On Tue, 08 Dec 2015 06:35:42 -0800, dr.s.lartius wrote:

A neighbour has a new-this-year UK-assembled generic Windows 7 PC, and a
decade-old flat-screen non-CRT Philips monitor from Denmark.

Nocturnally, these are turned off by closing Windows and by pressing the
little button on the lower front of the monitor.

What power, in watts, is each of these two devices each likely to be
drawing during the night?

If he's closing Windows, then he's switching the PC off. There'll be a
small draw, but it really will be absolutely minimal.

Have a google for the monitor - the 8yo 24" Samsung flat on my desk is
reputedly 0.5w on standby.

Call it a watt for the pair. So 1,000hrs from 1kWh or, at 15p/kWh, about
2.5 days per penny.