Scientists at the CSIRO have successfully developed a process which uses solar energy to increase the energy content of natural gas in a unique, hybrid fossil/solar reaction.
CSIRO scientists have demonstrated that SolarGasTM has approximately 26 per cent more energy than the natural gas feeding in to the process and produces 26 per cent less carbon dioxide during production. Best of all, the ‘bottled sunlight’ can be used in a variety of ways, powering all types of electricity generation and can even be used to produce hydrogen for use in fuel cells.
How it works
The process has three major components: the collection and concentration of sunlight onto a reactor, a chemical reforming process between the gas and water to produce syngas and hydrogen, and finally electricity generation.
“SolarGas combines two of Australia’s largest energy sources – solar and natural gas. The reaction is based on a conventional industrial process – reforming of methane – however this process is very greenhouse gas intensive. By using concentrated solar to provide the energy for the reaction, the resulting gas product embodies solar energy in its chemical bonds. This allows solar energy to be stored indefinitely, and transported. SolarGas can be used not only for electricity generation in advanced gas turbine cycles, but also to produce liquid transport fuels,” said CSIRO’s Division of Energy Technology Renewable Energy Manager Wes Stein.
Sunlight is collected by a modular solar array of 200 heliostats – mirrors that independently track the sun and reflect its energy onto a reactor mounted on a specially designed tower rising 20 metres above the ground. The unique feature of this solar array is that each mirror tracks the sun independently in relation to the sun and the tower in such a way that, regardless of meteorological conditions, maximises solar exposure.
The heliostats are concave, each with its own focal length, with two actuators driving each, such that it can move in any direction. The current array has 165 mirrors, with plans for a total of 200, which would generate temperatures up to 1,200ºC and 500 kilowatts of power – enough to supply 100 homes.
SolarGas was originally developed at the CSIRO Division of Energy Technology’s Lucas Heights facility in New South Wales, using a 107 m3 parabolic solar dish concentrator. The reactor consists of concentric tubes with water entering the inner tube and the gas flowing in the outer one. The accumulated solar thermal energy heats the water and the resulting steam exchanges heat with the natural gas in the outer tube. Catalysts in the outer tube mediate the chemical reaction.
“The gas is then treated to recover carbon dioxide in a concentrated form prior to using the steam for power generation. The process enables very high efficiency power generation with greatly reduced greenhouse gas emissions,” said Jim Edwards from CSIRO Energy Technology.
Breadth of application
Australia is particularly well-placed to take advantage of this new process, since it combines two abundant energy resources. Not only does Australia have the highest average amount of solar radiation per square metre per year on Earth, but the country is also blessed with sizable natural gas reserves, making it the fifth largest exporter of liquefied natural gas in the world. Additionally, Australia’s natural gas reserves are also located in areas exposed to high levels of sunlight, making the application a viable solution for our climate.
However, the real strength of solar gas is its flexibility. It can increase gas pipeline energy density, provide low-emission localised power generation and, after gas cleaning, can be used in fuel cells to power vehicles.
“The attraction of SolarGas is that it can store solar energy, thus overcoming the normal solar transients and diurnal fluctuations. This provides dispatchability, which means it can provide the grid stability needed by other forms of renewables such as PVs and wind,” said Mr Stein.
“Much of the thermochemical technology associated with SolarGas can also be used to solarise other carbon-containing fuels such as biomass waste. SolarGas is just the first stage in a series of processes that could recombine the syngas in a closed loop and provide heat for pure solar baseload power,” he added.
SolarGas can work around both distributed and centralised power and heat generation, using existing infrastructure. The technology can be used as a localised generation facility or else be built in a centralised location in Australia’s arid sunny regions, at the well-head or anywhere along gas pipelines. By having solar gas installations along pipelines or at the well-head, in such locations, solar-enriched fuels can be produced for resource processing, petrochemicals manufacture and metallurgical processing. The gas can also be liquefied and exported. Additionally, solar gas can be used to produce hydrogen for fuel cell-powered vehicles.
The future of SolarGas
The project has won many accolades, being highly commended at the 2006 Engineers Australia Engineering Excellence Awards (Newcastle) and recognised by the International Partnership for the Hydrogen Economy as one of the world’s top 10 demonstration projects. However, it is still being tested at the National Solar Energy Centre in Newcastle as part of the Energy Transformed National Research Flagship program.
Mr Stein has noted that the main challenge in developing the technology has been developing a new type of solar concentrator that maintains high levels of solar flux at all solar angles. He added that as the process runs at quite high temperatures (850ºC), high temperature material selection was an important factor. The third major challenge has been in raising awareness of concentrating solar power (CSP) plants as an option for large scale solar power generation.
“There has also been the non-technical challenge of introducing a new form of solar energy suitable for large scale solar power, when most people generally thought of solar energy as being for hot water or solar cells,” Mr Stein said.
“A difficulty for CSP in the past has been that it needed to be built in large capacities to achieve competitive costs. It is only now with the global call for deep cuts in greenhouse gas emissions that the ability of CSP technologies such as SolarGas to be built in large scale comes into its own.”
In order to minimise the technical and financial risks, CSIRO has developed the technology to be modular, enabling scale up to be easily achieved by simply multiplying repeatable units.
Mr Stein expects that the capital cost will be high initially, as was the case with coal-fired power stations when they were first built. However a combination of research and development, mass production and scale-up will see costs reduce dramatically over time. The cost reduction will also benefit from the global surge of investment in CSP plants. These alternative plants will help to establish new industries such as large scale mirror manufacturing for the various forms of CSP. It is expected the early markets will be in conjunction with existing gas turbines and combined cycles, and then over time the costs coming down sufficiently to allow large scale solar plants.
While the future looks bright in the near-term for the SolarGas project, further development is dependent on a coordinated effort between government and industry in energy technology research and development.
“It is important for industry that they are not one-off but will be in place for long enough for manufacturing capability to be established,” concluded Mr Stein. “Long term support for a pipeline of solar projects, rather than single concepts, will encourage industry and government to see the creation of the solar options as a process they can engage in, not just isolated ‘ideas’.”
The project is a collaboration led by CSIRO’s Division of Energy Technology and includes the Department of Education, Science and Training, NSW’s DEUS, Solar Heat and Power, DLR Germany and the Australian National University.
Appeared in issue: EcoGeneration — May/June 2008
Categories: Natural gas, Solar, Technology
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