Photovoltaic Technology & Installation
Contains background information on the development of PV technology
and several clarifications of terms used in the guide.
- Crystalline Silicon:
Detailed information on traditional PV technology.
- Thin-films: Detailed
information on established and emerging technologies.
Provides introductory information on energy conservation and
contains links to step-by-step sizing guide.
System: Direct link to sizing a
grid-tied PV array. Does not contain background information that
may be required in some calculations.
- Stand Alone
Systems: Direct link to sizing a stand-alone system.
Does not contain background information that may be required in
Australian Locations' Insolation
Appliance Load Calculator Spreadsheet
The information in this report may be used for educational
purposes provided the source is cited.
© Haines, B. and Baggs, D. 2006.
The photovoltaic effect is not a new phenomenon; in 1839 the
French physicist Antoine-Cesar Becquerel observed that by shining a
light on an electrode submerged in a conductive solution, an
electric current was produced.
The first silicon solar cell wasn't produced until 1941, but the
high price of manufacturing silicon wafers kept them out of common
applications until the late 20th century.
As PV technologies continue to improve and large carbon emitters
are being held increasingly accountable for their emissions,
photovoltaics are becoming increasingly cost competitive with
traditional energy sources.
This report attempts to demystify solar panel technologies and
some technical jargon used in the PV industry. Although this
report does its best to cover all major PV technologies and some
interesting and innovative PV applications, some emerging
technologies may not be covered.
When comparing the differences between PV materials in this
report or on a manufacturer's website, it is important to
understand the intricacies of a few descriptions:
- Energy Payback Period: This term is used to
quantify the amount of energy that is consumed in the production of
a PV module (embodied energy) and the amount of time before the
module has produced enough energy to offset its production. This
subject is a major source of contention and is difficult to get a
definitive energy payback timeframe by consensus. The figures
given in this report reflect Ecospecifier's best estimates based on
reliable scientific reports.
- Efficiency: Cell efficiency is the ratio of
power produced by the cell to solar energy hitting the cell. Cell
efficiency is generally tested under standards testing conditions
(STC) in the lab using a very small photovoltaic cell. Unlike a PV
module, where gaps between cells and frames increase the area but
not the efficiency of the module, 100% of the area in a cell is
producing power. Module efficiency is usually significantly smaller
than cell efficiency because these gaps and the frame must also be
included in the area that is receiving energy from the sun. Thus,
the ratio of energy hitting the module versus power being produced
by the module is much smaller.
Types of Photovoltaics:
There are two main categories of PV modules: crystalline silicon
and thin-film. Both types have their advantages, but with the terms
outlined above and some additional type-specific information below,
determining the most suitable PV technology for a particular
application will be much more simple.
PV Technologies References:
Traditional PV cells are made from silicon (Si), which, after
oxygen, is the second most abundant element in the Earth's
crust. However, PV-grade crystalline silicon must be highly
refined to a purity of 99.9999%. Melted silicon is 'grown'
into ingots, or rods, by dipping a seed into the melted silicon and
allowing it to cool slowly. These ingots are then sliced or
sawn into thin Si wafers, wasting 20% of the valuable silicon as
sawdust. The refining process and sawdust waste add considerably to
the embodied energy of crystalline silicon, but with a wafer
lifetime of 25 years, the embodied energy will be regained several
Two types of crystalline silicon technologies are currently used
in photovoltaics: monocrystalline and multicrystalline. Both types
arrange their Si molecules into a crystal lattice formation, which
provides the structure. Impurities, however, are more common in
multicrystalline silicon leading to lower efficiencies, uniformity,
Crystalline Si basics:
- 4-year energy payback period (C. Bankier and S. Gale,
Energy Bulletin) This payback time may be reduced if
the module frame is made of recycled materials. (aluminium)
- Highly temperature-sensitive
- Typical monocrystalline cell efficiency = 15 - 17%
- Typical multicrystalline cell efficiency = 13 - 15%
Australian manufacturers of Crystalline Si PV
Thin-film solar technology is considered to be a highly cost and
materials efficient alternative to crystalline silicon
technologies. Although thin-film efficiencies are generally lower,
reductions in the amount of expensive silicon used in the cells
requires a much shorter energy payback period. Manufacturing
these cells can be streamlined by using ink-jet printer-like
machines to deposit the silicon (or other PV material) onto the
substrate in layers that may only be as thick as a molecule or two.
