There is a nice Python adhoc tool created with love by good people in OpenSource Connections, which you can use to do this:
https://github.com/o19s/solr-to-es
Simply
./solr-to-es solr_url elasticsearch_url elasticsearch_index doc_type
For example, the command below will look at all the documents on the local Solr node with the name nodeand send them to the local Elasticsearch server in the index my_indexwith the document type my_type.
./solr-to-es.py localhost:8983/solr/node localhost:9200 my_index my_type