Hold a magnifying glass over a leaf and the sun’s rays will concentrate on a small spot. Wait a few minutes and the heat will become so intense, the leaf will catch fire.
CSIRO scientists and engineers are using this principle, well known to young children, to run a solar-energy power station in the Newcastle suburb of Mayfield West.
The magnifying glass has been replaced by large concave mirrors that concentrate the sun’s energy 1000 times its normal intensity onto a receiver, where it can heat air in a turbine engine to create electricity.
Some of the 451 mirrors, called heliostats, started bouncing the sun’s rays onto the receiver for the first time this week, making the plant the largest of its kind in the world.
The CSIRO’s energy system manager, James McGregor, says the beauty of this type of solar thermal technology, called a solar air turbine, is that it can create electricity from the limitless resources of air and the sun - crucially, it requires no water. In full production, the demonstration plant’s Brayton Cycle system will be able to produce 0.2 megawatts of electricity, enough to power about 100 to 200 houses.
With Australia home to some of the best solar resources in the world, solar thermal technologies are becoming a popular choice to increase the percentage of the country’s electricity produced by renewable energy. Advances in thermal storage technologies mean solar thermal power stations can overcome problems associated with intermittent sunshine to become a reliable source of baseload power.
The federal government plans to fund up to four commercial-scale, grid-connected solar power stations, using either solar thermal or photovoltaic technologies, as part of its solar flagships program, which aims to establish up to 1000 megawatts of solar power generation capacity.
As with all renewable energy plants, the biggest expense is the upfront capital cost, McGregor says. A price on carbon will improve the business case for solar thermal and all renewable technologies, as it would make them more competitive compared with carbon-based electricity generators, he says.
While solar air turbines are considered to be the next generation of solar thermal technology, there are many other examples, of which solar hot-water systems are considered the most basic. Water is heated during the day and stored in an insulated tank. It can then be used at night once the sun has set.
Commercial solar thermal systems that produce electricity also use mirrors to produce concentrated solar energy but, instead of heating air, the sun’s rays heat water to produce steam that creates electricity using a steam turbine.
Steam systems are well suited for large solar power plants but they need a lot of water and are therefore not ideal for the outback, McGregor says.
”The best solar regions in the world - like north-west Australia - are also the regions with the lowest rainfall.”
One of the proposals being considered for the solar flagship program would consist of this type of plant. The key advantage of solar air turbines, being trialled around the world, is they do not require water, McGregor says.
”A lot of the mining towns in that part of the world rely on diesel for generating electricity, so our initial target market over the next five years will be the mining industry.”