This process is known as 'roll-to-roll' or 'web' processing.
These innovations help to further reduce the cost of the PV
Thin-film Technologies covered in this Technical Guide:
Although this Technical Guide does not cover every type of
thin-film technology available, it attempts to cover the
predominant technologies and any that are being developed in
Australia or by Australian companies.
(a-Si): This thin-film technology avoids forming the
crystal lattice, as in crystalline silicon, by being passivated.
This occurs by introducing hydrogen gas into the Si bond structure,
which prevents the formation of tetrahedral bonds, or four Si atoms
bonding to each other. One main advantage of a-Si over
crystalline Si is that it is much more uniform over large areas.
Because it is naturally full of defects, any other impurities will
not have as great an effect on performance. Another advantage of
a-Si is that it can be deposited at much lower temperatures (75°C)
than crystalline Si, which allows for more variety in substrates,
particularly flexible plastics.
- Payback period similar to other thin-film technologies, about 2
- Typical cell efficiency = 5 - 8%
- Suffers serious degradation due to light exposure. (This levels
off at about a 20% decrease in efficiency)
Diselenide: This polycrystalline thin-film material has
extremely high absorptive ability, meaning 99% of light shining on
CIS will be absorbed in first micrometre of the material. CIS
technology uses a heterojunction interface, which means that an
electric field is created with an interface made of two different
semiconductor materials. This is in contrast to homojunction
interfaces used in crystalline Si cells, where two doped layers of
the same material are used.
- 2 year payback period. (2.7 yrs with frame)
- Typical module efficiency = 8 - 10%
- Max. cell efficiency = 18.8%
Telluride: Another prominent polycrystalline thin-film
material, CdTe shares many of the positive attributes with other
thin-film technologies such as high absorptivity, low cost, and
short energy payback period. There is, however, one issue with pure
CdTe cells; absorptive CdTe films tend to be very resistive to
electron flow, which leads to large internal losses. In order
to avoid these losses, a layer of p-type Zinc Telluride is added to
the underside of the intrinsic (not p-type or n-type) CdTe layer,
which is still able to create an electric field despite being
separated from the n-type layer.
- 0.9 year payback period. (1.9 yrs with frame)
- Typical module efficiency = 6 - 8%
- Max cell efficiency = 16%
Arsenide: GaAs is a monocrystalline thin-film material
that has extremely high efficiencies. It is very rarely used due to
the materials it contains; gallium is rarer than gold and is
therefore very expensive, while arsenic is a notoriously poisonous
element. Because of the expense of these cells, they are most
frequently used in solar concentrator systems, where the cell is
only about 0.25 cm2 in area.
- Holds record for highest ever cell efficiency of 34%
- One of the most expensive cells per unit area, roughly US
IntrinsicThin Layer (HIT) Doubles: This technology from Sanyo
Solar utilizes a bifacial effect for overall improved power
production. Light that is reflected off buildings and other
reflective surfaces is absorbed on the underside of these panels
and contributes to overall efficiency. A single thin crystalline
silicon wafer is surrounded on either side by ultra-thin amorphous
These panels are ideal for applications such as carport shading
due to the large open space below and high reflectivity potential.
In vertical panel installations, HIT Double panels can potentially
produce 34% more power than HIT Standards.
- HIT Double 190W module has efficiency of 15.7% (cell efficiency
- HIT Standard 205W module has efficiency of 17.4% (cell
efficiency of 20.2%)
*HIT panel efficiencies are measured at Standard Test Conditions
(STC), which do not take into account the bifacial
characteristics of the HIT Doubles. These panels may produce 110%
(or more) of their STC rating, depending on installation design,
location, and reflectivity.
