GHI to POA Transposition

[Lorenzo Petrini]

Dear pvlib community,

I'm trying to convert a GHI into POA using the code in the link:

https://pvlib-python.readthedocs.io/en/stable/gallery/irradiance-transposition/plot_ghi_transposition.html#sphx-glr-download-gallery-irradiance-transposition-plot-ghi-transposition-py

But I don't want to use GHI from a database, I want to use the GHI I measured in the site. But when I try to substitute the part of the code where it is defined the ghi variable:

ghi=clearsky['ghi']      with a vector (or list, I don't know yet the terms of phyton, I apologize for that) containing the values of GHI measured (each 1 min, for 24 hour) and I run the code, I got the following error:

TypeError: can't multiply sequence by non-int of type 'float'

Someone has already done this succesfully?

Thank you in advance for helping,

Kind Regards

Lorenzo Petrini

PS: the whole output is 

runfile('C:/Users/A474229/OneDrive - Enel Spa/Desktop/Sedeis V.py', wdir='C:/Users/A474229/OneDrive - Enel Spa/Desktop')
Traceback (most recent call last):

  File ~\AppData\Local\anaconda3\Lib\site-packages\spyder_kernels\py3compat.py:356 in compat_exec
    exec(code, globals, locals)

  File c:\users\a474229\onedrive - enel spa\desktop\sedeis v.py:1484
    summer_irradiance = get_irradiance(site, '04-21-2024', 30, 180)

  File c:\users\a474229\onedrive - enel spa\desktop\sedeis v.py:1469 in get_irradiance
    POA_irradiance = irradiance.get_total_irradiance(

  File ~\AppData\Local\anaconda3\Lib\site-packages\pvlib\irradiance.py:380 in get_total_irradiance
    poa_ground_diffuse = get_ground_diffuse(surface_tilt, ghi, albedo,

  File ~\AppData\Local\anaconda3\Lib\site-packages\pvlib\irradiance.py:597 in get_ground_diffuse
    diffuse_irrad = ghi * albedo * (1 - np.cos(np.radians(surface_tilt))) * 0.5

TypeError: can't multiply sequence by non-int of type 'float'

[Abed W Ayyad]

Hi, 

Have you tried "casting" the relevant object to the correct type:

https://pythonprinciples.com/blog/type-errors/#:~:text=You%20typically%20fix%20a%20TypeError,s)%20to%20the%20correct%20type.&text=In%20general%2C%20to%20fix%20a,really%20want%2C%20then%20use%20casts. 

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[Echedey Luis Álvarez]

Hi Lorenzo,

Everything in Python is an object, and it is up to each of them how to implement arithmetic operations.

If you run [1, 2, 3] * 1.5 you will get the same error. This is because a list (the first item) doesn't implement multiplication by non ints (the second item is a float). If you multiply by an int you will get another type of result: you can try running [1,2,3]*2 on the python console and checking the output.

Now, what you have to do is exactly what you expect: you need an object that defines the element-wise multiplication. For this kind of use, we usually either use numpy.ndarray or pandas.Series objects (there are other alternatives too).

Possibilities to convert a Python list into an array are:

• Numpy
  import numpy as np
  ghi = np.asarray(clearsky["ghi"])
• https://numpy.org/doc/stable/reference/generated/numpy.asarray.html (any dimensional data arrays)
  
• Pandas
  import pandas as pd
  ghi = pd.Series(data=clearsky["ghi"], name="Global Horizontal Irradiance")
• https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.Series.html (only 1D data; for 2D data use pd.DataFrame)
  

I heavily recommend you check out their docs, reading documentation in Python is a key part in the development.

I don't really know where are you getting the data from, but pandas has an extensive API of readers: CSV files, JSON, ... Just in case it can help you.

/Echedey.