Photovoltaics

What are Solar Cells?

Solar cells are devices which convert solar energy into electricity, either directly via the photovoltaic effect, or indirectly by first converting the solar energy to heat or chemical energy.

The most common form of solar cells are based on the photovoltaic (PV) effect in which light falling on a two layer semi-conductor device produces a photovoltage or potential difference between the layers. This voltage is capable of driving a current through an external circuit and thereby producing useful work.

The Origins of Solar Cells

Although practical solar cells have only been available since the mid 1950s, scientific investigation of the photovoltaic effect started in 1839, when the French scientist, Henri Becquerel discovered that an electric current could be produced by shining a light onto certain chemical solutions.
The effect was first observed in a solid material (in this case the metal selenium) in 1877. This material was used for many years for light meters, which only required very small amounts of power. A deeper understanding of the scientific principles, provided by Einstein in 1905 and Schottky in 1930, was required before efficient solar cells could be made. A silicon solar cell which converted 6% of sunlight falling onto it into electricity was developed by Chapin, Pearson and Fuller in 1954, and this kind of cell was used in specialised applications such as orbiting space satellites from 1958.

Today's commercially available silicon solar cells have light-to-electricity conversion efficiencies exceeding 15%, at a fraction of the price of thirty years ago. There are now a variety of methods for the practical production of silicon solar cells, such as amorphous, single crystal, polycrystalline, thick film, ribbon, sliver, etc. Solar cells can also be manufactured using many different materials (copper indium diselenide, cadmium telluride, gallium arsenide, etc).

How are Solar Cells Made?

Commonly, PV cells are made using either single crystal wafers, polycrystalline wafers or thin films of silicon.

Single crystal wafers are sliced (approx. 1/3  to 1/2 of a millimetre thick) from a large single crystal ingot, grown at around 1400°C. The silicon must be of a very high purity and have a near perfect crystal structure (see Figure 2 (a)).

Polycrystalline wafers are made by a casting process in which molten silicon is poured into a mould and allowed to set. Then it is sliced into wafers (see Figure 2 (b)). As polycrystalline wafers are made by casting they are significantly cheaper to produce, but are not as efficient as monocrystalline cells. The lower efficiency is due to imperfections in the crystal structure resulting from the casting process. Almost half the silicon is lost as sawdust in the two processes mentioned above.

Amorphous silicon, one of the thin film technologies, is made by depositing silicon onto a glass backing substrate from a reactive gas such as silane (SiH₄) (see Figure 2 (c)). Amorphous silicon is one of a number of thin film technologies. This type of solar cell can be applied as a film to low cost substrates such as glass or plastic. The silicon is called “amorphous” because it has a non-crystalline structure that is similar to glass found in windows and bottles etc..

Other thin film technologies include thin multicrystalline silicon, copper indium diselenide/cadmium sulphide cells, cadmium telluride/cadmium sulphide cells and gallium arsenide cells. There are many advantages of thin film cells including easier deposition and assembly, the ability to be deposited on inexpensive substrates or building materials, the ease of mass production and the high suitability to large applications.

In solar cell production the silicon has dopant atoms introduced to create a postive-type (p-type) and a negative-type (n-type) region and thereby producing a p-n junction. Dopant atoms (or dopants) are atoms of another element that are added to materials to control its conductivity. This doping can be done by high temperature diffusion, where the wafers are placed in a furnace with the dopant introduced as a vapour. There are many other methods of doping silicon. In the manufacture of some thin film devices the introduction of dopants can occur during the deposition of the films or layers.

A silicon atom has 4 relatively weakly bound (valence) electrons, which bond to adjacent atoms. Replacing a silicon atom with a dopant atom that has either 3 or 5 valence electrons will therefore produce either a space with no electron (a hole) or one spare electron that can move more freely than the others. This is the basis of how doping can be used to control the conductivity of materials. P-type doping, the creation of excess holes, is achieved by the incorporation into the silicon of atoms with 3 valence electrons, most often boron or aluminium. The “p” in p-type doping refers to what can be imagined as creating a positive “hole” in the valence band in Band Theory, which can move about under the influence of an electric potential. N-type doping, or the construction of extra electrons is achieved by incorporating an atom with 5 valence electrons, most often phosphorus. The “n” in n-type doping refers to the excess of negatively charged electrons to provide a constant supply of electrons that passes through the circuit in a PV system. (see Figures 3 and 4).

