Determining the PC wattage consumption

Hello!

My father is on vacations and I have remote access to his PC and I also visit the house once a week to collect the correspondence and check the flowers. He recently received a high electricity bill and he suspects the PC is using too much power. I doubt it, because it is an entry-level Intel Pentium G CPU with an entry level nVidia graphics card and a standard 500W PSU, however I would like to check that. A quick search in Google suggested that I can find out using HWiNFO. However, I need some help.