Questions regarding bifacial modules and effects on yield

[Torbjørn Heimvik]

Hi!

 

I cannot entirely understand how PVSOL deals with bifacial modules.

1. When choosing a module, there is a field in the "additional parameters" part of the specific PV module data, that can be changed. There, it is possible to choose a "Bifacial factor". I see several modules that have typically 70 % bifacial factor. 
   • Does this mean that these modules (that have a number larger than 0) can actually produce from the backside? That is, if a PV module is bifacial (has glass on both sides), there will be a value in this field?
   • In the PVSOL help section for bifacial modules, it says that it is required that the bifacial factor is larger than 1 in order for it to calculate bifaciality. As I understand this, the bifacial factor must be higher than 100 %?
   • For modules that are not bifacial, is it correct that the module parameter must be set to 0 %?
2. When looking at the report, I can see sometimes that it says 0 % and 0 kWh Bifaciality, even though the bifacial factor is set to 70 %. See illustration for this below, and also the PVSOL file attached:   
   • 
3. Some other sometimes it might say a negative % and negative kWh Bifaciality, even though the bifacial factor is set to 70 %. See illustration for this below, ("tosides" = "bifacial" in norwegian.
   • 
   • What is the explanation for this?

Liavegen 2 - solcelleanlegg_580Wp.pvprj

[developer_fw]

Hello Torbjørn Heimvik

On 12/8/2023 at 9:49 AM, Torbjørn Heimvik said:

When choosing a module, there is a field in the "additional parameters" part of the specific PV module data, that can be changed. There, it is possible to choose a "Bifacial factor". I see several modules that have typically 70 % bifacial factor. 

in our online help it is stated that typical bifacial factors are in the range of 0.7...0.8 which means 70...80%: https://help.valentin-software.com/pvsol/2024/en/calculation/pv-modules/bifacial-modules/

On 12/8/2023 at 9:49 AM, Torbjørn Heimvik said:

When looking at the report, I can see sometimes that it says 0 % and 0 kWh Bifaciality, even though the bifacial factor is set to 70 %. See illustration for this below, and also the PVSOL file attached:   

It is also stated that for roof-parallel systems as chosen within your project there is no radiation on the back side.
When changed in the used mounting system, there should be additional yield.

In your example project with a low module elevation in east-west configuration I assume there is probably no relevant gains anyway.

On 12/8/2023 at 9:49 AM, Torbjørn Heimvik said:

Some other sometimes it might say a negative % and negative kWh Bifaciality, even though the bifacial factor is set to 70 %. See illustration for this below, ("tosides" = "bifacial" in norwegian.

• 
• What is the explanation for this?

 

Hm, could you send the .pvprj file regarding those losses? Without the project file it is hard to pin down the responsible causes.

Kind regards
Frederik

[Torbjørn Heimvik]

Hi!

 

Thank you for the answers. I have attached the PVSOL file here.

 

Also, can you confirm that for "normal modules" (not bifacial), the "bifacial factor" must be set to zero?

Liavegen 2 - solcelleanlegg_450Wp.pvprj

[developer_fw]

Hi Torbjørn Heimvik

3 hours ago, Torbjørn Heimvik said:

I have attached the PVSOL file here.

Thank you for the project file.

The losses due to the bifaciality factor is just one side of the coin since you have to take into account radiation gains:

3 hours ago, Torbjørn Heimvik said:

Also, can you confirm that for "normal modules" (not bifacial), the "bifacial factor" must be set to zero?

That is correct.

Kind regards
Frederik

[Torbjørn Heimvik]

Thank you for the feedback!

As I believe I understand it, we are only able to retrieve 70 % of the irradiancee on the backside, leaving a 30 % loss = 3152 kWh?

[developer_fw]

That is correct, yes.