In this video we'll talk about how we can measure an IV curve.

You, of course already previously measured

your own IV curve using our virtual instrument.

However, there's more ways we can measure an IV curve other than using a resistive load.

There's a number of methods you can use to measure

the IV curve and the method you choose will likely depend on your need for accuracy,

the cost, or your budget,

or your need for modularity.

So are you measuring a single module?

Are you measuring a string of modules at high voltage?

Whichever method you choose it's important to have

a measurement circuit that can operate at both ISC and VOC.

So those are the two extremes of your IV curve.

So let's look at some possible methods,

some possible circuits to measure your IV curve.

The most simple is a resistive load, a variable resistor.

And, with this, you're essentially changing

the resistance or the impedance that the PV device sees.

So, you alter the resistance from near zero.

So ISC, and you change it all the way up

to near infinite resistance which is the VOC point of the curve.

If you turn the resistor in the opposite direction,

you can then measure the curve from VOC to ISC.

That would be the cheapest,

the most basic method of measuring IV.

To get a more accurate estimate of the IV curve,

you would use something like

a two quadrant electronic load or a four quadrant power supply.

One of the reasons it's more accurate than

a variable resistor is because you can get a better estimate of ISC.

So, when you use an electronic load,

we consider the PV device an ideal current source,

a constant current source.

So, that convention with constant current sources is to load them in voltage.

So we keep the load in constant voltage mode,

we step in voltage and measure current from ISC to VOC.

So the important difference between using a resistive load and

electronic load is that with the resistive load we,

can't get the full IV curve.

First of all, it's really hard to get

the ISC value because we need a really high resistance.

The other problem is, we cannot see the full IV curve.

We can not move below zero volts,

and we cannot go beyond the VOC value.

With an electronic load,

we can do this and we can get the full IV curve,

and from the full IV curve we can extract more data than we could otherwise.