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By technology reporter James Purtill
5 Apr 2023
Concentrated solar power is an old
technology making a comeback. Here's how it works
![](images/images_04_11_2023/pic1.jpg)
The 100MW Cerro Dominador CSP plant in the Atacama Desert, Chile.(Getty
Images: John Moore)
There was a time, not long ago, when the future of electricity
generation looked something like the opening scene of Blade Runner
2049, with endless arrays of mirrors in concentric circles.
Concentrated solar power (CSP) uses mirrors to focus heat from the Sun
to drive a steam turbine and generate electricity.
While CSP was once the great hope for replacing coal and gas-fired
generation, it's now generally considered to have been eclipsed by
cheaper forms of renewable generation, like solar panels and wind
turbines.
Recently, however, it's been making a quiet comeback.
The reason for this boils down to three words that describe one of the
major challenges of decarbonising the grid: overnight energy storage.
The CSIRO's
Renewable Energy Storage Roadmap, released last week, predicts
that by 2050, CSP will be the cheapest way to store energy for 8–24
hours.
Developing this "medium-duration" storage is a necessary step to
switching off coal- and gas-fired generators that produce most of the
power we use at night.
For this reason, CSP projects are starting to gather momentum.
![](images/images_04_11_2023/pic2.jpg)
A 50MW CSP plant in the Xingiang region of China.(Getty
Images: Cai Zengle)
The Australian Renewable Energy Agency (ARENA) recently approved $65
million in funding for a Sydney-based company, Vast Solar, to build
the country's first commercial-scale CSP plant in Port Augusta, South
Australia.
So how does CSP work?
And what role will CSP play in a net-zero Australia?
A technology that once rivalled solar panels
The idea of CSP is so simple that the technology
hasn't changed much in decades.
Italy built the first CSP plant in 1968, and California installed the
first commercial-scale array in 1981.
At the time, solar panels were expensive and mostly used in consumer
electronics, whereas CSP relied on familiar technologies, such as
steam turbines.
![](images/images_04_11_2023/pic3.jpg)
One of the three towers of the 386MW Ivanpah CSP plant
in the Mojave Desert, California.(Getty
Images: Bing Guan)
CSP plants also looked impressive: The popular
"power tower" design featured a circular field of thousands of
mirrors, focusing their light on the crown of a central tower, which
in some cases soared taller than 200 metres.
But then, more efficient panels and larger factories drove down the
price of photovoltaics (PV), while CSP plants ran into problems with
leaking fluids and dirty mirrors.
In 2019, South Australia scrapped a $650 million project to build
Australia's first commercial-scale CSP after the company behind the
project revealed it could not raise funding.
"It's been a bit of a tale of woe in Australia," said Keith Lovegrove,
director of the Australian Solar Thermal Energy Association.
"We've actually managed to snatch defeat from
the jaws of victory a couple of times."
As of 2021, the global installed capacity of CSP was 6.8 gigawatts,
which was many hundreds of times less than the figure for
photovoltaics.
But CSP is not dead. Spain, Morocco, South Africa, Israel and other
countries are using CSP in their grids, while China has dozens of
projects underway.
"China is the most active place at this, at this very moment," Dr
Lovegrove said.
CSP cannot generate daytime electricity as cheaply as solar PV, but it
has one advantage: built-in storage.
The heat from the Sun is stored in a medium such as molten salt. When
the Sun goes down, this stored heat can be tapped to drive the turbine
and generate electricity.
This combination of generation and storage makes CSP "dispatchable",
meaning the power can be sent to the grid when it's needed.
"The whole point about CSP is that it's dispatchable renewable
generation," Dr Lovegrove said.
"It's generation you can have when you need it at night, or peak
periods. It comes at a higher price because it's got this added value
and complexity."
What is CSP's role in the grid?
Last week, the CSIRO's Renewable Energy Storage Roadmap report
indicated the National Electricity Market (which is all of Australia
except NT and WA) could require a 10- to 14-fold increase in its
electricity storage capacity between 2025
![](images/images_04_11_2023/Chart%201.jpg)
As you can see from the graph above, most generation will be solar PV
and wind by the end of this decade.