Once a p-n junction is created, electrical contacts are made to the front and the back of the cell by evaporating or screen-printing metal onto the wafer. The rear of the wafer can be completely covered by metal, but the front only has a grid pattern or thin lines of metal, otherwise the metal would block out the sun from the silicon and there would not be any output from the incident photons of light.

How Do Solar Cells Work?

To understand the operation of a PV cell, we need to consider both the nature of the material and the nature of sunlight. Solar cells consist of two types of material, often the p-type and n-type silicon. Light of certain wavelengths are able to ionise the atoms in the silicon (causing atoms to either gain or lose electrons) and the internal field produced by the junction separates some of the positive charges ("holes") from the negative charges (electrons) within the photovoltaic device. The holes are swept into the positive or p-layer and the electrons are swept into the negative or n-layer. Although these opposite charges are attracted to each other, most of them can only recombine by passing through an external circuit outside the material because of the internal potential energy barrier. Therefore if a circuit is made (see Figure 4), power can be produced from the cells under light because the free electrons pass through the load to recombine with the positive holes.

The amount of power available from a PV device is determined by;

•  the type and area of the material;
•  the intensity of the sunlight; and
•  the wavelength of the sunlight.

For example, single crystal silicon solar cells cannot currently convert more than 25% of the solar energy into electricity, because the radiation in the infrared region of the electromagnetic spectrum does not have enough energy to separate the positive and negative charges in the material. However PV cells made of multi-junction gallium arsenide and other similar alloys have achieved efficiencies as high as 31%.

Polycrystalline silicon solar cells have an efficiency of just over 20% at present and amorphous silicon cells, are currently about 10% efficient, due to higher internal energy losses than single crystal silicon. Other thin film cells besides amorphous silicon such as cadmium telluride and copper indium diselenide have achieved research efficiencies of 16% and almost 18% respectively, and the records are often being rewritten. It should be noted that commercially available PV cells conversion efficiencies are lower than the above percentages.

A typical single crystal silicon PV cell of 100 cm² will produce about 1.5 watts of power at 0.5 volts DC and 3 amps under full summer sunlight, of which the approximation of 1000Wm^-2 is used (Wm^-2 are the symbols that represent the Watts of energy for every square metre). The power output of the cell is almost directly proportional to the intensity of the sunlight. For example, if the intensity of the sunlight is halved the power will also be halved (see Figure 5).

An important feature of PV cells is that the voltage of the cell does not depend on its size, and remains fairly constant with changing light intensity. However, the current in a device is almost directly proportional to light intensity and size. This means that when people want to compare different sized cells, they record the current density, or amps per square centimetre of cell area.

The power output of a solar cell can be increased quite effectively by using a tracking mechanism to keep the PV device directly facing the sun, or by concentrating the sunlight using lenses or mirrors. However, there are limits to this process, due to the complexity and cost of the mechanisms, and the need to cool the cells. The current output is relatively stable at higher temperatures, but the voltage is reduced, leading to a drop in power output as the cell temperature is increased. More information on PV concentrators can be found later in this Portal file.

PV Panels

As single PV cells have a working voltage of about 0.5 V, they are usually connected together in series (positive to negative) to provide larger voltages. Panels are made in a wide range of sizes for different purposes. They generally fall into one of three basic categories:

• Low voltage/low power panels are made by connecting between 3 and 12 small segments of amorphous silicon PV with a total area of a few square centimetres for voltages between 1.5 and 6 V and outputs of a few milliwatts. Although each of these panels is very small, the total production is large. They are used mainly in watches, clocks, calculators, cameras and devices for sensing light and dark, such as night lights.
• Small panels of 1 - 10 watts (and 3 - 12 V with areas from 100cm² to 1000cm²) are made by either cutting 100cm² single crystal or polycrystalline cells into pieces and joining them in series, or by using amorphous silicon panels. The main uses are for radios, toys, small pumps, electric fences and trickle charging of batteries.
• Large panels, ranging from 10 to 60 watts (and generally either 6 or 12 volts with areas of 1000cm² to 5000cm²) are usually made by connecting from 10 to 36 full-sized cells in series. They are used either separately for small pumps and caravan power (lights and refrigeration) or in arrays to provide power for houses, communications, pumping and stand-alone power supplies (SPS).

