October 27, 2020 • 41 mins
Daniel and Jorge break down the physics and engineering behind solar panels
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Speaker 1 (00:08):
Hey, Daniel, do you have solar power panels on your roof? Embarrassingly,
I don't. You don't? Why not? I just haven't gotten
around to it yet. It's the honest roof, so there's
kind of an energy barrier there. I know, I know
I should do it, but you know, prices keep falling,
and I guess that's what I say to myself to
justify my laziness. Oh man, you just cheap. We would
(00:29):
you get solar panels if they caused pennies or if
they could repair themselves and automatically reproduce. Well, that's an
offer so powerful I could hardly refuse. I am more
(00:54):
handmade cartoonists and the creator of PhD comics. I'm Daniel.
I'm a particle physicist, and like you, I haven't to
do list that's too long. Welcome to our podcast, Daniel
and Jorge Explain the Universe, a production of I Heart Radio,
in which we talk about all the things that are
amazing about the universe, all the places our curiosity has
taken us, all the questions we have asked and all
(01:15):
the answers we have found so far. But we love
to talk about the questions that we have in the
questions that you have, the things that you are curious
about the universe. Yeah, we like to take you to
the far reaches of the cosmos, to other galaxies and
inside of black holes, but we also like to take
you to your neighborhood, to the world around you and
talk about the things and the questions that we have
(01:37):
in our everyday lives, because physics is everywhere. It's not
just out there in the center of black holes and
the craziness of neutron stars. It is right here making
our lives better. Or maybe, Jorge, you'd say this is engineering. Yes, yes,
I would say that. Or maybe finally, this is physics
and engineering working harmoniously together. Yeah, because as humans, we've
(01:59):
made a lot of knowledgy and a lot of progress
in science and knowing how things work to the point
where we can create things that take advantage of nature
to make our lives easier. That's right, Because the universe
is out there pumping out energy into space, these crazy
nuclear bombs going off at the center of every solar system,
and so of course it's tempting to potentially take advantage
(02:20):
of that. Yeah, So today we will be tackling a
question that a lot of readers have sent in, right, Daniel,
that's right. A lot of folks see these things on
the roofs in their neighborhoods and they wonder how does
that work? What's going on in there? So to be
on the program, we'll be asking the question how do
solar panels work. It's a really fun question because you
(02:43):
see these on the roofs in your neighborhood, and you
know they generate electricity, but how does it actually happen.
I mean, we know the sun pumps out energy, but
how does that turn into zippy electrons in your iPhone battery.
I have solar panels in my roof. It's amazing. I
haven't paid any electricity bill in like years. In fact,
the electric company writes me checks for how much energy produce.
(03:06):
So you are the electric company now I am my
own company. Yes, yeah, I know. It's pretty awesome. I
mean you invest in it and then it pays off
over the years. Yeah. And it makes a lot of
sense because in the end, the sun is the direct
source of almost all the energy we use here on Earth.
Even fossil fuels originally just came from energy from the sun,
(03:26):
and so it's tempting to say, hey, let's just go
direct to the source. Why build a fusion reactor here
on Earth when we have a huge one in the
center of our solar system, Let's just suck up some
of that energy. Yeah, because it sort of feels like
a waste almost, you know, Like I think about all
of the energy that used to hit my roof before
I had a solar panels, and all the energy just
(03:46):
kind of goes to waste. It just hits the roof
and bounces and heats it up a little bit, but
then it cools down again at night. So I feel
so much more like I'm taking advantage of nature in
using up the energy that's there. Right, So you're not
just doing it for the econom benefits, You're doing it
because it makes you feel like a better person. Honestly. Yeah,
I feel like I invested in a more guilt free lifestyle.
(04:08):
Like in the summer, we can just turn on the
A C guilt free because it's all coming from the
sun and have a second box of cookies. Right. Yeah,
And you're right, there is a huge amount of energy there.
The amount of sunlight that falls on the Earth is
like a hundred and seventy three thousand terra wats. It's incredible.
It's a lot of wats. That's a lot of terra wats.
(04:29):
And it's actually a thousand times more than the entire
energy budget of our civilization. Wow, meaning that a thousand
times more energy falls on Earth from the Sun than
we use. Yeah, so if you could capture the solar energy,
you could easily power the entire civilization with just a
fraction of the energy that comes from the Sun. So
(04:49):
it's a huge resource. It's incredibly powerful. It's right there.
It seems awfully tempting to try to capture it. What
would be the number, Daniel is, So if it's a
thousand times more, does that mean that if we over
the earth the Earth in solar panels, we would be
set if it was efficient. Yeah. I've seen lots of
different calculations actually about how many solar panels you would need,
(05:11):
But you don't need to cover a significant fraction of
the Earth and solar panels to get enough energy to
power the Earth. We'll talk about a little bit more later.
One of the biggest challenges actually is getting that power
to the right place and storing it and having it
at the right time. But it's a big percentage these days,
or a significant percentage of the power that we consume
these days, right, I mean, it's not like zero. It's
(05:32):
not like zero. Here in the US we get about
three percent of the energy that we use from solar panels,
but in other countries it's higher. China's four percent, Germany
is eight percent, Australia goes to nine percent, and Honduras
tops it out at well A sairly as understandable. I mean,
everything is bigger in Australia and Sunnier, even their solar panels.
(05:55):
Spiders and solar panels. Yeah, it aren't like the kangaroos
hanging out on top of the solar panels blocking it.
I wonder if that gets factored in. And I guess
the great thing about it is that it's carbon free,
Like it doesn't give off any emissions? Does it have
operating the solar panels certainly doesn't. There's a question of
constructing solar panels and infrastructure to store that and create batteries,
(06:16):
and there's definitely some toxic materials that are used and
created there. But operating solar panels no, they have no
moving parts. They just sit there and turn photons into electricity.
So they're pretty awesome. Yeah, so a big question that
our readers have is how do they work, Like, how
do they convert solar energy sunlight into electricity you can
(06:37):
use for your devices and video games and televisions and Netflix,
and so we were wondering how many people out there
know how solar panels work? That's right, and so I
asked folks who volunteered to speculate without googling about how
solar panels work. And if you'd like to speculate without
reference materials on difficult questions in physics, please write to
(06:58):
me at questions at Daniel and Jorge dot com. Yeah,
so think about it for a second. Do you know
how solar panels work? Here's what people had to say.
You know, I've never thought about it, um and I
have no idea. The panels capture the photons from the
sun and stored. You know, it's a circle of life,
(07:18):
you know. I don't really know the specifics. I know
that they're also called like photo voltaic panels. I don't
know if I'm saying that right. I've only ever seen
the word written out, but which makes me think it's
got to have something to do with the photon specifically
interacting with the panel, you know, because I just saw
a small presentation last week. So sunlight activates the panels
(07:41):
the silly compounds, uh, and the cells produce electrical current,
which is converted in um electrical energy or no electrical
energy is converted in electrical power. My understanding is that
these solar energy hits these panels, and based on that energy,
(08:07):
there's some photo voltaic cells which translate that into electrical energy.
I'm not really sure how. Maybe because of the expanding heat,
it creates a differential and different metals. I know they
have photo voltaic cells in them, um, but I couldn't
explain the science behind it. All Right, A lot of
(08:28):
people seem to have some idea. A lot of people
said the words photo voltaic. That's pretty impressive. Yeah, that's
pretty awesome, and it goes to the core of the
physics that's happening inside solar panels. And I think often
they're called photo voltaic cells, and so that gives people
a clue about what's going on inside photo I guess
light will take just kind of a meaning electricity. Yeah,
(08:49):
and it is in the end of interaction between photons
and electrons, So it makes a lot of sense. All right,
Well let's break it down for folks. How do solar
panels work, Daniel? I mean, I assume they at sunlight
and somehow that gets transformed into electricity. So what's going on? Yeah,
So there's sort of two steps there. One is how
does the energy get from the photon into the material?
(09:12):
And the second is how can you construct a material
that it can effectively grab that energy and siphon it
off into electricity? And so the first step is called
the photovoltaic effect, or a photon hits a piece of
material and it basically passes that energy to an electron.
What does that mean, Like the electron absorbs the photon,
(09:33):
or like the photon hits the electron. How can I
visual life? Yeah, the photon is absorbed by the electron.
Remember that electrons interact electromagnetically, and that just means that
they trade photon. So every kind of electromagnetic interaction, every
push and pull by electric fields is mediated by photons.
So photons are the way that electrons talk to each
(09:53):
other and other charged particles. And photons are not eternal, right,
they can get absorbed by an electron, Their energy goes
right into the electron and then the electron has that energy.
So the way I visualize it as like a photon
coming in meets an electron and then only the electron continues.
So now the electron absorbs the photon and now I
guess it's charged up or something. Yeah, it's more exciting, exactly,
(10:16):
it's charged up. And there's two different effects here that
are very closely related. One is the photo voltaic effect,
which is what we're talking about, and the other is
something more famous that people might have heard about called
the photoelectric effect. They sound very similar and they are
very similar. Photoelectric effect it's when the photon has enough
energy that the electron gets kicked out of the materials.
