List all available items with Apache Solr if the search keyword is empty
Thanks Letharion, to answer your question I have found this option in the Advanced options region for the search pages. Here is how to get there:

admin/config/search/apachesolr/search-pages  

Create a new search page for Solr search with content type filter or enable one for taxonomy/term/% 

Select "Show enabled facets' blocks in their configured regions and first page of all available results" under the Advanced options for this page