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Welcome to this video tutorial.

Â We are to talk about IV curves.

Â It'll talk about how we can measure IV curve.

Â I'll talk about how we can extract parameters from an IV curve.

Â So, first of all,

Â we have a set up or a picture of a setup that can measure the IV curve.

Â Basically, this is a really simple set up.

Â We have our solar cell,

Â then we have two multimeters.

Â These two, and then we have our resistor.

Â Here, what we do is we have a load we can vary.

Â When we vary the load,

Â the current readout and the voltage readout will change.

Â In this way, we can get the load characteristics or the IV curve of the solar cell.

Â Of course, we can change the systems with these knobs,

Â but this one, we can change the resistance from the low.

Â Here, we have 10 times the changes.

Â In this way, it's really easy to

Â get the load characteristics of the IV curve of the solar cell.

Â The circuit, of course, looks like this.

Â What we have is, we have our solar cell just like before.

Â We have a voltmeter,

Â an ampmeter so we can measure both voltage and current,

Â and lastly, we have our variable resistor.

Â Our current will look like this before we start populating it.

Â What we do is we start out with a resistor value then we readout

Â the voltage and the current from the ampmeter and the voltmeter.

Â So we get readings like this and then we chance the resistor, get another reading,

Â read again, and we just keep repeating until we fill out.

Â That's overload characteristics of the IV curve.

Â Of course, you only populate one-quarter of the part here.

Â We'll get back to why an IV curve can look a little bit different later on,

Â but for now, let's just look at the IV curve as is and try to extract some parameters.

Â First of all, let's see what is the maximum voltage we can read out.

Â That we call the Voc, open circuit voltage.

Â That's when there's no load and we just have to read out the voltage,

Â and this, of course, we can measure right here,

Â so this is Voc.

Â Then, of course, we have the maximum current.

Â That's called Isc, short circuit.

Â That's when we just connect the wires

Â together and measure the current voltage in a short circuit.

Â The definition of course is when we have zero voltage along this line,

Â we can find the maximum current.

Â In some case, they won't be reading here,

Â we have to extrapolate or interpolate the data depending on the information,

Â and the same can be said for Voc.

Â The next important parameter that we need to extract is the Pmax.

Â The Pmax, the P will always be

Â a product of V and I, voltage and current.

Â Let's try and draw this out.

Â This current that I've drawn here is the product of V and I.

Â Here, you would have Pmax.

Â Associated with the Pmax, that of course,

Â a VPmax and IPmax.

Â We can try and draw this area,

Â but I just mark with VPmax and IPmax and get this area.

Â Another area we can draw is, of course,

Â the area that's defined by Voc and Isc.

Â We could take the ratio between these two areas within the fill factor.

Â The fill factor, FF, we already know it, is the IPmax so, FF= VPmax.IPmax/Voc.Isc.

Â We also write this as,

Â Pmax/Voc.Isc,

Â and this is how we calculate the fill factor.

Â Moving on. As I said,

Â there's another way to measure an IV curve and often when you see an IV curve,

Â it's drawn like this.

Â What happened is we didn't measure it using that set of drawn here.

Â That other set up, we didn't have the voltmeter, we don't have the variable resistor.

Â We still have the ampmeter,

Â but what we have is we have a voltage source here.

Â We can basically drive the solar cell both in forward and

Â in reverse bias so we can get the quadrants outside of the area here.

Â When we look at calculating the variables,

Â it's exactly the same as before.

Â We still have Voc here, we still have Isc down here.

Â We have some additional information,

Â but for now, this is just exactly the same.

Â As I'll ask here,

Â I'd like to show you how to calculate PCE.

Â The PCE is Power Conversion Efficiency.

Â Of course, the definition of efficiency is,

Â of course, we have Pout/Pin.

Â The output power, of course,

Â we know already, that is Pmax.

Â We have from the curve before.

Â Pin, we typically have to calculate based on the area of the cell.

Â Often, we know the power density so typically, we know that,

Â the sun is giving out 1,000 W/m2 and we typically know the area of our cell.

Â Let's say the area of our cell was 0.5 m2.

Â What we then have to calculate the PCE,

Â what we need to do is take Pmax because our power output,

Â we take that, divided by 1,000 divided by our area, which is 0.5.

Â If we look at units here,

Â you can see that square meters, canceled each out.

Â Pmax is course in watts so this ratio becomes unitless.

Â Okay, this is all for my short tutorial about IV curves.

Â