Arrays and Systems

If an application requires more power than can be provided by a single panel, then larger systems can be made by linking a number of panels together. However, complexities arise because often very large quantities of power are required at specific voltages, and at a time and level of uniformity than can be easily provided directly from the panels. In these cases, PV systems are used to customise the output of arrays to better cater for the energy needs of the user, and generally are comprised of the following parts (see Figure 6):

(a)     a PV panel array, ranging from two to many hundreds of panels.
(b)     a control panel, to regulate the power from the panels;
(c)     a power storage system, generally comprising of a number of specially designed batteries;
(d)     an inverter, for converting the direct current to alternating current (eg. 240 Volts AC – like most Australian homes).
(e)     backup power supplies such as diesel generators (this is optional).

A framework or structure as well as housing for the system is generally required to dependably support and orientate the array towards the sun and keep the other components dry and clean (see Figure 7). Trackers and sensors to optimise the performance of the system are often viewed as optional in a PV system. However to ensure reliable performance, the design and installation of all PV systems in Australia should always be completed according to the Australian Standards:

• AS 4509        Stand-alone Power Systems Parts 1, 2 and 3.
• AS 4086.2     Secondary batteries for use with SPS - installation and maintenance.
• AS 5033        Installation of photovoltaic (PV) arrays.
• AS 2676        Guide to installation, maintenance … of secondary batteries in buildings.
• AS 3011        Electrical installations - Secondary batteries installed in buildings (LV batteries).
• AS 3010        Electrical installations – Supply by generating set. 

Arrays of panels are being increasingly used in building construction (building integrated), where they serve the dual purpose of providing a wall or roof as well as providing electric power for the building. Eventually as the prices of solar cells fall, building integrated solar cells may become a major source of electric power.

Trackers are used to keep PV panels directly facing the sun, thereby increasing the output from the panels. Trackers can nearly double the output of an array (see Figure 8). Careful analysis is required to determine whether the increased cost and mechanical complexity of using a tracker is cost effective in particular circumstances. A variety of trackers, which will take about 10 panels, are manufactured in Australia.

Arrays generally run the panels in series & parallel with each other, so that the output voltage is limited to between 12 and 50 volts, with higher amperages (the amperage are the units used to measure current). This is due to safety issues and to minimise power losses.

In February 2006, panels cost between $3 – 10 per peak Watt, depending on the PV technology. That is, a 50 Watt panel presently costs around $200. Ten years ago, this same ‘standard’ panel may have cost about $500 at a cost of about $8 - 10 per Watt.

The daily energy output from PV panels will vary depending on the orientation, location, daily weather and season. On average, in summer, a panel will produce about five times its rated power output in watt hours per day, and in winter about two times that amount. For example, in summer a 50 watt panel will produce an average of 250 watt-hours of energy, and in winter about 100 watt-hours. These figures are indicative only, and professional assistance should be sought for more precise calculations.

Energy storage is often necessary when power is required when the sun is not shining - either at night or in cloudy periods - or in quantities greater than can be supplied directly from the array. Specially designed "deep-cycle" lead acid batteries are generally used. Unlike normal batteries, they can discharge about half of their stored energy several thousand times before they deteriorate. Each battery is usually 2V, and the total battery bank usually has many batteries in series and parallel to give the required power rating. Battery banks need to be individually sized to suit the particular applications, depending on total daily solar radiation, total load, peak load and the number of days storage required. Generally, battery storage costs about $250 per kWh of energy stored for domestic sized systems.

Inverters transform low voltage DC power (eg 12V, 24V, 32V or 48V from batteries) into high voltage AC (generally 240 V in Australia). Inverters are necessary if mains-voltage appliances are to be used. In assessing the cost of the total system, it may be more economical to purchase an inverter and mass-produced consumer appliances than to use low voltage DC appliances, which may be more expensive than normal appliances.

Some appliances, such as high efficiency light globes are not presently available for low voltages. In this case, the cost of more panels must be balanced against the cost of an inverter. As a rule of thumb, inverters cost about $1 - $2 per watt of output, depending on size and features. For example a 1.2 kW sine wave inverter with energy management features costs approximately $2500. The major production costs of inverters are derived from the design, development, raw material, and product assembly factors of production. There are several Australian companies that manufacture inverters for the local and export market and currently local research is being conducted that focuses on substantially reducing the cost of large inverters.

Backup or auxiliary power supplies are required when complete reliability of electricity supply must be guaranteed, when it is uneconomical to provide battery storage for infrequent extended cloudy periods, or when some appliances have large and intermittent power requirements that cannot be met economically from the PV system. For further information on batteries, inverters and other enabling technologies, see the RISE Technology files.

