Photovoltaic Technology & Installation

Photovoltaic Technology:

  • Overview: 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.

Photovoltaic Installation:

  • Overview: Provides introductory information on energy conservation and contains links to step-by-step sizing guide.
  • Grid-Tied 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 some calculations.

Australian Locations' Insolation Spreadsheet

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.

Photovoltaic Technology:


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:

Crystalline Silicon

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 times over.

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, and cost.

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 Modules:


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 modules.

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.

Amorphous Silicon (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.

a-Si basics:

  • Payback period similar to other thin-film technologies, about 2 years.
  • Typical cell efficiency = 5 - 8%
  • Suffers serious degradation due to light exposure. (This levels off at about a 20% decrease in efficiency)

Copper Indium 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.

CIS Basics:

  • 2 year payback period. (2.7 yrs with frame)
  • Typical module efficiency = 8 - 10%
  • Max. cell efficiency = 18.8%

Cadmium 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.

CdTe Basics:

  • 0.9 year payback period. (1.9 yrs with frame)
  • Typical module efficiency = 6 - 8%
  • Max cell efficiency = 16%

Gallium 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.

GaAs Basics:

  • Holds record for highest ever cell efficiency of 34%
  • One of the most expensive cells per unit area, roughly US $40/cm2.

Heterojunction with 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 silicon layers.

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 of 18.8%)*
  • 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 period.

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 locations.

DSC Basics:

  • 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 reflected light)
  • 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
  • BIPV
  • Manufacturing is cheap and easy, needs only commonly available processing equipment
  • Significantly lower embodied energy than other solar cells

Australian Manufacturers of DSC PV modules:

Photovoltaic Installation:


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 emissions.

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 to:

  • 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 the grid?
  • What is the likely annual income from the Renewable Energy Certificates (RECs)?
  • 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.

System Options

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 are:

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 eliminated.

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 needs.

  • 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 system.
  • 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 location.

To skip directly to the sizing worksheets, follow the links below:

Electric Demand

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.

Site Evaluation

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:

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 facing south.

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 electricity.

Sizing the Array

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 below.

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

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 the cost.

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.

To find:             PAC (kW)

Equation:          PAC (kW) = Delec / (Iavg x 365 d/yr)

Where:             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.

To find:             Tcell

Equation:          Tcell = Tamb + [(NOCT - 20°) / 0.8] x S

Where:             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 thus:

To find:             Ploss

Equation:          Ploss = .004 x (Tcell - 25°)

Temperature derate = (1 - Ploss)

Where:             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.

To find:             PDC, STC

Equation:          PDC, STC = PAC / (dirt x mismatch x inverter x temp derate)

Where:             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.

To find:            A (m2)

Equation:          A (m2) = PDC, STC/ PV eff.

Where:             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 Systems

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.

Battery Basics

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)

Sizing the Battery Bank

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.

To find:             Cbank

Equation:          Cbank = (Whtot / 0.9) / 24V x cloud factor

Where:             Cbank = battery bank capacity, (Ah)

Whtot = total Watt-hours of building, calculated on spreadsheet

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 efficiency.

To find:             Ah to batt.

Equation:          Ah to batt. = Cbank / Coulomb

Where:             Cbank = 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;

Temperature (°C)
















The equation below is intended to account for these corrections and determine the rated (nominal) capacity of the batteries. Assume an MDOD of 80%.

To find:             Cnominal

Equation:         Cnominal = (Cbank x Mtemp) / MDOD

Where:            Cnominal = 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.

To find:             Bparallel

# of Strings

Equation:          Bparallel = Cnominal / Cbattery

# of Strings = Vsys / Vbatt

Where:             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

Sizing the Array

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.

To find:            Ah from PV

Equation:         Ah from PV = (Ah to batt.) / Dirt

Where:             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).

To find:             PV rated Amps

Equation:          PV rated Amps = (Ah from PV) / (hrs @   1-sun)

Where:              PV rated Amps = Amps(A) needed @ 1-sun

Ah from PV = Amp-hrs produced by PV array before derating

To find:             Mparallel

Equation:          Mparallel = (A needed @ 1-sun) / rated current (A)

Where:            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 24V system.

To find:             # of strings

Equation:          # of strings = Vsys / Vmodule

Where:             # 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,

M. Raugei, S.Bargigli, and S. Ulgiati, Energy and Life Cycle Assessment of Thin Film CdTe Photovoltaic Modules,

Sanyo Solar,


All websites last accessed on 9/4/13.