Hello, folks. Welcome back.
So I want to introduce the concept of energy
payback time in this Photo-voltaic systems in this video.
And since I'm an engineer and engineers love Three and four letter acryonyms.
So I can abbreviate this energy payback time as EPBT, or Energy PayBack Time.
And the definition of this energy payback
time is essentially contained in the title itself.
So what it represents, or what it means is the amount of time which is required.
To payback, or payback or record the amount of energy, which was which
was used to make the solar panel or the module in the first in the first place.
So, I can express this mathematically as this EPBT, or energy pay back time.
It's essentially equal to, it's equal to the
amount of energy, which was required to make the
solar cells, divided by the rate at which
the solar cell or module is, producing this energy.
So this energy pay back time is essentially given by this formula.
Which is essentially the amount
of energy which was used to make this, the sort of module.
And I can also write this as the specific energy of my solar module.
So it's the specific energy of my solar
module. Divided by, divided by the rate at which,
the rate at which my solar module is producing or generating electricity.
So my energy payback time or EPBT, I
can represent it by by this formula. And further
I'm plotting over here or I'm borrowing this chart from
NREL or National Renewable Energy Lab which which has
you know, projected and plotted these energy payback time for both
multi crystalline and thin Thin film based, solar technologies.
So what these report, which was released in, in 2001, it's says that,
these are solar modules which are made of multicrystalline or, single crystalline
based, solar cells, they have a Energy payback time of 3.8
years and solar cells or solar modules
which are made using thin film based technologies.
They have an energy payback time of three years.
And you might think, you know, three years is a very long time, you know, I'm making
a solar module and it just takes three years
to, you know, it takes three years to recover.
The amount of energy, which was just used to make the solar panel.
But, it's it's, it's exactly not.
I mean, if we need to contrast this three years
with the lifetime of these solar modules, so usually, these
solar panels, they come with a rated lifetime of 30 years.
And what this number is saying that you
can recover back, you can recover back the amount
of energy which was required to produce this
solar cell or the solar module in three years.
So for the remaining 27 years, remaining 27 years, we are,
essentially in energy positive or. We are net posit-,
positive in the amount of energy that is, being produced by this, solar, module.
Another way to look at this number is essentially, You required three
years to recover back the energy, which was, used to make these, solar panels.
So, as compared to the lifetime of this,
lifetime of this, solar module. It's producing nine times.
It's producing nine times. So.
27 divided by 3 is producing 9 times the
energy which was required to make this solar module.
Since it's, we are, you know, assuming that this
solar module will continue to work for 30 years.
And it might continue to work even longer, but you know just to take
a conservative number.
So it's producing nine times the energy which
was required to make or produce this solar module.
So the next thing I want to bring to your attention is that how these how these
energy payback time, it compares for a multicrystalline and thin film.
solar technology. So this report which was released by
NREL, it says that, you know,
the multicrystalline-based crystalline-based solars cells have an
energy payback time of three years, and
thin-film based solar cells are actually better.
And I find it surprising and, you know, I'll,
I'll just tell you why I find it surprising
But what is even more surprising or you know
even more interesting is that going forward or you know
going and looking into the future, what this report or
this report by Enrel anticipated is that multicrystalline based solar
cell will have going forward, so you know looking into
the future the energy payback time of multicrystallin based solar cell.
Will reduce from three years to, reduce to three years to, approximately two years.
So why would
this energy payback time reduce?
And the answer is essentially contained in this formula.
So, going forward, what you can anticipate is that the
amount of energy will, which will be required to make this
solar mod module or solar panel, will will decrease because because
will become more and more Efficient in making these solar panels.
At the same time, the energy or the efficiency,
sorry the efficiency of these, solar, panels will increase, so the
rate at which these solar panels are Generating electricity will increase.
So the energy pay back time, it's supposed to, it's supposed to degrade
or you know, it's supposed to decrease as we look into the future.
But the thing I find surprizing is that. These thin-film based
solar modules, these are, are anticipated to be
become even better so these thin-film based solar modules.
They are anticipated to have an energy payback time for one year.
