Thank you for the replies. On CentOS 7 Linux with pgdg 9.5.3 the lower() method works and I have:
# \l List of databases Name | Owner | Encoding | Collate | Ctype | -----------+----------+----------+-------------+-------------+ postgres | postgres | UTF8 | en_US.UTF-8 | en_US.UTF-8 | template0 | postgres | UTF8 | en_US.UTF-8 | en_US.UTF-8 | | | | | | template1 | postgres | UTF8 | en_US.UTF-8 | en_US.UTF-8 | | | | | | words | postgres | UTF8 | en_US.UTF-8 | en_US.UTF-8 |