36 | New Scientist | 10 August 2019Orbiting power plants
More importantly, perovskite is just as
abundant and cheap as silicon, and much
easier to work with. “You can start with a jar
of liquid and print it, with any kind of printing
press you can think of, at room temperature,”
says Wheeler. He mentions one company that
has bought an old Kodak factory in New York
and repurposed its printers to deposit thin
layers of perovskite onto plastic film for use in
photovoltaic cells. “An old newspaper printing
press could be retrofitted too,” says Wheeler.
There is a problem, though. Silicon
photovoltaic cells are incredibly durable. If you
install some on your roof, you can confidently
bet that they will work for 25 years. Until
recently, perovskite cells were only stable for a
few hours. But NREL now has cells in its lab that
work at 90 per cent of their starting efficiency
for 250 days. “It turns out that perovskite is
not inherently unstable,” says Wheeler. “It’s
the materials next to it that have been the
problem. If you can engineer them, you get
good stability.”
Chase warns against premature excitement.
“There’s no commercial product yet,” she says.
But she says that longer term, perovskite could
be an interesting possibility. She and Wheeler
both have hopes for hybrid cells, with a layer of
perovskite sitting under one made of silicon,
because they absorb different wavelengths and
so would push efficiency even higher.
Another fundamental problem with solar
energy is that the sun doesn’t shine over an
area all the time. You get more sun at noon
than at midnight and at higher latitudes you
get more in midsummer than in midwinter.
But you need energy all day and all year. So
other researchers are working to harness the
sun’s energy in a more storable way.The storage problem
“In the coming world of sustainable energy –
with high levels of electrification – we’re going
to have a serious storage issue,” says Atwater.
“Batteries will be part of the solution, but
imagine you’re in Norway or Sweden where
they have 10 times as much sun in summer as
winter. You won’t be able to store energy for
six months in a battery.” He contrasts this with
fossil fuels, which have stored solar energy for
millions of years. “We use them every day
because they’re amazingly energy-dense,
storing them is inexpensive and they’re
portable. Chemicals represent the ultimate
form of energy storage,” he says
The goal is to use sunlight to create chemical
fuels. Atwater’s lab is working on artificial
photosynthesis: harnessing the sun’s energy toAt New Scientist, writers are
steered away from comparing
new developments to science
fiction because this can become
a prop that is reached for too
readily. But here, we can’t avoid
it. Harry Atwater at the California
Institute of Technology is working
on a project that is literally the
stuff of science fiction: space
solar. “This is an idea that was
first floated in 1941 in an Isaac
Asimov short story,” says Richard
Madonna, a consultant on the
project. “He envisaged sending
sunlight from space to Earth via
electromagnetic energy.”
In the 1960s, scientists started
to look seriously at the idea. But
launching things into space was
expensive and the components –
solar panels, solar reflectors and
radio transmitters – were all
heavy, bulky and inflexible. So
it was economically infeasible.
But the Caltech group,
including Atwater and a
colleague called Sergio
Pellegrino, recently revisited
the idea. The resulting plan was
for carbon booms that could be
wrapped up and would spring
back into shape to provide
structure, as well as flexible
perovskite photovoltaic cells that
would be just a micrometre thick.
“The whole thing could be rolled
into a cylinder for launch,” saysMadonna. He envisages
60-square metre structures
that would be linked to form a
superstructure in orbit. SpaceX’s
Falcon Heavy rocket, “which is
now becoming a feasible space
vehicle”, could carry about 10 of
them in a launch, says Madonna.
Instead of having a single,
central radio transmitter, which
would have needed lots of copper
wire to transport the electricity,
each cell would act as its own
transmitter, beaming radio
frequency energy down to Earth
out of the side facing away from
the sun. Diffraction effects mean
that the larger the structure, the
more tightly focused the beam
could be, and the more efficient
the transmission. These
structures would have to be large.
“It depends on how efficient it is,”
says Madonna. “But to power a
city, it would have to be
kilometres across.”
This technology isn’t
imminent. The Caltech group
hopes to have a small-scale test
in low orbit in the next 10 years,
but it could be decades before it is
really possible, if it happens at all.
Madonna says it won’t be like
nuclear fusion though: always
the next big thing but never quite
arriving. “It’ll either happen or it
won’t,” he says. “It won’t be 20
years away for the next 50 years.”An orbiting array
could one day
beam electricity
JAXA to Earth