# Understanding PV Cell Modeling: Single vs Double Diode

• willDavidson
In summary, the purpose of the double diode model is to represent a PN junction. The equation for I has I wrapped up in the exponential as well. Trying to solve for J by hand, I either have J in an exponential or J ln(J).
willDavidson
TL;DR Summary
I an trying to understand the PV cell diode and double diode model
I am looking at modeling a PV cell and I'm trying to understand the real difference between the single diode and double diode mode. I now realize that I don't fully understand the purpose of the diode in the model in the first place. I've just learned that it was there and went with it. I understand that it's supposed to represent a PN junction but I'm not sure what that really means at the end of the day.

Any discussion on this topic would be helpful. Also if anyone has suggestions on when to use the single or double diode model that would be helpful too. I am currently reading on the topic too.

Baluncore said:
Thanks, PVEducation is a useful. One of the parts that's got me on all of the equations is they seem to use the current (or current density) that you're looking for in the equation. Here I see J defined as the current density. There's also J01 and J02. I understand that I'm looking for J and J01 and J02 are a parameter for diodes 1 and 2 respectively. How do you solve the equation for J and J is part of the equation in the exponential?

Other equations I've found use current I but either term make sense to me.

willDavidson said:
How do you solve the equation for J and J is part of the equation in the exponential?
The equations requiring solution will depend on what type of model you are contemplating.
What is the purpose of the model?

I would like to find the current at a given voltage.

willDavidson said:
I would like to find the current at a given voltage.
Do you mean this curve?

anorlunda said:
Do you mean this curve?
View attachment 280165
Yes, basically I would like to find a value along that curve. Looking at the equations for the single and double diode model, The equation for I has I wrapped up in the exponential as well. I'm not sure how to solve that or if I in the exponentials are a different I than the output current.

willDavidson said:
I would like to find the current at a given voltage.
It is probably rational to model the PV cell performance parameters at a specified fixed illumination. The operating point may be dynamic, determined by small variations of the external loading. If the load is defined as a voltage with a series resistance, then a load line can be plotted that intersects the VI curve. That would model a battery or capacitor being charged through a series resistance. The changing load voltage and resistance may be determined by a controller searching in real time for the maximum power point.
The model will be determined by why you need to model the PV cell ?
What software system will use the model ?

Baluncore said:
If the load is defined as a voltage with a series resistance, then a load line can be plotted that intersects the VI curve. That would model a battery or capacitor being charged through a series resistance. The changing load voltage and resistance may be determined by a controller searching in real time for the maximum power point.
The model will be determined by why you need to model the PV cell ?
What software system will use the model ?

I was hoping to model a PV cell to look at the transient performance due to changes in irradiance due to issues like rapid shading since the response time of a PV panel is pretty much instant. I'll be using Matlab for this part which is why I'm interested in solving the equation referenced above. I know that I can use the solve function in Matlab and it will do its thing to solve it, but that still leaves me lost about the general equation. Breaking apart each piece of the equation it seems to make sense except having J (or I) on on both sides. Trying to solve for J by hand, I either have J in an exponential or J ln(J). Is it only possible to solve this using a iterative or numerical methods?

willDavidson said:
Is it only possible to solve this using a iterative or numerical methods?
Probably.
At some point you must connect the PV cell to a load.
When you do that you may find that the system is constrained and the equation becomes more tractable.

Ok thanks. I think my question from here may be more math related so I'll take continue the math topic there. I'm not sure how to link the thread in case anyone else is interested, but I'm really curious how to solve that thing. Even if I make some highly inaccurate assumptions to simplify it as much as possible, I get something like J*exp(J)=[constant]. I'm still lost on how to solve for J in the very simplest form.

That is letting J01=1, q/kt=1, Rs=1, Rshunt=infinity, V=0

## 1. What is the difference between single and double diode models for PV cells?

Single diode models are simpler and assume that current flows through only one diode in the cell. Double diode models are more complex and account for the presence of a second diode, which can better represent the behavior of a real PV cell.

## 2. How do single and double diode models affect the accuracy of PV cell simulations?

Single diode models are less accurate, as they do not account for all the factors that affect the behavior of a PV cell. Double diode models are more accurate, but also more computationally intensive.

## 3. What are the main parameters used in single and double diode models?

The main parameters used in both models are the diode ideality factor, reverse saturation current, and series and shunt resistances. However, double diode models also include a second ideality factor and reverse saturation current for the second diode.

## 4. How do temperature and irradiance affect single and double diode models?

Both temperature and irradiance have an impact on the parameters used in single and double diode models. As temperature increases, the reverse saturation current and series resistance also increase, while the ideality factor decreases. Irradiance affects the diode ideality factor and reverse saturation current.

## 5. Which model should be used for PV cell simulations?

The choice between single and double diode models depends on the level of accuracy required for the simulation. If a quick estimate is needed, a single diode model may be sufficient. However, for more accurate results, a double diode model should be used, especially for cells with complex behavior.

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