Is the plugin compatible with opensolr.com ?

Yes, Opensolr does provide all the details necessary to integrate with any major CMS system, including wordpress, where opensolr also provides an out of the box template collection as well.
Here are some sample settings from opensolr:

Url: http://ro.opensolr.com/solr/wordpress
Hostname: ro.opensolr.com
Path: solr/wordpress
Port: 80

You can actually use that to try it out.

Here’s also where you’d browse your data:
http://ro.opensolr.com/solr/wordpress/select?q=*:*&wt=json&indent=true&start=0&rows=50

Just create your free opensolr account to start your own wordpress collection with just a few clicks.
https://opensolr.com/register