In this video, I want to walk you through a data sheet of a
solar, solar panel, and I've just picked one of these solar panels randomly.
So I've picked this Panda Series solar panels
which is sold by this company Yingli Solar.
It is one of the larger manufacturers of crystalline and multi-crystalline
based silicon solar panels. And this solar panel is is
made up of these single crystalline, or mono-crystalline silicon.
Okay, so, one thing I should point out is that these data
sheets typically are a couple of pages, maybe two or three pages.
and the first page is always filled with this marketing information, which I
should warn you, you should take it with a grain of salt.
So for example it talks about how much the installation
how much of capacity of modules, this company has installed.
And then it says that you know
it can supply these aesthetically pleasing black modules.
I don't know what, how, you know, making this thing black instead of of
white, would make it more aesthetically appealing.
But they do send to tell, they do tend to sell like these these modules with,
you can choose the color of this plastic or these
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sheet, and you can choose it to be either white or black.
The other information that this this data sheet
claims is that this module has the highest PTC by STC ratio.
So, there are two terms over here, one is STC and PTC.
And then there's a ratio of these two terms.
Wo let me explain now what they, what they mean.
Let me go over here so I can write some stuff down.
So this PTC essentially what it
means it corresponds to PVUSA
Test Conditions. And that particular test condition, it
essentially corresponds, it corresponds to having a intensity,
having a solar spectrum
with and intensity which is normalized to 1000 watt per meter squared.
And you use a AM 1.5G spectrum.
And, then you assume that your ambient
is essentially you have a temperature, of the ambient,
Is, essentially equal to 20 degrees centigrade.
You assume that there's a certain, wind blowing.
And this wind is blowing at the rate of
one meter per second, which is equal to 2.25 mph.
And you
know, this was what, this is what corresponds to PTC.
Note that there's no specification given on the temperature of the cell.
So all you specify is the temperature of the ambient.
And this wind speed.
And this wind is also, you know, something which would, if you have
a module like this, and you have a solar panel placed over here,
your wind is essentially, it's going to be more effective cooling
the panel when it blows at the bottom of this panel.
Because note that this panel essentially consists of this it, it's,
encapsulated with this glass at the top, which has a very poor, poor conductivity.
So it's it's very hard to get heat out or, you know, convective flow
of heat out from the top surface of your of your of your panel.
So
I want to state again that there's no specification
given on the temperature of the cell.
So the temperature of the cell for sure
would be higher than the temperature of the ambient,
because you have this light with the intensity of,
1000 watt per meter square shining upon this panel.
And this glass is a poor, poor conductor of heat,
so there's no way for this heat to escape as well.
Besides from the bottom, if there's a wind flowing.
So this temperature would be definitely higher than 20 C.
And it would depend largely on these, on how your
module is designed, how efficient your cell is, and so on.
So this PTC rating, or this this power rating under these PVUSA Test Conditions,
it's usually measured, measured by an independent body.
So for example for
the state of California there's this California Energy Commission.
And they have this website where they
measure measure the efficiency of different modules.
Also they list out, they make a list
of what are the manufacturer of these modules,
what is the module number,
what is it what's its description, It is suitable for BIPV?
Is it suitable for integration
into a building while the building is being constructed?
That's called BIPV.
And then it specifies this PTC rating of these, of these panels.
And this list is updated quite frequently.
And the panels which are given in this list are suitable, you know,
California will give you a subsidy if you use the panels from this list.
So let me search for Yingli over here.
So Yingli.
And then the panel number which I was using was this
30b panel over here, so I see that
it says that you know, it's it's made in China.
This is the panel number.
Then it says you know, it's a Monocrystalline Silicon Module and then it
has a PTC rating of 235 watts, so let me write it down.
So this panel.
The PTC rating as, as specified
by, by the California Energy Commission is, is 235, 235 watts.
Okay.
So now what is this STC? What is this STC over here.
So this STC essentially it corresponds
to, it corresponds to standard test conditions.
So this STC corresponds to standard test conditions.
And this
essentially corresponds to having a intensity of light.
which is again 1000 watt per meter square and
the AM 1.5G spectrum which is the same as what we used for PTC.
But now we give a specification on the cell temperature
and we specify that, it's, it is 25 degrees Centigrade.
And this, this STC test is
very often used when these cells are being manufactured in a line.
So one of the steps, that is performed is
to generate this solar spectrum using a solar simulator.
And these, measures the efficiency of
these cells, while holding their temperature
constant, or, you know, while holding their temperature to be 25 C.
So you know that whenever we operate the cell, and if we operate it under this,
PTC condition, the temperature of the cell
will rise because you have this light shining,
and also the cell is, essentially it's
thermally sealed by this glass from the top.
So this efficiency of the cell will, will decrease as I increase the temperature.
So this efficiency will decrease in the PTC test condition.
So that's why this PTC to STC ratio is important.
And it's important to find out what is this PTC to STC ratio.
So this STC rating is often given in the data sheet itself.
So I'm going to just look into that.
