Isn`t there something u can plug between the mains and u`r pc that will clock the power ?
All it`d do is measure the current over a period, voltage more or less a given - seems a simple device to me ?!??!
Infact, in the current climate, if some1 were to run a few 1000 of these up with kits/stuff from maplin and sell then - u`d make a fortune. Probably with little outlay as u could get a grant initially. Tell the gov u`r making an "Environmental effectiveness meter", color the thing bright green and u`d rake it in.