Online uses the device mnchrmtr to get/set the energy. Here is an example from P02 (/online_dir/online.xml):
<device> <name>mnchrmtr</name> <type>type_tango</type> <module>motor_tango</module> <device>p02/dcmener/oh.01</device> <control>tango</control> <hostname>haspp02oh1:10000</hostname> </device>