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Australia receives more solarradiation per square metre,
onaverage, than any other continent.
Although turning this radiation intoelectricity is one option,
another isfinding ways to make use of its heat. Wespoke to
Australian proponents of twovery different solar-thermal
systems,both rather confusingly known as solartowers: Roger Davey,
executive chairmanand chief executive of EnviroMission,based in
Melbourne; and Wes Stein, fromthe Energy Technology Division of
theCommonwealth Scientific and Industrial
Research Organisation, based in Newcastle.
How does your solar-thermalproject work?Roger Davey: In our
solar tower, solar radia-tion is used to heat the air captured
under alarge greenhouse. The roof of the greenhouseis sloped
towards the centre, where there areturbines and a very tall tower
that creates achimney effect. Hot air rises up and out of thetower,
rushing through turbines at the base ofthe tower to produce
power.Wes Stein: We have 200 small mirrors thattrack the Sun during
the day and concentrate its
rays onto a single point on the tower. This pro-vides
temperatures hot enough to drive a chem-
ical reforming reaction. Methane and steam goin, energy and a
catalyst are added; the resultinggas [carbon monoxide and hydrogen]
is calledsyngas in the industry we call it SolarGas.This gas has
26% more energy per kilogramthan methane it is solar energy
embeddedin chemical bonds. So the plant improves theenergy value of
the gas, and provides a precur-sor for other energy products, such
as liquidfuels. We could link this process with carbonburial so
that the carbon dioxide from thefossil-fuel component was
sequestered.
How big is your solar tower?RD:
The original concept design made it 1 kilo-metre high and 7
kilometres in diameter, butwe have developed new technologies that
willmake it substantially smaller and more power-ful. A 50-megawatt
demonstration plant willbe built at Tapio Station, about 22
kilometresnortheast of Mildura in New South Wales. Thisis not
necessarily the optimum size, but it is theoptimum size to build in
the first instance toshow the robustness of the technology.
Thefront-end engineering and design are currentlyunder way, and it
would be premature of me totalk heights and sizes now, and then
alter themin a weeks time.WS:
The tower reactor is 15 metres above themirrors, and the tops of
the mirrors are about
3 metres off the ground. The total ground areais 4040 metres,
but that is because of oursite constraints it doesnt necessarily
rep-resent the ideal module size. So I dont wantto make a big deal
of the specific dimensions.It will produce up to 250 kilowatts of
electric-ity. However, this is a research-size system. Wedesigned
this tower to represent a single mod-ule that could be replicated
again and again tomake it up to any desired capacity.
How does your system fit into theexisting energy
infrastructure?RD: It operates as a power plant and feeds intothe
normal electricity grid.WS: The gas can be used in gas turbines
tomake electricity or we can turn it into liquidtransport fuels. We
are investigating the use ofexisting gas pipelines to transport
SolarGas.One idea is to do the solar-reforming reactionout in the
desert region, where many gas pipe-lines originate, putting the
SolarGas into thepipeline and transporting it downstream. Wecan
have all the convenience of gas but with allthe benefits of solar
energy.
SolarGas can make liquid transport fuels andalso fertilizer.
After power plants, transport
RADIATIONNATION
These mirrors in the Australian landscape focus theSuns rays to
power the production of SolarGas.
SOLAR ENERGY NEWS FEATURE
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and agriculture are the biggest greenhouse-gasemitters in
Australia, so it gives us an opportu-nity to target more than
electricity.
How are you trying to improve thetechnology?RD: We can now
create far greater heat under
the collector roof. It captures more heatand retains more heat
its a bit like double-glazing.
We now also have a method of storing heatin brine ponds, so that
on days of lower solarradiation we can bring in that stored heat
tocreate the temperatures we need. That meanswe have a system that
could operate 24 hours aday, 7 days a week, 365 days a year.WS: We
believe cost reductions will comefrom improving the efficiency of
the reac-tion and reducing the cost of the mirror fieldthrough mass
production. We have two areasof research we are working on. One is
to reduce
the reaction temperature to around 550 C[from around 800 C].
That greatly reduces thecapital costs of the mirror field, because
fewermirrors are required. We are using a novelarrangement of
membranes to allow amuch lower reaction temperature. Weare in the
middle of a patent applica-tion, so thats all I can say at
present.
