Bypass diode configuration included?

[Yvar BAM]

Dear PV-sol experts,

I'm currently simulating a solarpark with portrait PV panels. Due to the lack of space, we only have a rather small space between the panels, which causes shading on the next panel in line. Because we don't have panels with a bypass configuration for portrait, this would mean that shading the lowest row of the panel, will activate all bypass diodes and will therefore more of less shut off the panel.

My question is; is this effect taken into account for the simulation or is shading taken as an average decrease in illumination? 

As what I understand you do take it into account, but i really need to be sure, because the continue of the project more or less depends on the simulation.

(and maybe a follow-up question; is there a way in PV-Sol to search for PV-panels with a 'portrait bypass configuration'?)

Kind regards,

 

Yvar 

[developer_mm]

Hello Yvar,

welcome to our forum!

PV*SOL simulates on substring level of the PV modules so that the losses due to active bypass diodes are taken into account.

Each substring will be checked whether there is a shadow in this substring or not. If there is a shadow, the bypass diode is active (curve 2 & curve 3), otherwise not. PV*SOL assumes from this that the shaded substring are never completely in shadow, but that there is always diffused radiation on the shaded parts (curve 2).  There is therefore a I-V-curve with lower current for these cells as well. If the resultant MPP phase current is less than the short circuit current for the shaded cells, the bypass diode is not active and the complete module works with low current and high voltages. We therefore take these effects into account by working with yellow phase curve 2 when calculating the complete generator characteristic curve.

I-V-curve (pretty old one, but it represents thematic well enough)

 

Kind regards,

Marcel

[developer_mm]

To your second question: Is there a way in PV-Sol to search for PV-panels with a 'portrait bypass configuration?

Unfortunately, it is not possible to search directly in PV*SOL to check whether there are landscape or portrait bypass configurations. But you can check a specific PV module in the database. On the page "Electrical Data" you will find the information you need.

 

[Yvar BAM]

Hi Marcel,

Thank you very much for your clear and fast response. 

Kind regards,

 

Yvar

[Jasper]

Hello, I have a question regarding the string-power calculation.

 

I am trying to simulate a system which has two identical modules with different orientations connected in series. I am aware that this is not recommended, but I want to see how badly the different orientations (one 5 degrees south, one 55 degrees south) influence the yield of the system compared to both modules having the same orientation (25 degrees south).

As far as I understand, PV-Sol calculates a new I-V curve for each module at each timestep (either 1 hour or 1 minute), depending on the number of shaded cells/cell-strings parallel to one bypass diode. Using the individual I-V curves of each module, the software then determines the string characteristic curve. Because of the bad angle, the 55-degree module should have a much worse I-V curve than the almost horizontal module in most cases (at least around noon). Because of the series connection, the string current should be limited to the current of the 55-degree module and therefore result in a much worse performance of the whole string (in case no bypass diodes are used). Will the simulation take this into consideration?

I already simulated both cases, and the results only showed a minor difference in yearly yield, much less than I expected.

Trying to check if the series-connection losses are taken into consideration, I simulated two modules with no bypass diodes wired in series and one of them being completely shaded. The simulation results only dropped to the yield of one module alone rather than even lower, which I expected. How does this fit together?

Right now, I'm not convinced that the simulation results of the "two orientations in series connection" are representative. Can I expect accurate simulations in this scenario?

Kind regards,

Pablo

[hotline_oh]

Dear Pablo,

Thank you for your inquiry.

Please send the relevant project file (*.pvprj) to hotline@valentin-software.com so that we can take a closer look at it.

[Jasper]

23 hours ago, hotline_oh said:

hotline@valentin-software.com

Thanks for getting back to me!

I think I have figured out what the real issue is. Somehow the simulation doesn't seem to factor in the voltage drop at the activated bypass diodes of the 5-degree module.

Below you can see the simulated I-V curve of the two modules connected in series at 12:00 and a plot of their irradiance and the resulting output. The first one has an orientation of 5 degrees south and the second one 55 degrees south. Both modules have six integrated bypass diodes. As you can see in the top plot, the module is being operated at the first (global) MPP in order to reach the plotted output power of around 45 W. Unfortunately, the MPP in the I-V curve is located at a voltage of approximately 15 V, which is exactly the rated MPP voltage at STC.

But in order to run the series connection at the higher current of the 55-degree module, the second module actually must be bridged via the 6 integrated bypass diodes, each resulting in a voltage drop of 1 V (as defined in the module parameters). Therefore, the first local MPP should be located at around 9 V and consequently have a much lower resulting power of about 29 W.

Do you know why the simulation doesn't seem to factor in the voltage drop at the bypass diodes?

I sent you the project via e-mail.

Kind regards,

Pablo