Desktop IBM PC Core 2 Duo 2.6GHx, 2GB RAM, Running Windows XP
Standard running is using ~45W.
The peak occurs during startup or when the harddrive is rapidly asked for information - peaks reached 88W but only for a few seconds.
The moving clock screensaver boosts this to 60W therefore increase +15W so a blank one is better.
Putting the machine into standy mode reduces power to 3-4W.
IBM Flat panel monitor 17inch screen.
Standard running is using ~40W.
A peak of 44W was reached but that's negligible change really.
Screensaver blank / moving clock, both reduce power by ~2W, but we know a blank one is better for the PC.
Powersave mode drops the power to 2.3W.
Switching it off with the button drops this to 1W.
What does this mean for us?
If we set the PCs and Monitors to go into standby mode we would save 40 + 38 = 78W and with the monitor off, let's say 80W can be saved overnight or during downtime.
0.08 kW can be saved per hour by doing this. so in theory overnight unless an update or antivirus scan takes place we could gain from 5pm to 7am (14hours) 14 * 0.08 = 1.12 KWh per unit.
We have ~ 500 PCs therefore we could save 560 kWh per night.
BUT to put it into context, most machines do have automatic power save modes and therefore we are already getting a lot of this saving. Nonetheless smart usage of the power save modes during the day and an intelligent choice of screen saver could save more money as well as be better for the environment.