Dye Solar Cell (DSC, 3rd
Generation PVs): This thin-film technology uses a
roll-to-roll manufacturing process that is inexpensive and enables
the use of flexible substrates. The process can be highly automated
by using machinery that is very similar to those used in laminated
glass manufacturing plants.
As a result of this simple production process, the overall
embodied energy of the cells is very low. As stated in the DCS
Solar Technology brochure, "Calculations carried out in Europe and
Australia have determined that the manufacturing processes… should
result in low embodied energy of 32 kWh per sq. metre with the main
contribution due to the embodied energy of the two glass
substrates." The energy payback period calculation in the DSC
Basics section below proves this to be an extremely short payback
Titanium dioxide (TiO2) nanocomposites, also known as
Titania, attempts to replicate the photosynthetic process in
plants. The titania material is referred to as a 'light sponge'
because of its high surface area, which allows it to perform in
less than ideal conditions, such as cloudy, smoky, or shady
- Cell efficiency = 9-10%
- Module efficiency = 5-7%
- 0.31 year payback period = (32 kWh/m2) / [(1700 kWh/m2-yr) *
0.06] , where:
- 1700 kWh/m2-yr = average yearly insolation
- 0.06 = average module efficiency
Dye-sensitised cell: a dye monolayer chemically absorbed on the
semiconductor is a primary absorber of sunlight; free charge
carriers are generated by electron injections from a dye molecule,
excited by visible raditation.
Advantages of DSC:
- Much less sensitive to angle of incidence (good in refracted in
- Can be designed for operation at very low light levels because
of the high internal surface area of titania ('light sponge')
- Wide range of optimal temperatures
- Much less sensitive to partial shading
- Manufacturing is cheap and easy, needs only commonly available
- Significantly lower embodied energy than other solar cells
Australian Manufacturers of DSC PV modules:
Sizing a photovoltaic (PV) system is easy to do. PV systems can
reduce greenhouse gas emissions and provide free electricity. Due
to the low current cost of electricity, system costs can generate a
range of payback periods depending on where the system is to be
installed. If it is in a rural or remote situation, PVs can be less
expensive than connecting to the grid. In close-grid connection or
urban contexts, payback periods can be from 12 to 20 years.
Nonetheless, many new developments are finding installation of
PVs worthwhile either from a marketing or PR 'feel good' standpoint
or as part of a legislative compliance pathway. One such pathway is
through BASIX, which is a way of minimizing overall greenhouse
The best way of reducing the capital cost of a new PV system is
to reduce the energy load on the system. The best way to do this is
- avoid consumption where possible e.g. use climate
sensitive design and materials selection to minimise space
heating and cooling;
- shift energy sources where possible e.g. use gas cooking
and gas backup solar hot water systems; and
- use the most efficient appliances and lighting possible.
A decision as to whether the system should be stand alone or
grid connected then needs to be made. Among the factors to be
considered in making this decision are:
- Is the grid reliable?
- Is the extra cost and maintenance of batteries warranted?
- What will the supply authority pay for the power supplied into
- What is the likely annual income from the Renewable Energy
- How does the peak energy consumption within the development
relate to the peak demand in the grid?
All of these issues can have an impact on the decision to grid
connect or stand alone. In urban situations the most ecologically
and socially sustainable decision is likely to be grid connected.
This ensures that excess energy is available for others to use and
as the initial system costs are generally lower and the excess
energy is sold to generate additional income, grid connected
systems are likely to have the lowest overall cost. A counter view
that grid connected systems do nothing to modify overall
consumption is worthwhile noting.
To reduce energy consumption across all dwellings, new
regulations have been implemented across Australia that require a
minimum standard of performance for most household appliances. Such
standards include the Minimum Energy Performance Standards (MEPS)
and the Water Efficiency Labelling and Standards (WELS)
Scheme. When buying a new dishwasher or refrigerator, for
example, keep in mind that a more energy and (hot) water efficient
appliance will facilitate smaller PV array size (and cost).
The following links provide a step-by-step guide to sizing a
photovoltaic system. As individual's needs vary significantly, so
will PV systems. This guide attempts to cover most scenarios, but
modifications may be necessary to optimize system performance.