The pink bars at the bottom show dispatchable storage, which is mostly
pumped hydro and large-scale lithium-ion batteries.
CSP will be competing for this dispatchable storage market.
![](images/images_04_11_2023/Chart%202.jpg)
The graph above shows the "levelised cost of
storage" (the cost per megawatt-hour, factoring in everything from the
cost of charging, to installation and maintenance) for up to eight
hours.
According to the CSIRO's forecasts, by 2050 CSP will be the cheapest
form of this medium-duration storage.
For household energy consumers, this overnight cost of storage will
directly affect how much they pay for power at night.
And if you're planning on buying an EV, you'll probably use more
energy at night, as this is when most people charge their car (and
most don't have a household battery).
At the moment, the power we use at night mostly
comes from coal- and gas-fired generation, said Dominic Zaal, director
of the Australian Solar Thermal Research Institute within the CSIRO.
"But coal is exiting ... and you have to replace it with something,"
he said.
"[Renewable energy at night] is going to become very expensive, we
believe at over $200 per MWh."
By comparison, that's twice the average price across the National
Electricity Market late last year.
Large-scale batteries are good for smoothing spikes in demand through
the day and early evening, but an expensive way of storing large
amounts of energy for longer than a few hours.
"Batteries become very, very expensive after a period of time," Dr
Zaal said.
"So what are the alternatives?"
A new design for CSP
In February, ARENA announced $65 million in funding to Vast Solar to
construct VS1, a first-of-a-kind 30 MW/288 MWh CSP plant in Port
Augusta.
"History has proven that PV won the race to be the dominant solar
technology," said Craig Wood, the company's CEO.
"But what's becoming clear now is that it's about dispatchability."
That is, daytime power is so cheap there's a greater premium being
placed on delivering power to the grid when it's needed, rather than
when it's plentiful.
In 2019, Vast Solar won the International Energy Agency's technical
innovation award for the world's most innovative CSP technology.
Unlike the "power tower" designs in the Californian desert, Vast
Solar's design uses multiple, smaller towers to reduce the power lost
if one tower goes down.
![](images/images_04_11_2023/pic6%20copy.jpg)
Vast Solar's 1MW CSP pilot plant at Jemalong, near
Forbes in NSW.(Supplied:
Vast Solar)
Parabolic mirrors, known as
heliostats, track the Sun to ensure the beam of reflected light
remains aimed at the receiver tower.
The heat is first stored in liquid sodium metal at 565 degrees
Celsius, then in molten salt at 550C, and finally as steam to drive a
turbine.
"We can spin a turbine at 538C, which is the standard temperature for
a high-efficiency steam turbine," Mr Wood said.
At 30MW, the Port Augusta plant will test and prove the design before
larger plants are built.
"If you're on-grid, it needs to be typically 100MW-plus.
"CSP gets extremely cheap once you get up to 150–200MW in size.
"At those sorts of sizes, you would expect to be building the plants
with somewhere between 12–20 hours of storage."
In February, Vast Solar also announced a merger with a US energy
company in a deal valued at $US586 million, as well as plans to list
on the New York Stock Exchange.
According to Mr Wood, several Australian companies are leading the
world in some energy storage technologies.
"There's a bunch of American companies that are basically trying to
play catch-up," he said.
Mixing PV and concentrated solar
In Victoria, RayGen is developing a new kind of power plant that
borrows elements of photovoltaics and concentrated solar thermal
technology.
Also partially funded by ARENA, its design uses a field of aligned
mirrors to focus sunlight onto a tower-mounted receiver.
![](images/images_04_11_2023/pic7.jpg)
RayGen's 3MW/50MWh "solar hydro" power plant in Carwarp,
north-east Victoria.(Supplied:
RayGen)
Unlike the Vast Solar design, this receiver has
an array of PV modules, which convert sunlight directly to
electricity.
The heat from the sunlight is stored at 90C in an insulated,
rubber-lined reservoir.
A second pit stores water chilled to near freezing, using electricity
from the grid or the solar PV receivers.
The temperature differential allows electricity to be generated using
an organic Rankine cycle turbine, which transforms thermal energy into
electricity.