(10:37):
So people saw this about a hundred years ago. If
you shine light at a material, you will get electrons
boiling off the surface, and that's because they have so
much energy they can leave the trap of the material,
meaning like a you know, an electron is orbiting the
nucleus of an atom because the nucleus is positive, but
now it has so much energy it just pops up. Yeah,
(10:58):
it just pops out. And this electric effect is actually
what Einstein won his Nobel Prize for explaining and was
one of the key experiments that led us to understand
that light is not just electromagnetic waves, what actually comes
in little particles, because we saw these weird relationships between
the intensity of the light and the wavelength and how
many electrons were boiled off. But we have a whole
(11:19):
other podcast episode about that about how we know that
light is quantized made out of these little photons. But
that's very similar to the photovoltaic effect. But the voltaic
effect is when the photon comes in and the electron
gets enough energy, but not enough to actually leave the material.
It gets excited, but it's still hanging out sort of
in the same blob of stuff I see. So it's
(11:40):
just a matter of whether or not it gets enough
energy to pop out, basically. Yeah, And there are some
materials where electrons don't have to be isolated to one
specific atom, like the picture you described as correct, you
have an electron it's orbiting a nucleus, for example, although
we don't really like to think of them as actually orbiting.
It's hanging around quantum mechanically near it's nuclear is. But
(12:00):
in lots of crystals, you have electrons that can flow
between atoms, and so, for example, in semiconductors, you have
electrons that are trapped that are around individual atoms, and
then if they get enough energy, they can jump up
over a little gap into a band where they can
move around more freely and jump from atom to atom. Yeah,
they sort of float around, right, They're not bound to
one atom. They can you know, hang out. Yeah, they're
(12:24):
like social butterflies. They just float around. They have enough energy,
they're sort of like flying high above all of these
little gaps. And so that's what happens in the photovoltaic effect,
that a phoeton comes in and knocks an electron off
from being stuck around one of the atoms, and so
they can float around free. Wait, that's the photo electric
or photovoltaic. Poto voltaic is when it knocks it off
(12:44):
so we can float around inside the material. Photo electric
is when it gets so much energy that it flies
free the material and out into space. It's like abandons
its original family. Oh, I see, I see you Like
one is like pop out out of the material, like
out out of like a way and bolt take it
leaves the atom. But it hangs out in the lattice,
(13:05):
in the structure of the material. Yeah, it's just jumping
around from atom to atom, floating free inside the material.
The photo electric effect, it's like totally liberated and may
never come back to home. All right. So that's the
two effects, and the one in solar panels is the
photovoltaic effect exactly. And so the key thing for solar
panels is to take advantage of the photovol take effect.
(13:25):
Because now you have this electron, it's got more energy.
If you could grab that energy somehow, if you could
funnel it into an electric current, then you could turn
effectively that photons energy into electricity. And so that's why
you need a special kind of material. Now, any kind
of material can have the photovol take effect. Your hand
or a rock or whatever. When it absorbs a photon,
(13:46):
the electrons that absorb it don't fly off the material.
Right then you're having the photovol take effect. You're grabbing
that energy into the object. But you need a special
kind of material to effectively gather that energy and funnel
it off into electricity. And that's where the silicon diode
comes in. And we had an a whole episode about diodes, right,
and transistors. Yeah, we did because we talked about how
(14:08):
L E d s work, and diodes are like a
really key foundational element of modern computing because you can
use them to make L D s and transistors and
all sorts of stuff. And it comes from semiconductors. And
that's why silicon is so important to the computing industry
because it's the most important semiconductor for building these kinds
of things, right, And it's important because it's kind of
(14:29):
a special material, right, Like it has just the right
number of loose electrons and it's pretty stable. Yeah, because
the electrons have these two different regimes they can be in.
A conductor is where the electrons just flow freely everywhere
from atom atom and insulator is one with the electrons
are all stuck around their individual atoms. And a semiconductor
is one that has both and has the electrons around
(14:50):
the atoms and electrons at a higher energy that can
hop freely from atom to atom. So that's what a
semiconductor is, and silicon is a great example of it.
And what happened and silicon is exactly that the electrons
jump over this band and then they can float around free. Yeah,
and so that's how you make a solar panel. As
you use silicon to make a solar panel. But and
then do you have to like create these different areas
(15:13):
where one one area is like a P type and
the other ones in N type. Yeah, you can't just
use normal silicon. You need to create something that's going
to funnel off the electrons. So the way that works
is that you have two different kinds of silicon. It's
not pure silicon. You've added stuff to it slightly to
change the behavior. And so you have one kind you
called N type, which has like extra electrons there are
(15:34):
a bunch of electrons floating around that sort of don't
have a chair to sit in if you played musical chairs.
And another kind where you've added other kinds of materials
like gallium or arsenide or whatever. So they're called P type.
They don't have enough electrons. They're like empty spots for
electrons to sit in. And semiconductor physicists they talk about
these things as holes, and they treat them as if
(15:55):
they're sort of like positively charged electrons. They think of
them sort of like as particles. I remember we talked
about the quasi particles like things that are not particles
but sort of act like particles. This is a good
example of one. It's a hole. It's like a missing
spot for a particle, but it moves around sort of
as if it was a positively charged particle. Right. It's
like if you had five people for six chairs and
(16:16):
they move around and change seats. It's like you keep
track of worth of the empty seat, not the people. Yeah,
and the empty seat moves like a particle, right, because
if one person slides from one seat to the other,
then the empty spot slides the other direction. Sort of
cool to have that idea in your mind of an
emptiness being a thing. Anyway, So you have these two
kinds of the lookon the P type that has extra
(16:38):
holes and the end type that has extra electrons, And
because they match up together, there's the sort of you know,
too much electrons on one side and too many holes
in the other. Some of the electrons flow across the
junction between them and fill up some of the holes
on the other side, and that makes an electric field
across them. That's the key thing. The electrons have flowed
(16:59):
in one to action, and now they make an electric
field going the other way right. I think what happens
is that like the material that has too many electrons
loses some of them because they all go to the
side that has the holes. And now you have like
this build up of too much too many electrons in
in one place, and so that creates like a like
a barrier, like a something that repels other electrons. Yeah, exactly.
(17:22):
It's sort of like you know, diffusion of temperature. If
a hot thing next to a cold thing, then the
heat's going to flow over the cold side. And so
you put this N type stuff with too many electrons
next to the P type stuff without enough electrons, some
of them flow over, and you're right, it creates this barrier.
So now you have this P N junction, you have
the silk, and it's all primed to get your photon.
(17:42):
Because what happens when a photon hits this special diode,
this combination of P type and N type silicon, is
that when the electron gets kicked free, it doesn't just
wander around loosely. Is now an electric field created by
the P N junction that pushes the electron all away
in one direction, and then you just have to have
something at the edge there to gather these electrons, these
(18:02):
electrons that have the solar energy absorbed, so they can
move along and create electric current. All right, well, I
have some questions about that, and let's get into some
of the details in and also maybe let's talk about
some of the larger issues about solar panels. But first,
let's take a quick break. Right. We're talking about solar
(18:34):
panels and how they work, and they do work, they're
pretty good. I have some how Well, do your solar
panels work? You generate enough electricity for your house every day? Yeah?
In fact, they generate so much energy we get a
check from the electric company. They're like, you gave up
too much electricity. Here's some money back, and your energy
goes back to the electric company and then back to
(18:55):
your house. Right. You don't directly use the electricity created
on your roof, do you, right? Yeah? No, I don't
have a battery, So it just goes back into the
grid and then we get from the grid. But they
keep track and if we make more than we take,
then they give us a small amount of money for them. Awesome. Yeah,
So we were talking about how it works, and it
involves silicon and p type and type of materials that
(19:16):
have holes and extra electrons, and so is the idea
then that you know, the side that has too many
electrons gives them to the side that doesn't have enough electrons,
and that creates kind of like a like a standoff
almost like a barrier for any more electrons to flow.
But once the light comes in, then that kind of
kicks things up. Yeah, and then these new electrons get
(19:37):
pushed away from that barrier as you said, and towards
the edge, and then they get gathered up and the
current forms with all these energetic electrons and you can
draw that off. And that's basically what electricity is. It's
energetic electrons. It's electrons moving along. That's what current is.
It's just the motion of charged particles. It feels kind
of like almost like magic. I mean, like the sunlight
(19:59):
is actually creating energy, is just kind of like triggering
the flow of energy. Yeah, well, sunlight is energy, right,
It's energy that was released from the fusion of hydrogen
into helium in the center of the sun and that
has been flying nine million miles through space. And the
cool thing is that that energy doesn't like evaporate or
run out. You know, photons can fly through space basically
(20:21):
forever without losing any energy, doesn't take them any energy
to fly the speed of light, and then that energy
gets deposited, you know, on your solar cell and gets
slurped up into that electron. It's really pretty awesome, and
the coolest thing about it, I think is that it's
quantum mechanics. You know, this is not something you can
explain with classical physics. So it's something we only could
have invented pretty recently. Well, we we understand it now,
(20:46):
but didn't we sort of invented before understanding how it works? Yeah,
you're right, we understand it now, which allows us to
like optimize it. And we certainly never could have built
like these complicated p N junctions without understanding quantum mechanics.