Prior to installing a PV system, a building owner needs to
decide what percentage of their electricity demand they would like
the PV system to provide. Two basic categories of PV systems
Stand-alone: A stand-alone PV system uses
battery banks to store electricity for use at night or during
cloudy periods. This option is most practical in rural areas where
connecting to the power grid is prohibitively expensive. A major
benefit of this system is that a house or building's carbon
emissions from electricity generating sources are entirely
Grid-tied: This system uses PV panels to
augment the electric grid's supply of power, to varying degrees.
This allows for many system options, as it is not necessary for the
PV system to provide one hundred percent of the building's power
- Zero (Net) Consumer: This system uses the infrastructure of the
electricity grid as a storage medium, where the PV array produces
excess electricity during daylight hours, receiving a credit from
the power supplier, and buys it back at night using the credit.
This system eliminates a building's net carbon emissions.
- Maximise Roof Coverage: Recent technological developments have
allowed photovoltaic cells to be integrated into building
materials. In order to maintain continuity, roofs are being made
entirely of photovoltaic modules or roofing tiles that have PV
cells built-in (e.g. GreenPlate and PV Solar). Although
aesthetically pleasing, design and site evaluation is critical for
this option as shadows can have a large impact on some PV types
(polycrystalline in particular).
- Maximise Payback and Net Present Value: One of the most
appealing features of PV systems is their practicality for
small-scale applications. However, in order to minimise the time it
takes for the system to pay for itself (payback period), it is
important to properly match system components and size them
appropriately. e.g. : With some systems, jumping from 24 to 28 or
48 to 52 cells requires an additional inverter. This small gain in
electricity production does little to offset the cost of another
inverter, which is usually one of the most expensive parts of a PV
- Meeting a Percentage of the Demand: This is the most common
application of grid-connected PV systems. The arrays may be
sized to provide electricity for a certain appliance or to fit
conveniently and discretely on a roof. A useful technique to
consider in modifying consumption to offset the tendency to not
draw limits around power consumption is to use inverters with
sophisticated inbuilt communication software. Many systems have
this as a standard offer and can be read via LED/liquid crystal
displays on the unit or remote display panel, or on a resident's PC
where daily power generation is displayed against use.
Benefits and limitations of each system should be carefully
considered when choosing a system, as several options may not be
economical or spatially practical depending on the project
To skip directly to the sizing worksheets, follow the links
The first step in designing a PV system is to quantify the
electric demand needed to be satisfied. Depending on the
system option chosen the previous section, an appliance-specific
interactive sizing spreadsheet is available here,
or previous electricity invoices may be used to estimate quarterly
and yearly electricity consumption in retrofits. This approach will
not be as useful if new appliances, energy sources or renovations
are involved. If referring to utilities invoices, including power
consumed (kWh) at each tariff rate is critical, as it is the same
electricity sold at differing rates. e.g. In Queensland, Energex
has a 3-tiered rate for household power. Tariff 11, 31, and 33 are
priced differently and are listed separately on the invoice. The
total power consumed at each rate (kWh) is additive.
One of the most common causes of PV owners being unhappy with
the performance of their system is poor array placement. It is
extremely important to be aware of the year-round solar access of
an area when placing a PV system; a rooftop that is fully exposed
to the sun in January may be shaded by trees or other buildings for
9 months of the year. The impact of shading can be reduced by
specifying system types that are less susceptible to shadow
impacts, e.g. amorphous cells. The easiest method for determining a
site's solar access is with a Solar Pathfinder. This device shows
the sun's path across the sky for every month of the year and the
corresponding shadows produced at the device's location. For more
information visit: http://www.solarpathfinder.com/homepower.html
Another important consideration when sizing a PV array is the
amount and intensity of sunlight your particular area receives on a
yearly basis. In some locations with moderate to low levels of
solar energy (insolation) or too much overshading, photovoltaics
may not be the most economical source of 'green' power. Most
locations in Australia, however, receive more than enough sunlight
to make PV systems cost competitive with any energy source.
