A photon walks into a bar
Transcriber: Amanda Zhu
Reviewer: Peter Van de Ven
Since April,
I’ve been working the morning shift,
and I’ve learned two things.
Four o’clock in the morning -
that continues to be painfully early.
It has also taught me, though,
that a sunrise
can be stunningly beautiful.
There’s something magical
about the light that we get from the sun.
Light, of course, is photons,
and the photon
is this interesting particle
that has no mass,
always travels at the speed of light,
and it packs a real punch of energy.
Now the photons we get from the sun
come to us in a wide range
of energy levels,
ranging all the way
from the very energetic blue light,
that has so much energy
that it can interact
with the molecules of the air -
and their scattering
is the reason the sky is blue -
to the lazier red photons
that travel unimpeded
in a straight line through the atmosphere,
which is why a sunrise can be red.
So we get all of
these photons from the sun,
all of these different energy levels.
And here’s the tragedy.
When we try to harvest that energy,
we’re optimized for just one wavelength;
everything else is sub-optimal.
To understand why,
let me explain to you
how a solar panel works.
A solar panel is made
out of a semiconductor material,
and to get useful electricity
out of a semiconductor,
you have to lift the electron
from its natural state
to the conduction band.
The amount of energy needed to do that
is called the bandgap.
Now, there’s three scenarios.
One, the photon has exactly
the same energy as the bandgap;
in that case, you can lift the electron
to the conduction band
where it can do useful work.
The second case,
the photon has less energy
than the band gap;
in that case,
the photons go unused
because they don’t have enough energy
to free any electrons.
And then the third case,
the photon has more energy
than the bandgap.
Well, that extra energy is wasted as well
because you’re still going to get
just one electron for one photon.
The best we can do with today’s technology
is to harvest around 24 percent
of the available energy.
And today’s solar panels are getting
very close to that fundamental limit.
This year,
solar panels will provide
around five percent
of the electricity we use globally.
Clearly, that’s not good enough.
To change our energy mix,
we have to install
many, many more solar panels,
and we have to increase
the power of each panel.
But we’re up against
the fundamental limit.
So how do we get out of that box?
Well, there is a solution;
it’s called tandem.
In laboratories in Europe
and the United States,
mostly privately funded,
breakthroughs have now made it possible
to make a cost-effective tandem module
that uses two semiconductors.
The top material is a high bandgap
harvesting the high energy photons,
and the bottom material is a low bandgap
capturing the long wavelength photons.
Tandem is going to increase
the energy output of a solar panel by 35%.
To make this possible,
we have to solve
all manner of difficult engineering
and manufacturing problems,
and it’s just now
that cost-effective solutions
are becoming available
and commercially viable tandem modules
are becoming a reality
in the very near future.
This is the most important
innovation in solar
since solar was first conceived
in Bell Labs, in 1954.
Wherever they’re going to be deployed,
tandem is going to increase
the energy yield per acre.
They’re going to make
every installation more efficient.
This is such an important technology.
We have to urgently deploy it
everywhere where it’s needed most,
places like India.
India is at the forefront
of the battle against climate change.
Its people are hungry for new solutions,
and they have some of the lowest
energy use per capita in the world.
India deserves an opportunity
to industrialize with something
more appealing than coal,
and tandem modules
can be that opportunity.
Imagine powerful tandem modules
splitting water into oxygen and hydrogen.
Thanks to the increased energy yield
of the tandem module,
clean hydrogen can become
economically feasible.
And once you have clean hydrogen,
now you can store vast amounts of energy
for long periods of time
and fuel industrial processes
such as steel making.
Tandem modules are transformational.
By themselves, they are not good enough.
Winning the battle
against climate change
is a huge challenge.
It’s a battle we are currently losing.
We’re not decreasing but we’re increasing
our CO2 admissions.
To change that,
we need a dramatic psychological shift.
We need to get past a tipping point,
a point in time where the majority of us
believes that we are responsible for
and need to take care of our planet.
Today, we’re nowhere
near that tipping point,
but with the advent of tandem,
our tools are getting better.
And now it’s up to all of us
to put them to good use.