Extract from ABC News
It's an idea that sprang from mid-century science fiction and was being seriously considered in the 1970s, in the golden years of space flight.
Key points:
- Space-based solar power involves beaming clean energy to Earth from orbital solar farms
- If it works, it could supply non-intermittent renewable electricity
- But the technology is unproven and may end up costing more than projected
Space-based solar power (SBSP) was eventually dismissed as too expensive, and consigned to the attic of Space Age fantasies, along with lunar bases and ray guns.
Now, it's back. Space agencies are returning to the idea of constructing enormous orbital arrays of solar panels, then beaming the power to Earth via microwaves.
Putting solar panels in space may seem unnecessary (when there's still room on our roofs), but this vision of the future has powerful backers.
Millions of dollars are being ploughed into the concept of vast photovoltaic "islands in the sky".
The UK, US and Chinese governments are funding research, while the European Space Agency (ESA) has approved a 3-year study named Solaris.
So how would these orbital arrays work? And how does this idea stack up against terrestrial solar power?
Clean energy beamed from above
Space is an ideal place for a solar panel.
With the right orbit, the Sun is always shining. Plus, without an atmosphere absorbing and scattering the solar radiation, the sunlight is brighter, and the photovoltaic cells gather more energy.
In theory, SBSP can provide non-intermittent clean energy at a scale similar to nuclear power.
The two main challenges are getting the solar panels into space, then getting the energy down here.
These challenges are partly economic. One reason that SPSB is back on the agenda is the plummeting cost per kilogram of launching payloads into space.
Thanks to reusable rockets, this figure has fallen nearly 20-fold in two decades, while solar panels have become lighter.
To generate a useful amount of energy, each orbital solar farm would have to be many times larger than the current largest structure in space, the International Space Station.
However, because the SBSP array would be orbiting much further out, it would appear smaller than the space station — about the size of a small star.
The solar energy collected by the satellites would be converted into microwaves and beamed to "rectifying antennas" or "rectennas" on Earth, which would, in turn, convert them to electricity.
This energy beam won't fry birds that cross its path, experts say. The intensity at its centre would be about 3 per cent as strong as a typical microwave oven, according to a 2009 report.
The process of wirelessly transmitting electricity, while technically feasible, is very inefficient. Most of the collected energy is lost in the process.
But according to two cost-benefit studies commissioned by the ESA, that's not necessarily a deal breaker.
So long as just 10 per cent of the power that falls on the panels is delivered to the grid, SBSP can be economically viable, these studies say.
It won't be cheaper than rooftop solar or wind power, but it could be cheaper than intermittent renewables plus storage, the ESA says in its public explanatory documents:
"SBSP doesn’t compete with intermittent renewables, but rather could serve a complementary role to terrestrial intermittent renewables, helping to provide stability and reliability to the grid. It therefore needs to be compared to other baseload sources like nuclear, carbon and gas with carbon capture technology or very large-scale deployment of storage solutions."
Dispatching power where it's needed
SBSP has one further advantage, says John Mankins, a former NASA physicist and current co-chair of the International Academy of Astronautics' Permanent Committee on Space Solar Power.
"Space solar power is dispatchable on a continental scale.
"One solar power satellite could deliver power this morning to Melbourne, and this evening that exact same solar power satellite could turn its attention to morning in India."
That is, the power generated by the satellite can be transmitted to any city within line of sight that has the appropriate rectenna.
"An orbital slot that can see Australia can also see India, can see China, can see South-East Asia, can see Japan, can see South Korea.
"That band of slots above Australia serves 60 per cent of the world's population."
He envisions a future where hundreds of photovoltaic orbital platforms are beaming "hundreds of gigawatts" down to Earth.
"These are like islands in the sky … once they're established, they're going to serve humanity basically forever."
'This is a moonshot'
SBSP on this scale could be achieved before 2050, Dr Mankins says.
That may sound ambitious, but others in the field have reached similar conclusions.
