 84.2%
9.1.
Performance Ratio
The
performance ratio is a measure of the quality of a PV plant that is independent
of location and it therefore often described as a quality factor.
The
performance is stated as percent and describes the relationship between the
actual and theoretical energy outputs of the PV plant. It thus shows the
proportion of the energy that is actually available for export to the grid
after deduction of energy loss (e.g. due to thermal losses and conduction
losses) and of energy consumption for operation. The closer the PR value
determined for a PV plant approaches 100 %, the more efficiently the respective
PV plant is operating.
A value
of 100 % is too perfect to be achieved ,as there is always loss and no system
is 100% efficient 80% efficiency is considered a very efficient PV System
With
the performance ratio you can compare the energy output of this PV power system
with that of other PV plants or monitor the status of your PV plant over a
prolonged period. [16] The graph below shows the
simulation of the PR of the system during a 12 months period.
9.2. Balances and Main Results
9.3. Loss Diagram and Final Energy Injection
9.4. System Output Power Distribution
9.5. Module Quality Loss
9.6. Study and Evaluation of the Site Electrical System
In
2012 alone, the U.K. solar market has seen over 500 MW installed,
bringing total cumulative photovoltaic capacity to over one gigawatt [[17]].
The feasibility of the project depends on the total generated electricity and
its economic viability.
9.7.
Economic Feasibility
Economics
are crucial to the success of any energy utilisation system, and photovoltaic power
systems are never an exception At present, development of such converters is in
the stage in which prices are still being reduced at a rapid rate. It is,
nevertheless, difficult to compare photovoltaic with other systems solely on
the basis of investment cost. While Solar power systems have low operating
costs, the average power would vary a lot depending on many different variable
factors such as sun incidence and the efficiency of the sun tracking system.
New generation tariffs for large
scale solar and anaerobic digestion under the Government’s green electricity
scheme have been recently introduced. The large scale scheme would pay a rate
of:
·
250 kW – 5 MW TIC and stand-alone
installations - 8.5p/ kWh.
Since the nominal calculated
production of the system is 745 kWh, this means that St. Mary’s power system
would qualify under this category.
10. Implementation and Field Installation Test
As solar PV systems are multidisciplinary in nature requires
considerable experience in a multitude of
ofdiscplines, including electrical engineering, civil engineering and
power system management.
Furthermore, large scale power system installations require a team
of technical personnel who have fundamental skills in solar power systems and
knowledge and experience in electronic engineering.
All the design plans should be first studied and evaluated by the
implementation team especially as large
scale PV systems are complicated and required hundreds of PV panels. It is also
crucial that the implementation team follows strict electrical field safety
procedure during installation and maintenance.
10.1. System Integration Test
Unlike conventiona electrical systems solar power systems require
a well-organized document test and verification procedure. As hundreds of solar
panel strings , PV arrays and subarrays are and feeder systems, solar power
systems require continuous system testing during the system integration. As
such prior to final assembly of each combinor box, each PV string must be
measured to verify that the string will deliver the expected power output under
given environmental aspects and conditions. Thus it is important that the
system test is not considered as a single test event that takes place at the
end, when in fact it is continuous throughout the implementation phase.
10.1.1. Instantaneous Solar Power Out Performance Measurement
1.
Measurment of Peak DC power output. This value is the sum of all
PV modules PSTC value as shown on the manufacturer’s Module Specification. See
Appendix A.
2.
Calculation of Solar irradiance factor Ki, which can be measures
by a pyrano-metre.
3.
Calculations of PV module temperature factor as described earlier.
4.
Calculation of solar Power System deteriation factor
10.2. System Maintenance
System maintenance must be performed periodically.
Performing the required maintenance:
o
Extends the life of the equipment
o
Improves the lifetime kilowatt production
o
Allows replacement of defective parts while still under warranty.
The periodical maintenance of should ensure the following:
10.2.1. Cleaning Panels
According to cleaning the PV panels periodically can result in a
5% increase in the production.[18]
Cleaning panels will reduce heat build-up and increase exposure to sun light.
10.2.2. Filters
Dust has very negative impact the inverter. The inverter uses a
filter to remove potentially damaging dust and airborne adhesive chemical
compounds. Inverter filters should be cleaned as advised by the inverter
catalogue.
11. Carbon Savings
According to the USA Environmental
Protection Agency calculator a 909 MWh/Year system would save up to 627 metric
tonnes of carbon emissions a year.
12. Conclusion
After researching the environmental
factors that will affect the outcomes of the project and assessing the
different available forms of Solar power systems a grid connected solar PV
system was designed using PVsyst. The research concluded that a photovoltaic
system would be more feasible to the climate of the UK over a concentrated
power system The system’s main component included monochrystalinePV panels
spread over an available area of 5,000m2. A simulation was done for
the system considering as many environmental variables as possible and the
results indicated a potential output production of 909 MWh / year at a
performance ratio of 84%. The system would qualify to the large scale
feed-in-tariff of 0.85p per Watt. Despite
improvements that solar power still requires, this clean energy
remains
one of the most attractive choices for the future for both homeowners
and
communities.Maintenance
shut-downs are the main limit to full utilization of the installed power
capacity. In the case of wind and solar power, the main limitation comes from
the unreliability and intermittence of the wind or the sun, respectively.
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[2]John Orton, 2004. The Story of Semiconductors.Edition.
Oxford University Press, USA.
[3]Cook, G., Billman, L. and Adcock R. 1995. “Photovoltaic Fundamental,” DOE/Solar Energy Research Institute Report No. DE91015001, February 1995.
[4]R. Patel, Wind and Solar Power Systems, CRC Press, Washington, 1999.
[5]Gevorkia, Peter, Alternative Energy Systems in
Building Design, McGraw- Hill, New York, 2010.
[10]R. Patel, Wind and Solar Power Systems, CRC Press, Washington, 1999
[11]Gevorkia, Peter, Alternative Energy Systems in
Building Design, McGraw- Hill, New York, 2010.
[12]Mukund R. Patel, 2005. Wind and Solar Power Systems: Design,
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[13]R. Patel, Wind and Solar Power Systems, CRC Press, Washington, 1999
[14]Gevorkia, Peter, Alternative Energy Systems in
Building Design, McGraw- Hill, New York, 2010.
[15]Robert Foster, 2009. Solar Energy: Renewable Energy and the Environment. 1
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[18]John R. Balfour, 2011. Advanced Photovoltaic System Design
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Learning
