Over recent months we’ve looked at various small-scale battery systems that are suitable for domestic use. This time we’re going large-scale and looking at Concentrated Solar Thermal power (CST) – a method of generating electricity that also enables solar energy to be stored in the form of heat. You’re not likely to have one of these systems on your roof any time soon, but CST has huge potential for large-scale generation and storage.
How it works
A CST power station typically consists of an array of sun tracking mirrors (‘heliostats’) that concentrate sunlight by focusing it onto a target at the top of a tower. Some towers heat water directly to create steam to drive turbines, while others heat molten salt. Molten salt towers work by pumping ‘cold’ salt (about 280°C) up to the top of the tower where it is heated, and then it is pumped back down the tower for storage or immediate use. The advantage of molten salt is that the energy from the heat can be stored and used at a later time, or released immediately into a heat exchanger that produces steam to power a standard steam turbine. The molten salt has a 30+ year life span and can be repurposed as a high grade fertiliser.
The method of electricity generation works best in a large scale; the bigger the plant, the more efficient they are. However studies are being completed looking into the viability of small- and medium-scale rooftop installations (these smaller installations would use a water heating method, but research into using molten salt for hot water systems is underway)
The largest high concentration solar array in the southern hemisphere is operated by the CSIRO in Newcastle. Operating temperatures at the facility can be in excess of 1000°C.
Advantages and problems
Because of the ability to store energy as already mentioned, CST has the potential to provide 24-hour ‘baseload’ power. It also provides a dispatchable energy supply – power output can be adjusted based on grid demand.
Currently CST cannot compete economically with wind, hydro and PV solar power stations. There is also a potential danger to wildlife – if birds fly in between the mirrors and the tower they will most likely die from the heat.
Australia’s climate and geography makes it an ideal candidate for large-scale CST projects. The Australian Solar Institute predicts that solar thermal has the potential to make up between 30 and 50 per cent of Australia’s power consumption by 2050.