So, in little more than a year, you can recover all
the amount of energy which was, spent in making these thin-frame
based, so let's say then if they have a lifetime of
30 years, for the rest of the 29 years you're you're net
positive in the amount of energy total energy spent.
So, the why, why do I find these this this this trend or this
comparison between multicrystalline and thin film based solar cell surprising?
So the reason I find this surprising or, you know, unexpected is because the
efficiencies of the efficiency of thin film based solar
panels, are much smaller as compared to,
as compared to multicrystalline based solar cells.
So, you know, roughly the efficiency of these thin film based solar
panels, they are half the efficiency of what you get in multicrysttaline
based solar panel , so you know, just to, just to give
you some estimate I'll assume efficiency of 6% for a thin film based
solar module and for a single crystalline or
multi crystalline based solar modules I'll, I'll expect
efficiency of twice what I get for my thin film, so I'll expect efficiency of 12%.
And these are pretty conservative numbers for
efficiency of these modules, but I want
to use them anyway to give you a feel of feel of the topic.
So now I have the efficiency
of thin film as thin film based module as 6%.
So what is the rate at which it generates energy,
or what is the amount of energy it generates per year?
And I can calculate that essentially equal to, that is equal to the efficiency of
my, efficiency of my solar module multiplied by
the incoming solar radiation or the solar insulation
which is the amount of radiation which is incoming per year
per meter squared of area. And this incoming solar radiation or
insulation is is typically a number which is taken to be 1700
kilowatt hour per meter squared per year.
The US average is slightly higher than this.
It's actually 1800 kilowatt hour per meter square per year.
But this the number which is most commonly tauted about or cited
in literature, so I'll just use this to you know, calculate the amount of energy.
That, these different,
modules are generating, per year.
And then I'll use, my energy pay back, time, my
energy pay back, time, to give me a estimate of
Give me a estimate of the amount of energy which
was required, which was required to actually makes these, solar cells.
So let's, let's, you know? Let's essentially fill up, this,
table.
So, for my, for my, for my thin film based.
solar module I have an efficiency of, 6%.
So the amount of energy that I'll be generating per year is essentially equal
to. It's equal to 0.06 multiplied
by 1700, and this essentially gives me 17 into 6
is 102, so this gives me 102 kilowatt hour per meter squared per year.
So, that is the amount of energy that I'll be generating per year.
in one meter squared of area.
And, since singular crystalline-based solar cells have twice the
efficiency of that, so they'll be, essentially, generating 204
kilowatt hour of energy per meter squared per year.
And now what I'm anticipating is that my my thin film
base solar cells, they have a energy payback time of one
year, and these single base, single crystalline based multicrystalline
based solar cells they have an energy payback time anticipated of two years.
So now, my energy, which is essentially required to
make the cell with my energy payback time, multiplied by
the rate at which I am generating this multiplied
by the rate at which I am generating this energy.
That comes from, again, the way I define my energy payback time.
So my energy payback time was essentially E divided by this E dot,
so E, or the amount of energy which is required to make this
solar cell, is my energy payback time multiplied by the
rate at which I am generating this electricity from this module.
So, now, my energy, which is required to make this thin film based
based module is essentially equal to this 102 into one year,
so this will give me a number of This will give me essentially 102
kilowatt hours.
So it says that energy which was required to
make one meter square of this thin film module.
Now the thing I'm surprised by is that, thin slim based solar cell has a
much higher frequency that's it's Generating, a much
higher rate, electricity at a much higher, rate.
And, but still it has a much higher, it has twice the energy payback time.
What it means is that the energy which is required now to, you know, which was,
estimated to make this solar panel is essentially given by this generation rate
multiplied by this energy payback time, so this is 204 multiplied by
2 so this would be 408 kilowatt hour per
meter squared, so what is surprising is that amount of energy which is required to
make these single crystalline based, based solar panel is essentially 4x, 4x
amount of energy which was required to make this thin film based solar
module, so even though this energy payback, this rate of generating.
This energy is twice, the efficiency of single
crystalline cell is twice of what you get.
For thin film, but still it, because of this.
High amount of, four times higher energy required.
The single crystalline based solar cell is .
Still takes twice.
This amount of time to pay back this energy.
And we'll, I'll discuss in the next video why this is the case.