Panel Mounting Angles
Most small PV arrays have fixed panels that do not track the
sun's daily path across the sky. Panels achieve their maximum
efficiency when they are perpendicular to the sun at solar noon,
which often does not equate to 12:00 PM. Solar noon is defined as
the time at which the sun is at its daily zenith. In the southern
hemisphere, out of the tropics, panels should be facing north to
take advantage of the sun's daily zenith. Conversely, in the
northern hemisphere, also out of the tropics, panels should be
The tropics are defined as the area that lies between the Tropic
of Cancer, at latitude +23.45° and the Tropic of Capricorn, at
-23.45°, with the equator dividing the region in two. In this
region, the sun's daily path may pass to the north or south,
depending on the time of year. This leads to complications in
sun-tracking systems, but for fixed panels, using the panel angle
guideline for sub-tropical locations is sufficient.
The angle at which panels are mounted varies according to the
time of year when it is desirable for the PV array to be most
efficient. In order to determine this angle properly, the
project location's approximate latitude must be known. A list of
Australian locations is available here.
Panel angle guidelines:
- Year-round optimal power:
Angle = Latitude
- Maximum power in
winter: Angle =
Latitude + 15°
- Maximum power in summer: Angle =
Latitude - 15°
For grid-tied applications, fixing the panel angle equal to a
location's latitude provides the best results on a year-round
basis. For stand-alone systems, however, an angle setting that
makes the most of the weak winter sun will ensure ample year-round
Once a site has been chosen and the amount of electricity the
array needs to provide is determined, the PV system can be sized.
Most appliances run on AC power, while PV arrays produce DC power.
A conversion process is required to create useable AC power, which
incurs small losses. These will be accounted for in the equations
Sunlight is clearly the most important element in photovoltaic
systems, but just how much power can a household derive from the
sun? This depends entirely on its location, which determines the
amount of insolation, or solar energy it is exposed to over a given
period of time. To find a value for average yearly insolation at a
location near the project site, refer to this table.
At this point in the sizing process, it is necessary to describe
grid-tied and stand-alone systems separately. Follow the links
below for more information on each system.
Grid-tied systems have the luxury of a free storage device,
the electric grid. When arrays produce more power than they are
consuming, a building's electric metre spins backwards. In
small-scale applications, the PV system simply slows the rotation
of the metre, saving the owner money and reducing greenhouse gas
emissions. Grid-tied systems also eliminate several components of
stand-alone systems that reduce the overall efficiency and increase
Now that yearly AC power demand (kWh/yr) and the insolation of a
location have been determined, the AC power rating (kW) of the
grid-tied PV/ inverter system can be calculated. Insolation is
given in units of kilowatt-hours per square metre per day
(kWh/m2-d) and because the amount of energy that hits
the earth's surface from the sun is roughly 1 kW/m2,
units of kWh/m2-d can be equated to hours of sunlight
per day. e.g.: From the table above, Perth receives a
yearly average of 6 kWh/m2-d. This is the same as saying
it receives sunlight for 6 hours a day at 1kW/m2.
PAC (kW) = Delec / (Iavg x 365 d/yr)
PAC = AC power of PV/ inverter system (kW)
Delec = electric demand of building (kWh/yr)
Iavg = average insolation of location (kWh/m2-d)
Photovoltaic modules operate at lower efficiencies as their
temperatures increase. In sizing an array, we need to consider the
effect temperature will have on the performance of the array. A
list of average daily high temperatures for locations across
Australia is located here.
= Tamb + [(NOCT - 20°) / 0.8] x S
Tcell = cell temperature (°C)
Tamb = ambient temperature (°C)
NOCT = Nominal Operating Cell Temperature, 45°C
0.8 = solar irradiance, 0.8 kW/m2
S = wind speed, 1 m/s
As the temperature of the cell increases beyond 25°C, the power
produced by the cell drops by approximately 0.4% / °C. An
equation to determine the amount of power that is lost from an
array using the location's average daily high temperature appears
Ploss = .004 x (Tcell - 25°)
Temperature derate = (1 - Ploss)
Ploss = power lost due to temperature (kW)
Tcell = cell temperature (°C)
.004 = temperature derating constant, 0.4% / °C
i.e. for every increase of 1°C above 25°C, there is an
efficiency drop of 0.4%
Imperfections in the manufacturing process can cause some PV
panels to be rated slightly higher than others in an array. When
these unequal panels are linked together the power output will be
slightly less than the down rated power multiplied by the number of
panels. This is referred to as 'mismatch' and can account for up to
a 3% reduction in the power output. An additional 3% decrease in
efficiency can be caused by mismatch due to dust or dirt on the
panels. Inverter inefficiencies also contribute to the loss of
power when converting from DC to AC power. 85-92% efficient
inverters are common in PV system applications. For these
calculations, a 90% efficiency is assumed.
