Negative value of PV Generation

[Shane]

Hello all,

I have an odd question to ask, I'm using the below information to generate a PV profile for one day, however, I have negative values and I'm a bit confused about what to conclude from these values. I'm using Matlab to generate the plot 

Formula: PV =  1/1000.* (et.*Av.*Ir .*(1-0.005.*(Tou-25))), where Tou is the outdoor temperature, Ir is the solar irradiance, et is efficiency (20%),  Av is the area=1.6 meter square, 1/1000 to convert into kw. The solar irradiance and outside temperature are given by, noting that the location is in the south of Finland.
 

 Ir= [ -1.6   -0.8   -1.0   -1.0  -1.2   -0.8   -1.3   -0.5    6.9   27.6   43.9  38.8   15.9    2.1   -1.6   -1.3   -1.1   -1.1   -1.5   -1.4   -1.3   -1.7   -1.7   -1.4]

Tou=[-20.3  -19.4  -18.6  -18.4  -18.0  -17.5  -16.9  -16.0  -15.3  -14.9  -14.5  -14.6  -14.6  -13.6  -12.4  -11.6  -11.3  -11.2  -11.0  -10.9  -10.9  -10.7  -10.5  -10.7]

[Bruno Wittmer]

Where do the irradiance values come from, and what do the negative irradiance values mean exactly?

With the formula you are using, negative irradiance leads to negative generation.

[Shane]

Hello Bruno!!

Thanks for your message, the negative irradiance values come from actual data from the Finnish Meteorological Institute. Yes, you are right! and it is hard for me to interpret, but do you know any formula (with reference) I should use or is there any drawback of this formula? any suggestions/interpret? Thanks in advance

[dtarin]

Irradiance sensors sometimes (or often) report negative values. Set these to zero to resolve your issue. Also, this is the suggestion thread for suggesting features or changes to PVsyst.

Edited March 2, 2023 by dtarin

[Shane]

@dtarin Thanks for the response. What could be the proper justification to make negative values zero? secondly, I didn't fully get your last sentence's meaning, can you elaborate?

[dtarin]

The justification is that when performing calculations, as you have found, a negative number can lead to negative generation. While PVs plants do have negative generation at night (i.e. transformers, fans, etc.), it is not coming from irradiance or the modules. The last part was with reference to the forum topics and organization. This is a general question and would be better suited for the how to or meteo data forum categories. 

Edited March 6, 2023 by dtarin

[Shane]

@dtarin Thanks for the response.  I appreciate it, I'm new here so I don't know about the forum categories.

Edited March 10, 2023 by Shane