But I suppose some clever engineer could have put it
together without a deep physics understanding. Suppose, like I guess,
(21:07):
if they were like a super special genius engineer. You're
you're absolutely right. And there's lots of examples of times
when we build something we saw do something cool and
we didn't understand what was happening, and that led to
lots of really awesome questions, you know, like that's how
electrons were discovered. People didn't understand crooks tubes and these
glowing rays they saw inside them, and so it led
to lots of awesome stuff. So yes, absolutely, you can
(21:29):
build stuff before you understand it. It It is pretty cool
to the thing now that you mentioned it. It's amazing
how like these photons were made in the Sun and
they traveled millions of miles really sort of uninterrupted, like
they don't lose any energy in the way. It's like
almost like a perfect transmission. And then they hit my
solar panel and powers my devices. Yeah, exactly. So really,
(21:50):
solar power is fusion power. You know. It's just like
you are a blanket to absorb energy from a fusion device.
We talked about either a few weeks ago and how
a big problem they have is how to absorb the
energy that either creates, like haven't really tackled that problem yet,
And you're basically doing that for the Sun. You know,
the Sun is this huge fusion engine and you're putting
(22:11):
up a little panel to grab a tiny little slice
of all. Man. I wonder how much any more panels
they would sell. They called it dead. You know, fusion
panels probably fewer fusian generator on the roof, a hydrogen
bomb on your roof where your kids sleep. Who doesn't
want their computer, their work powered by fusion energy? Me?
(22:34):
I don't. No, No, honestly I do. That's super awesome.
I think it's wonderful. And also it works pretty well.
You know, it's sort of shocking how efficient it is.
But I mean, what's the efficiency. Well, the record efficiency
for like the most highly engineered solar panels so far
is about forty that's the fraction of the energy of
the photons coming in that you can effectively gather out
(22:56):
as electricity. And that's pretty good. That's like a one
out of every two holdons you actually use it for something. Yeah,
And it's not a hundred percent efficient because not all
the energy goes into one electron, or that electron loses
some of its energy along the way as it moves
along through the silicon and gets to the thing that
stirps it out, or it goes into you know, exciting
(23:17):
the nucleus or stuff like that. And most devices that
you would have on your roof are not that efficient.
Mostly they're like fifteen to twenty percent efficient, though they've
climbed a lot in recent years. It's incredible the prices
are dropping and the efficiencies are rising, and even is
really pretty efficient. Yeah, what happens to the other percent?
Like where does all the other energy go gets reflected
(23:37):
or absorbed? It just goes into heating the material. You know,
there's lots of ways for silicon to absorb energy, not
just one electron getting kicked up an energy level. The
nucleus can absorb energy, or the electron can absorb the
energy and then lose it to something else, and so
there's a lot of delicate engineering involved in getting those
electrons to be the place where the energy lands and
(23:58):
getting them to deliver it to the edge of the
p N junction. You know, this stuff is really cool
because it's actually very similar to what we do with
the large Hadron collider. We use silicon devices to detect
the passage of particles photons but also like muans or
other particles, and you detect particles in exactly this same way.
The particle passes through the detector and it leaves a
(24:20):
trail of electrons behind it, which we then slurp off
and use that as evidence to say, hey, there was
a particle that passed through, So we should maybe think
about rebranding it that way too, Like, don't call them
solar panels, call them melon absorbers, particle detectors, particles. Yeah,
who doesn't want a particle detector on the roof? And
(24:41):
you know the same basic principle works also in every
digital camera, right, That's how digital camera turns a photon,
which is the picture you're seeing, into an electrical signal,
which is what your computer needs to record it. The
photovo take effect. It turns a photon into little electrons
which then get gathered up at the edge of your
little pixel and recorded as evidences stead of photon came
(25:02):
through as like, oh, that's right. Yeah, that means everyone
who has a camera on their phone has a solar
panel in their pocket. That's right, that's right, except that
it draws power instead of generating it. Unfortunately, it generates images,
but it doesn't generate power. Does I mean I have
a giant camera on my roof taking pictures of the
sun every day? Absolutely? And you know we have done
(25:23):
the calculations. Can you use solar panels as particle detectors?
Could we use everybody's solar panels? Is like a huge
telescope to understand cosmic rays. Unfortunately you can't because you're
swamped by the photons from the Sun which make a
huge signal. And everything else we're interested in, like little
muans or positrons or protons, is swamped by that huge
(25:44):
blinding light from the sun. But it does you're you're saying,
my solar panels do detect these other particles. It is
technically like catching them and converting them to a signal.
It totally is. If you covered your solar panels, if
you made them light proof, which would be terrible for
your electrical efficiency, But if you made them light proof
and cover them up so they were in a black box,
then they would be great detectors for muans or other
(26:07):
kinds of particles that could penetrate that seal and leave energy. Interesting.
All right, I am ready to do scientific experiments at
the expense of actually generating any electricity. Wow, some sacrifices
might have to be made. How important is science to you?
All right? Well, um, that's sort of how they work.
(26:27):
I guess. Maybe a question is they're pretty great, but
why aren't there more of them out there? Why doesn't
everyone jump into this solar energy bandwagon. Is it political
or are there other limitations? There are some other limitations.
You're right there, pretty great, but there are some downsides
to solar panels. One is that the sun is not
always above you in the sky. Right, Sometimes there are
(26:50):
clouds or it's night time, and so you're generating power
whenever the sun is above your solar panels. But that's
not always the case, and you need power some times
at night or when it's cloudy, and so you need
a complicated system there to buffer, to gather energy into
like a battery, and to save it for you for
when you need it. Right, But that's not really a negative.
(27:11):
It just means that, you know, you need a like
a buffer, you need like a something that stores it
like a battery. Yeah, but it adds to the cost,
you know, just like the transport issues. Say, for example,
you have a huge solar panel array out in the
desert to gather energy really efficiently, then you need to
send that energy hundreds or thousands of miles to where
it needs to go because you have a mismatch sometimes
(27:32):
between where the energy is used and where the energy
is created. I mean, if every device could just create
solar power whenever it needed it wherever it was. That
would be awesome. But one of the main costs of
solar power is fabricating the devices themselves, of course, which
is not trivial and not cheap, but also transporting and
buffering building these batteries. You know, battery technology is complicated
(27:53):
and also quite toxic, right, but I think that you
know you need to do these things anyways for any
kind of power, don't you Like, do you still need
the infrastructure for um, burning coal or for nuclear powered energy? Right? Well,
you know you can turn your coal power plant on
any time of day or night, right, and so it
(28:13):
can be a much steadier source of power doesn't have
these fluctuations. You don't need the same kind of buffer
for a coal power plant. A coal power plant, essentially
the energy is already in a battery. That battery is
called coal, and it's available for whenever you need it.
You just have to transform it into electricity. Now, of course,
coal is terrible for lots of other reasons. I'm not
selling coal. But one of the disadvantages of solar power
(28:34):
is that it's not always created when you need it, right, right,
But fortunately I'm mostly asleep at night. Well, actually, that's
not true for me, but I think for most of humanity,
you're sort of asleep at night, so you don't actually
use that much energy at night, right, and it's cooler
and you so you don't need the a C. Really like,
I think most people's power consumption matches sort of daylight. Yeah.
(28:56):
Do you use less power when it's cloudy outside, Yeah,
because you know you don't need to your house as
much right now, You're absolutely right. It's not a killer
for solar power for sure. It just means, you know,
you have to build this infrastructure and you have to
have batteries, you have to do this kind of stuff.
But you're right, people use more energy when it's daytime,
and they need more A C when it's sunny outside,
and so that's not that big an issue. Well, obviously
(29:18):
it's not like free energy, and it's not super simple
to get solar energy, but it's still I think overall,
it's it's renewable, right, and we don't create carbon emissions,
and still more positive than most other sources of energy, right, absolutely,
And it's getting cheaper, you know, the more we work
on it, the easier it is to fabricate these solar panels,
(29:39):
they last longer, they're more efficient, they're cheaper, they're easier
to produce, and it's sort of something that builds on itself.
The larger the market is, the more companies get involved,
the more competition there is, the more clever engineers get
on board from making these things effective, the better batteries get.
It seems like an excellent option for the future. It
just takes sort of an investment. It just takes us
(30:00):
deciding to make this happen. Yeah, and it's like we're
getting this energy from space for free. It feels great
to you. It does, and there's lots of really fun
ideas for how you could tap into it. You know,
you don't need to build a huge array of solar
panels in the middle of your city. You can put
them in the desert. We have lots of huge areas
of the earth where nobody's living because it's just sand,
(30:21):
and you could put vast solar arrays there. You can
even have them like floating on things in the ocean,
just gathering up solar energy. So if you built enough
infrastructure there, you could really power a lot of our
civilization's energy needs. Yeah, and create a lot of shade
in the desert, which would be pretty good probably for
all the animals there. All right, well that's sort of
(30:43):
the big picture and the little picture of solar power.
