mikeymike said:that depends on far too many variables, your electric costs, any reductions you get for time of day, how much load the server is typically under, how economical your PSU is, the list goes on and on
if you can get one of those nifty plugs that sits between pc and wall socket and monitors watt/hour then you will be able to work it out from that, but no one on here will be able to give you an accurate figure