Sometimes wind generators are used in conjunction with PV systems if the combination of sun and wind is viable. Small petrol or diesel generators are often used as the backup supply of power. These petrol or diesel generators are relatively cheap to purchase (less than $1000 per kW) but expensive to run. Several Australian companies are developing total hybrid supply systems that optimise the use of each component to the specific conditions of the application.

Reliability of PV's

All PV's are now manufactured to rigorous International Standards, which ensure a lifespan of at least 25 years. PV panels are generally made by sandwiching the solar cells between specially toughened high transparency glass, and an impervious backsheet of plastic. This is to exclude moisture from entering the panel and cause corrosion. This ‘laminated’ construction is so durable that all manufacturers of PV panels now offer a 10 year performance warranty. This guaranteed durability enhances the cost effectiveness of PV's, particularly in applications where maintenance is a prime consideration.

Figure 9 Graph showing component costs of PV system and price reduction over time.

Figure 9 shows the past and expected future relative proportion of cost of each element in a PV system. The cost of the cells makes up a very substantial proportion of the final cost, mainly due to the high purity silicon required.

PV Concentrators

Concentrator systems use large mirrors or lenses to concentrate and focus the sunlight onto a string of cells, thereby increasing the illumination and power output. The saving comes from the reduction in the number of cells required for a given power output by using the concept that "more light = greater power output" for solar cells (see Figures 10 and 11). The maximum concentration achievable is limited in practice to the equivalent of about 50 suns. Such facilities could be attractive for large, central power stations. Two drawbacks of these systems are that they can only use direct sunlight and therefore must track the sun, and they must also have some system to cool the cells. Several companies world-wide are looking into these systems including a group at Australian National University, which is currently constructing a large concentrating solar system to provide both electricity and hot water to a new student residence on the ANU campus.

Figure 10 PV Concentrator System (Courtesy of ACRE Ltd).

An Australian company, Solar Systems successfully converted 14 solar thermal concentrators at White Cliffs, South Australia, installed in the 1980s, to photovoltaic power generation in 1996 (see Figure 11). The 40 kW grid connected power station ran for around 6 years, generating valuable data on the performance and efficiency of this technology. The project ceased operation in December 2004 and the installation was dismantled (Solar Systems, 2007).

Solar Systems have also constructed four new concentrator dish power stations at Hermannsburg (192 kW), Yuendumu (240 kW), Lajamanu (288 kW) and Umuwa (220 kW) . Together they generate 940 kW and save 560,000 litres of diesel and 2060 tonnes of greenhouse emissions each year (Solar Systems, 2007).

Solar Systems are also developing a $420 million large-scale solar power plant in north-west Victoria. The 154MW solar power station will be connected to the national grid and generate clean electricity directly from the sun to meet the annual needs of over 45,000 homes with zero greenhouse gas emissions. The power station will be comprised of around 250 heliostats (sun tracking mirrors) in multiple arrays and towers that will concentrate the sun's energy by around 500 times into the high performance photovoltaic cells in the fixed 40 m high towers. Solar Systems has attracted a $75 million grant to the project under the Federal Government’s Low Emissions Technology Demonstration Fund (LETDF). The station will be constructed and commissioned over a six-and-half-year period to 2013, incorporating technology optimisation and commercial rollout stages (Solar Systems, 2007).

The PV Industry

The photovoltaic industry is growing rapidly as concern increases about global warming and as a result of falling prices from technological advancement. Australia has three main manufacturing plants (BP Solar, Sustainable Technologies International and Origin), which together have a manufacturing capacity of around 50MW of panels each year.

BP Solar’s Sydney Olympic Park facility is the largest manufacturing centre in the southern hemisphere and employs around 300 people. The facility has a maximum annual cell production capacity of 40MW, and a module production capacity of 10MW per year which operates continuously around the clock to supply the market (BP Solar, 2006).

Origin's US$15M plant in Adelaide is the latest edition to Australia’s manufacturing capacity and is now producing a small amount of PV panels with an approximate total capacity of 5 MW annual production. There are other smaller manufacturers such as Dyesol and CGCsolar. For a list of Australian manufacturers, wholesalers, consultants, associations and sales companies click here.

