GHI to POA Irradiance Conversion

[chrisolar]

I have a rooftop system with multiple orientations--same tilt, but two different azimuths. There is a single GHI sensor installed which I have pulled the operating data from. The only recorded data I have is GHI, E_Grid, and T_amb. I would like to convert this GHI data to POA for both orientations (two POA outputs), or as a single, weighted POA (one POA output, or as PVsyst calls it--GlobInc) for the entire system. Is there a straightforward method of performing this conversion? To my understanding, the data will need to be decomposed into various components and then transposed in order to get POA.

[Michele Oliosi]

There are basically two ways to do this.

First of all you want to import your weather data into PVsyst.

Then the easiest way is to make a PVsyst simulation with an output file. You can do so by going to the "advanced simulation" menu. There please define the "Output file". Among the outputs you can choose GlobInc. Once you are done, you should launch a simulation from the same "advanced simulation" window.

The second way is to use the "meteo tables and graphs" window, which you get either from the "Databases" menu, or from a project by opening the meteo file. From there, you have a series of tools to display the hourly data, including the Global irradiance on a tilted plane (so you have to choose a plane tilt and azimuth). You can export the data after showing it in a graph or table.

[Madela]

On The Second way you have mentioned, that plane azimuth is required. If my panels facing south, what degree angle should be input, considering that our location is in the northern hemisphere?

[Michele Oliosi]

In the Northern Hemisphere, South is Az. = 0.
In the Southern Hemisphere, North is Az. = 0.

[Madela]

Thank you for this. Can you kindly help me to understand it more given the following examples.

If the following roof facing :

1. South - 177 degree

2. East - 95.3 degree

3. West - 275 degree

What degree should be input on the plane orientation?

As you have mention - South facing which have 180degree is equivalent to 0 degrees azimuth in the Northern Hemisphere area

[Michele Oliosi]

Hi,
I am not sure how you count your degrees (where is 0?, what is the direction of positive angles?), but I am sure it should be easy to figure out using a drawing.

[Madela]

 

Attached here i have measure through solmetric roof azimuth tools. If the location was in northern hemisphere, how can invert the measured degrees in line with PVsyst system. Thank you. 

[Michele Oliosi]

Eastern side of roof azimuth = -90° + 6.1° = -83.9°
Western side of roof azimuth = 90° + 6.1° = 96.1°

[Madela]

Thank you for this. 

 

 

Does it also mean if I have measured N= 42.2° , SE 132.2°

The azimuth southern facing will be 0° + 42.2° = 42.2°  ? 

[Michele Oliosi]

Why 0°?
Southern facing side will have an azimuth of -90° (E) + 42.2° = -47.8°.