How much power does a mac mini uses?
If the idle power consumption was 11 W and the maximum was 85 W, the average might be something like 15 W if it's under very low load.

That would be about 500 MJ per year (15*86400*365).

If you paid 0.15 USD per kilowatt hour for electricity and the Mac mini was on all the time, it would cost about 20 USD per year (0.15*0.015*24*365).

15 W is about 65 mA with 230 V (European) voltage and 125 mA with 120 V (North American) voltage.