Differences in results in almost identical simulations

[Ricardo]

Hi,

I recently simulated a big project which could be broken down into three separate smaller projects. I noticed that if I simulated the small projects, the sum of the kWh/year generated in each of them does not add up to the kWh/year generated by the big project. The difference is small (around 0,8%), but still puzzling.

 

In order to find out where the difference might come from, I then simulated a project twice, the second time adding a very minor change which should have no influence in results (a small wall far away from any modules). Again the results changed, by a very small amount, but I would have expected them to be identical.  Please see below the wall I placed (1 m long, 0,5 m high), with the closest modules placed on an 8 meter high roof.

 

 

As mentioned, the difference is minimal, but just out of curiosity, can someone please explain why there is a difference in the first place?

 

Thanks for your support!

[developer_mh]

Hi Ricardo,

this is an interesting case! Could you please provide the project files (the big one and the three small ones), so that I can have a look what is happening there?

You can either send them here directly or by private message.

Thanks a lot,

Martin

[developer_mh]

Hi Ricardo,

thank you for the project files. The differences are induced by an update of the PV module data by Longi. The newer module data are taken for simulation once you enter the 3D environment. The reflection behaviour of the modules is now different which is why the simulation results are deviating slightly.

That is, when I do the following, I get identical results for the inverter groups:

1. Load the project where the whole plant with all inverters is defined
2. Go into 3D environment, return and adopt the data
3. Simulate
4. Save results, e.g. for Inverter 1
5. Then re-enter 3D environment
6. Delete all configurations except configuration 1
7. Return to main program and adopt the data
8. Simulate
9. See the results for Inverter 1 are the same as from step 4

Hope that helps, kind regards,

Martin

[Ricardo]

Hi Martin,

It does, thanks a lot!

Kind regards,

Ricardo