The standard delivery format of SolarGIS data files is .csv and when you open such file using excel, all data values may be in the first column.
By default, all values should be in numeric format. However if your computer recognises ',' or 'comma' as the decimal character instead of '.' some values may appear in date format. In such case you may want to change file extension to .txt and then open with excel.
You can then convert all data from first column to multiple columns using following steps:
1. Choose the column with all the text and run 'Text to columns wizard' (can be found under Data tab)
2. Set Delimited, Next
3. Select Semicolon, unselect Tab
4. Select Text as Column Data format