PDC, STC = PAC / (dirt x mismatch x inverter x temp derate)
PDC, STC = PV array's DC rated power (kW)
PAC = PV array's AC rated power (kW)
- dirt = .97
- mismatch = .97
- inverter = .90
- temp. derate = .88
The PDC, STC value that has just been calculated is the amount
of power that the PV array needs to produce in order to supply
adequate AC power in the building. This value is also the relevant
kW rating value used to purchase PV modules. The equation
below can be used to determine the amount of PV panel area that is
required to produce this power. The value will vary according to
the panel's efficiency.
A (m2) = PDC, STC/ PV eff.
A = area of PV panels (m2)
PDC, STC= PV array's DC rated power (kW)
PV eff. = PV panel efficiency (decimal)
The result of this equation may then be divided by the area of
an individual PV module and rounded up to the nearest whole number.
This will be the total number of PV modules required in the array.
In a grid-connected system, arrays are generally wired in series to
increase the voltage through the wires and minimise losses. By
operating at a high voltage, current, which is inversely
proportional to voltage, is reduced. This allows for the use of
smaller diameter wires which can help to save money.
Stand-alone photovoltaic systems allow a building to become
electrically autonomous, but require a more detailed analysis and
design of the system than the basic grid-connected PV arrays. These
systems also require a significantly higher capital investment.
However, the capital cost of a PV array and battery bank for a
stand-alone system will generally be a fraction of the cost of
installing high voltage power lines between the project's location
and the nearest grid.
Sizing a stand-alone PV system requires a different approach
than a grid-connected array. The load, or demand, on the
grid-connected system was able to be quantified in Watts due to its
simplicity. For stand-alone sizing, appropriate voltages and
currents must be used in order to increase transmission efficiency
and reduce the risk of overloading the system. Because the product
of voltage (V) and current (I) equals the power (P) of the system
in Watts, these values can be altered inversely of each other while
keeping the same system Wattage. (P = I x V)
Battery capacity (C) is described in terms of Amp-hours (Ah),
which is the amount of current available over a given period of
time. In order to calculate the required battery capacity for a
stand-alone system, refer to the interactive appliance-specific sizing spreadsheet, and
take note of the total Watt-hours (Wh) consumed. A true stand-alone
system will at some point have to rely on this battery bank due to
inclement weather. To provide enough storage to remain autonomous
during these periods, multiply the day-long capacity requirement by
the maximum number of consecutive cloudy days expected.
Cbank = (Whtot / 0.9) / 24V x cloud factor
Cbank = battery bank capacity, (Ah)
Whtot = total Watt-hours of building, calculated on
0.9 = assumed inverter efficiency, 90%
24V = assumed system voltage
cloud factor = maximum number of consecutive cloudy days
The Coulomb efficiency of a battery is its ability to convert
input energy into energy that is available for use. This correction
factor is used to quantify the amount of Amp-hours that need to be
delivered to the batteries from the PV array. Assume a 90% Coulomb
Ah to batt.
Ah to batt. = Cbank / Coulomb
= battery bank capacity, (Ah)
Coulomb = 0.9, Coulomb efficiency
Batteries are sold with a standard rating that allows comparison
and specialization for certain applications. When sizing a battery
bank, the capacity value that is needed to supply the demands
within a building does not directly correlate to the rated capacity
of the batteries. Also known as the nominal capacity (Cnominal),
this value must be over-sized to account for additional losses.