Martin Soltau is an analyst at Frazer-Nash Consultancy and co-chair of the UK's Space Energy Initiative, which is a consortium of companies, universities and government helping to develop SBSP.
A solar power station at the "gigawatt scale" is achievable within 12 years, he says.
"After that … we think we can build and commission a 2GW power station every year."
The Space Energy Initiative's commercial entity, Space Solar, has raised about $200 million in initial funding and was seeking about $150 million more, according to Mr Soltau, who is a co-CEO of the venture.
"This is a moonshot, but our program is very much aimed at doing this rapidly.
"There's nothing here that we've seen that is not possible.
"There are many challenges, but they are all surmountable, given political will, given the funding."
But do we really need this?
The main criticism of the SBSP "moonshot" is that it isn't necessary.
Terrestrial solar power is already generating the cheapest electricity in history.
Why take a punt on an experimental technology that could either fail or end up costing far more than projected?
"I find it very difficult to imagine how [SBSP] could ever compete with ground-based PV, even when storage costs are included to provide 24-hour supply," says Thomas White, a solar expert at the Australian National University.
He says even if it's technically possible, it just doesn't make economic sense.
A cost-benefit analysis commissioned by the ESA calculated the average cost of electricity generation by SPSP over the lifetime of a generator unit, including construction, maintenance and decommissioning.
It arrived at a figure of 0.038-0.106 euros per kilowatt-hour by 2045 ($0.059-$0.16 per kWh).
By comparison, Dr White says, ground-based solar has a cost of around 0.03 euros per kWh — and falling.
The figure doesn't take into account the need for storage, but "the cost of storage is also coming down rapidly."
Space-based solar, he says, is a "hypothetical future technology that may be able to match today's ground-based solar power costs in 20 years' time.
"While we should be considering a wide range of strategies to achieve net-zero emissions as rapidly as possible, I am yet to see a compelling argument for space-based solar power being one of these."
Space agencies investigating the idea
At stake in the debate over SBSP is the answer to a broader question about the energy transition: does the world need new technologies to reach net-zero greenhouse gas emissions by 2050?
Will solar and wind, plus storage like batteries and pumped hydro, be enough to decarbonise the electricity grid?
In Australia, there's a general consensus that these will be enough.
SBSP advocates such as John Mankins and Martin Soltau disagree, arguing that, for many countries, a grid powered entirely by intermittent renewables requires too much storage to be feasible.
"The problem is we won't get to net zero with our current technologies. It's just not viable," Mr Soltau said.
Whether or not that is the case, research into the technologies needed for SBSP is quietly proceeding in laboratories around the world.
In May, NASA announced it was commencing a study to re-examine the viability of SBSP.
A month later, China's main spacecraft development and production facility erected a 75-metre-high steel tower to demonstrate the steps of collecting solar power, converting the energy to microwaves, and then transmitting these to a receiving antenna on the ground.
In July, the UK government committed a further 3 million pounds ($5.4m) in funding to support SBSP projects.
In September, Airbus engineers sent 2kW of power wirelessly to collectors more than 30 metres away.
That's a long way from sending gigawatts thousands of kilometres, but it's a start.
The ESA's recent decision to proceed with Solaris will give the concept impetus and lead to further research.
Even so, the ESA is at least three years away from committing to even a trial version of a space-based power station.
In Australia, meanwhile, there's been little public discussion of SBSP.
In October, the UK government, along with Mr Soltau, approached Australian state governments to gauge their interest in partnering on SBSP.
"In our development programme actually Australia works really, really well from the point of view of some of the orbits we're considering and beaming power down," Mr Soltau said.
So far, no partnership agreement has been announced.
In 2019, as director of Melbourne-based company Solar Space Technologies, Dr Mankins unveiled a plan for an SBSP network, which he said could be operational within 8 years.
At the time, he pressed Australia to forge ahead of countries such as China.
Three years on, Solar Space Technologies was still "trying to gain the attention" of the federal government, Dr Mankins said.
"It is an ongoing enterprise."
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