And we're gonna do something a little bit interesting next,
which is compare them to photo synthesis. But first, let's
take a quick break. All right, we're talking about solar power,
(31:06):
and we talked about how solar panels work, and so, Daniel,
you thought something interesting would be too, sort of compare
this man made machine and device that we've made to
capture solar energy to what nature has done. Plants use
solar power and so through something called photosynthesis, And so
how do the two compare. Do they use a similar
mechanism or is it totally different? Yeah? I thought this
(31:29):
was really fascinating because, you know, we've been working on
this technology for decades, but nature has been doing this
for literally billions of years, and it's got a really
refined process for making things more efficient and more effective
in finding solutions. And so naively, I thought to myself, well,
I'm sure that our efficiency is pretty good, but Nature's
efficiency must be even higher because it's been fine tuned
(31:51):
for for so long. But you know, you start to
read about photosynthesis, and you discover that it's actually less efficient,
that a smaller fraction of the light that comes from
the sun and hits a plant gets turned eventually into energy,
and it's using a completely different process. So they're not
as good as solar panels, I guess, and absorbing energy,
(32:11):
I guess. They don't have the advantage of like having
silicon and all these dope materials and highly engineered materials.
How do they work? How do plants absorb? Some might Yeah,
you're right. The plants don't necessarily have access to some
of the rarer elements that we use to dope our
silicon to make these diodes work. What they do is
they have the light come in and it interacts with
(32:31):
carbon dioxide and water inside the leaf, and essentially what
it does is it builds a sugar. They turn light,
not into electricity, because plants aren't interested in electricity. They
don't run air conditioning or sit on their phones all day. Right.
It basically turns light into plant food, which is these
complex carbohydrates, these carbons and hydrogens and oxygen's all built
(32:52):
together into things that are fiber or what we would
call sugar. They do it through chemistry. Like you know,
they have the ingredients, they're sort of on the leaf,
and then the sunlight triggers a reaction or triggers like
a molecules kind of coming together. Yeah, exactly. Chemistry is
all about energy flows, right, So you can store energy
in chemical bonds. You can build something that has energy
(33:14):
inside of it, but then you need to put the
energy in. Right. You can't just have the ingredients. They're
sort of like baking a cake. You can just mix
the ingredients. You need to supply the heat. And so
in order to make these sugars, these sugars which store energy,
you need to bring the wrong ingredients together, which is
carbon dioxide and water, and then you need to apply
the energy. And that's where the photon comes in. As
(33:35):
the photon comes in and chemistry happens, and then you
get out, You get sugar, and you get oxygen as
a byproduct, which is wonderful for all of us oxygen breathers, yeah,
and all of those salad eaters. Yeah, and for the
plant specifically. It's basically turned the energy into plant food. Right.
So we want to generate electricity and plants. What they
(33:56):
want to do is they want to generate these sugars.
And really the answer to the question of you know
why is photosed in this is less efficient than solar
power is really that they're doing different things. Plants have
optimized turning photons into plant food, into this fuel which
they can store and then very easily use later on,
whereas we've optimized for creating these electrons which we can
either use immediately or try to funnel into batteries. It's
(34:19):
almost like they've invented the battery and the panel at
the same time. Yeah, it's really pretty impressive technology. Right.
This plant fuel is a great way to store energy,
and so it's a really nice thing for them because
they can use it whenever they need it. They don't
have to worry about creating the battery. Right And if
I get takes carbon diotside from the era, yeah exactly
and produces oxygen and delicious vegetables and delicious vegetables exactly.
(34:44):
And you know it also it captures a different fraction
of the solar energy. Like photobole take cells, the ones
that we build, they can capture energy that's out of
the visible spectrum. You don't have to be able to
see the photon for your solar panel to be able
to slurp it up and turn it into electricity. You
can also captured the energy of photons that have a
wavelength it's too long they're in the infrared, or photons
(35:05):
that have a wavelength it's too short there in the
ultra violet. Your photovolt take cells made from silicon can
slurk that up. Plants are mostly sensitive to the visible spectrum,
so they get sort of a smaller slice of all
the light that comes in. But I think solar panels
also use a photo will take effect a little bit similar.
I mean, they're optimized for certain wavelengths, right, Yeah, I
(35:27):
mean we certainly are optimized for the wavelengths that come
from the sun. Right. They've chosen a material that can
absorb it, and you're right, this is quantum mechanical, and
so you can't absorb just any photon that comes in.
It has to be a good match for the material,
because every material has certain wavelength of light it can
absorb and other wavelengths it's transparent to. And so one
(35:47):
of the reasons silicon has chosen it's not just because
it's a semiconductor, but because they can absorb light in
the wavelength that's hitting the earth. So plants aren't as efficient,
but they're pretty good at other things, right, Like a
plant you know, need to hose it down when it
gets too dusty. That's right. Plants are a much nicer
option compared to solar panels in some way because, for example,
(36:07):
they build themselves. Right if you could just sprinkle like
solar panel seeds on your roof and they like sprouted
up and created working solar panels, that would be pretty awesome.
That would be pretty awesome. Yeah, that sounds like crazy
science fiction, right, but that's basically what plants can do.
They self assemble from a seed. Ma. You ever look
at it like a huge tree and wonder like where
did all this stuff from that tree come from? Well,
(36:30):
that tree has basically built itself out of the air.
It has pulled the carbon out of the air to
construct itself. That's pretty awesome engineering. You know, without any supervision,
no project management, no Excel spreadsheets, you know, no invoices,
no meetings. It just did it. That's the most attractive
part to you right now, Like no zoom meetings were
(36:51):
required to make this tree. That's that's the apex of
of cleverness and a cheatment there, yeah, exactly. And and
on top of that, they fix themselves. You know, if
you shadow your solar panel, you can't come back the
next day and see it started to heal. But if
a leaf falls off your plant, it'll just grow a
new one, you know, it'll just fix itself. So they're
(37:12):
really pretty awesome, and they can be grown basically anywhere
using the materials readily at hand. You don't have to
mind this delicate material out of the crust of the earth.
So I've got a lot of good things to say
about plants. And even though technically their energy transmission rate
is less efficient than photovoltaic panels, they're pretty awesome. Yeah. Now,
for sure, plants are amazing, But they can't power my
(37:34):
computer or our podcast recorder here, No, not directly. But
you know, there are folks who are working on electric leaves.
What what do you mean? These are mechanical devices or
electrical devices that are trying to replicate photosynthesis instead of
replicating you know, photovoltaic process. So you have the stuff
inside this device, basically water and carbon dioxide, and you
(37:58):
want to replicate photosynthesis to produce sugar and oxygen. So
electric leaf is different from a photovoltaic cell, right, So
it will produce sugar as an output. Like you can
have a sugar factory on your roof. You feed in
carbon dioxide and water and sunlight, and yes, it will
give you sugar and oxygen. So there's a whole group
(38:20):
of folks working on these artificial leaves instead of working
on photobo take cells. Interesting, so you can put it
in your cold coffee because you don't have any electricity
to heat it up. Yeah, but you know, artificial leaves
still do not grow themselves or fix themselves, and there
are a lot more expensive than a seed. So it's
a tough engineering challenge to beat nature at its own game. Yeah. Well,
(38:41):
what if Daniel, you build like a factory with AI
that makes its own solar panel to power itself. That
would be sort of like making a self growing solar panel. Yeah.
If you design robots that could build solar panels and
manage them and fix them, then yeah, that would be
pretty awesome. That's kind of what a plant is, isn't it.
(39:02):
It's like a little robot. I mean, it's just following
the instructions in the DNA. It's just kind of like
a little robot that's following its own instructions. Yeah, it's
a little organic, evolved robot. But then I guess so
are we, right until your AI goes crazy and then
just covers the whole planet with solar panels, right, which
would be give us a lot of energy there you go,
(39:22):
but to be nobody to use it, right, like sorry,
or have to knock down your house to build solar panels.
Those are my instructions. Well, I can live under the panel.
I'm just saying. You know, I'm imagining this science fiction novel,
a future dystopia where we all live in the darkness,
but we have a lot of energy from the solar panels. Yeah,
well you can build windows. I mean, come on, they
can spare a few percentage of the square footage there
(39:46):
and then the robot comes along and filled it in
with a solar panel. Alright, a little off topic here.
So solar panels, Yes, they take sunlight and converted to electricity,
and they do it through these silicon sir kids. But
you know, they take some infrastructure, but overall, the infrastructure
sort of worth it, right because it's clean energy, absolutely,
(40:07):
and the infrastructure can get cleaner and simpler and cheaper.
That's an engineering that's a technology barrier. It's not something
fundamental to the process, like with nuclear fission, which will
always produce some toxic waste, or with fossil fuels, which
will always release some sort of carbon. This at its
core is a really clean, cheap source of energy that's
already produced and being beamed to us from the facility
(40:27):
ninety million miles away. Yeah, and it's a guilt free
that's right. It's negative guilt. So you can turn on
your solo panel and have an extra box of cookies.
There you go, and the electric company will send you
a box of cookies every month or money, whichever you prefer.
All right, well, we hope you enjoyed that. Thanks for
joining us, see you next time. Thanks for listening, and
(40:57):
remember that Daniel and Jorge explain. The univer is a
production of I Heart Radio. Or more podcast from my
heart Radio. Visit the I Heart Radio app, Apple Podcasts,
or wherever you listen to your favorite shows.
