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Australia receives abundant quantities of direct insolation from the sun. Most of the country receives over 1600kWh per square metre per year of solar radiation, while in an area near the Western Australia-Northern Territory border over 2500kWh per square metre per year of solar radiation is received.24 This is only 10% less than the amount of solar radiation received in the Sahara Desert, where the greatest incidence of solar insolation occurs.25 The amount of solar radiation received by the earth is far in excess of the present and foreseeable needs of the human race. On a worldwide basis, it has been calculated that enough sunlight reaches earth every day to satisfy mankind's energy requirements for 15 years.26 It also helps to put the projected shortage and depletion of non-renewable energy resources into context when it is realised that the earth's surface receives every year approximately 1000 times the amount of energy contained in the total known reserves of petroleum.27

The problem with solar energy is not the supply, but the means of harnessing the supply. As stated by Ewers:28

Since the sun's rays are diffuse, utilizing solar energy [is] like trying to harness 100 million fleas and then teaching them all to jump in the same direction at the same time.

21 C Flavin, Electricity's Future: The Shift to Efficiency and Small-ScalePower,Worldwatch Institute, Washington, DC, at 30.

22 For a general discussion of renewable energy resources and their role in modern society, see Richard Ottinger and Rebecca Williams, 'Renewable Energy Sources for Development' (2002) 32 Environmental Law 331, available at <www.law.pace.edu/energy/documents.html> (accessed 26 January 2005); RHaas, W Eichhammer et al, 'How to Promote Renewable Energy Systems Successfully and Effectively (2004) 32 Energy Policy 833.

23 For a general discussion of solar energy technology, see the material available at <www.worldenergy. org/wec-geis/publications/reports/ser/solar/solar.asp> (accessed 18 January 2005); UNDP et al, World Energy Assessment, at 235ff; World Energy Council, Energy for Tomorrow's World, ch 2.

24 National Energy Advisory Committee, Renewable Energy Resources in Australia, AGPS, Canberra, 1981, at 7.

25 Australian Academy of Science, Report of the Committee on Solar Energy Research in Australia, Report No 17, Canberra, 1973, 25.

26 Solar Energy Research Institute of Western Australia, The Solar Prospect, Perth, 1981, at 1; Business Week, 9 October 1978, 92; W Lawrence and J Minan, 'The Competitive Aspects of Utility Participation in Solar Development' (1979) 54 Indiana LJ 229 at 230.

27 TWest, 'Photovoltaics: A Quiet Revolution' (1982) 3 (No. 14) Energy Detente 1 at 1. See also D Halacy, The Coming Age of Solar Energy, Harper & Row, New York, 1973, at 24; H Lof, 'Solar Energy: An Infinite Source of Clean Energy' (1973) 410 Annals 52.

28 W Ewers, Solar Energy: A Biased Guide, ANZ Book Co, Sydney, 1977, at 9.

One aspect of the problem is the relatively low energy intensity of direct sunlight. The worst aspect of the problem, however, is the variability of the energy supply at any given location on earth, due to cloud cover and seasonal effects.

Solar energy can be used for both space and water heating and cooling and for the generation of electricity. Solar heating and cooling systems can be divided into active systems and passive systems. An active system is that in which solar collectors are installed to capture solar energy that is conveyed by some mechanical means to the space or water to be heated or cooled. The mechanical means may consist of pumps, fans, valves and thermostats. Under this system the solar radiation is converted into thermal energy that is used to heat a working fluid (commonly air or water). This fluid is then transported to the area where it is applied to space or water heating or cooling.29 In contrast to the active system, a passive system does not employ any solar collector panels or mechanical devices but seeks to control temperature by the architectural features of the building itself. Critical features in a passive solar home are the size and placement of windows, the type of materials of which the walls and ceiling are constructed and the orientation of the building towards the sun. The building should be oriented on an east-west axis with a long wall facing north; in this way the whole north wall acts as a built-in solar collector.30

Electricity can be generated by solar energy using the principles of thermal generation and by photovoltaic conversion. In a solar thermal conversion system, the solar radiation is used either directly or via a heat exchanger to generate steam, which drives a conventional steam turbo-generator plant and produces electric-ity.31 There are two thermal methods of generating electricity by solar radiation, the 'power tower' concept and the dispersed power applications. The 'power tower' concept involves a central receiver located at the top of a tower receiving radiation from a collection of surrounding reflecting mirrors (heliostats) which track the sun. A heat transfer fluid circulates through the central receiver and transports the heat energy to an energy conversion system.32 The dispersed power applications employ rows of parabolic reflectors to focus solar radiation onto pipes where gases or molten salts transfer the heat to storage tanks. From there the stored heat is used to generate steam to drive a conventional turbine.33

29 See, e.g., J Riley, R Odland and H Barker, Standards, Building Codes and Certification Programs for Solar Technology Applications, ReportNo. SERI/TR-53-095, United States Department of Energy, Washington, D.C., 61; W Berryhill and W Parcell, 'Guaranteeing Solar Access in Virginia' (1979) 13 URichmond L Rev 423,428; CSIRO, Information Service, Solar Heating and Cooling of Buildings, Melbourne, 1978, at 1-2.

