In what sources agree may be a world’s first, three solar thermal power stations in Australia will store thermal energy in purified graphite, allowing generation on demand while providing peak and backup power and reducing the need to upgrade transmission systems in the local area. A pilot plant is operating now, and one small plant is nearing completion in Tasmania. Two much larger plants are planned for Australia’s mainland.

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Lloyd Energy Systems

Graphite is the best storage medium, for thermal energy, says Steve Hollis, chief executive of Lloyd Energy Systems (LES), the Sydney-based company that has developed the graphite energy-storage technology. Graphite has high thermal capability—to 3,500° C, low emissivity, very high thermal conductivity, as well as being non-toxic and nonexplosive and stable over many temperature cycles, he notes. It also has the desirable property of increasing its heat storage capacity as the storage temperature rises. “The advantage of this technology over other solar-power-generation technologies is the ability to store thermal energy at the point of collection and hold it before converting it to electricity,” Hollis explains.

LES built a pilot plant at Polo Flat, near Cooma, New South Wales, that was commissioned in November 2007. It will be followed by construction of a 3-MW plant in Lake Cargelligo, New South Wales. Both projects together will cost $9.4 million, including a $4.7 million grant from the federal government.

The LES technology involves refining low-grade graphite into high-quality crystalline graphite with an energy storage capacity ranging from 300 kWh (thermal) per tonne at a storage temperature of 750°C up to 1,000 kWh (thermal) per tonne at 1,800°C.

Lloyd Energy Systems

Lloyd Energy Systems Base of graphite block is focus of mirrors concentrating solar thermal energy.

Sun-tracking mirrors called heliostats focus the sun’s rays into holes in the base of the blocks, which sit on top of 20-m-tall towers. The blocks act as energy collectors, energy storage and boilers. Water is passed through heat exchangers—tubes embedded in the graphite—to generate steam. The steam drives turbines on demand.

At Lake Cargelligo, 2,200 heliostats will focus solar thermal energy on 16 tower-mounted graphite blocks. A 10-MW station with 7,200 heliostats and 54 graphite blocks will be built at Cloncurry, Queensland.

LES has an agreement with Ergon Energy Corp. Ltd., Queensland’s government-owned utility, to build the $28.3-million Cloncurry plant, and has a $6.6-million contribution from the Queensland government. When the plant is operational, Ergon Energy will purchase the power generated to supply the Cloncurry community. Commissioning is scheduled for September 2009.

LES has made the system modular to allow its deployment in remote rural locations and overseas, says Hollis. All of the sites for the initial deployments are in remote areas. Increasing power supply to the areas would have required new diesel-powered generation or long transmission line upgrades with power losses.

Smaller Footprint

“Ergon Energy has interest in the completion of this project for both network augmentation and efficiency reasons,” says John Chisholm, executive general manager of corporate sustainability and innovation. “The development of the power station would negate the need for a network upgrade, potentially achieving significant cost savings. The power station will also help reduce Ergon Energy’s carbon footprint and bring significant benefits to the environment.”

A once-through steam generator (OTSG) will produce superheated steam. The steam will run through a condensing Rankine-cycle steam turbine with an air-cooled condenser.

Due to the use of air condensers and OTSGs, there will be little water loss from the process. All water used will be treated and recycled back through the system, with only a small amount of make-up water required per year. There will be rainwater storage tanks on site with 200,000 liters total capacity.

A third project using graphite for storing heat is nearing completion on Tasmania’s King Island. It consists of four components: six photovoltaic units capable of generating 110 kW, six graphite energy-storage units heated by electric elements, a resistor system to control energy frequency and a wind farm able to generate up to 2.5 MW.

The graphite blocks will be heated with electricity from the wind turbines to a temperature of 800°C. The project uses LES’ graphite-storage system and is a joint venture of CBD Energy Ltd., Double Bay, New South Wales, and Hydro Tasmania.

The amount of steam delivered to the turbines will be determined by feed pumps and valves to control the amount of water flowing into the system.

Snowy Mountains Engineering Corp., Cooma, is the consulting engineer on all of the LES projects.