Hey, Daniel, do you have solar power panels on your roof? Embarrassingly,
I don't. You don't? Why not? I just haven't gotten
around to it yet. It's the honest roof, so there's
kind of an energy barrier there. I know, I know
I should do it, but you know, prices keep falling,
and I guess that's what I say to myself to
justify my laziness. Oh man, you just cheap. We would
(00:29):
you get solar panels if they caused pennies or if
they could repair themselves and automatically reproduce. Well, that's an
offer so powerful I could hardly refuse. I am more
(00:54):
handmade cartoonists and the creator of PhD comics. I'm Daniel.
I'm a particle physicist, and like you, I haven't to
do list that's too long. Welcome to our podcast, Daniel
and Jorge Explain the Universe, a production of I Heart Radio,
in which we talk about all the things that are
amazing about the universe, all the places our curiosity has
taken us, all the questions we have asked and all
(01:15):
the answers we have found so far. But we love
to talk about the questions that we have in the
questions that you have, the things that you are curious
about the universe. Yeah, we like to take you to
the far reaches of the cosmos, to other galaxies and
inside of black holes, but we also like to take
you to your neighborhood, to the world around you and
talk about the things and the questions that we have
(01:37):
in our everyday lives, because physics is everywhere. It's not
just out there in the center of black holes and
the craziness of neutron stars. It is right here making
our lives better. Or maybe, Jorge, you'd say this is engineering. Yes, yes,
I would say that. Or maybe finally, this is physics
and engineering working harmoniously together. Yeah, because as humans, we've
(01:59):
made a lot of knowledgy and a lot of progress
in science and knowing how things work to the point
where we can create things that take advantage of nature
to make our lives easier. That's right, Because the universe
is out there pumping out energy into space, these crazy
nuclear bombs going off at the center of every solar system,
and so of course it's tempting to potentially take advantage
(02:20):
of that. Yeah, So today we will be tackling a
question that a lot of readers have sent in, right, Daniel,
that's right. A lot of folks see these things on
the roofs in their neighborhoods and they wonder how does
that work? What's going on in there? So to be
on the program, we'll be asking the question how do
solar panels work. It's a really fun question because you
(02:43):
see these on the roofs in your neighborhood, and you
know they generate electricity, but how does it actually happen.
I mean, we know the sun pumps out energy, but
how does that turn into zippy electrons in your iPhone battery.
I have solar panels in my roof. It's amazing. I
haven't paid any electricity bill in like years. In fact,
the electric company writes me checks for how much energy produce.
(03:06):
So you are the electric company now I am my
own company. Yes, yeah, I know. It's pretty awesome. I
mean you invest in it and then it pays off
over the years. Yeah. And it makes a lot of
sense because in the end, the sun is the direct
source of almost all the energy we use here on Earth.
Even fossil fuels originally just came from energy from the sun,
(03:26):
and so it's tempting to say, hey, let's just go
direct to the source. Why build a fusion reactor here
on Earth when we have a huge one in the
center of our solar system, Let's just suck up some
of that energy. Yeah, because it sort of feels like
a waste almost, you know, Like I think about all
of the energy that used to hit my roof before
I had a solar panels, and all the energy just
(03:46):
kind of goes to waste. It just hits the roof
and bounces and heats it up a little bit, but
then it cools down again at night. So I feel
so much more like I'm taking advantage of nature in
using up the energy that's there. Right, So you're not
just doing it for the econom benefits, You're doing it
because it makes you feel like a better person. Honestly. Yeah,
I feel like I invested in a more guilt free lifestyle.
(04:08):
Like in the summer, we can just turn on the
A C guilt free because it's all coming from the
sun and have a second box of cookies. Right. Yeah,
And you're right, there is a huge amount of energy there.
The amount of sunlight that falls on the Earth is
like a hundred and seventy three thousand terra wats. It's incredible.
It's a lot of wats. That's a lot of terra wats.
(04:29):
And it's actually a thousand times more than the entire
energy budget of our civilization. Wow, meaning that a thousand
times more energy falls on Earth from the Sun than
we use. Yeah, so if you could capture the solar energy,
you could easily power the entire civilization with just a
fraction of the energy that comes from the Sun. So
(04:49):
it's a huge resource. It's incredibly powerful. It's right there.
It seems awfully tempting to try to capture it. What
would be the number, Daniel is, So if it's a
thousand times more, does that mean that if we over
the earth the Earth in solar panels, we would be
set if it was efficient. Yeah. I've seen lots of
different calculations actually about how many solar panels you would need,
(05:11):
But you don't need to cover a significant fraction of
the Earth and solar panels to get enough energy to
power the Earth. We'll talk about a little bit more later.
One of the biggest challenges actually is getting that power
to the right place and storing it and having it
at the right time. But it's a big percentage these days,
or a significant percentage of the power that we consume
these days, right, I mean, it's not like zero. It's
(05:32):
not like zero. Here in the US we get about
three percent of the energy that we use from solar panels,
but in other countries it's higher. China's four percent, Germany
is eight percent, Australia goes to nine percent, and Honduras
tops it out at well A sairly as understandable. I mean,
everything is bigger in Australia and Sunnier, even their solar panels.
(05:55):
Spiders and solar panels. Yeah, it aren't like the kangaroos
hanging out on top of the solar panels blocking it.
I wonder if that gets factored in. And I guess
the great thing about it is that it's carbon free,
Like it doesn't give off any emissions? Does it have
operating the solar panels certainly doesn't. There's a question of
constructing solar panels and infrastructure to store that and create batteries,
(06:16):
and there's definitely some toxic materials that are used and
created there. But operating solar panels no, they have no
moving parts. They just sit there and turn photons into electricity.
So they're pretty awesome. Yeah, so a big question that
our readers have is how do they work, Like, how
do they convert solar energy sunlight into electricity you can
(06:37):
use for your devices and video games and televisions and Netflix,
and so we were wondering how many people out there
know how solar panels work? That's right, and so I
asked folks who volunteered to speculate without googling about how
solar panels work. And if you'd like to speculate without
reference materials on difficult questions in physics, please write to
(06:58):
me at questions at Daniel and Jorge dot com. Yeah,
so think about it for a second. Do you know
how solar panels work? Here's what people had to say.
You know, I've never thought about it, um and I
have no idea. The panels capture the photons from the
sun and stored. You know, it's a circle of life,
(07:18):
you know. I don't really know the specifics. I know
that they're also called like photo voltaic panels. I don't
know if I'm saying that right. I've only ever seen
the word written out, but which makes me think it's
got to have something to do with the photon specifically
interacting with the panel, you know, because I just saw
a small presentation last week. So sunlight activates the panels
(07:41):
the silly compounds, uh, and the cells produce electrical current,
which is converted in um electrical energy or no electrical
energy is converted in electrical power. My understanding is that
these solar energy hits these panels, and based on that energy,
(08:07):
there's some photo voltaic cells which translate that into electrical energy.
I'm not really sure how. Maybe because of the expanding heat,
it creates a differential and different metals. I know they
have photo voltaic cells in them, um, but I couldn't
explain the science behind it. All Right, A lot of
(08:28):
people seem to have some idea. A lot of people
said the words photo voltaic. That's pretty impressive. Yeah, that's
pretty awesome, and it goes to the core of the
physics that's happening inside solar panels. And I think often
they're called photo voltaic cells, and so that gives people
a clue about what's going on inside photo I guess
light will take just kind of a meaning electricity. Yeah,
(08:49):
and it is in the end of interaction between photons
and electrons, So it makes a lot of sense. All right,
Well let's break it down for folks. How do solar
panels work, Daniel? I mean, I assume they at sunlight
and somehow that gets transformed into electricity. So what's going on? Yeah,
So there's sort of two steps there. One is how
does the energy get from the photon into the material?
(09:12):
And the second is how can you construct a material
that it can effectively grab that energy and siphon it
off into electricity? And so the first step is called
the photovoltaic effect, or a photon hits a piece of
material and it basically passes that energy to an electron.
What does that mean, Like the electron absorbs the photon,
(09:33):
or like the photon hits the electron. How can I
visual life? Yeah, the photon is absorbed by the electron.
Remember that electrons interact electromagnetically, and that just means that
they trade photon. So every kind of electromagnetic interaction, every
push and pull by electric fields is mediated by photons.
So photons are the way that electrons talk to each
(09:53):
other and other charged particles. And photons are not eternal, right,
they can get absorbed by an electron, Their energy goes
right into the electron and then the electron has that energy.
So the way I visualize it as like a photon
coming in meets an electron and then only the electron continues.
So now the electron absorbs the photon and now I
guess it's charged up or something. Yeah, it's more exciting, exactly,
(10:16):
it's charged up. And there's two different effects here that
are very closely related. One is the photo voltaic effect,
which is what we're talking about, and the other is
something more famous that people might have heard about called
the photoelectric effect. They sound very similar and they are
very similar. Photoelectric effect it's when the photon has enough
energy that the electron gets kicked out of the materials.