30 See e.g., US Dept of Energy, Passive Solar Heating, Cooling and Daylighting, <www.eere.energy.gov/ RE/solar_passive.html> (accessed 20 July 2005); 'Passive Solar Guidelines', in A Sourcebook for Green and Sustainable Building, <www.greenbuilder.com/Sourcebook/PassSolGuide1-2.html> (accessed 20 July 2005); National Renewable Energy Laboratory, Introduction to Passive Solar Heating and Daylighting, <www.nrel.gov/clean_energy/passivesolar.html> (accessed 20 July 2005); Note, 'The Right to Light: ACom-parative Approach to Solar Access' (1978) 4 Brooklyn JInt L 221, at 221; Texas Energy and Natural Resources Advisory Council, Citizens' Solar Guide, Austin, Texas, 1982, at 6, 19.

31 See Australian Academy of Science, Report of the Committee on Solar Energy Research in Australia, AGPS, Canberra, 1973, at 47.

32 Riley, Odland and Barker, Standards, 109; A Skinrood, 'Recent Developments in Central Receiver Systems' (1982) 6 Sunworld 98; A Hunt, 'Small Particle Heat Exchange Receiver' (1982) 6 Sunworld 60.

33 Law Reform Committee of South Australia, Solar Energy and the Law in South Australia, Discussion Paper, Adelaide, 1978, at 57-58.

Figure 2.2 Operation of silicon solar cell (Source: West, 'Photovoltaics: A Quiet Revolution' (1982) 3 (No. 14) Energy Detente 1, at 5.)34

The photovoltaic effect is the tendency of certain materials to generate electricity when exposed to direct solar radiation. What occurs is that the sunlight causes electrons to be released, resulting in an increase in the electrical conductivity of the material. If the material is constructed so as to have a built-in force that drives the electrons to the front or back, an electric current will flow through externally connected wires.35

The photovoltaic effect is created in photovoltaic cells. These cells can consist of any materials that are classed as 'semi-conductors', the most common type consisting of a thin wafer of crystalline silicon coated on each side with boron and phosphorus. When silicon is exposed to sunlight, electrons are released and a 'P/N'junction is created. This is where the electrons and the spaces where the electrons were originally are separated. The effect of this is to create a voltage across the thickness of the silicon wafer.36 An electric current will flow if an external electrical circuit is connected to the front and back surfaces of the solar cell. This is shown inFigure 2.2.Groups of cells are usually mounted onto a module with a generating capacity of 100 watts. For increased power supplies, modules are connected into larger arrays. The electricity generated by the array is stored in a battery bank via a charge controller, which prevents overcharging during the day and discharge at night. Equipment operating on direct current electricity can

34 See also 'How Do Photovoltaic Cells Work?' <www.sustainable.energy.sa.gov.au> (accessed 22 January 2005).

35 D Nevin, 'Solar Technology', in J Minan and W Lawrence (eds), Legal Aspects of Solar Energy, Lexington Books, Massachusetts, 1981, at 22-3; Redfield, 'Photovoltaics: An Overview' (1981) 3 Solar Law Reporter 217 at 217; Chalmers, 'The Photovoltaic Generation of Electricity (1976) 235 Scientific American 34.

36 See West, 'Photovoltaics', at 5; D Fousel, 'New, Newer, Newest in Photovoltaics' (1982) 8 (No. 9) Northern Cal Sun 6, at 7.

obtain electricity directly from the battery bank. Equipment requiring alternating current must have an inverter inserted between the equipment and the battery bank.

The major advantages of solar cells are that they have no moving parts, require little maintenance, require no fuel and do not create any pollution. In addition, the material from which they are usually manufactured, silicon, is found in abundant quantities throughout the earth. Unfortunately, however, the cells have a low efficiency, and as a consequence large arrays of cells are required to produce useful quantities of electricity. The other closely allied disadvantage is that of cost. Although silicon is abundant in supply, solar cells require an extremely pure monocrystalline form, which is complex and expensive to manufacture. Despite this cost disadvantage, solar cells have already been put to a variety of different uses, mostly in remote areas where the reliability and low maintenance requirements of the cells compensate for their cost of construction.

Legal issues associated with the exploitation of solar energy include the need to guarantee access to the direct rays of the sun and the removal of building and planning controls that act as a barrier to resource development.37

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