In this video we'll do a small experiment. So we'll try and see if we can measure the power output from a solar cell. I have a solar cell here. This is a polymer solar cell which you will learn more about in a later module. This solar cell is comprised of several individual solar cells, so it's actually a module. So if you want to measure the power output of this solar cell, we obviously need more than the solar cell itself. We also need multi-meter. So I have one right here. And we need a light source. The one like I have here. So let me just hook up the solar cell to the multi-meter and let's do a measurement. So as you can see the voltage drop across the solar module is around four volts. And the reason for this is obviously that I have a lot of light in the studio. If I shadow the solar cell with my hand, you can see the voltage will drop significantly. But let's try and put it underneath the light source and get some actual readings out. So now we can see the solar cell is producing roughly five and half volts, and let's see the current is producing, roughly 38 milliamps, so that's the voltage and the current. It might be easy to think that we can simply calculate the power output from a solar cell by just multiplying together the voltage and the current that we measure. However, it's not as simple as that, and in order to illustrate that principle I'd like to introduce what I call virtual instruments so you can see I can bring it up here. So this virtual instrument is exactly the same set up that we have with the lamp here, the multi-meter and the solar cell. You can see down here, I have a reading out that's the voltage the solar cells is producing, and if I click the solar cell, you can see I can turn on the light and we get a reading out, and the reading will not be exactly the same as we see here because the virtual instrument is not modeling this solar cell. But as with the multi-meter, I can switch between voltage and amps by just clicking the multimedia part of the virtual instrument. So with this virtual instrument we can redo exactly the measurement we had before. Let's look at the numbers we get out. So we have roughly half an amp of current and 2.3 volts of potential drop. So let's now switch to a slightly more advanced version of the virtual instrument. You can see, I have another version of the instrument. I have both, a volt meter and an amp meter connected at the same time. So let's see what happens when we turn on the light. So now we can see we get the same reading as before. So roughly half an amp, but we get zero voltage. So in this case the power we are producing will be equal to half an amp multiplied by zero volts, which means we get zero watts as a result. So this solar cell in this configuration does not produce any power. Let's try and see if we can reorganize the wiring a little bit, and switch to this version of the virtual instruments. If I switch back and forth, you can see the wires are going a slightly different way. Let's now try and turn on the light here. Now, we see the opposite situation. We get the voltage reading but no amperes. And the reason is we need to look at how the volt meter and the amp meter is working. So first let's take a look at the amp meter. An amp meter is essentially a serial resistance load. It needs to be, because all of the current needs to run through the amp meter for it to measure the current. And that means we can see all the current run from the solar cell to the amp meter and back to the solar cell. That means we get the full reading of the current but we will not see any potential drop. In the other situation, we see the connections are a bit different. That means now all the current needs to run through the volt meter before it reaches the amp meter, and the problem with this is, the volt meter is essentially an infinite resistive load. So that means no current will run through the volt meter. And thus, no current will also run through the amp meter and we get zero current out. This will also explain which terms lie behind the readings we're getting. So this voltage we're reading here, is what we call open circuit voltage. That means it's when no current is running and there's an open circuit. So it means, we don't have any leads connected to the solar cell. And this is in essence what we have here, since the volt meter is an infinite resisted load. So we might as well not have connected it, at least from the perspective of the amp meter in this case. In the other situation we get what we call the short circuit current, and this is because we measure the current when we short circuit the solar cells or when all the current is just running from one electrode to the other. And this is where we get the reading of the current. So with this in mind, if you want to measure the power of the solar cell can produce, we need to find the values in between. That means we need to put a load into the system and measure the voltage and current at different loads. So this we can do with this instrument. So here we've placed a variable resistor into the circuit and this will allow us to change the load in the circuit, and we can go from essentially the short circuit condition at one end, and all the way to what is essentially an open circuit situation at the other end. And all the values in-between, we can see that we vary the voltage and the current we are producing. And as you know, the power is the product of the voltage and the current. So at some point when we vary this resistive load, we'll find a maximum power point. So the point where the solar cell can produce the most power, and then in the next assignment you'll have to find the maximum power point for this virtual instrument.