Maximum Depth of Discharge, or MDOD, is a safety factor for the
battery bank that prevents it from being completely discharged,
which rapidly makes the battery unusable and unrecoverable. Unlike
PV panels, the efficiency of batteries decreases as the ambient
temperature decreases below 25°C. The following chart provides
rough temperature-adjusted multipliers to be included in the
nominal battery capacity equation;
The equation below is intended to account for these corrections
and determine the rated (nominal) capacity of the batteries. Assume
an MDOD of 80%.
= (Cbank x Mtemp) / MDOD
= rated battery bank capacity able to provide ample Cbank
Cbank = battery bank capacity (Ah)
Mtemp = Temperature multiplier, from above chart
MDOD = 0.8, Maximum Depth of Discharge
This nominal capacity value is the relevant Amp-hr value used to
purchase and connect batteries. The following equations help
determine the number of batteries that should be wired as a string
in parallel, and the number strings that should be wired in
series. Parallel wiring allows the current of a system to be
increased by adding each battery's current together. This is done
by wiring positive terminals to positive terminals and negative to
negative for each battery. Voltage stays constant across a parallel
arrangement. Series wiring adds voltages while the current stays
the same, and is achieved by wiring a positive terminal from one
string to a negative terminal on another string.
# of Strings
Bparallel = Cnominal / Cbattery
# of Strings = Vsys / Vbatt
Bparallel = number of batteries wired in parallel
# of Strings = number of strings wired in series
Cnominal = nominal battery bank capacity (Ah)
Cbattery = individual battery capacity (Ah)
Vsys = 24V, system voltage
Vbatt = 12V, individual battery voltage
Now that the battery bank has been sized, calculations must be
made that allow the PV array to provide this power. The equation
above that calculates the number of Amp-hrs to be delivered to the
battery bank. This value then needs to be adjusted for dirt and
mismatch that may occur on the PV array. The amount of power that
the PVs should provide before this derating is generally 5% more
than what is needed at the battery bank. Assume 5% derate for dirt
and other mismatch.
Ah from PV
from PV = (Ah to batt.) / Dirt
Dirt = 0.05
Insolation at the location's latitude is required to calculate
the number of modules that should be included in the array. The
same Amp-hrs required in Darwin could be provided by a PV system
that is much smaller than one in Hobart because of the higher
intensity of the sun at lower latitudes. A list of insolations at
various locations throughout Australia is available here. The following equations calculate the
required rating of each module, and the number of modules and how
they should be wired. Recall that 6 kWh/m2-d is equivalent to 6 hrs
of sun @ 1kw/m2 (1-sun).
PV rated Amps
PV rated Amps = (Ah from PV) / (hrs @ 1-sun)
PV rated Amps = Amps(A) needed @ 1-sun
Ah from PV = Amp-hrs produced by PV array before derating
Mparallel = (A needed @ 1-sun) / rated current (A)
Mparallel = number of modules wired in parallel
A needed @ 1-sun = Amps needed to be produced by array
Rated current (A) = individual module's rated power in Amps
The product of this equation should be rounded to the next
highest whole number in order to provide sufficient power. This is
the number of panels that should be wired in parallel, or with
positive terminals wired to positive terminals and negative
terminals to negative terminals. As with the battery bank, it is
assumed that the system's voltage is 24V in order to keep the
current under 100A. The majority of PV modules are 12V, so two
strings of modules wired in series must be connected to produce a
# of strings
Equation: # of
strings = Vsys / Vmodule
# of strings = number of PV strings wired in series
Vsys = 24V, system voltage
Vmodule = 12V, module voltage
The product of the number of modules wired in parallel and the
number of strings wired in series will give the total number of PV
modules that are required to produce the desired power.
US Department of Energy, Solar Technologies Program, http://www1.eere.energy.gov/solar/
M. Raugei, S.Bargigli, and S. Ulgiati, Energy and Life Cycle
Assessment of Thin Film CdTe Photovoltaic Modules, http://www.nrel.gov/pv/thin_film/docs/20theuropvscbarcelona4cv114_raugei.pdf
Sanyo Solar, sanyo.com/solar
All websites last accessed on 9/4/13.