Supercharging solar
One of the reasons I find solar technology so fascinating is that there is an inexhaustible source of energy and myriad different ideas on how to capture it.
Unlike coal and gas, where the technologies are pretty much standardised – although there is a lot of effort now in improving the efficiency, and thereby lowering the emissions – solar is a new discipline at the commercial scale, and the race is still wide open to find the system that best captures the energy at the least cost.
Most solar thermal technologies have focused on different ways of heating water or other liquids and creating steam to drive turbines – be they in flat mirrored arrays called linear Fresnel, curved mirrors such as parabolic troughs, dish-based technologies that look like space telescopes, or solar towers, where the energy of an array of heliostats (mirrors) is focused on one spot.
A new solar array at the CSIRO’s energy research centre in Newcastle is the world’s largest demonstration of a new technology that uses concentrated solar energy to heat air rather than liquids. In many ways it works the same as a gas turbine: compressed air is heated, and then the air expands through a turbine to create power. “We’ve just eliminated the combustor,” said Robby McNaughton, the engineering manager at the National Solar Energy Center, during a visit to the centre last week.
The technology is known as a solar air turbine, but it’s official name is a Solar Brayton Cycle. And because it needs no water, it is uniquely suited to Australian conditions, where the best solar radiation often coincides with the least amount of available water. And because it lacks the complexity of rival technologies, and can operate as a modular, stand-alone system, it is also suitable for remote locations such as mine sites.
The CSIRO is not yet talking costs per megawatt hour, but it sees its big opportunity in undercutting the price of diesel, which is soaring because of rising fuel and transportation costs. In fact, the rising cost of diesel is proving to be a fillip to a range of renewable technologies in Australia and overseas – wherever there is no coal- or gas-fired energy grid.
“Until you build it it’s very difficult to estimate cost and performance. What you are hoping is that cost of operating this is less than cost of running diesel,” McNaughton says. “This technology is more suited to the smaller scale – I suspect you will see these in the ranges of 1MW-10MW, whereas steam plants will run into the 100s of megawatts.”
The installation at the Newcastle suburb of Mayfield West, built in conjunction with the Australian National University, boasts a 30m tower and more than 440 heliostats, which focus the sun’s energy on a single receiver and can generate temperatures of more than 900°C. Under the current deployment, the field can generate 200kW of electricity or 1MW of thermal energy. Efficiencies are expected to improve dramatically.
The solar field has been commissioned in this past month, and a gas turbine will be installed later this year. “Once we prove that the whole cycle works, then we will start to work out how we can get it hotter,” McNaughton says. The CSIRO has got to 900°C and is aiming for 1500°C. “Beyond this stage it is the industrial partners that take hold.” The CSIRO is hopeful that a commercial partner will take the technology and build a demonstration plant, possibly in the 10MW range.
The new solar array has been erected alongside another array that has also delivered ground-breaking achievements in using solar energy for industrial uses. Known as SolarGas, the technology has been under development for more than a decade, and essentially captures the sun's energy in an endothermic process (chemical reaction caused by absorbing heat), which transforms the natural gas and water feedstock into a higher energy product. The CSIRO says it is a bit like 'solar supercharging' the fuel, and one of the remarkable features of this chemical reaction is that the reformed gas has an energy content around 20-25 per cent higher than what was put in.
McNaughton says there are numerous potential uses, most notably in the industrial sector. (He says areas with the best solar radiation can operate at 95 per cent capacity and be quite predictable, and unlike solar PV, which tends to operate best for just a few hours a day, solar thermal can deliver a much flatter curve over longer hours.)
The most interesting application, however, might be using the system to create “solar fuels” such as diesel and methanol, because the product can be stored, transported and exported in liquid form. It’s a fascinating thought – transport fuels created by the sun – and it happens that a lot of Australia’s best solar radiation can also be found with accompanying gas reserves.
The technology may also be able to be used to create solar hydrogen, suitable for powering fuel cell-powered vehicles, and using a combined cycle gas turbine for electricity generation, the CSIRO says SolarGas can achieve efficiencies of around 60 per cent, much higher than the 40 per cent achieved by conventional Steam Rankine Cycle power generation.
The CSIRO is also pursuing avenues in thermal storage, using different types of salts and fluids and heat transfer systems, and a high temperature steam project, looking to generate higher temperatures from the more “traditional” solar thermal technologies that look to create steam to drive turbines. The hotter the steam, the more efficient, and cost effective, the system becomes.
Comments on this article
It is the future in my
It is the future in my opinion and I am sure that many of you will have the same opinion. http://www.profiletimelinecover.com/
Solar technologies are
Solar technologies are broadly characterized as either passive or active depending on the way they capture, convert and distribute sunlight. Active solar techniques use photovoltaic panels, pumps, and fans to convert sunlight into useful outputs. Passive solar techniques include selecting materials with favorable thermal properties, designing spaces that naturally circulate air, and referencing the position of a building to the Sun. Thanks. Regards, phone number lookup
Supercharging Solar
Producing a LIQUID FUEL to replace petrol & diesel seems a worthwhile exercise IF it can be done at a competetive price ( preferably without a government rip-off fuel tax being imposed as presently exists on all of our current fuels ).