The total international production in 1997 was 130 MW worth more than $500 million. In 2004 the consolidated world total production of PV cells increased to 1146 MW in 2004 or around. $7 billion (see Figure 15). In 2004 the top five manufacturers of PV cells were; Sharp, Kyocera, Shell Solar, BP Solar, and RWE Schott Solar which accounted for 60 percent of the market.

Current Installations

In Australia and the USA, the emergence of green power schemes, which permit customers to choose renewable energy options, has added considerable impetus to the growth of the industry (click here to download a pdf of accredited green power generators). Some grid connected solar farms have been constructed including one at Kalbarri in WA, (see Figure 16), Singleton (Hunter Valley, see Figure 17), the Western Plains Zoo, the Sydney Olympic Village in NSW, Wilpena Pound in SA, and the King's Canyon National Park in NT. A recent announcement was the proposed development of the very large-scale photovoltaic power generation project for Perenjori. This project in the north-west of Western Australia comprises the construction of a 10 MW pilot plant, developed jointly by Perenjori Shire, Murdoch University and Prime Solar Ltd. This would be the largest PV installation in Australia, however there are economic and technical issues to be resolved at present.

For a list of more PV installations visit the BCSE Solar Installations page.

Many demonstration and education sites have been established in Western Australia to showcase PV including the Research Institute for Sustainable Energy’s Renewable Energy Display Centre, the Environmental Technology Centre, both at Murdoch University and the solar demonstration at Fremantle by APACE. There is also an Environmental Education Centre at Piney Lakes Reserve, the Rockingham Regional Environmental Centre, and Western Power’s World of Energy in Fremantle.

On the world stage, Australia is only a small player with an estimated current installed capacity of around 60 MW. The world total installed capacity is estimated to be around 3500 MW.

Bavaria, in Germany boasts the world’s largest single PV installation of 10 MW (comprising 3 solar parks), which is now fully operational adding to the collection of large German PV installations. For a list of the world's current top 50 largest photovoltaic power plants click here. In addition to constructed PV capacity, there is much generating capacity under construction and many proposed sites for new PV power plants. In the US the Stirling Energy Systems (SES) and Southern California Edison (SCE) have unveiled plans for the construction of an expansive 4,500-acre 500 MW solar generating station in Southern California. Another large PV farm that is in the planning stages is the system planned for former NATO airport in Rhineland-Palatinate, Germany. The area is 400,000 m² – enough space to build a 15 to 18 MW PV system.
 

The Future

The market for photovoltaic cells is presently growing at over 30% per year, and the cost of panels is declining continuously in real terms, due to both new technologies and mass production. There are confident predictions from leading PV manufacturers in USA, Japan and Europe that the price of PV power will be competitive with mains electricity within a few years.

These predictions generally refer to power at the panel, and do not take into account the various other system costs mentioned above. The price of the balance of systems components are not declining as rapidly as the cost of panels, so the total system costs will decline more slowly. This factor is encouraging research into appliances that can be used directly from the panels, and do not need to rely on inverters and battery storage. Integrating panels into buildings also reduces the balance of systems costs.

PV Research & Development in Australia

Photovoltaics Special Research Centre, University of NSW.

High efficiency polycrystalline cells, where the polycrystalline material is cheaper than single crystal silicon. In Australia both UNSW and ANU have research programs in this area.

School of Photovoltaic and Renewable Energy Engineering, Australian National University.

UNSW has an area of thin film device research and ANU, with their commercial partners, have developed the new  Sliver® technology that uses 90% less silicon than current solar PV modules at competitive cell and module efficiencies (see Figure 19).

Dyesol

Pacific Solar & CSG Solar

In 2002, Pacific Solar produced a small Crystalline Silicon on Glass (CSG) module (660 cm²) which has a solar conversion efficiency under standard conditions of 8.2%, which sets a world record for thin-film crystalline silicon. The crystalline nature of the silicon film ensures that it will last for decades even when exposed daily to harsh sunlight. Several scientific papers have been published that describe the CSG technology in detail. These are currently available from CSG Solar's website (Pacific Solar, 2004). CSG Solar AG, based in Thalheim near Bitterfeld (Sachsen-Anhalt), is preparing to expand manufacturing of photovoltaic (PV) modules using its patented CSG technology. This technology is the result of a ten-year research and development effort by an international team based in Sydney, Australia, under the leadership of world renowned experts in the field of crystalline solar cell technology. The CSG technology allows the production of PV modules using less than 2 µm thick crystalline silicon on a textured sheet of glass (CSG Solar AG, 2006).