(10:37):
So people saw this about a hundred years ago. If
you shine light at a material, you will get electrons
boiling off the surface, and that's because they have so
much energy they can leave the trap of the material,
meaning like a you know, an electron is orbiting the
nucleus of an atom because the nucleus is positive, but
now it has so much energy it just pops up. Yeah,
(10:58):
it just pops out. And this electric effect is actually
what Einstein won his Nobel Prize for explaining and was
one of the key experiments that led us to understand
that light is not just electromagnetic waves, what actually comes
in little particles, because we saw these weird relationships between
the intensity of the light and the wavelength and how
many electrons were boiled off. But we have a whole
(11:19):
other podcast episode about that about how we know that
light is quantized made out of these little photons. But
that's very similar to the photovoltaic effect. But the voltaic
effect is when the photon comes in and the electron
gets enough energy, but not enough to actually leave the material.
It gets excited, but it's still hanging out sort of
in the same blob of stuff I see. So it's
(11:40):
just a matter of whether or not it gets enough
energy to pop out, basically. Yeah, And there are some
materials where electrons don't have to be isolated to one
specific atom, like the picture you described as correct, you
have an electron it's orbiting a nucleus, for example, although
we don't really like to think of them as actually orbiting.
It's hanging around quantum mechanically near it's nuclear is. But
(12:00):
in lots of crystals, you have electrons that can flow
between atoms, and so, for example, in semiconductors, you have
electrons that are trapped that are around individual atoms, and
then if they get enough energy, they can jump up
over a little gap into a band where they can
move around more freely and jump from atom to atom. Yeah,
they sort of float around, right, They're not bound to
one atom. They can you know, hang out. Yeah, they're
(12:24):
like social butterflies. They just float around. They have enough energy,
they're sort of like flying high above all of these
little gaps. And so that's what happens in the photovoltaic effect,
that a phoeton comes in and knocks an electron off
from being stuck around one of the atoms, and so
they can float around free. Wait, that's the photo electric
or photovoltaic. Poto voltaic is when it knocks it off
(12:44):
so we can float around inside the material. Photo electric
is when it gets so much energy that it flies
free the material and out into space. It's like abandons
its original family. Oh, I see, I see you Like
one is like pop out out of the material, like
out out of like a way and bolt take it
leaves the atom. But it hangs out in the lattice,
(13:05):
in the structure of the material. Yeah, it's just jumping
around from atom to atom, floating free inside the material.
The photo electric effect, it's like totally liberated and may
never come back to home. All right. So that's the
two effects, and the one in solar panels is the
photovoltaic effect exactly. And so the key thing for solar
panels is to take advantage of the photovol take effect.
(13:25):
Because now you have this electron, it's got more energy.
If you could grab that energy somehow, if you could
funnel it into an electric current, then you could turn
effectively that photons energy into electricity. And so that's why
you need a special kind of material. Now, any kind
of material can have the photovol take effect. Your hand
or a rock or whatever. When it absorbs a photon,
(13:46):
the electrons that absorb it don't fly off the material.
Right then you're having the photovol take effect. You're grabbing
that energy into the object. But you need a special
kind of material to effectively gather that energy and funnel
it off into electricity. And that's where the silicon diode
comes in. And we had an a whole episode about diodes, right,
and transistors. Yeah, we did because we talked about how
(14:08):
L E d s work, and diodes are like a
really key foundational element of modern computing because you can
use them to make L D s and transistors and
all sorts of stuff. And it comes from semiconductors. And
that's why silicon is so important to the computing industry
because it's the most important semiconductor for building these kinds
of things, right, And it's important because it's kind of
(14:29):
a special material, right, Like it has just the right
number of loose electrons and it's pretty stable. Yeah, because
the electrons have these two different regimes they can be in.
A conductor is where the electrons just flow freely everywhere
from atom atom and insulator is one with the electrons
are all stuck around their individual atoms. And a semiconductor
is one that has both and has the electrons around
(14:50):
the atoms and electrons at a higher energy that can
hop freely from atom to atom. So that's what a
semiconductor is, and silicon is a great example of it.
And what happened and silicon is exactly that the electrons
jump over this band and then they can float around free. Yeah,
and so that's how you make a solar panel. As
you use silicon to make a solar panel. But and
then do you have to like create these different areas
(15:13):
where one one area is like a P type and
the other ones in N type. Yeah, you can't just
use normal silicon. You need to create something that's going
to funnel off the electrons. So the way that works
is that you have two different kinds of silicon. It's
not pure silicon. You've added stuff to it slightly to
change the behavior. And so you have one kind you
called N type, which has like extra electrons there are
(15:34):
a bunch of electrons floating around that sort of don't
have a chair to sit in if you played musical chairs.
And another kind where you've added other kinds of materials
like gallium or arsenide or whatever. So they're called P type.
They don't have enough electrons. They're like empty spots for
electrons to sit in. And semiconductor physicists they talk about
these things as holes, and they treat them as if
(15:55):
they're sort of like positively charged electrons. They think of
them sort of like as particles. I remember we talked
about the quasi particles like things that are not particles
but sort of act like particles. This is a good
example of one. It's a hole. It's like a missing
spot for a particle, but it moves around sort of
as if it was a positively charged particle. Right. It's
like if you had five people for six chairs and
(16:16):
they move around and change seats. It's like you keep
track of worth of the empty seat, not the people. Yeah,
and the empty seat moves like a particle, right, because
if one person slides from one seat to the other,
then the empty spot slides the other direction. Sort of
cool to have that idea in your mind of an
emptiness being a thing. Anyway, So you have these two
kinds of the lookon the P type that has extra
(16:38):
holes and the end type that has extra electrons, And
because they match up together, there's the sort of you know,
too much electrons on one side and too many holes
in the other. Some of the electrons flow across the
junction between them and fill up some of the holes
on the other side, and that makes an electric field
across them. That's the key thing. The electrons have flowed
(16:59):
in one to action, and now they make an electric
field going the other way right. I think what happens
is that like the material that has too many electrons
loses some of them because they all go to the
side that has the holes. And now you have like
this build up of too much too many electrons in
in one place, and so that creates like a like
a barrier, like a something that repels other electrons. Yeah, exactly.
(17:22):
It's sort of like you know, diffusion of temperature. If
a hot thing next to a cold thing, then the
heat's going to flow over the cold side. And so
you put this N type stuff with too many electrons
next to the P type stuff without enough electrons, some
of them flow over, and you're right, it creates this barrier.
So now you have this P N junction, you have
the silk, and it's all primed to get your photon.
(17:42):
Because what happens when a photon hits this special diode,
this combination of P type and N type silicon, is
that when the electron gets kicked free, it doesn't just
wander around loosely. Is now an electric field created by
the P N junction that pushes the electron all away
in one direction, and then you just have to have
something at the edge there to gather these electrons, these
(18:02):
electrons that have the solar energy absorbed, so they can
move along and create electric current. All right, well, I
have some questions about that, and let's get into some
of the details in and also maybe let's talk about
some of the larger issues about solar panels. But first,
let's take a quick break. Right. We're talking about solar
(18:34):
panels and how they work, and they do work, they're
pretty good. I have some how Well, do your solar
panels work? You generate enough electricity for your house every day? Yeah?
In fact, they generate so much energy we get a
check from the electric company. They're like, you gave up
too much electricity. Here's some money back, and your energy
goes back to the electric company and then back to
(18:55):
your house. Right. You don't directly use the electricity created
on your roof, do you, right? Yeah? No, I don't
have a battery, So it just goes back into the
grid and then we get from the grid. But they
keep track and if we make more than we take,
then they give us a small amount of money for them. Awesome. Yeah,
So we were talking about how it works, and it
involves silicon and p type and type of materials that
(19:16):
have holes and extra electrons, and so is the idea
then that you know, the side that has too many
electrons gives them to the side that doesn't have enough electrons,
and that creates kind of like a like a standoff
almost like a barrier for any more electrons to flow.
But once the light comes in, then that kind of
kicks things up. Yeah, and then these new electrons get
(19:37):
pushed away from that barrier as you said, and towards
the edge, and then they get gathered up and the
current forms with all these energetic electrons and you can
draw that off. And that's basically what electricity is. It's
energetic electrons. It's electrons moving along. That's what current is.
It's just the motion of charged particles. It feels kind
of like almost like magic. I mean, like the sunlight
(19:59):
is actually creating energy, is just kind of like triggering
the flow of energy. Yeah, well, sunlight is energy, right,
It's energy that was released from the fusion of hydrogen
into helium in the center of the sun and that
has been flying nine million miles through space. And the
cool thing is that that energy doesn't like evaporate or
run out. You know, photons can fly through space basically
(20:21):
forever without losing any energy, doesn't take them any energy
to fly the speed of light, and then that energy
gets deposited, you know, on your solar cell and gets
slurped up into that electron. It's really pretty awesome, and
the coolest thing about it, I think is that it's
quantum mechanics. You know, this is not something you can
explain with classical physics. So it's something we only could
have invented pretty recently. Well, we we understand it now,
(20:46):
but didn't we sort of invented before understanding how it works? Yeah,
you're right, we understand it now, which allows us to
like optimize it. And we certainly never could have built
like these complicated p N junctions without understanding quantum mechanics.
