Negative E_Grid values with night disconnect and no self-consumption

[mja]

Hello all,

I have recently come across a simulation result where negative E-grid values were recorded. These negative values are relatively small compared to the total system (30MW). 

The simulation has no auxiliaries but the inverters that I use for the simulation do have night consumption. However, given that I select 'night disconnect' on my MV transformer, wouldn't these loses be excluded?

A snippet of the results are shown below.

 

 

Do you know what is causing these losses?

Edited May 10, 2023 by mja

[mja]

Hello once again. I may have found the reason for the negative E_Grid values.

As the values occur during early morning and early evenings with low irradiance, could it be that PVsyst assumes that the site is still 'connected' to the grid at these times.

And as a result the transformer constant losses are applied, which are higher than the energy produced by the system for the given low irradiance, resulting in a negative E_Grid.

I ran the simulation again and got the following results with available energy at inverter output parameter - EOutInv (Sorted by lowest first) and MV transformer losses parameter - EMVTrfL,  which supports the above explanation. 

Please correct me if this explanation is incorrect. 

Thank you.

[Hizir Apaydin]

Dear mja,

Yes transformer constant loss and auxiliaries consumption can result in a negative E-Grid value if the consumption is higher than the solar production.

Regards