Solar Sailor

Solar Sailor Holdings Ltd (SSHL) is an Australian unlisted Public Company founded in 1999 with over 130 shareholders. It owns three 100%-owned subsidiaries, Advanced Technology Watercraft Pty Ltd (ATW) an engineering company, Solar Sailor Pty Ltd (SSPL) a research and development company and Olympia Pty Ltd, which owns the Sydney Solar Ferry operated by Captain Cook Cruises (Solar Sailor, 2005).

In 2004 SSHL founded a 49% owned US subsidiary in Virginia USA, UOV LLC for the sole purpose of commercialising unmanned ocean vehicles using the SS 'hybrid marine power' (HMP) and 'solar wing' technology. The Chairman of SSHL is Hon Mr Bob Hawke, ex Prime Minister of Australia and the CEO is Dr Robert Dane, founder and ex NSW Green Ambassador. SSPL owns several patents in hybrid and solar wing technology and ATW is expressly focused on the engineering and design of HMP drives and 'solar wing' technology for a range of applications. The Sydney Solar Sailor Ferry has been used as a test platform for component technologies and has attracted over $1.5M in grants and sponsorship, as well as winning a string of environment, design, innovation and product acceptability awards. It has been operating commercially and profitably for 3 years in a tough market. (Solar Sailor, 2005).

Further Information

RISE Resources - Information regarding available renewable energy resources.

RISE Technologies - An extensive collection of information regarding renewable energy technologies.

RISE Applications & System Design - Renewable energy application information and system designs.

RISE System Displays - Case studies and information on installed renewable energy systems & performance data.

PV Applications - RISE Information Portal

For a comprehensive list of Australian PV suppliers, manufacturers, consultants and associations see Solarbuzz

IEA WEB PV Resources

Renewable Energy Pages from Oregon Department of Energy

IEA Australian PV Information

IEA PV Building Integrated

IEA Australia’s Cumulative Installed PV Power by Sub-Market

IEA Grid Connected Systems Case Studies

British Photovoltaic Association - PV WEB

Sandia's Photovoltaic Systems Program

Florida Solar Energy Centre - Photovoltaics Q&A

PV Research Centre, UNSW

CitiPower Energy Park

Energy Australia

Country Energy

Australia and New Zealand Solar Energy Society (ANZES)

CREST

International Solar Energy Society (ISES)

National Renewable Energy Laboratory (USA)

Photovoltaic Insider’s Report

Publications

Books
Green, Martin. A., Solar Cells: Operating Principles, Technology and System Applications, Englewood Cliffs, N.J.; Sydney: Prentice Hall, 1992
Komp, Richard, J. Practical Photovoltaics, Electricity From Solar Cells. Kampmann & Company, Inc. New York, 1984
Koltun, M.M. Solar Cells, Their Optics and Metrology. Allerton Press Inc. 1988.
Markvart, Tomas (ed), Solar Electricity, John Wiley & Sons Ltd, Chichester, 1995.
Zweibel, Kenneth., Harnessing Solar Power: The Photovoltaics Challenge, Plenum Press, New York, 1990

Magazines and Journals
Solar Progress - Published by Australia and New Zealand Solar Energy Society (ANZES).
ReNew Technology for a Sustainable Future - Published by Australian Alternative Technology Association (ATA).
 

References

BP Solar Webpage “An Introduction to BP Solar in Australia” (Online) http://www.bp.com.au/solar/default.asp (Accessed 16 Februrary 2007).

CSG Solar AG Webpage “CSG Solar AG signs Supply Agreement with IBC SOLAR AG and Blitzstrom GmbH” (Online) http://www.csgsolar.com/pages/medias_ne.php?lang=en (Accessed 16 February 2007).

Dyesol, 2005. Webpage “Technology” (Online) http://www.dyesol.com/index.php?page=Technology  (Accessed 16 February 2007).

Pacific Solar, 2004. Webpage “CSG” (Online) http://www.pacificsolar.com.au/csg.html (Accessed 16 February 2007).

Photovoltaic Insider’s Report - Vol. X No. 2 February 1991, Vol. XIV No. 4 April 1995, Vol XVII No. 2 February 1998.

Solar Sailor, 2005. Homepage (Online) http://www.solarsailor.com (Accessed 16 February 2007).

Solar Systems, 2007. Webpage (Online) http://www.solarsystems.com.au/White%20Cliffs%20case%20study.pdf (Accessed 16 February 2007).