But I suppose some clever engineer could have put it
together without a deep physics understanding. Suppose, like I guess,
(21:07):
if they were like a super special genius engineer. You're
you're absolutely right. And there's lots of examples of times
when we build something we saw do something cool and
we didn't understand what was happening, and that led to
lots of really awesome questions, you know, like that's how
electrons were discovered. People didn't understand crooks tubes and these
glowing rays they saw inside them, and so it led
to lots of awesome stuff. So yes, absolutely, you can
(21:29):
build stuff before you understand it. It It is pretty cool
to the thing now that you mentioned it. It's amazing
how like these photons were made in the Sun and
they traveled millions of miles really sort of uninterrupted, like
they don't lose any energy in the way. It's like
almost like a perfect transmission. And then they hit my
solar panel and powers my devices. Yeah, exactly. So really,
(21:50):
solar power is fusion power. You know. It's just like
you are a blanket to absorb energy from a fusion device.
We talked about either a few weeks ago and how
a big problem they have is how to absorb the
energy that either creates, like haven't really tackled that problem yet,
And you're basically doing that for the Sun. You know,
the Sun is this huge fusion engine and you're putting
(22:11):
up a little panel to grab a tiny little slice
of all. Man. I wonder how much any more panels
they would sell. They called it dead. You know, fusion
panels probably fewer fusian generator on the roof, a hydrogen
bomb on your roof where your kids sleep. Who doesn't
want their computer, their work powered by fusion energy? Me?
(22:34):
I don't. No, No, honestly I do. That's super awesome.
I think it's wonderful. And also it works pretty well.
You know, it's sort of shocking how efficient it is.
But I mean, what's the efficiency. Well, the record efficiency
for like the most highly engineered solar panels so far
is about forty that's the fraction of the energy of
the photons coming in that you can effectively gather out
(22:56):
as electricity. And that's pretty good. That's like a one
out of every two holdons you actually use it for something. Yeah,
And it's not a hundred percent efficient because not all
the energy goes into one electron, or that electron loses
some of its energy along the way as it moves
along through the silicon and gets to the thing that
stirps it out, or it goes into you know, exciting
(23:17):
the nucleus or stuff like that. And most devices that
you would have on your roof are not that efficient.
Mostly they're like fifteen to twenty percent efficient, though they've
climbed a lot in recent years. It's incredible the prices
are dropping and the efficiencies are rising, and even is
really pretty efficient. Yeah, what happens to the other percent?
Like where does all the other energy go gets reflected
(23:37):
or absorbed? It just goes into heating the material. You know,
there's lots of ways for silicon to absorb energy, not
just one electron getting kicked up an energy level. The
nucleus can absorb energy, or the electron can absorb the
energy and then lose it to something else, and so
there's a lot of delicate engineering involved in getting those
electrons to be the place where the energy lands and
(23:58):
getting them to deliver it to the edge of the
p N junction. You know, this stuff is really cool
because it's actually very similar to what we do with
the large Hadron collider. We use silicon devices to detect
the passage of particles photons but also like muans or
other particles, and you detect particles in exactly this same way.
The particle passes through the detector and it leaves a
(24:20):
trail of electrons behind it, which we then slurp off
and use that as evidence to say, hey, there was
a particle that passed through, So we should maybe think
about rebranding it that way too, Like, don't call them
solar panels, call them melon absorbers, particle detectors, particles. Yeah,
who doesn't want a particle detector on the roof? And
(24:41):
you know the same basic principle works also in every
digital camera, right, That's how digital camera turns a photon,
which is the picture you're seeing, into an electrical signal,
which is what your computer needs to record it. The
photovo take effect. It turns a photon into little electrons
which then get gathered up at the edge of your
little pixel and recorded as evidences stead of photon came
(25:02):
through as like, oh, that's right. Yeah, that means everyone
who has a camera on their phone has a solar
panel in their pocket. That's right, that's right, except that
it draws power instead of generating it. Unfortunately, it generates images,
but it doesn't generate power. Does I mean I have
a giant camera on my roof taking pictures of the
sun every day? Absolutely? And you know we have done
(25:23):
the calculations. Can you use solar panels as particle detectors?
Could we use everybody's solar panels? Is like a huge
telescope to understand cosmic rays. Unfortunately you can't because you're
swamped by the photons from the Sun which make a
huge signal. And everything else we're interested in, like little
muans or positrons or protons, is swamped by that huge
(25:44):
blinding light from the sun. But it does you're you're saying,
my solar panels do detect these other particles. It is
technically like catching them and converting them to a signal.
It totally is. If you covered your solar panels, if
you made them light proof, which would be terrible for
your electrical efficiency, But if you made them light proof
and cover them up so they were in a black box,
then they would be great detectors for muans or other
(26:07):
kinds of particles that could penetrate that seal and leave energy. Interesting.
All right, I am ready to do scientific experiments at
the expense of actually generating any electricity. Wow, some sacrifices
might have to be made. How important is science to you?
All right? Well, um, that's sort of how they work.
(26:27):
I guess. Maybe a question is they're pretty great, but
why aren't there more of them out there? Why doesn't
everyone jump into this solar energy bandwagon. Is it political
or are there other limitations? There are some other limitations.
You're right there, pretty great, but there are some downsides
to solar panels. One is that the sun is not
always above you in the sky. Right, Sometimes there are
(26:50):
clouds or it's night time, and so you're generating power
whenever the sun is above your solar panels. But that's
not always the case, and you need power some times
at night or when it's cloudy, and so you need
a complicated system there to buffer, to gather energy into
like a battery, and to save it for you for
when you need it. Right, But that's not really a negative.
(27:11):
It just means that, you know, you need a like
a buffer, you need like a something that stores it
like a battery. Yeah, but it adds to the cost,
you know, just like the transport issues. Say, for example,
you have a huge solar panel array out in the
desert to gather energy really efficiently, then you need to
send that energy hundreds or thousands of miles to where
it needs to go because you have a mismatch sometimes
(27:32):
between where the energy is used and where the energy
is created. I mean, if every device could just create
solar power whenever it needed it wherever it was. That
would be awesome. But one of the main costs of
solar power is fabricating the devices themselves, of course, which
is not trivial and not cheap, but also transporting and
buffering building these batteries. You know, battery technology is complicated
(27:53):
and also quite toxic, right, but I think that you
know you need to do these things anyways for any
kind of power, don't you Like, do you still need
the infrastructure for um, burning coal or for nuclear powered energy? Right? Well,
you know you can turn your coal power plant on
any time of day or night, right, and so it
(28:13):
can be a much steadier source of power doesn't have
these fluctuations. You don't need the same kind of buffer
for a coal power plant. A coal power plant, essentially
the energy is already in a battery. That battery is
called coal, and it's available for whenever you need it.
You just have to transform it into electricity. Now, of course,
coal is terrible for lots of other reasons. I'm not
selling coal. But one of the disadvantages of solar power
(28:34):
is that it's not always created when you need it, right, right,
But fortunately I'm mostly asleep at night. Well, actually, that's
not true for me, but I think for most of humanity,
you're sort of asleep at night, so you don't actually
use that much energy at night, right, and it's cooler
and you so you don't need the a C. Really like,
I think most people's power consumption matches sort of daylight. Yeah.
(28:56):
Do you use less power when it's cloudy outside, Yeah,
because you know you don't need to your house as
much right now, You're absolutely right. It's not a killer
for solar power for sure. It just means, you know,
you have to build this infrastructure and you have to
have batteries, you have to do this kind of stuff.
But you're right, people use more energy when it's daytime,
and they need more A C when it's sunny outside,
and so that's not that big an issue. Well, obviously
(29:18):
it's not like free energy, and it's not super simple
to get solar energy, but it's still I think overall,
it's it's renewable, right, and we don't create carbon emissions,
and still more positive than most other sources of energy, right, absolutely,
And it's getting cheaper, you know, the more we work
on it, the easier it is to fabricate these solar panels,
(29:39):
they last longer, they're more efficient, they're cheaper, they're easier
to produce, and it's sort of something that builds on itself.
The larger the market is, the more companies get involved,
the more competition there is, the more clever engineers get
on board from making these things effective, the better batteries get.
It seems like an excellent option for the future. It
just takes sort of an investment. It just takes us
(30:00):
deciding to make this happen. Yeah, and it's like we're
getting this energy from space for free. It feels great
to you. It does, and there's lots of really fun
ideas for how you could tap into it. You know,
you don't need to build a huge array of solar
panels in the middle of your city. You can put
them in the desert. We have lots of huge areas
of the earth where nobody's living because it's just sand,
(30:21):
and you could put vast solar arrays there. You can
even have them like floating on things in the ocean,
just gathering up solar energy. So if you built enough
infrastructure there, you could really power a lot of our
civilization's energy needs. Yeah, and create a lot of shade
in the desert, which would be pretty good probably for
all the animals there. All right, well that's sort of
(30:43):
the big picture and the little picture of solar power.
