The article provides the easiest way to put the data into excel in the PHP enviornment. Without using any lib. Simply implement the functions provided in the first step.
However, you cannot format the cell with this method. (background colors, font size, etc.)

There is another php library can do the full control over the php to excel but I havent used it for few years. If you would like to do more on this topic, try google the PEAR and the keywords.

This method in the provided link can do the basic data exporting.