So it says that under standard test, test conditions,
wo the maximum power is for this panel is 270 watts.
So, the PTC to STC ratio is essentially
235 divided by, 270. So this is this is your
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it's you know, its let me see, it's close to 90% over here.
Then it also says that, these, these, effi-,
these panels, they give a efficiency, these cells which are used in this panel.
They give a efficiency of 90 per, of 90%, but that's, you know, not relevant.
The, what's relevant is the module efficiency.
And
that is given to be 16.5%.
Again, the thing you should be asking yourself is that under
what what what kind of test conditions is this efficiency measured?
And so it has you know, some other, other marketing information
such as it uses anti-reflective coating, that it specifies
what kind of warranty is available on these panels.
And then what certification and these what quality certifications it has passed.
So for example to, to operate them in
California a very important certification is this CEC certification.
Which is the California Energy Commission. So now, the, let's come
to the second page of this data sheet. And this is where most of the meat or
most of the information which makes a electrical engineer's heart sing, or
even a mechanical engineer's heart sing, lies over here.
So, as soon as, you know, I look at some, of
these metrics, I recognize, some of the terms that I have learned.
That is, I recognize my efficiency over here.
I recognize my, power max point, my current max,
open circuit voltage, short circuit current.
So these are things, you know, I'm very familiar with.
And, again, I note over here that this are specified in in for a, for two cases.
One is a standard test condition. And if you read the footnotes over here,
they say again that, that standard test condition had corresponds to 1000 watt
per meter square
with a cell held at a temperature of 125 C, and the AM 1.5 G spectrum.
Another thing to notice is that there are these different columns over here.
And they have, you know, they have very
similar similarly lettered names, but you see over here
that the efficiencies of these are different and
they're varying by you know, varying from all the
way from 16.5 to 15.3.
So what have what have been done over here is that they all use the same cell.
But the highest efficiency cells have been binned over
into this module which has the highest efficiency of 16.5.
And all the bad cells, you know all the black sheep in the, in the
manufacturing line, they have been binned over into this particular module
which has efficiencies of 15.3. But, from a manufacturing process
or from a cell perspective, they came out, all from the same manufacturing line.
Okay?
So, another thing I notice is my open circuit voltage
and I notice that this is equal to 39 volt.
And then the next thing I'll check is how many, how many cells I had.
So let me count the number
of cells, so 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 and then I have
six, six columns of these ten cells. So total number
of cells I had was around, or not around but exactly 60.
So for 60 cells, I get a open circuit
voltage of 39 volt, assuming all of them are,
all the cells in a panel are connected in series.
This corresponds to a Voc of each individual cell to be approximately
39 by 60 or approximately 0.65 volt.
That's the Voc of my, one, one of these silicon
cells and that sounds approximately right given that these are made out of silicon.
So another thing to notice over here is this these, some of these metrics
are also reported for this nominal operating cell temperature.
So these the STC conditions, they corresponds to a cell temperature of 25 C.
But there's this also, this nominal operating cell temperature.
Which essentially
you know it's similar to the PT, similar to the PTC condition.
But it uses it uses a irradiance of 800 watt
per meter squared instead of 1000 watt per meter squared.
Again 20 degrees centigrade ambient,
and one meter per, one meter per second speed.
So the cell will essentially rise up, in temperature.
Typically for these, crystalline-silicon-based, based cells, it
can, vary all the way from, you know, the cell temperature for this particular ambient
condition in this area, irradiance, It can vary all the way from 40 degrees C
to all the way up to 70 degrees C, depending upon depending upon how good
is your, how good is your module design to carry away this heat.
And also it depends upon what is your irradiance level as well.
So again, at some of these these nominal operating
test conditions so they spec, specify some
of these metrics for these conditions otherwise.
And then another important metrics to is to note is specified in this table over here,
where it gives a temperature coefficient of of my power,
the temperature coefficient of my voltage, the temperature coefficient of my current.
So I
notice that as I increase my temperature, my Voc decreases as as I
increase my temperature because my Voc has a negative coefficient over temperature.
So, it decreases by 0.31 percentage points.
So, these things are reported by percentage points
per degree centigrade.
So if I increase my temperature by one degree centigrade, this
Voc will essentially decrease by 0.31%. Similarly, if I increase my temperature,
my short circuit current typically increases.
Because my bandgap
of my solar cell decreases.
So my short circuit current increases,
so this has a positive temperature coefficient.
The overall power of my cell essentially decreases, and you can see that my power
decreases with this negative temperature coefficient of 0.42%.
Sometimes these, they also specify the nominal operating test conditions.
So they say that if you do operate the cell at this irradiance level of
800 watt per meters square.
And this is the temperature of the ambient and the
wind speed,
the temperature of the cell is going to be between 46 plus, minus 2
degree centigrade, so it's going to operate between 44 to 48 degree centigrade.
So these are some of the things to keep in mind. What we
need, what we desire for is a good PTC versus STC ratio.
And also low cell operating temperature, because the higher
the temperature the cell will operate at,
the more would be the efficiency degradation.