Is PoE more efficient than plugging in adapters for each network device?
And at what scale does it start to matter?
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From my perspective; I’m going for a 3 node mesh router, plus 2 switches, and was considering if in 5 years time the electricity difference would be less than the extra upfront cost. The absolute max length of cable would probably be around 30m
As other posters have remarked, it’s difficult to offer a generalized statement on PoE efficiency. One thing I will point out that hasn’t been mentioned yet is that PoE switches tend to have poor “wall to device” efficiency when lightly loaded. Certifications like 80 Plus only assess efficiency at specific loading levels.
Hypothetically, a 400W PoE switch serving only a 5W load may cause an additional 10W to be drawn from the wall, which is pretty horrific. But if serving loads totalling 350 W, could draw 390 W from the wall, which might be acceptable efficiency.
Your best bet is to test your specific configuration and see how the wall efficiency looks, with something like a Kill-o-Watt. Note that even a change from 120V input voltage to 240V input voltage can affect your efficiency results.