The 'solar array' is a bit of a worry though ! It heats the air !? I thought that was the problem with the CO2 & why we need to go to all this trouble to avoid the air getting heated ! Also , I understood that when you compressed air it got hot just by compression,so it seems they are going to heat it further !?? Also , where does the energy come from to compress the air ? Is that from a solar panel or from the turbine powered by releasing the compressed air? This is beginning to sound like a Heath Robinson perpetual-motion affair to me !
Solar Fuels
I can't help but think that solar fuels, or perhaps more broadly, "renewable fuels" is where Australia's export future should lie. As a country with capability to generate energy through virtually every type of renewable source going, but very few people to use it (relative to our land mass & coastal waters), we have the potential to be a major energy exporter without having to rely on coal and gas.
Having lost our world leadership on solar, and not looking like being a technology exporter in other renewables, perhaps renewable fuels are the one area where we have both what economists call a comparative advantage and the opportunity to be technology leaders.
If we can bottle it and transport it safely, there will be a hungry world demanding other transport fuels post peak oil. Surely then our national investment and innovation focus should be on creating a transport fuel or fuels from renewables.
WHAT ABOUT USING SOLAR AUGMENTATION?
Would it make sense to use solar air heating as a form of augmentation for CCGT. The solar heating reduces daytime emissions while the gas (or oil) firing provides power when the sun isn't shining.
Air as working fluid has benefits
The text makes it quite clear what is happening by just saying, it works like a gas turbine. That is, cool atmospheric air is drawn in, heated, then expanded through a turbine or engine, then exhausted as hot air through a stack higher into the atmosphere than the intake.
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It is true that by not having to boil water to steam, efficiency is greater, however single stage gas turbines only achieve an efficiency of about 25%.
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As an open system, rather than a cycle, a further efficiency is often be made. Any open system using air as the working fluid can be be made more efficient, by taking in cooler air than the atmosphere that the exhaust is dumping into. At times of low demand/supply ratio, ice can be created to be used later to chill the intake during high demand/supply ratio. That is one way of storing energy between supply and demand !
Confused Ideology
Adam, they are great ideas and the power of human innovation cannot be underestimated. However, on one hand to be proposing that some 'central' government organisation oversees this innovation and uses its power and wisdom to pick the winners; then on the other hand to be criticising a carbon tax/CPRS policy as government meddling in income distribution is really confused ideology.
I think we all know that any government, blue or red or green is incapable of such omniscience let alone execution. The CSIRO does just fine with doing the breakthrough innovation without political interference and then partners or licences the results to great effect. If the CSIRO has developed a dud then industry won't be knocking on the door. The market has spoken.
Let's price carbon properly then the market will do the 'central' management of competing technologies.
Carbon power alternatives
Great to hear about yet another idea to harness solar. Clearly this idea and its peers require long term funding with a centralised oversight to manage a portfolio of ideas and support those with better relative prospects. The sort of thing a government may do. Perhaps the ideal use of carbon taxes? Certainly a better use than the present intention of creating the greatest redistribution of wealth in living memory.
renewable energy
Good ideas if they work. Wont work if not tried. Economics depend on rising scarsity and cost of conventional energy sources. To diverge slightly and get a realisic handle on climate change, Google < global warming: A Chilling Perspective >. All data can be verified. Much propoganda on AGW by those eyeing the dollars to be made from taxing and trading. But as Joseph Gobells said, "If you tell a lie ofen enough people will come to believe it, you may even believe it yourself"
No progress on CST without a National FIT law
GIles, great article. However it seems that under the present federal REE Act 2000 creating the tradeable RECs scheme, there will be little or no progress on concentrating solar thermal power. Australia needs to follow the lead of countries which have made significant progress on solar thermal such as Spain and seriously consider enacting a national feed-in tariff law which offers a specific rate of remuneration for ST electricity generation. Under the federal REC scheme the financial incentive offered is insufficient to incentivise solar thermal in the near future. With the small minded, short term thinking at State level of shutting down FIT laws we need to consider whether it's time to move to a national FIT law. There is abundant evidence that the federal REC law is ill-suited to encouraging emerging technologies such as ocean energy, geothermal energy, and solar thermal which have made little progress in Australia compared to other jurisdictions.
Renewables
Yes Denis, coal fired power stations consume coal (cheap and easy to dig up), nukes uranium (a little harder but you need a LOT less of it) and "renewable" power stations consume replacement parts. I guess that's why they are called "renewable".
Limitations of the technology
The article details progress being made in some measures using insolation to supply electricity and fuels. However, all the systems will have a limited life due to natural wear and tear. The article discusses only the nature of the processes so does not convey an impression of how realistic they may be for meeting demand over a relatively short period and what will happen when they wear out.
Solar Brayton cycle
Certainly an interesting technology, but a few points:
- Steam-based solar thermal does not necessarily need a water supply either. The water for steam is in a closed loop, so the main need for a supply is in the cooling stage, and air cooling is feasible, though less efficient.
- Some water is still required for cleaning heliostats
- Unless I've missed something, it offers no heat storage, so will not operate overnight. CST with molten salt storage can. To bridge the gap, need a high density heat storage that works at over 1000 deg C(!)