Here are some of the issues I've found with your code. But there are
many more left and it is very hard to review your code without seeing
some sample data files. Consider rewriting your code, taking these
suggestions into account and then posting another request for code
Avoid mixing import styles
from datetime import datetime
The first thing I would do is change the
from tkinter import filedialog
from tkinter import *
import tkinter as tk
It is generally seen as bad form to 'pollute' the namespace by doing from tkinter import *, see the last paragraph in PEP 8's section on imports. By using import tkinter as tk and referencing everything as e.g. tk.filedialog it stays ...
avoid data type float, unless you don't care about not accurate rounding.
Solar_panel_rack, solar_panel and wind_turbine I would change structure:merge solar panel with solar_panel_rack if possible also would probably join wind turbine with solar panel_rack. It could potencialy have columsn like:
ItemId, ItemTypeId(wind turbine or solar), ...