Your desktop computer uses between 100 - 250 watts when in use (depending on the components) and around 3 watts when turned off (on average). NIPSCO is currently charging $0.1165 per kilowatt-hour. How much would you pay for electricity each year even if you never turned your computer on? What if you had it on 24 hours per day, every day? What if you turned it off every night, and only turned it on every evening for a few hours?