In very round numbers, a year has 10,000 hours, and we pay about 20 cents for a kilowatt-hour. Any device that uses 1 watt full time will cost $2 a year. An electric clock (check the name-plate) may use 4 watts — that is an operation cost of $8 a year. For about half the year (the heating season) that energy will be useful in helping heat the house. “One watt, one year — two bucks.”