Modelling a solar cell

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From the course by Technical University of Denmark (DTU)

Introduction to solar cells

501 ratings

Technical University of Denmark (DTU)

Introduction to solar cells

501 ratings

How do solar cells work, why do we need, and how can we measure their efficiency? These are just some of the questions Introduction to solar cells tackles. Whether you are looking for general insight in this green technology or your ambition is to pursue a career in solar, “Introduction to Solar Cells” is an excellent starting point. The course is a tour through the fundamental disciplines including solar cell history, why we need solar energy, how solar cells produce power, and how they work. During the course we cover mono- and multi-crystalline solar cells, thin film solar cells, and new emerging technologies. The course includes hands-on exercises using virtual instruments, interviews with field experts, and a comprehensive collection of material on solar cells. At the end of the course you will have gained a fundamental understanding of the field. This will allow you to identify the most interesting or relevant aspects to be pursued in your future studies or in your professional career.

From the lesson

Modelling a solar cell

In this module we will introduce an equivalent circuit of a solar cell and use it to explain key concepts including short circuit current, open circuit voltage, parasitic resistances, and more. We will also talk about connected solar cells, and their behavior in shaded conditions.

Modelling a solar cell3:24

Meet the Instructors

Morten Vesterager Madsen
Researcher
DTU Energy
Martin Helgesen

In this video we'll talk about how we can model a solar cell.

And we do this by setting up an equivalent circuit to the solar cell.

The performance of PV devices is often times modeled with equivalent circuits.

The most commonly used equivalent circuit in PV is the one diode model.

So there's four components in the one diode model.

There's an ideal current source which is driven by light intensity.

In parallel with that,

we have a diode which gives us the diode effect on the IV curve.

And then we have two parasitic resistances,

namely the parallel or shunt resistance and our series resistance.

So if you look at an ideal PV device,

we know that it should have a high R_shunt value and a low R_series value.

Both the R_series and R_shunt values can be extracted from the IV curves.

So, the R_series can be extracted from the slope of the IV curve near VOC.

The R_shunt can be extracted from the IV curve near ISC.

We can actually make an even simpler circuit than the one Nicholas showed.

So, if we want to model a solar cell in the simplest possible way,

we can set up a model where we don't even include the parasitic resistances.

So this is the model we see here.

So we have the current generator in the solar cell and we have a diode.

And this model allows us to draw an IV curve.

And as you can see, the IV curves will be dependent on the amount of incident radiation.

So when we model it, we see that the current

of this solar cell is linearly proportional to the incident radiation,

while the voltage is logarithmically dependent.

However, the simple model with only the diode only takes us so far,

and it can be quite useful to expand the model to

include the series resistance and the shunt resistance.

So the series resistance allows us to model the effect of the w wires and the bypass,

while the shunt resistance allows us to

motor if current is leaking across the PV junction.

And in order to get a better feel for how series and

shunt resistance affect the IV curve,

we can take a look at a virtual instrument.

So, with this virtual instrument,

we can change both the series resistance and the shunt resistance.

And as you can see, when we change the shunt resistance,

the slope of the IV curve changes around the ISC value,

while if we change the series resistance,

we can see we change the slope near the VOC value.

So to sum up, we can determine the R_shunt value as the slope near

the ISC value while the R_series is the slope near the VOC value.

And by doing this we can take real data that we measured from

a solar cell and we can look at the R_shunt and the R_series value.

And this will tell us a lot about where

we can improve the device in order to get a better efficiency.

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