Solar energy is special. Together, photovoltaics and solar heat can eliminate the need for fossil fuels. The solar resource utilised by photovoltaics and solar heat is hundreds of times larger than all other energy resources combined, including fossil, nuclear, geothermal and the other renewables, and is hundreds of times larger than required to provide all of the world’s energy.
Australia receives 30,000 times more solar energy each year than all fossil fuels combined. Collection of solar energy uses only very common materials and has minimal environmental impact over unlimited time scales. No other energy source can make claims that come anywhere near these.
Australia has a particularly strong presence in the worldwide photovoltaics industry that can be built upon to create a major export-oriented technology-rich industry.
Photovoltaics
Photovoltaics (PV) is an elegant technology for the direct production of electricity from sunlight.
About 90 per cent of the world’s PV market is serviced by crystalline silicon solar cells. Sunlight causes electrons to become detached from their host silicon atoms. Near the upper surface is a ‘one-way membrane’ called a pn-junction. When an electron crosses this junction it cannot easily return, causing a negative voltage to appear on the sunward surface (and a positive voltage on the rear surface). The sunward and rear surfaces can be connected together via an external circuit containing a battery or a load in order to extract current, voltage and power from the solar cell.
PV initially found widespread use in niche markets such as consumer electronics, remote-area power supplies and satellites. Now, as costs decline, millions of PV systems are being installed on house roofs in cities. The worldwide PV industry has been doubling every 20 months since 2000. Production is currently five to six gigawatts per year. Mass production is causing steady reductions in cost.
Most PV systems are mounted on fixed support structures, such as house roofs. Some PV systems are mounted on sun-tracking platforms to maximise output. Others use sun-tracking concentrators to concentrator light, by 10 to 1000 times, onto a small number of highly efficient solar cells. The concentrators can be reflecting parabolic troughs or dishes, a central tower surrounded by a field of reflecting heliostats or a refracting Fresnel lens. These concentrators are essentially identical to those used by concentrating solar thermal systems.
PV systems mounted on house roofs can be used to achieve household carbon neutrality. A collector area of about 25m2 is needed to neutralise a 5-star (energy rating) house that has gas space heating, solar/gas water heating and efficient electrical appliances. Such a house exports more electricity to the grid during the day than it imports at night. An additional 10m2 of PV panel is required to offset the annual greenhouse gas emissions of an efficient car.
Hybrid PV/thermal micro-concentrator systems on house roofs are being developed by the Australian National University and partners to provide solar PV electricity, solar water heating, solar air heating and solar air conditioning – a complete home energy solution.
PV panels on house roofs compete with retail electricity prices, which are three times higher than wholesale electricity prices. When the cost of rooftop PV generation falls below the daytime retail electricity price (‘grid parity’) then the PV industry will enjoy explosive growth as hundreds of millions of homeowners adopt the technology. Grid parity is soon expected to be achieved in many countries due to falling PV costs, rising fossil fuel costs, the introduction of carbon pricing and the introduction of time-of-use tariffs.
Time-of-use tariffs properly reward PV systems for generating during sunny summer afternoons when peak loads caused by air conditioning, commerce and industry lead to high energy prices. In common with solar thermal electricity, production of PV power in large systems in arid sunny regions is constrained by lack of carbon pricing, but is likely to soon become common.
Baseload power and storage
It is sometimes claimed, wrongly, that solar energy cannot dominate energy production because the sun doesn’t shine at night.
Options for the provision of stable and continuous solar power include: actively shifting loads from night to daytime; wide geographical dispersion of solar systems to minimise the effect of cloud; precisely predicting solar energy output using satellite imagery; diversification of energy supply to include many renewable sources; the judicious use of small amounts of natural gas; and storage.
Pumped hydro (where water is pumped uphill during the day and released through turbines at night to provide energy) is an economical and commercially available storage option. Lakes covering only 25km2 (one square metre per person!), either fresh water or seawater, can provide 24-hour storage of Australia’s entire electricity production. In the longer term, intercontinental high voltage DC transmission could greatly reduce the need for storage.
Environmental impacts
The solar energy industry has minimal environmental impact – only about 0.3 per cent of the world’s land area would be required to supply all of the world’s energy requirements. The area of roof is sufficient to provide all of Australia’s electricity, using PV panels.
We will never run out of the raw materials for solar energy systems because the principal elements required (silicon, oxygen, hydrogen, carbon, sodium, calcium, aluminium and iron) are among the most abundant on earth. Old PV systems can be recycled without the generation of toxic by-products. Gram for gram, advanced silicon solar cells produce the same amount of electricity over their lifetime as nuclear fuel rods. Per tonne of mined material, solar and wind energy systems have 100-fold better lifetime energy yield than either nuclear or fossil energy systems.
The time required to displace CO2 equivalent to that invested in construction of a PV system is in the range of two to four years, compared with typical lifetimes of 30 years. CO2 payback and price are directly linked (via material consumption), so CO2 payback times will continue to fall, and will end up below one year.
The future of solar energy
All high-temperature solar thermal systems are based on sun-tracking concentrators. There is extensive crossover between the technology of PV and solar thermal concentrators. The concentrating systems are essentially the same, with the major technical difference being the solar receiver mounted at the focus – a black solar absorber in one case, and a PV array in the other. Since current efficiencies are similar, the cost of energy produced by the two types of system is also similar.
The efficiency of PV is eventually likely to rise above 60 per cent, compared with the current world record efficiency of 43 per cent. The cost of PV systems can be confidently expected to continue to decline for decades – as has happened with the related integrated circuit industry. The fact that PV uses sunlight directly, rather than converting the light into heat or other forms, gives PV a thermodynamical advantage.
PV and solar heat are natural partners. Together, they can eliminate fossil fuels. In conjunction with pumped hydro and intercontinental transmission, 60 per cent efficient solar cells manufactured from highly engineered materials, and placed at the focus of 1000 sun concentrators, can provide much of the world’s electricity.
Low-temperature solar collection can heat water for domestic and industrial use, and to heat and cool buildings. High-temperature solar can provide power, storage, process heat and thermochemicals.
The Australian PV industry
Photovoltaics is an area of real Australian research and commercialisation strength. Photovoltaics is by far Australia’s strongest innovation performer in the area of renewable energy technology in terms of performance metrics (research papers, citations, patents, students, prizes, competitive grants, peer review, royalties and commercialisations).
Two large, well-known PV research groups are at the Australian National University (ANU) and the University of NSW (UNSW). Many smaller groups are building strength. ANU and UNSW have many active commercialisations, including the buried contact, crystalline silicon on glass and SLIVER solar cell designs, and a
PV/thermal hybrid system.
BP Solar manufactures solar cells in Sydney, and several other Australian companies are soon to commence Australian manufacturing of PV cells. Solar Systems is commercialising large PV concentrator systems, and will soon construct a world-scale 154 megawatt PV solar system in Mildura.
It is important for Australia to have a balanced energy portfolio, without an excessive focus on carbon capture and storage. Greatly increased support is needed for solar energy R&D, demonstration, commercialisation and market incentives. Photovoltaics will soon be a $100 billion-a-year industry.
Support for solar energy in Australia should be focused on intellectual property (IP) generation and the export of IP-rich, high-value products and services. This strategy should entail substantial support for R&D, and professional education, coupled with strong incentives for companies to manufacture high-value products in Australia for export and to license IP overseas.
Further information
Centre for Sustainable Energy Systems, Australian National University (ANU)
School of Photovoltaic Engineering, University of New South Wales (UNSW) |
