There is no doubt about it, virtually every survey taken of the public’s attitude towards the range of energy-generation technologies puts renewables, and particularly solar energy, right at the top of the heap (and usually nuclear at the bottom).
And taken on face value, Australia still has the wide-open spaces with possibly the best average solar irradiation of any continent. In fact solar radiation is Australia’s largest potential energy source. The average amount of solar energy that falls on Australia is about 15,000 times the national energy use.
We also have the R&D and manufacturing skills to develop our solar resources into a major industry. So why is it so slow?
Well, there are a few barriers, and all have to do, in the end, with the costs of the outputs. The fact is that the sun does not shine at night, energy storage in either electrical and/or heat forms is expensive, reasonable-size plants take up a lot of area, they need to be appropriately sited (usually in more remote locations) and, even with storage, the output will be subject to a degree of intermittency.
The major ‘barrier’ to solar thermal uptake has been the relatively low cost of power from our predominantly coal-fired electricity generation. It has just not been possible for a relatively expensive technology such as solar thermal to compete. However, things are changing.
For example, the Australian Government’s Renewable Energy Target (RET) will require 20 per cent of Australia’s energy be supplied from renewable sources by 2020. Much of this capacity is expected to be initially supplied by wind generation (with a contribution from geothermal, depending on the state of development) although, as the most attractive sites become used, solar technologies are then likely to play a key role in helping to meet the target.
The Carbon Pollution Reduction Scheme (CPRS), involving an emissions trading scheme (ETS), beginning in 2010, will set a price of carbon emissions and this will change power generation cost relativities to favour greater up take of renewables, including solar generation. Currently, carbon prices well in excess of $50, and as high as $100, per tonne of CO2 will be required to shift solar thermal generation into a cost-competitive position with coal-fired power.
Will these policy measures be enough to drive an increased implementation of solar technologies? They will certainly help, and the technology itself must not, and is not, standing still.
Solar thermal energy
Solar thermal refers to the capture and utilisation of solar radiation for use in heat or electricity production. Harnessing the energy of the sun to heat water is an established technique in Australia, which has been a world leader in the development of, and is a significant exporter of, solar hot water systems.
Higher-value energy products, such as electricity, require the solar radiation to be concentrated to produce higher temperatures. This higher-grade heat can then be used to operate a conventional power cycle, for example, through a gas or steam turbine, to produce electricity.
Parabolic trough systems use trough-shaped mirror reflectors to concentrate sunlight onto receiver tubes through which a thermal transfer fluid is heated to around 400˚C and then used to produce superheated steam. This is now a mature technology and a variation is being trialled at a Hunter Valley coal-fired power station as an additional, relatively low-grade, heat source.
Central receiver (solar tower) systems use a circular array of individually tracking heliostats to concentrate sunlight onto a central receiver mounted on top of a tower with the heat transferred for power generation through a variety of fluid media.
Parabolic dish systems are comparatively small units that use dish-shaped reflectors to concentrate sunlight to a focal point, with the high temperatures used to heat a working fluid for various uses.
Because of the high temperatures (in excess of 1000˚C, if desired) produced by tower and dish collectors, the high-grade heat can be used for a variety of purposes. One of the simplest is the generation of high-pressure steam that could be directly integrated into existing power stations and to operate as a hybrid process.
In Australia, the heat from a solar dish is being used by ANU to store energy in a thermochemical cycle in which ammonia is dissociated into nitrogen and hydrogen for storage. These gases can then be converted back to ammonia, thus releasing the energy of conversion.
CSIRO has also demonstrated a thermochemical cycle in which methane is reacted with water vapour at temperatures of 800˚C to produce carbon monoxide and hydrogen. The mixture can be combusted in a turbine for power generation or the components can be converted back to methane and water with the release of the stored solar heat.
The tower and dish systems can also be used for physical heat storage for later conversion, in molten salt and mass heat, such as storage in graphite blocks.
The future
Notwithstanding the current relatively high cost of solar thermal power generation in Australia compared with conventional power costs, there are grounds for optimism that the technology’s time is rapidly approaching. There have been remarkable shifts in the energy policy framework over a relatively short time, all encouraging the development and implementation of low emission generation to satisfy Australia’s growing energy needs.
In addition to policy, the Federal Government has allotted $100 million for the establishment of the Australian Solar Institute (ASI) to develop specifically solar thermal (and photovoltaic) technologies. This will add to the already strong solar R&D base through the universities and CSIRO.
Demonstration of systems will play a key future role in ramping up the rate of implementation.
One brake on progress in Australia could be the lack of large companies willing to take the investment risk in setting up demonstrations. In this regard there will be a facilitation role for government to seed this most important future technology for Australia.
Further reading
Public attitudes
Ashworth, P., Reiner, D., Gardner, A., Littleboy. Kyoto or Non-Kyoto: people or politics. Results of recent public opinion surveys on energy and climate change. Greenhouse 2007 Conference, October, Sydney.
Energy futures/energy costs
The Heat is On – the Future of Energy in Australia, CSIRO, December 2006
Fuels for Thought report
Solar thermal technology
Solar Thermal – Introduction, Department of Environment, Water, Heritage and the Arts
Concentrated Solar Thermal Power – Now! |
