How to export posts in excel?
Use the Forena module to create a "report" that includes the data that you're interesting in (Post title, Post URL, Author, publish Date). As part of the report design, indicate which export formats you want to allow for exporting the data included in it. XLS is one of the typical formats that are supported, but their could be other formats enabled also, such as CSV,  XML, HTML, etc.

Have a look at the Simple Table of States example, and think of it as the equivalent of your "posts that you want to export". And note the hyperlinks in the upper right, which are:


CSV.
XLS.
HTML.
XML.


Try any of these links to get the equivalent of the extracted information, but in the format you requested (there or other supported formats such as PDF, DOC, JSON, etc).

Checkout Forena's Community Documentation for (way) more details, and/or the documentation that comes with the module.

Disclosure: I'm a co-maintainer of Forena.