And we're gonna do something a little bit interesting next,
which is compare them to photo synthesis. But first, let's
take a quick break. All right, we're talking about solar power,
(31:06):
and we talked about how solar panels work, and so, Daniel,
you thought something interesting would be too, sort of compare
this man made machine and device that we've made to
capture solar energy to what nature has done. Plants use
solar power and so through something called photosynthesis, And so
how do the two compare. Do they use a similar
mechanism or is it totally different? Yeah? I thought this
(31:29):
was really fascinating because, you know, we've been working on
this technology for decades, but nature has been doing this
for literally billions of years, and it's got a really
refined process for making things more efficient and more effective
in finding solutions. And so naively, I thought to myself, well,
I'm sure that our efficiency is pretty good, but Nature's
efficiency must be even higher because it's been fine tuned
(31:51):
for for so long. But you know, you start to
read about photosynthesis, and you discover that it's actually less efficient,
that a smaller fraction of the light that comes from
the sun and hits a plant gets turned eventually into energy,
and it's using a completely different process. So they're not
as good as solar panels, I guess, and absorbing energy,
(32:11):
I guess. They don't have the advantage of like having
silicon and all these dope materials and highly engineered materials.
How do they work? How do plants absorb? Some might Yeah,
you're right. The plants don't necessarily have access to some
of the rarer elements that we use to dope our
silicon to make these diodes work. What they do is
they have the light come in and it interacts with
(32:31):
carbon dioxide and water inside the leaf, and essentially what
it does is it builds a sugar. They turn light,
not into electricity, because plants aren't interested in electricity. They
don't run air conditioning or sit on their phones all day. Right.
It basically turns light into plant food, which is these
complex carbohydrates, these carbons and hydrogens and oxygen's all built
(32:52):
together into things that are fiber or what we would
call sugar. They do it through chemistry. Like you know,
they have the ingredients, they're sort of on the leaf,
and then the sunlight triggers a reaction or triggers like
a molecules kind of coming together. Yeah, exactly. Chemistry is
all about energy flows, right, So you can store energy
in chemical bonds. You can build something that has energy
(33:14):
inside of it, but then you need to put the
energy in. Right. You can't just have the ingredients. They're
sort of like baking a cake. You can just mix
the ingredients. You need to supply the heat. And so
in order to make these sugars, these sugars which store energy,
you need to bring the wrong ingredients together, which is
carbon dioxide and water, and then you need to apply
the energy. And that's where the photon comes in. As
(33:35):
the photon comes in and chemistry happens, and then you
get out, You get sugar, and you get oxygen as
a byproduct, which is wonderful for all of us oxygen breathers, yeah,
and all of those salad eaters. Yeah, and for the
plant specifically. It's basically turned the energy into plant food. Right.
So we want to generate electricity and plants. What they
(33:56):
want to do is they want to generate these sugars.
And really the answer to the question of you know
why is photosed in this is less efficient than solar
power is really that they're doing different things. Plants have
optimized turning photons into plant food, into this fuel which
they can store and then very easily use later on,
whereas we've optimized for creating these electrons which we can
either use immediately or try to funnel into batteries. It's
(34:19):
almost like they've invented the battery and the panel at
the same time. Yeah, it's really pretty impressive technology. Right.
This plant fuel is a great way to store energy,
and so it's a really nice thing for them because
they can use it whenever they need it. They don't
have to worry about creating the battery. Right And if
I get takes carbon diotside from the era, yeah exactly
and produces oxygen and delicious vegetables and delicious vegetables exactly.
(34:44):
And you know it also it captures a different fraction
of the solar energy. Like photobole take cells, the ones
that we build, they can capture energy that's out of
the visible spectrum. You don't have to be able to
see the photon for your solar panel to be able
to slurp it up and turn it into electricity. You
can also captured the energy of photons that have a
wavelength it's too long they're in the infrared, or photons
(35:05):
that have a wavelength it's too short there in the
ultra violet. Your photovolt take cells made from silicon can
slurk that up. Plants are mostly sensitive to the visible spectrum,
so they get sort of a smaller slice of all
the light that comes in. But I think solar panels
also use a photo will take effect a little bit similar.
I mean, they're optimized for certain wavelengths, right, Yeah, I
(35:27):
mean we certainly are optimized for the wavelengths that come
from the sun. Right. They've chosen a material that can
absorb it, and you're right, this is quantum mechanical, and
so you can't absorb just any photon that comes in.
It has to be a good match for the material,
because every material has certain wavelength of light it can
absorb and other wavelengths it's transparent to. And so one
(35:47):
of the reasons silicon has chosen it's not just because
it's a semiconductor, but because they can absorb light in
the wavelength that's hitting the earth. So plants aren't as efficient,
but they're pretty good at other things, right, Like a
plant you know, need to hose it down when it
gets too dusty. That's right. Plants are a much nicer
option compared to solar panels in some way because, for example,
(36:07):
they build themselves. Right if you could just sprinkle like
solar panel seeds on your roof and they like sprouted
up and created working solar panels, that would be pretty awesome.
That would be pretty awesome. Yeah, that sounds like crazy
science fiction, right, but that's basically what plants can do.
They self assemble from a seed. Ma. You ever look
at it like a huge tree and wonder like where
did all this stuff from that tree come from? Well,
(36:30):
that tree has basically built itself out of the air.
It has pulled the carbon out of the air to
construct itself. That's pretty awesome engineering. You know, without any supervision,
no project management, no Excel spreadsheets, you know, no invoices,
no meetings. It just did it. That's the most attractive
part to you right now, Like no zoom meetings were
(36:51):
required to make this tree. That's that's the apex of
of cleverness and a cheatment there, yeah, exactly. And and
on top of that, they fix themselves. You know, if
you shadow your solar panel, you can't come back the
next day and see it started to heal. But if
a leaf falls off your plant, it'll just grow a
new one, you know, it'll just fix itself. So they're
(37:12):
really pretty awesome, and they can be grown basically anywhere
using the materials readily at hand. You don't have to
mind this delicate material out of the crust of the earth.
So I've got a lot of good things to say
about plants. And even though technically their energy transmission rate
is less efficient than photovoltaic panels, they're pretty awesome. Yeah. Now,
for sure, plants are amazing, But they can't power my
(37:34):
computer or our podcast recorder here, No, not directly. But
you know, there are folks who are working on electric leaves.
What what do you mean? These are mechanical devices or
electrical devices that are trying to replicate photosynthesis instead of
replicating you know, photovoltaic process. So you have the stuff
inside this device, basically water and carbon dioxide, and you
(37:58):
want to replicate photosynthesis to produce sugar and oxygen. So
electric leaf is different from a photovoltaic cell, right, So
it will produce sugar as an output. Like you can
have a sugar factory on your roof. You feed in
carbon dioxide and water and sunlight, and yes, it will
give you sugar and oxygen. So there's a whole group
(38:20):
of folks working on these artificial leaves instead of working
on photobo take cells. Interesting, so you can put it
in your cold coffee because you don't have any electricity
to heat it up. Yeah, but you know, artificial leaves
still do not grow themselves or fix themselves, and there
are a lot more expensive than a seed. So it's
a tough engineering challenge to beat nature at its own game. Yeah. Well,
(38:41):
what if Daniel, you build like a factory with AI
that makes its own solar panel to power itself. That
would be sort of like making a self growing solar panel. Yeah.
If you design robots that could build solar panels and
manage them and fix them, then yeah, that would be
pretty awesome. That's kind of what a plant is, isn't it.
(39:02):
It's like a little robot. I mean, it's just following
the instructions in the DNA. It's just kind of like
a little robot that's following its own instructions. Yeah, it's
a little organic, evolved robot. But then I guess so
are we, right until your AI goes crazy and then
just covers the whole planet with solar panels, right, which
would be give us a lot of energy there you go,
(39:22):
but to be nobody to use it, right, like sorry,
or have to knock down your house to build solar panels.
Those are my instructions. Well, I can live under the panel.
I'm just saying. You know, I'm imagining this science fiction novel,
a future dystopia where we all live in the darkness,
but we have a lot of energy from the solar panels. Yeah,
well you can build windows. I mean, come on, they
can spare a few percentage of the square footage there
(39:46):
and then the robot comes along and filled it in
with a solar panel. Alright, a little off topic here.
So solar panels, Yes, they take sunlight and converted to electricity,
and they do it through these silicon sir kids. But
you know, they take some infrastructure, but overall, the infrastructure
sort of worth it, right because it's clean energy, absolutely,
(40:07):
and the infrastructure can get cleaner and simpler and cheaper.
That's an engineering that's a technology barrier. It's not something
fundamental to the process, like with nuclear fission, which will
always produce some toxic waste, or with fossil fuels, which
will always release some sort of carbon. This at its
core is a really clean, cheap source of energy that's
already produced and being beamed to us from the facility
(40:27):
ninety million miles away. Yeah, and it's a guilt free
that's right. It's negative guilt. So you can turn on
your solo panel and have an extra box of cookies.
There you go, and the electric company will send you
a box of cookies every month or money, whichever you prefer.
All right, well, we hope you enjoyed that. Thanks for
joining us, see you next time. Thanks for listening, and
(40:57):
remember that Daniel and Jorge explain. The univer is a
production of I Heart Radio. Or more podcast from my
heart Radio. Visit the I Heart Radio app, Apple Podcasts,
or wherever you listen to your favorite shows.
Hosts And Creators
Daniel Whiteson
Kelly Weinersmith
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