Matrix Irradiance-Temperature with Egrid

[RobSolar]

Hello guys,

 

I am working in a personal Excel tool where I want to know at specific hour, what is the E_grid of a project based on the Irradiance GTI and the Ambient Temperature.

 

I can get an hourly output file with this information, but I can see I have many gaps. For instance, for an irradiance between 800 and 900 W/m2, I don't have any hour where the Ambient Temperature is below 8°C. 

 

So I was thinking on creating my own TMY model with the GHI and Ambient Temperature that I need to create a more accurate table. However, I think this is not an easy job, because of the model that PVSYST uses "clear sky index". If the irradiance that I use in my customized TMY is too far from PVSYST model, it won't let me do the simulation.

 

I think this can be bypassed modifying some hidden parameters (ktcc and clear), but I am not sure what I should change. Can anyone please tell me?

 

Does anyone has any different solution for this problem? I mean for having quick E_grid with GTI and Temp as inputs. Doing the matrix I noticed that different hours with same irradiance and same temperature, PVSYST gives different E_grid values (I guess there are many other variables). But the difference is for most of the points less than 10%, which is accurate enough for me.

[André Mermoud]

I don't see well what you want to do.

For such an approximation, you can use the Input/Output diagram as reference (draw E_Grid as a function of GlobInc). Without power overload, this should fit this distribution with a rather well defined straight line.

You will have a dispersion of points, depending namely of the array temperature. You should apply the temperature model for the array temperature, based on the ambient temperature. If you apply the temperature loss to each hourly point, you should probably reduce the dispersion. 

 

 

 

[RobSolar]

Thanks André for your answer.

 

The Input/Output diagram is very helpful. Is it possible to get a hourly graph instead of daily? I believe after that I would be able to apply the correction due to the temperature.

[André Mermoud]

Yes, you can indeed define any kind of customized plot to be accumulated during the simulation. In the project's dialog, please open "Advanced simulation > Special graphs". 

Now for your case a much better way would be to create a CSV file of Hourly values, that you can manage in EXCEL.

For this open "Advanced simulation > Output file". Here you can choose any variable among the 100+ variables of the simuation.