![](images/images_04_11_2023/pic8.jpg)
The high-efficiency solar module used by RayGen was
first developed for satellites.(Supplied:
RayGen)
The key to the design is the ultra-efficient PV
receiver, said Will Mosley, RayGen's chief commercial officer.
"You just need 4 square metres to make 1MW of electricity and 2MW of
heat.
"It's about 2,000 times the power density of a traditional solar
panel, and twice the electrical efficiency."
Why don't you have one on your roof? To be economic, it needs a
focused beam of sunlight, 1,000 times the usual concentration.
"The beam is strong enough to melt steel," Mr Mosley said.
He added that the PV module generates energy at about the same cost as
standard solar panels, and the array of mirrors uses about the same
amount of land.
In addition to this, the system uses heat that would be otherwise
wasted.
![](images/images_04_11_2023/pic9.jpg)
The series of rubber-lined pits can hold water at 90C
and near freezing for months on end.(Supplied:
RayGen)
The insulated pits may lose up to 10 per cent of
their thermal energy over six months.
The process of converting stored energy to electricity was about 70 to
80 per cent efficient.
"It has a similar performance to pumped hydro and can be co-located in
solar renewable energy zones where long-duration energy is needed
most," Mr Mosley said.
"And it can be delivered quickly."
But what about pumped hydro?
While CSP is still at the trial-project scale, the big investments are
in pumped hydro.
Australian governments have announced about 15GW of pumped hydro
energy storage, including 7GW in Queensland.
"Pumped hydro is 95 per cent of the global storage market," said
Andrew Blakers, a professor of engineering at the Australian National
University.
"There's a lot of arm-waving that we need new technologies, but the
fact is you cannot grow new technology from zero to something very
large in a very short time."
Supporters of CSP argue that it would be suited to hot, dry areas
where there are fewer options for pumped hydro, like in parts of
Western Australia.
It could also provide storage and generation for remote, off-grid
mining operations.
If that's the case, the CSP will be a niche solution, with pumped
hydro doing most of the storage.
Are there other uses of CSP?
Other uses for concentrated solar are to generate and store thermal
energy for high-temperature industrial processes, or to make
low-carbon "green" fuels.
Mars Petcare in Wodonga, for instance, has installed a graphite
battery to store heat at 900C, as a way to reduce the factory's gas
consumption.
In that case, the heat is generated by
electricity purchased from the grid.
But the heat could also be generated by a field of aligned mirrors,
like with CSP. This kind of technology is known as concentrated solar
thermal.
Vast Solar is currently working on a concentrated solar thermal
project for a "major global food company" with a "couple of facilities
on the east coast of Australia".
"We're retrofitting CSP to displace gas in their process," Mr Wood
said.
"We're putting in a CSP plant immediately adjacent to where they are
that's going to use the Sun's energy to create steam to replace the
gas that they're otherwise burning."
Dominic Zaal estimated concentrated solar thermal could serve 20 per
cent of the industrial processed heat market.
"Some of the big mining entities, some of the big food
manufacturing entities, they're all looking at renewable heat now."
Another emerging use of CSP is making "green methanol", which is made
by first producing green hydrogen and then combining this with carbon
dioxide.
The result is a fuel that's easier to store and transport than
hydrogen, and with a lower carbon footprint than other liquid fuels
(although higher than green hydrogen). Green methanol can be used for
shipping, converted into aviation fuel, or used to make plastics.
"You need the power to create the hydrogen, but you need the heat to
do the green methanol synthesis," Dr Zaal said.
"You've got to take a source of CO2, and smash it with the hydrogen at
about 300 degrees to give you green methanol."
The Australian and German governments are investing $40 million in
Vast Solar to build a solar methanol production plant next to the Port
August facility.
The proposed plant will produce 7,500 tonnes of green methanol each
year, using hydrogen from an electrolyser at the site and CO2 captured
from the process of making cement at a co-located facility.
"What's emerging from our methanol project is that if you're able to
use a combination of heat plus electricity, that ends up being quite a
bit cheaper than if you're trying to do the same job with electricity
alone," Mr Wood said.
"It's giving us some confidence that we can enter the green fuels
market and be competitive with the existing black fuel prices."
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