New solar thermal tower power plant being built that requires only sun and air
The new heliostats being installed to create a solar thermal field at CSIRO's Solar Energy Centre in Newcastle (Image: CSIRO)
Although electrical devices have evolved rapidly over the last few decades, the plants used to generate the electricity that power these devices are still dominated by the use of steam turbines that convert thermal energy, usually from the burning of fossil fuels, into mechanical energy. Even newer solar thermal power plants concentrate the sun’s rays to heat water into high-pressure steam to drive a turbine. But with water not always readily available in locations suited to harnessing solar energy, such as deserts, a new type of solar thermal field, tower and research facility is being built in Australia that requires only air and the sun, making it ideal for parts of the world that receive minimal rainfall.
The technology, developed by Australia’s national science agency the Commonwealth Scientific and Industrial Research Organisation (CSIRO), functions in much the same way as a conventional solar power tower plant. It focuses the sun’s rays with a field of mirrors known as heliostats onto a 30-meter (98 ft) high solar tower. But instead of heating water into steam to power a turbine, the solar Brayton Cycle system uses the concentrated solar energy to heat compressed air, which expands through a 200kW turbine to generate electricity. To overcome sun variability the compressed air can also be heated by natural gas combustion.
This week the CSIRO began installing 450 large heliostats at the agency’s National Solar Energy Centre (NSEC) in Newcastle, New South Wales. Once installed, the heliostats will form Australia’s largest solar-thermal tower system and will concentrate the sun’s rays to create temperatures of up to 1,000 degrees Celsius (1,832 F). The heliostats, manufactured by Performance Engineering Group, are smaller than many heliostats currently being used around the world and consist of a lightweight steel frame with a simple design specially created for mass production for the commercial market to make solar fields more cost effective to build and operate.
The CSIRO says the aim of developing the technology was to make solar generated electricity at the same cost or cheaper than fossil fuel generated electricity when the cost of carbon is taken into account.
The solar Brayton Cycle project will also incorporate the option of a future solar thermal storage system that would allow extended operation during peak demand times and address the challenge of continuous operation from renewable energy sources.
Once completed the solar Brayton Cycle field will be the largest of its type in the world, covering an area of 4,000 square meters (43,055 square feet). The field will be used to refine the technology in order to make it a cheaper, more efficient energy source suitable for many desert locations in Australia and around the world. Although the facility will be used for researching solar technology, the CSIRO says a field of this size could generate enough electricity to power nearly 100 homes.
About the Author
Darren's love of technology started in primary school with a Nintendo Game & Watch Donkey Kong (still functioning) and a Commodore VIC 20 computer (not still functioning). In high school he upgraded to a 286 PC, and he's been following Moore's law ever since. This love of technology continued through a number of university courses and crappy jobs until 2008, when his interests found a home at Gizmag.
All articles by Darren Quick
But what about at night when there is no sun?
Paul Bennet - \"But what about at night when there is no sun?\"
That\'s alright Paul. Australia is on the other side of the world so the sun is actually shining there at night time.
Paul, if you read the article again you will notice that natural gas is used when there is no sun.
No sun at night?
What a disturbing concept, lol.
As for the power plant... Archimedes would have been proud :)
So, for one home it would take 40 square meters (431 square feet) - A collector that is 6.3 meters (21 feet) on a side should easily fit in any persons lot. Sounds like some enterprizing investor should start a company to develop individual units.
The problem with using the Brayton cycle for solar energy conversion is the turndown characteristics. The system must be designed for peak radiation at the lowest ambient temperature to ensure that the equipment is never damaged by overheat. However these conditions seldom exist. Typically the sun offers less than peak and the outside air temperature gets hot. The Brayton cycle can lose 50% of its efficiency when the radiation is 80% of peak. The Brayton cycle can lose 25% of its efficiency when the ambient temperature rises 20°C. Effects of lower radiation and higher ambient combine. The solution is to peak the turbine inlet temperature with natural gas. The result is a %u201Csolar assisted%u201D gas turbine. Oh, by the way, you get to burn natural gas at night as well. Pass it to the marketers and it all sounds really good.
And how are we compressing the air? Compressing air takes a **itload more work than you can get out of it..granted we are adding energy via the heating, but we\'re still running compressors constantly and constantly lose the heat of compression. Even if we just use a ginormous resivoir that sucks air in overnigt as it cools or whatever, the size of the equipment would have to be massive compared to a steam plant (as water expands some 1700 times when boiled) Don\'t be idiots - put some frikkin water or heat transfer fluid in there.
Actually, Lloyd, you misunderstand the Brayton cycle and then confuse its trade-offs with the Rankine cycle. Whereas the Rankine cycle pressurizes liquid using very little energy it can%u2019t get power from the latent heat used to boil it which is where the majority of the heat input goes. Using your words, boiling water %u2026takes a **itload more (energy) than you can get out of it.
Yes, air takes a lot of energy to compress and the turbine expansion must supply it but there is no latent heat energy loss. The solar input must be sufficient to power the compressor plus excess for work output. This is the way jet engines work. The CSIRO system adds a recuperator to further heat the hot compressed air using the low pressure turbine exhaust. The CSIRO system will give higher efficiency than a steam system under best conditions. (The Hybrid Brayton Cycle will work better but is not public at this time.)
We already have working Baseload solar thermal plants.
In spain Gemasolar is a 15hour storage plant by SENER/Torresol Energy and it runs 75% capacity factor using binary molten salts (60% Sodium Nitrate / 40% Potassium Nitrate) the competitor UTC/Solar Reserve is building projects in Rice CA, Tonopah Nevada and Arizona at 110 and 150MWe and in Spain at 50MWe
What we now need is high temperature working fluid and storage. Something stable at 1000-1450 degrees C. This is where the CSIRO and other Solar Thermal researchers should be working. If you can achieve 1450C you will be able to get the same energy out of 2/3 as much mirror field. Or another way of looking at it is that the high temperature storage will allow combined cycle operation (Brayton air/gas Rankine liquid/steam) meaning you get 50% more electricity out of the same field. A massive change to the economics of Solar Thermal if this is achieved. A great job for materials experts.
But lets just be clear - baseload solar thermal already exists, and on-sun (such as this plant) is destined to lose when compared to very economical photovoltaic that is riding a massive cost reduction curve.
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