The second concept uses carbondioxide as the reforming agent
ratherthan steam, so we would be using awaste stream. Coal-seam
methane is arapidly growing resource in Australia.Methane from coal
seams comes out
with a fair amount of CO2. Normally,that CO2 is stripped off
before the gasgoes into the downstream pipeline so we would make
use of that dis-carded CO2. But we need to developnew catalysts for
that reaction.How much does it cost?RD:The original-concept
200-megawatt plantwould have cost around Aus$800 million(US$610
million). The 50-megawatt plant willbe substantially less, owing to
a reduction inthe structural dimensions, with final
costingsanticipated at the completion of the front-end
engineering and design. We are working onthe engineering of the
optimally sized power
plant with the optimum output, incorporat-ing the new
technologies. I could guess, butits better to be sure than to
mislead.WS:This solar tower has cost us Aus$1.5 mil-lion to build.
But we think that if we apply thesame learning curve that turbines
have expe-rienced over the past 1520 years, this samesystem would
cost us around Aus$300,000 tobuild in the future.
What are your advantages over rivalsolar technologies?RD: We can
guarantee output to meet thedemand, just like coal-fired
plants.WS:The advantages are that we can use Solar-Gas in a broader
range of sectors, not justelectricity; the very-low-cost potential;
andthe fact that it overcomes the transport andstorage issues of
solar energy.
Solar thermal has been around for awhile why has it not caught
on?RD: I think it has caught on. Thats why were
here.WS: One of the difficulties it has had is theconcept that
it has to be built large for costreductions to occur. Its one thing
to build asystem at the small demonstration level andenthuse
everyone with that, and then say nowI need to build 100,000 of
these to be cost-effective in a 50-megawatt system. I think thejump
from that small to large scale has beentoo much for investors to
handle, even thoughthe modelling and calculations have alwaysshown
that it would be cost-effective.
Worldwide, investment in solar-thermal
research is fairly low; why do you thinkthat is?RD: If you take
the solar tower as an example,the original design had to be big to
produce
enough power to make enough money to payfor the capital costs.
But with the additionaltechnology we have added, we have created
farmore power out of a smaller plant.WS: It is because of the
difficulty investorshave in biting off big chunks compared with
the easier task of biting off small chunks. Photo-voltaics are
very sexy they dont move, they
dont make any noise sitting on top of a roof,and they can be
made to look good on build-ings. They are still very expensive, but
theycome in small chunks. It is much easier forinvestors to go with
that concept than with aone-off, large, solar-thermal power
station. Itsonly now, as a result of initiatives and incen-
tives around the world, that solar-thermaltechnology is starting
to take off globally.
What stops power companies frommaking big investments in solar
thermal?RD: Power companies have investments inother assets, dont
they?WS:Purely cost. At the end of the day, it comesdown to cost of
the technology.
How much of Australias electricityneeds could solar thermal
provide in20 years or in 50?RD: We plan to develop
approximately
2,100 megawatts of installed capacity by 2020.By 2030, we plan
to have installed in excessof 6,500 megawatts of power, which would
bethe equivalent of the electricity usage of about
10 million households based on cur-rent energy use.WS: I see no
reason why, by 2050, solarenergy couldnt be supplying at least25%
of Australias energy mix.
Is your technology really onlysuitable for countries with
big,empty deserts?RD: No. Our solar tower operates on
temperature differentiation thecreation of an environment
withstrong differentiation to ambient tem-perature will regulate
where develop-ment is able to occur. Unfortunately,big, empty
deserts do not serve elec-tricity grids and have inherent
supply-chain issues.
WS: Sensibly, yes. Technically, there is no rea-son why you cant
do it in lower solar regionsbut the cost will be higher. Im not
advocatingsolar being a single solution for all Australiasenergy
needs. Theoretically it could be, butpractically I dont think that
will happen. Carina Dennis is Natures Australasian
correspondent.
We have a
system that
could operate
24 hours a day,
7 days a week,
365 days a
year.
Roger Davey
We can use
SolarGas in a
broad range
of sectors,
not justelectricity.
Wes Stein
Artists impression of EnviroMissions solar tower, which will
harness the Suns heat to generate electricity.
J.SMITH/AAPIMAGE
ENVIROMISSION
W.S
TEIN/CSIRO
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