these are very power efficient providing you stick with SFP+.
they seem to only power on the port when a cable or transceiver is plugged in.
Mine draws around 10-15 watts at 240v from my UPS. with 4 SFP+, 2 DACs and 1 RJ45 running at gigabit.
Direct Attached Copper is very hit and miss in regards to support. see the similar forum threads for info. this is apparently being worked on by ubiquiti on their forum.