Hi folks.
So in this last video I introduced the concept of energy payback
time, and we defined this as amount of time required which is the
amount of time required to payback or recover the energy which went
into the production of energy which was spent into making this solar module.
I must, you know, mention that this is not to
be confused with the payback time or which is also sometimes
known as the financial payback time, which represents
the amount of time which you require to
recur back your investment, or your money spent,
or your dollars spent in making these solar panels.
And this is, you know, this is an important metric as well and we'll devote
a few other videos to talk about
this financial payback time or this payback time.
But right now, you know, I'm just interested in
the reco-, in finding out the energy payback time or the time required to
recover the amount of energy which was used to make this solar panel.
So, we saw some numbers of this energy payback time in the last video.
And I also, you know, we ended by saying that the
energy payback time for a thin-film based solar cell, it looks
much more favorable or much less as compared to the energy
payback time for a single crystalline or a multi-crystalline based solar cell.
And my share, I shared my surprise which I felt by looking at this data by, you know,
by giving some analysis that in fact, the efficiency
of the single crystal based model is quite higher
as compared to the thin-film one.
But still it has it has a higher payback
time because the amount of energy, which is required
to make these solar panels of single crystalline based
material is much higher, it's actually four times higher.
So even though you have twice higher efficiency, you still need
two times more, two times more the amount of time to
recover back that energy.
So what I want to do in this video is to, is pull
the curtains on this a little bit and, you know, dive in a little
more detail that why are we requiring you, why the heck we require
four times the amount of energy to make a single crystalline based solar cell.
So, this was analyzed by Carl Knapp and Theresa Jester.
So what they did, was it was a pretty neat study.
So what they did was they looked at a Siemens factory, you know, Theresa
Jester was an employee of Siemens, which used to have a solar division back then.
And they essentially looked at the amount of,
energy that was being, used in the, in the
factory, so they looked at the amount of kilowatt
hour which was, being spent, in the factory as
a function of the production capacity of the factory.
The production capacity of a lot of solar factories is
measured by this, Matrix call as kilowatt of peak power.
So this kilowatt of peak power is
an interesting way to measure the production capacity
of a factory and it's essentially it's
proportional to the number of panels that the
factory is producing.
And it's also proportional to the efficiency of these panels.
And what it means is that, what this kilowatt of peak
power means is that if you take the total number of
panels produced by this factory, and place them in a laboratory
condition with the lights shining from the top at normal incidence.
So what is the amount of kilowatt of power that these
this total output from the factory will produce?
So what Knapp and Jester did was, they, they essentially plotted this
amount of electricity, or the amount of power which was being consumed in
the factory as a function of the kilowatt of peak power, as
a function of the production capacity measured in kilowatt peak of the factory.
And if you take the slope of this line,
this will essentially give you the amount of
kilowatt hour, or the amount of energy required,
to produce a panel which produces a one
kilowatt which produces one kilowatt of peak power.
So this analysis and you know, using this analysis we
could figure out how much was amount of electricity required.
Similarly this analysis with amount of gases which will
consume, the amount of different material that will consume.
And they compared this, and they compared this for a single crystalline
silicon based process, and they also had, Siemens also had at
the time line for making thin-film solar cell out of CIS, which stands for
copper indium diselenide or sometime, you know, abbreviated as CIS.
So one thing which immediately
jumps out, if you compare this process flow for making a solar cell, with
a single crystalline silicon, versus the process flow for making a solar cell with
CIS is that how simple the process for making this thin-film based solar cell is.
In fact you see that there are a much lower number of
total steps in making at each stage making, starting from the ingot.
To making
the cell. To making the modular.
Less number of steps involved in a
thin-film process cell versus a crystalline silicon.
And you see that some sections are completely
absent in you know, CIS based process flow.
For example, to make a module with single-crytalline silicon, you need to
have a n-gate of silicon, which is made using a Czochralski growth process, and
then it has to be, you know, sliced into wafers, ond
which you subsequently make do different processing steps, and make your cell.
As compared to in a, in a CIS
process flow, this, this module is completely absent.
You can just start with the pieces of glass and then you know deposit a few
different thin-films on top, and then you are done with this process flow.
So you see that there are, you know there are less
number of process steps involved in a thin-film based solar cell.
And then again, that can be represented, these
two people, they are represented in these bar
charts, where they represent, you know, the total
number of materials, the total number of process steps.
So, as you can see, there are much more number of materials and much
more process steps.
So there are, you know, roughly 2,875 And
you know, over here is one, three, four, five.
That is you know, the total amount of energy associated with the materials here,
is for making for making single crystalline based silicon based solar cell
is much higher as compared to compared to what is involved into making a,
CIS based cell.
And again one thing the highest bar which stands out in terms of so
this bar chart what it's plotting, it is plotting this kilowatt
hour per kilowatt peak so this, it's representing this energy consumed.
By this using, kilowatt hour by kilowatt peak, which may sound,
confusing, at the beginning, but, we, saw where it comes from.
It comes from the slope of this graph.
So the slop of this graph will have
essentially the unit kilowatt hour by kilowatt peak.
So the efficiency of the panel is already accounted, Into this, slope.
So what you see over here is that the
biggest, biggest energy adder, or you know the biggest
energy adder for this, single crystalline silicon
based, process flow Is involved in generating the
silicon, or, you know, generating the starting material
or the starting wafer for making the silicon.
That's what is adding most of the energy cost and that is what is the
prime driver for this difference between the total
energy cost for a single crystalline silicon based
solar cell.
What is the total energy cost for CIS, base, based based solar cell.
And that is further exemplified in this chart where again what they're plotting
is the amount of energy, you know, components of this energy pay back time.
So the total energy pay back time,
according to data analysis for, single crystal
in silicon is three point, 3.3 years.
And, for, CIS based thin frame solar cell it's, 1.8 years.
And you, if you see, you know in this, 3.3 years, majority of,
you know, our 59% of this energy cost is coming from making this.
Making this silicon grid.
Or making these wafers, in which these
subsequently these cells and modules are being
made, versus thin film based solar cells. Since that does not need this ingot and
this slicing of wafer to, to start the process flow.
So you see this, this component is essentially absent and that is
what is the prime driver of Reduction in this energy payback time.
So, if you see that, you know the different process step, the ingate itself,
you know the ingate itself is responsible for, you know, is responsible
for It is responsible for 1.6 years out of this
3.3 years of energy payback time so if you can get rid of that we can
essentially reduce the energy payback time significantly.
Another thing too, I want to mention is that I did not take, we did not take the
battery, or, you know, the energy spent in making the battery into this analysis.
In fact, if we take the amount
of energy, which go in to making a battery, which can stored the energy being
generated from this panel that adds to
this EPBT, or this energy payback time significantly.
You know, in fact, a battery can add up to, can
add up to 6 years to your energy payback time, but.
We don't, we have you know, ignored that in this analysis.